From 55d4bd6e0ea23dcf55dc33a964514230ee785bbe Mon Sep 17 00:00:00 2001
From: John Ericson <John.Ericson@Obsidian.Systems>
Date: Mon, 22 Jun 2020 18:08:27 +0000
Subject: [PATCH 01/30] Improve content address parsing

 - Ensure hash is in form <algo>-<prefix> and not SRI.

 - Better errors if something goes wrong

 - string_view for no coppying
---
 src/libstore/content-address.cc | 77 ++++++++++++++++++++-------------
 src/libutil/hash.cc             |  4 +-
 src/libutil/hash.hh             |  4 +-
 3 files changed, 50 insertions(+), 35 deletions(-)

diff --git a/src/libstore/content-address.cc b/src/libstore/content-address.cc
index 3d753836f..216d7eb03 100644
--- a/src/libstore/content-address.cc
+++ b/src/libstore/content-address.cc
@@ -1,3 +1,4 @@
+#include "args.hh"
 #include "content-address.hh"
 
 namespace nix {
@@ -40,38 +41,52 @@ std::string renderContentAddress(ContentAddress ca) {
 }
 
 ContentAddress parseContentAddress(std::string_view rawCa) {
-    auto prefixSeparator = rawCa.find(':');
-    if (prefixSeparator != string::npos) {
-        auto prefix = string(rawCa, 0, prefixSeparator);
-        if (prefix == "text") {
-            auto hashTypeAndHash = rawCa.substr(prefixSeparator+1, string::npos);
-            Hash hash = Hash(string(hashTypeAndHash));
-            if (*hash.type != htSHA256) {
-                throw Error("parseContentAddress: the text hash should have type SHA256");
-            }
-            return TextHash { hash };
-        } else if (prefix == "fixed") {
-            // This has to be an inverse of makeFixedOutputCA
-            auto methodAndHash = rawCa.substr(prefixSeparator+1, string::npos);
-            if (methodAndHash.substr(0,2) == "r:") {
-                std::string_view hashRaw = methodAndHash.substr(2,string::npos);
-                return FixedOutputHash {
-                    .method = FileIngestionMethod::Recursive,
-                    .hash = Hash(string(hashRaw)),
-                };
-            } else {
-                std::string_view hashRaw = methodAndHash;
-                return FixedOutputHash {
-                    .method = FileIngestionMethod::Flat,
-                    .hash = Hash(string(hashRaw)),
-                };
-            }
-        } else {
-            throw Error("parseContentAddress: format not recognized; has to be text or fixed");
+    auto rest = rawCa;
+
+    // Ensure prefix
+    const auto prefixSeparator = rawCa.find(':');
+    if (prefixSeparator == string::npos)
+        throw UsageError("not a content address because it is not in the form \"<prefix>:<rest>\": %s", rawCa);
+    auto prefix = rest.substr(0, prefixSeparator);
+    rest = rest.substr(prefixSeparator + 1);
+
+    auto parseHashType_ = [&](){
+        // Parse hash type
+        auto algoSeparator = rest.find(':');
+        HashType hashType;
+        if (algoSeparator == string::npos)
+            throw UsageError("content address hash must be in form \"<algo>:<hash>\", but found: %s", rest);
+        hashType = parseHashType(rest.substr(0, algoSeparator));
+
+        rest = rest.substr(algoSeparator + 1);
+
+        return std::move(hashType);
+    };
+
+    // Switch on prefix
+    if (prefix == "text") {
+        // No parsing of the method, "text" only support flat.
+        HashType hashType = parseHashType_();
+        if (hashType != htSHA256)
+            throw Error("text content address hash should use %s, but instead uses %s",
+                printHashType(htSHA256), printHashType(hashType));
+        return TextHash {
+            .hash = Hash { rest, std::move(hashType) },
+        };
+    } else if (prefix == "fixed") {
+        // Parse method
+        auto method = FileIngestionMethod::Flat;
+        if (rest.substr(0, 2) == "r:") {
+            method = FileIngestionMethod::Recursive;
+            rest = rest.substr(2);
         }
-    } else {
-        throw Error("Not a content address because it lacks an appropriate prefix");
-    }
+        HashType hashType = parseHashType_();
+        return FixedOutputHash {
+            .method = method,
+            .hash = Hash { rest, std::move(hashType) },
+        };
+    } else
+        throw UsageError("content address prefix \"%s\" is unrecognized. Recogonized prefixes are \"text\" or \"fixed\"", prefix);
 };
 
 std::optional<ContentAddress> parseContentAddressOpt(std::string_view rawCaOpt) {
diff --git a/src/libutil/hash.cc b/src/libutil/hash.cc
index c8fcdfed0..012fa727d 100644
--- a/src/libutil/hash.cc
+++ b/src/libutil/hash.cc
@@ -342,7 +342,7 @@ Hash compressHash(const Hash & hash, unsigned int newSize)
 }
 
 
-std::optional<HashType> parseHashTypeOpt(const string & s)
+std::optional<HashType> parseHashTypeOpt(std::string_view s)
 {
     if (s == "md5") return htMD5;
     else if (s == "sha1") return htSHA1;
@@ -351,7 +351,7 @@ std::optional<HashType> parseHashTypeOpt(const string & s)
     else return std::optional<HashType> {};
 }
 
-HashType parseHashType(const string & s)
+HashType parseHashType(std::string_view s)
 {
     auto opt_h = parseHashTypeOpt(s);
     if (opt_h)
diff --git a/src/libutil/hash.hh b/src/libutil/hash.hh
index 0d9916508..e4abe72ce 100644
--- a/src/libutil/hash.hh
+++ b/src/libutil/hash.hh
@@ -121,9 +121,9 @@ HashResult hashPath(HashType ht, const Path & path,
 Hash compressHash(const Hash & hash, unsigned int newSize);
 
 /* Parse a string representing a hash type. */
-HashType parseHashType(const string & s);
+HashType parseHashType(std::string_view s);
 /* Will return nothing on parse error */
-std::optional<HashType> parseHashTypeOpt(const string & s);
+std::optional<HashType> parseHashTypeOpt(std::string_view s);
 
 /* And the reverse. */
 string printHashType(HashType ht);

From 7ba0fae0ddc815d7d7b2c3a9cd3d60879baeab54 Mon Sep 17 00:00:00 2001
From: Carlo Nucera <carlo.nucera@protonmail.com>
Date: Tue, 30 Jun 2020 11:57:09 -0400
Subject: [PATCH 02/30] Create the spitPrefix function in parser.hh

---
 src/libutil/parser.hh | 25 +++++++++++++++++++++++++
 1 file changed, 25 insertions(+)
 create mode 100644 src/libutil/parser.hh

diff --git a/src/libutil/parser.hh b/src/libutil/parser.hh
new file mode 100644
index 000000000..64689e283
--- /dev/null
+++ b/src/libutil/parser.hh
@@ -0,0 +1,25 @@
+#pragma once
+
+#include <optional>
+
+namespace nix {
+
+// If `separator` is found, we return the portion of the string before the
+// separator, and modify the string argument to contain only the part after the
+// separator. Otherwise, wer return `std::nullopt`, and we leave the argument
+// string alone.
+std::optional<std::string_view> splitPrefix(std::string_view & string, char separator);
+
+std::optional<std::string_view> splitPrefix(std::string_view & string, char separator) {
+    auto sepInstance = string.find(separator);
+
+    if (sepInstance != std::string_view::npos) {
+        auto prefix = string.substr(0, sepInstance);
+        string.remove_prefix(sepInstance+1);
+        return prefix;
+    }
+
+    return std::nullopt;
+}
+
+}

From 77b51f4598763f0b3a435ed0e4ce98178d9e99da Mon Sep 17 00:00:00 2001
From: Carlo Nucera <carlo.nucera@protonmail.com>
Date: Tue, 30 Jun 2020 11:57:46 -0400
Subject: [PATCH 03/30] Factor the prefix splitting in content-address

---
 src/libstore/content-address.cc | 27 ++++++++++++---------------
 1 file changed, 12 insertions(+), 15 deletions(-)

diff --git a/src/libstore/content-address.cc b/src/libstore/content-address.cc
index 4599cd924..8152e5215 100644
--- a/src/libstore/content-address.cc
+++ b/src/libstore/content-address.cc
@@ -1,5 +1,6 @@
 #include "args.hh"
 #include "content-address.hh"
+#include "parser.hh"
 
 namespace nix {
 
@@ -43,23 +44,19 @@ std::string renderContentAddress(ContentAddress ca) {
 ContentAddress parseContentAddress(std::string_view rawCa) {
     auto rest = rawCa;
 
-    // Ensure prefix
-    const auto prefixSeparator = rawCa.find(':');
-    if (prefixSeparator == string::npos)
-        throw UsageError("not a content address because it is not in the form \"<prefix>:<rest>\": %s", rawCa);
-    auto prefix = rest.substr(0, prefixSeparator);
-    rest = rest.substr(prefixSeparator + 1);
+    std::string_view prefix;
+    {
+        auto optPrefix = splitPrefix(rest, ':');
+        if (!optPrefix)
+            throw UsageError("not a content address because it is not in the form \"<prefix>:<rest>\": %s", rawCa);
+        prefix = *optPrefix;
+    }
 
     auto parseHashType_ = [&](){
-        // Parse hash type
-        auto algoSeparator = rest.find(':');
-        HashType hashType;
-        if (algoSeparator == string::npos)
-            throw UsageError("content address hash must be in form \"<algo>:<hash>\", but found: %s", rest);
-        hashType = parseHashType(rest.substr(0, algoSeparator));
-
-        rest = rest.substr(algoSeparator + 1);
-
+        auto hashTypeRaw = splitPrefix(rest, ':');
+        if (!hashTypeRaw)
+            throw UsageError("content address hash must be in form \"<algo>:<hash>\", but found: %s", rawCa);
+        HashType hashType = parseHashType(*hashTypeRaw);
         return std::move(hashType);
     };
 

From a1f66d1d9e70d4204a3686002b02277465a6b7ab Mon Sep 17 00:00:00 2001
From: Carlo Nucera <carlo.nucera@protonmail.com>
Date: Tue, 30 Jun 2020 12:49:00 -0400
Subject: [PATCH 04/30] Factor the prefix splitting in hash

---
 src/libutil/hash.cc | 17 ++++++++---------
 1 file changed, 8 insertions(+), 9 deletions(-)

diff --git a/src/libutil/hash.cc b/src/libutil/hash.cc
index e060700d9..26ab5a110 100644
--- a/src/libutil/hash.cc
+++ b/src/libutil/hash.cc
@@ -7,6 +7,7 @@
 #include "args.hh"
 #include "hash.hh"
 #include "archive.hh"
+#include "parser.hh"
 #include "util.hh"
 #include "istringstream_nocopy.hh"
 
@@ -144,17 +145,15 @@ Hash::Hash(std::string_view original, std::optional<HashType> optType)
     // Parse the has type before the separater, if there was one.
     std::optional<HashType> optParsedType;
     {
-        auto sep = rest.find(':');
-        if (sep == std::string_view::npos) {
-            sep = rest.find('-');
-            if (sep != std::string_view::npos)
+        auto hashRaw = splitPrefix(rest, ':');
+
+        if (!hashRaw) {
+            hashRaw = splitPrefix(rest, '-');
+            if (hashRaw)
                 isSRI = true;
         }
-        if (sep != std::string_view::npos) {
-            auto hashRaw = rest.substr(0, sep);
-            optParsedType = parseHashType(hashRaw);
-            rest = rest.substr(sep + 1);
-        }
+        if (hashRaw)
+            optParsedType = parseHashType(*hashRaw);
     }
 
     // Either the string or user must provide the type, if they both do they

From b798efb829415eb47a532e9479523afdff74eca7 Mon Sep 17 00:00:00 2001
From: Carlo Nucera <carlo.nucera@protonmail.com>
Date: Tue, 30 Jun 2020 14:10:30 -0400
Subject: [PATCH 05/30] WIP initial design

---
 src/libutil/hash.cc   | 17 ++++++++++++-----
 src/libutil/hash.hh   |  7 +++++--
 src/libutil/parser.hh |  5 ++---
 3 files changed, 19 insertions(+), 10 deletions(-)

diff --git a/src/libutil/hash.cc b/src/libutil/hash.cc
index 26ab5a110..36de293bb 100644
--- a/src/libutil/hash.cc
+++ b/src/libutil/hash.cc
@@ -132,10 +132,13 @@ std::string Hash::to_string(Base base, bool includeType) const
     return s;
 }
 
-Hash::Hash(std::string_view s, HashType type) : Hash(s, std::optional { type }) { }
-Hash::Hash(std::string_view s) : Hash(s, std::optional<HashType>{}) { }
+Hash fromSRI(std::string_view original) {
 
-Hash::Hash(std::string_view original, std::optional<HashType> optType)
+}
+
+Hash::Hash(std::string_view s) : Hash(s, std::nullopt) { }
+
+static HashType newFunction(std::string_view & rest, std::optional<HashType> optType)
 {
     auto rest = original;
 
@@ -161,13 +164,17 @@ Hash::Hash(std::string_view original, std::optional<HashType> optType)
     if (!optParsedType && !optType) {
         throw BadHash("hash '%s' does not include a type, nor is the type otherwise known from context.", rest);
     } else {
-        this->type = optParsedType ? *optParsedType : *optType;
         if (optParsedType && optType && *optParsedType != *optType)
             throw BadHash("hash '%s' should have type '%s'", original, printHashType(*optType));
+        return optParsedType ? *optParsedType : *optType;
     }
+}
 
-    init();
+// mutates the string_view
+Hash::Hash(std::string_view original, std::optional<HashType> optType)
+    : Hash(original, newFunction(original, optType))
 
+Hash::Hash(std::string_view original, HashType type) : Hash(type) {
     if (!isSRI && rest.size() == base16Len()) {
 
         auto parseHexDigit = [&](char c) {
diff --git a/src/libutil/hash.hh b/src/libutil/hash.hh
index a55295912..42bd585a2 100644
--- a/src/libutil/hash.hh
+++ b/src/libutil/hash.hh
@@ -40,13 +40,16 @@ struct Hash
        is not present, then the hash type must be specified in the
        string. */
     Hash(std::string_view s, std::optional<HashType> type);
-    // type must be provided
-    Hash(std::string_view s, HashType type);
     // hash type must be part of string
     Hash(std::string_view s);
 
+private:
+    // type must be provided, s must not include <type> prefix
+    Hash(std::string_view s, HashType type);
+
     void init();
 
+public:
     /* Check whether a hash is set. */
     operator bool () const { return (bool) type; }
 
diff --git a/src/libutil/parser.hh b/src/libutil/parser.hh
index 64689e283..d3bfafe75 100644
--- a/src/libutil/parser.hh
+++ b/src/libutil/parser.hh
@@ -1,6 +1,7 @@
 #pragma once
 
 #include <optional>
+#include <string_view>
 
 namespace nix {
 
@@ -8,9 +9,7 @@ namespace nix {
 // separator, and modify the string argument to contain only the part after the
 // separator. Otherwise, wer return `std::nullopt`, and we leave the argument
 // string alone.
-std::optional<std::string_view> splitPrefix(std::string_view & string, char separator);
-
-std::optional<std::string_view> splitPrefix(std::string_view & string, char separator) {
+static inline std::optional<std::string_view> splitPrefix(std::string_view & string, char separator) {
     auto sepInstance = string.find(separator);
 
     if (sepInstance != std::string_view::npos) {

From c2e7f7a7129fc5366a4cad337fcd6ae319a58ce5 Mon Sep 17 00:00:00 2001
From: Carlo Nucera <carlo.nucera@protonmail.com>
Date: Wed, 1 Jul 2020 17:32:06 -0400
Subject: [PATCH 06/30] Fixed build, we still have test errors

---
 src/libutil/hash.cc | 46 +++++++++++++++++++++++++++++----------------
 src/libutil/hash.hh |  4 +++-
 src/libutil/util.cc |  2 +-
 3 files changed, 34 insertions(+), 18 deletions(-)

diff --git a/src/libutil/hash.cc b/src/libutil/hash.cc
index 36de293bb..e8d290d13 100644
--- a/src/libutil/hash.cc
+++ b/src/libutil/hash.cc
@@ -132,17 +132,24 @@ std::string Hash::to_string(Base base, bool includeType) const
     return s;
 }
 
-Hash fromSRI(std::string_view original) {
+Hash Hash::fromSRI(std::string_view original) {
+    auto rest = original;
 
+    // Parse the has type before the separater, if there was one.
+    auto hashRaw = splitPrefix(rest, '-');
+    if (!hashRaw)
+        throw BadHash("hash '%s' is not SRI", original);
+    HashType parsedType = parseHashType(*hashRaw);
+
+    return Hash(rest, std::make_pair(parsedType, true));
 }
 
-Hash::Hash(std::string_view s) : Hash(s, std::nullopt) { }
+Hash::Hash(std::string_view s) : Hash(s, std::nullopt) {}
 
-static HashType newFunction(std::string_view & rest, std::optional<HashType> optType)
+static std::pair<HashType, bool> newFunction(std::string_view & original, std::optional<HashType> optType)
 {
     auto rest = original;
 
-    size_t pos = 0;
     bool isSRI = false;
 
     // Parse the has type before the separater, if there was one.
@@ -166,16 +173,23 @@ static HashType newFunction(std::string_view & rest, std::optional<HashType> opt
     } else {
         if (optParsedType && optType && *optParsedType != *optType)
             throw BadHash("hash '%s' should have type '%s'", original, printHashType(*optType));
-        return optParsedType ? *optParsedType : *optType;
+        return {
+            optParsedType ? *optParsedType : *optType,
+            isSRI,
+        };
     }
 }
 
 // mutates the string_view
 Hash::Hash(std::string_view original, std::optional<HashType> optType)
-    : Hash(original, newFunction(original, optType))
+    : Hash(original, newFunction(original, optType)) {}
 
-Hash::Hash(std::string_view original, HashType type) : Hash(type) {
-    if (!isSRI && rest.size() == base16Len()) {
+Hash::Hash(std::string_view original, std::pair<HashType, bool> typeAndSRI)
+    : Hash(typeAndSRI.first)
+{
+    auto [type, isSRI] = std::move(typeAndSRI);
+
+    if (!isSRI && original.size() == base16Len()) {
 
         auto parseHexDigit = [&](char c) {
             if (c >= '0' && c <= '9') return c - '0';
@@ -186,15 +200,15 @@ Hash::Hash(std::string_view original, HashType type) : Hash(type) {
 
         for (unsigned int i = 0; i < hashSize; i++) {
             hash[i] =
-                parseHexDigit(rest[pos + i * 2]) << 4
-                | parseHexDigit(rest[pos + i * 2 + 1]);
+                parseHexDigit(original[i * 2]) << 4
+                | parseHexDigit(original[i * 2 + 1]);
         }
     }
 
-    else if (!isSRI && rest.size() == base32Len()) {
+    else if (!isSRI && original.size() == base32Len()) {
 
-        for (unsigned int n = 0; n < rest.size(); ++n) {
-            char c = rest[rest.size() - n - 1];
+        for (unsigned int n = 0; n < original.size(); ++n) {
+            char c = original[original.size() - n - 1];
             unsigned char digit;
             for (digit = 0; digit < base32Chars.size(); ++digit) /* !!! slow */
                 if (base32Chars[digit] == c) break;
@@ -214,8 +228,8 @@ Hash::Hash(std::string_view original, HashType type) : Hash(type) {
         }
     }
 
-    else if (isSRI || rest.size() == base64Len()) {
-        auto d = base64Decode(rest);
+    else if (isSRI || original.size() == base64Len()) {
+        auto d = base64Decode(original);
         if (d.size() != hashSize)
             throw BadHash("invalid %s hash '%s'", isSRI ? "SRI" : "base-64", original);
         assert(hashSize);
@@ -223,7 +237,7 @@ Hash::Hash(std::string_view original, HashType type) : Hash(type) {
     }
 
     else
-        throw BadHash("hash '%s' has wrong length for hash type '%s'", rest, printHashType(this->type));
+        throw BadHash("hash '%s' has wrong length for hash type '%s'", original, printHashType(this->type));
 }
 
 Hash newHashAllowEmpty(std::string hashStr, std::optional<HashType> ht)
diff --git a/src/libutil/hash.hh b/src/libutil/hash.hh
index 42bd585a2..570e50dd4 100644
--- a/src/libutil/hash.hh
+++ b/src/libutil/hash.hh
@@ -43,9 +43,11 @@ struct Hash
     // hash type must be part of string
     Hash(std::string_view s);
 
+    Hash fromSRI(std::string_view original);
+
 private:
     // type must be provided, s must not include <type> prefix
-    Hash(std::string_view s, HashType type);
+    Hash(std::string_view s, std::pair<HashType, bool> typeAndSRI);
 
     void init();
 
diff --git a/src/libutil/util.cc b/src/libutil/util.cc
index 1268b146a..ed43c403f 100644
--- a/src/libutil/util.cc
+++ b/src/libutil/util.cc
@@ -1433,7 +1433,7 @@ string base64Decode(std::string_view s)
 
         char digit = decode[(unsigned char) c];
         if (digit == -1)
-            throw Error("invalid character in Base64 string");
+            throw Error("invalid character in Base64 string: '%c'", c);
 
         bits += 6;
         d = d << 6 | digit;

From 274a8136fbf3d0fffb564f33464da26aab924b60 Mon Sep 17 00:00:00 2001
From: Carlo Nucera <carlo.nucera@protonmail.com>
Date: Wed, 1 Jul 2020 17:47:15 -0400
Subject: [PATCH 07/30] Correct FIXMEs in libfetchers

---
 src/libfetchers/fetchers.cc | 3 +--
 src/libfetchers/tarball.cc  | 6 ++----
 src/libutil/hash.hh         | 2 +-
 src/libutil/util.cc         | 1 +
 4 files changed, 5 insertions(+), 7 deletions(-)

diff --git a/src/libfetchers/fetchers.cc b/src/libfetchers/fetchers.cc
index 9174c3de4..91d0d6a1d 100644
--- a/src/libfetchers/fetchers.cc
+++ b/src/libfetchers/fetchers.cc
@@ -35,8 +35,7 @@ std::unique_ptr<Input> inputFromAttrs(const Attrs & attrs)
         auto res = inputScheme->inputFromAttrs(attrs2);
         if (res) {
             if (auto narHash = maybeGetStrAttr(attrs, "narHash"))
-                // FIXME: require SRI hash.
-                res->narHash = newHashAllowEmpty(*narHash, {});
+                res->narHash = Hash::fromSRI(*narHash);
             return res;
         }
     }
diff --git a/src/libfetchers/tarball.cc b/src/libfetchers/tarball.cc
index f5356f0af..732fac8c3 100644
--- a/src/libfetchers/tarball.cc
+++ b/src/libfetchers/tarball.cc
@@ -242,15 +242,13 @@ struct TarballInputScheme : InputScheme
 
         auto hash = input->url.query.find("hash");
         if (hash != input->url.query.end()) {
-            // FIXME: require SRI hash.
-            input->hash = Hash(hash->second);
+            input->hash = Hash::fromSRI(hash->second);
             input->url.query.erase(hash);
         }
 
         auto narHash = input->url.query.find("narHash");
         if (narHash != input->url.query.end()) {
-            // FIXME: require SRI hash.
-            input->narHash = Hash(narHash->second);
+            input->narHash = Hash::fromSRI(narHash->second);
             input->url.query.erase(narHash);
         }
 
diff --git a/src/libutil/hash.hh b/src/libutil/hash.hh
index 570e50dd4..887952ce5 100644
--- a/src/libutil/hash.hh
+++ b/src/libutil/hash.hh
@@ -43,7 +43,7 @@ struct Hash
     // hash type must be part of string
     Hash(std::string_view s);
 
-    Hash fromSRI(std::string_view original);
+    static Hash fromSRI(std::string_view original);
 
 private:
     // type must be provided, s must not include <type> prefix
diff --git a/src/libutil/util.cc b/src/libutil/util.cc
index ed43c403f..ea28ee70d 100644
--- a/src/libutil/util.cc
+++ b/src/libutil/util.cc
@@ -1,5 +1,6 @@
 #include "lazy.hh"
 #include "util.hh"
+#include "hash.hh"
 #include "affinity.hh"
 #include "sync.hh"
 #include "finally.hh"

From 6faeec3b2a5446e3fa511ce8cb4b1a12621c6186 Mon Sep 17 00:00:00 2001
From: Carlo Nucera <carlo.nucera@protonmail.com>
Date: Wed, 1 Jul 2020 17:50:34 -0400
Subject: [PATCH 08/30] Keep the previous name, for diffing

---
 src/libutil/hash.cc | 28 ++++++++++++++--------------
 1 file changed, 14 insertions(+), 14 deletions(-)

diff --git a/src/libutil/hash.cc b/src/libutil/hash.cc
index e8d290d13..448eb25f9 100644
--- a/src/libutil/hash.cc
+++ b/src/libutil/hash.cc
@@ -184,36 +184,36 @@ static std::pair<HashType, bool> newFunction(std::string_view & original, std::o
 Hash::Hash(std::string_view original, std::optional<HashType> optType)
     : Hash(original, newFunction(original, optType)) {}
 
-Hash::Hash(std::string_view original, std::pair<HashType, bool> typeAndSRI)
+Hash::Hash(std::string_view rest, std::pair<HashType, bool> typeAndSRI)
     : Hash(typeAndSRI.first)
 {
     auto [type, isSRI] = std::move(typeAndSRI);
 
-    if (!isSRI && original.size() == base16Len()) {
+    if (!isSRI && rest.size() == base16Len()) {
 
         auto parseHexDigit = [&](char c) {
             if (c >= '0' && c <= '9') return c - '0';
             if (c >= 'A' && c <= 'F') return c - 'A' + 10;
             if (c >= 'a' && c <= 'f') return c - 'a' + 10;
-            throw BadHash("invalid base-16 hash '%s'", original);
+            throw BadHash("invalid base-16 hash '%s'", rest);
         };
 
         for (unsigned int i = 0; i < hashSize; i++) {
             hash[i] =
-                parseHexDigit(original[i * 2]) << 4
-                | parseHexDigit(original[i * 2 + 1]);
+                parseHexDigit(rest[i * 2]) << 4
+                | parseHexDigit(rest[i * 2 + 1]);
         }
     }
 
-    else if (!isSRI && original.size() == base32Len()) {
+    else if (!isSRI && rest.size() == base32Len()) {
 
-        for (unsigned int n = 0; n < original.size(); ++n) {
-            char c = original[original.size() - n - 1];
+        for (unsigned int n = 0; n < rest.size(); ++n) {
+            char c = rest[rest.size() - n - 1];
             unsigned char digit;
             for (digit = 0; digit < base32Chars.size(); ++digit) /* !!! slow */
                 if (base32Chars[digit] == c) break;
             if (digit >= 32)
-                throw BadHash("invalid base-32 hash '%s'", original);
+                throw BadHash("invalid base-32 hash '%s'", rest);
             unsigned int b = n * 5;
             unsigned int i = b / 8;
             unsigned int j = b % 8;
@@ -223,21 +223,21 @@ Hash::Hash(std::string_view original, std::pair<HashType, bool> typeAndSRI)
                 hash[i + 1] |= digit >> (8 - j);
             } else {
                 if (digit >> (8 - j))
-                    throw BadHash("invalid base-32 hash '%s'", original);
+                    throw BadHash("invalid base-32 hash '%s'", rest);
             }
         }
     }
 
-    else if (isSRI || original.size() == base64Len()) {
-        auto d = base64Decode(original);
+    else if (isSRI || rest.size() == base64Len()) {
+        auto d = base64Decode(rest);
         if (d.size() != hashSize)
-            throw BadHash("invalid %s hash '%s'", isSRI ? "SRI" : "base-64", original);
+            throw BadHash("invalid %s hash '%s'", isSRI ? "SRI" : "base-64", rest);
         assert(hashSize);
         memcpy(hash, d.data(), hashSize);
     }
 
     else
-        throw BadHash("hash '%s' has wrong length for hash type '%s'", original, printHashType(this->type));
+        throw BadHash("hash '%s' has wrong length for hash type '%s'", rest, printHashType(this->type));
 }
 
 Hash newHashAllowEmpty(std::string hashStr, std::optional<HashType> ht)

From d63a5ded76079008b09256aa36ef0c222919e8fa Mon Sep 17 00:00:00 2001
From: Carlo Nucera <carlo.nucera@protonmail.com>
Date: Wed, 1 Jul 2020 17:53:24 -0400
Subject: [PATCH 09/30] Remove unused import

---
 src/libutil/util.cc | 1 -
 1 file changed, 1 deletion(-)

diff --git a/src/libutil/util.cc b/src/libutil/util.cc
index ea28ee70d..ed43c403f 100644
--- a/src/libutil/util.cc
+++ b/src/libutil/util.cc
@@ -1,6 +1,5 @@
 #include "lazy.hh"
 #include "util.hh"
-#include "hash.hh"
 #include "affinity.hh"
 #include "sync.hh"
 #include "finally.hh"

From c8c4bcf90e065b47c3ee2984b1f8ff696da889af Mon Sep 17 00:00:00 2001
From: Carlo Nucera <carlo.nucera@protonmail.com>
Date: Wed, 1 Jul 2020 18:03:22 -0400
Subject: [PATCH 10/30] Inline Hash::init()

---
 src/libutil/hash.cc | 2 +-
 src/libutil/hash.hh | 4 +---
 2 files changed, 2 insertions(+), 4 deletions(-)

diff --git a/src/libutil/hash.cc b/src/libutil/hash.cc
index 448eb25f9..2087e3464 100644
--- a/src/libutil/hash.cc
+++ b/src/libutil/hash.cc
@@ -27,7 +27,7 @@ static size_t regularHashSize(HashType type) {
     abort();
 }
 
-void Hash::init()
+Hash::Hash(HashType type) : type(type)
 {
     hashSize = regularHashSize(type);
     assert(hashSize <= maxHashSize);
diff --git a/src/libutil/hash.hh b/src/libutil/hash.hh
index 887952ce5..766009438 100644
--- a/src/libutil/hash.hh
+++ b/src/libutil/hash.hh
@@ -32,7 +32,7 @@ struct Hash
     HashType type;
 
     /* Create a zero-filled hash object. */
-    Hash(HashType type) : type(type) { init(); };
+    Hash(HashType type);
 
     /* Initialize the hash from a string representation, in the format
        "[<type>:]<base16|base32|base64>" or "<type>-<base64>" (a
@@ -49,8 +49,6 @@ private:
     // type must be provided, s must not include <type> prefix
     Hash(std::string_view s, std::pair<HashType, bool> typeAndSRI);
 
-    void init();
-
 public:
     /* Check whether a hash is set. */
     operator bool () const { return (bool) type; }

From 263ccdd48923b730fd7e6f687583160d7b24039b Mon Sep 17 00:00:00 2001
From: Carlo Nucera <carlo.nucera@protonmail.com>
Date: Wed, 1 Jul 2020 18:34:18 -0400
Subject: [PATCH 11/30] Rename two hash constructors to proper functions

---
 src/libexpr/primops/fetchGit.cc          |  2 +-
 src/libexpr/primops/fetchMercurial.cc    |  2 +-
 src/libfetchers/git.cc                   |  8 ++++----
 src/libfetchers/github.cc                |  8 ++++----
 src/libfetchers/mercurial.cc             |  6 +++---
 src/libfetchers/path.cc                  |  4 ++--
 src/libstore/content-address.cc          |  4 ++--
 src/libstore/daemon.cc                   |  2 +-
 src/libstore/derivations.cc              |  4 ++--
 src/libstore/legacy-ssh-store.cc         |  2 +-
 src/libstore/local-store.cc              |  2 +-
 src/libstore/nar-info-disk-cache.cc      |  4 ++--
 src/libstore/nar-info.cc                 |  2 +-
 src/libstore/remote-store.cc             |  2 +-
 src/libstore/store-api.cc                |  2 +-
 src/libutil/hash.cc                      | 14 ++++++++++----
 src/libutil/hash.hh                      |  6 ++++--
 src/nix-prefetch-url/nix-prefetch-url.cc |  2 +-
 src/nix-store/nix-store.cc               |  4 ++--
 src/nix/hash.cc                          |  2 +-
 20 files changed, 45 insertions(+), 37 deletions(-)

diff --git a/src/libexpr/primops/fetchGit.cc b/src/libexpr/primops/fetchGit.cc
index dd7229a3d..0421318d1 100644
--- a/src/libexpr/primops/fetchGit.cc
+++ b/src/libexpr/primops/fetchGit.cc
@@ -29,7 +29,7 @@ static void prim_fetchGit(EvalState & state, const Pos & pos, Value * * args, Va
             else if (n == "ref")
                 ref = state.forceStringNoCtx(*attr.value, *attr.pos);
             else if (n == "rev")
-                rev = Hash(state.forceStringNoCtx(*attr.value, *attr.pos), htSHA1);
+                rev = Hash::parseAny(state.forceStringNoCtx(*attr.value, *attr.pos), htSHA1);
             else if (n == "name")
                 name = state.forceStringNoCtx(*attr.value, *attr.pos);
             else if (n == "submodules")
diff --git a/src/libexpr/primops/fetchMercurial.cc b/src/libexpr/primops/fetchMercurial.cc
index 9bace8f89..236219a6f 100644
--- a/src/libexpr/primops/fetchMercurial.cc
+++ b/src/libexpr/primops/fetchMercurial.cc
@@ -31,7 +31,7 @@ static void prim_fetchMercurial(EvalState & state, const Pos & pos, Value * * ar
                 // be both a revision or a branch/tag name.
                 auto value = state.forceStringNoCtx(*attr.value, *attr.pos);
                 if (std::regex_match(value, revRegex))
-                    rev = Hash(value, htSHA1);
+                    rev = Hash::parseAny(value, htSHA1);
                 else
                     ref = value;
             }
diff --git a/src/libfetchers/git.cc b/src/libfetchers/git.cc
index 75ce5ee8b..909bac78d 100644
--- a/src/libfetchers/git.cc
+++ b/src/libfetchers/git.cc
@@ -225,14 +225,14 @@ struct GitInput : Input
         if (isLocal) {
 
             if (!input->rev)
-                input->rev = Hash(chomp(runProgram("git", true, { "-C", actualUrl, "rev-parse", *input->ref })), htSHA1);
+                input->rev = Hash::parseAny(chomp(runProgram("git", true, { "-C", actualUrl, "rev-parse", *input->ref })), htSHA1);
 
             repoDir = actualUrl;
 
         } else {
 
             if (auto res = getCache()->lookup(store, mutableAttrs)) {
-                auto rev2 = Hash(getStrAttr(res->first, "rev"), htSHA1);
+                auto rev2 = Hash::parseAny(getStrAttr(res->first, "rev"), htSHA1);
                 if (!rev || rev == rev2) {
                     input->rev = rev2;
                     return makeResult(res->first, std::move(res->second));
@@ -301,7 +301,7 @@ struct GitInput : Input
             }
 
             if (!input->rev)
-                input->rev = Hash(chomp(readFile(localRefFile)), htSHA1);
+                input->rev = Hash::parseAny(chomp(readFile(localRefFile)), htSHA1);
         }
 
         bool isShallow = chomp(runProgram("git", true, { "-C", repoDir, "rev-parse", "--is-shallow-repository" })) == "true";
@@ -426,7 +426,7 @@ struct GitInputScheme : InputScheme
             input->ref = *ref;
         }
         if (auto rev = maybeGetStrAttr(attrs, "rev"))
-            input->rev = Hash(*rev, htSHA1);
+            input->rev = Hash::parseAny(*rev, htSHA1);
 
         input->shallow = maybeGetBoolAttr(attrs, "shallow").value_or(false);
 
diff --git a/src/libfetchers/github.cc b/src/libfetchers/github.cc
index 0bee1d6b3..449481092 100644
--- a/src/libfetchers/github.cc
+++ b/src/libfetchers/github.cc
@@ -76,7 +76,7 @@ struct GitHubInput : Input
                 readFile(
                     store->toRealPath(
                         downloadFile(store, url, "source", false).storePath)));
-            rev = Hash(std::string { json["sha"] }, htSHA1);
+            rev = Hash::parseAny(std::string { json["sha"] }, htSHA1);
             debug("HEAD revision for '%s' is %s", url, rev->gitRev());
         }
 
@@ -140,7 +140,7 @@ struct GitHubInputScheme : InputScheme
         if (path.size() == 2) {
         } else if (path.size() == 3) {
             if (std::regex_match(path[2], revRegex))
-                input->rev = Hash(path[2], htSHA1);
+                input->rev = Hash::parseAny(path[2], htSHA1);
             else if (std::regex_match(path[2], refRegex))
                 input->ref = path[2];
             else
@@ -152,7 +152,7 @@ struct GitHubInputScheme : InputScheme
             if (name == "rev") {
                 if (input->rev)
                     throw BadURL("GitHub URL '%s' contains multiple commit hashes", url.url);
-                input->rev = Hash(value, htSHA1);
+                input->rev = Hash::parseAny(value, htSHA1);
             }
             else if (name == "ref") {
                 if (!std::regex_match(value, refRegex))
@@ -185,7 +185,7 @@ struct GitHubInputScheme : InputScheme
         input->repo = getStrAttr(attrs, "repo");
         input->ref = maybeGetStrAttr(attrs, "ref");
         if (auto rev = maybeGetStrAttr(attrs, "rev"))
-            input->rev = Hash(*rev, htSHA1);
+            input->rev = Hash::parseAny(*rev, htSHA1);
         return input;
     }
 };
diff --git a/src/libfetchers/mercurial.cc b/src/libfetchers/mercurial.cc
index 2e0d4bf4d..29f2a9d5b 100644
--- a/src/libfetchers/mercurial.cc
+++ b/src/libfetchers/mercurial.cc
@@ -167,7 +167,7 @@ struct MercurialInput : Input
         });
 
         if (auto res = getCache()->lookup(store, mutableAttrs)) {
-            auto rev2 = Hash(getStrAttr(res->first, "rev"), htSHA1);
+            auto rev2 = Hash::parseAny(getStrAttr(res->first, "rev"), htSHA1);
             if (!rev || rev == rev2) {
                 input->rev = rev2;
                 return makeResult(res->first, std::move(res->second));
@@ -210,7 +210,7 @@ struct MercurialInput : Input
             runProgram("hg", true, { "log", "-R", cacheDir, "-r", revOrRef, "--template", "{node} {rev} {branch}" }));
         assert(tokens.size() == 3);
 
-        input->rev = Hash(tokens[0], htSHA1);
+        input->rev = Hash::parseAny(tokens[0], htSHA1);
         auto revCount = std::stoull(tokens[1]);
         input->ref = tokens[2];
 
@@ -293,7 +293,7 @@ struct MercurialInputScheme : InputScheme
             input->ref = *ref;
         }
         if (auto rev = maybeGetStrAttr(attrs, "rev"))
-            input->rev = Hash(*rev, htSHA1);
+            input->rev = Hash::parseAny(*rev, htSHA1);
         return input;
     }
 };
diff --git a/src/libfetchers/path.cc b/src/libfetchers/path.cc
index ba2cc192e..1caab4165 100644
--- a/src/libfetchers/path.cc
+++ b/src/libfetchers/path.cc
@@ -101,7 +101,7 @@ struct PathInputScheme : InputScheme
 
         for (auto & [name, value] : url.query)
             if (name == "rev")
-                input->rev = Hash(value, htSHA1);
+                input->rev = Hash::parseAny(value, htSHA1);
             else if (name == "revCount") {
                 uint64_t revCount;
                 if (!string2Int(value, revCount))
@@ -129,7 +129,7 @@ struct PathInputScheme : InputScheme
 
         for (auto & [name, value] : attrs)
             if (name == "rev")
-                input->rev = Hash(getStrAttr(attrs, "rev"), htSHA1);
+                input->rev = Hash::parseAny(getStrAttr(attrs, "rev"), htSHA1);
             else if (name == "revCount")
                 input->revCount = getIntAttr(attrs, "revCount");
             else if (name == "lastModified")
diff --git a/src/libstore/content-address.cc b/src/libstore/content-address.cc
index 8152e5215..2d96fb0c0 100644
--- a/src/libstore/content-address.cc
+++ b/src/libstore/content-address.cc
@@ -68,7 +68,7 @@ ContentAddress parseContentAddress(std::string_view rawCa) {
             throw Error("text content address hash should use %s, but instead uses %s",
                 printHashType(htSHA256), printHashType(hashType));
         return TextHash {
-            .hash = Hash { rest, std::move(hashType) },
+            .hash = Hash::parseAny(rest, std::move(hashType)),
         };
     } else if (prefix == "fixed") {
         // Parse method
@@ -80,7 +80,7 @@ ContentAddress parseContentAddress(std::string_view rawCa) {
         HashType hashType = parseHashType_();
         return FixedOutputHash {
             .method = method,
-            .hash = Hash { rest, std::move(hashType) },
+            .hash = Hash::parseAny(rest, std::move(hashType)),
         };
     } else
         throw UsageError("content address prefix \"%s\" is unrecognized. Recogonized prefixes are \"text\" or \"fixed\"", prefix);
diff --git a/src/libstore/daemon.cc b/src/libstore/daemon.cc
index 0b48e04c0..cc4827e64 100644
--- a/src/libstore/daemon.cc
+++ b/src/libstore/daemon.cc
@@ -706,7 +706,7 @@ static void performOp(TunnelLogger * logger, ref<Store> store,
         auto deriver = readString(from);
         if (deriver != "")
             info.deriver = store->parseStorePath(deriver);
-        info.narHash = Hash(readString(from), htSHA256);
+        info.narHash = Hash::parseAny(readString(from), htSHA256);
         info.references = readStorePaths<StorePathSet>(*store, from);
         from >> info.registrationTime >> info.narSize >> info.ultimate;
         info.sigs = readStrings<StringSet>(from);
diff --git a/src/libstore/derivations.cc b/src/libstore/derivations.cc
index 42551ef6b..30ce32354 100644
--- a/src/libstore/derivations.cc
+++ b/src/libstore/derivations.cc
@@ -118,7 +118,7 @@ static DerivationOutput parseDerivationOutput(const Store & store, istringstream
         const HashType hashType = parseHashType(hashAlgo);
         fsh = FixedOutputHash {
             .method = std::move(method),
-            .hash = Hash(hash, hashType),
+            .hash = Hash::parseAny(hash, hashType),
         };
     }
 
@@ -416,7 +416,7 @@ static DerivationOutput readDerivationOutput(Source & in, const Store & store)
         auto hashType = parseHashType(hashAlgo);
         fsh = FixedOutputHash {
             .method = std::move(method),
-            .hash = Hash(hash, hashType),
+            .hash = Hash::parseAny(hash, hashType),
         };
     }
 
diff --git a/src/libstore/legacy-ssh-store.cc b/src/libstore/legacy-ssh-store.cc
index 35caf23e7..f9d95fd2b 100644
--- a/src/libstore/legacy-ssh-store.cc
+++ b/src/libstore/legacy-ssh-store.cc
@@ -113,7 +113,7 @@ struct LegacySSHStore : public Store
 
             if (GET_PROTOCOL_MINOR(conn->remoteVersion) >= 4) {
                 auto s = readString(conn->from);
-                info->narHash = s.empty() ? std::optional<Hash>{} : Hash{s};
+                info->narHash = s.empty() ? std::optional<Hash>{} : Hash::parseAnyPrefixed(s);
                 info->ca = parseContentAddressOpt(readString(conn->from));
                 info->sigs = readStrings<StringSet>(conn->from);
             }
diff --git a/src/libstore/local-store.cc b/src/libstore/local-store.cc
index 9259d8f61..b75e2bdfe 100644
--- a/src/libstore/local-store.cc
+++ b/src/libstore/local-store.cc
@@ -647,7 +647,7 @@ void LocalStore::queryPathInfoUncached(const StorePath & path,
             info->id = useQueryPathInfo.getInt(0);
 
             try {
-                info->narHash = Hash(useQueryPathInfo.getStr(1));
+                info->narHash = Hash::parseAnyPrefixed(useQueryPathInfo.getStr(1));
             } catch (BadHash & e) {
                 throw Error("in valid-path entry for '%s': %s", printStorePath(path), e.what());
             }
diff --git a/src/libstore/nar-info-disk-cache.cc b/src/libstore/nar-info-disk-cache.cc
index 9ddb9957f..92da14e23 100644
--- a/src/libstore/nar-info-disk-cache.cc
+++ b/src/libstore/nar-info-disk-cache.cc
@@ -193,9 +193,9 @@ public:
             narInfo->url = queryNAR.getStr(2);
             narInfo->compression = queryNAR.getStr(3);
             if (!queryNAR.isNull(4))
-                narInfo->fileHash = Hash(queryNAR.getStr(4));
+                narInfo->fileHash = Hash::parseAnyPrefixed(queryNAR.getStr(4));
             narInfo->fileSize = queryNAR.getInt(5);
-            narInfo->narHash = Hash(queryNAR.getStr(6));
+            narInfo->narHash = Hash::parseAnyPrefixed(queryNAR.getStr(6));
             narInfo->narSize = queryNAR.getInt(7);
             for (auto & r : tokenizeString<Strings>(queryNAR.getStr(8), " "))
                 narInfo->references.insert(StorePath(r));
diff --git a/src/libstore/nar-info.cc b/src/libstore/nar-info.cc
index c403d4bec..2a52e4098 100644
--- a/src/libstore/nar-info.cc
+++ b/src/libstore/nar-info.cc
@@ -12,7 +12,7 @@ NarInfo::NarInfo(const Store & store, const std::string & s, const std::string &
 
     auto parseHashField = [&](const string & s) {
         try {
-            return Hash(s);
+            return Hash::parseAnyPrefixed(s);
         } catch (BadHash &) {
             throw corrupt();
         }
diff --git a/src/libstore/remote-store.cc b/src/libstore/remote-store.cc
index 305a47340..890d96388 100644
--- a/src/libstore/remote-store.cc
+++ b/src/libstore/remote-store.cc
@@ -375,7 +375,7 @@ void RemoteStore::queryPathInfoUncached(const StorePath & path,
             info = std::make_shared<ValidPathInfo>(StorePath(path));
             auto deriver = readString(conn->from);
             if (deriver != "") info->deriver = parseStorePath(deriver);
-            info->narHash = Hash(readString(conn->from), htSHA256);
+            info->narHash = Hash::parseAny(readString(conn->from), htSHA256);
             info->references = readStorePaths<StorePathSet>(*this, conn->from);
             conn->from >> info->registrationTime >> info->narSize;
             if (GET_PROTOCOL_MINOR(conn->daemonVersion) >= 16) {
diff --git a/src/libstore/store-api.cc b/src/libstore/store-api.cc
index e4083bbe1..080ce9823 100644
--- a/src/libstore/store-api.cc
+++ b/src/libstore/store-api.cc
@@ -703,7 +703,7 @@ std::optional<ValidPathInfo> decodeValidPathInfo(const Store & store, std::istre
     if (hashGiven) {
         string s;
         getline(str, s);
-        info.narHash = Hash(s, htSHA256);
+        info.narHash = Hash::parseAny(s, htSHA256);
         getline(str, s);
         if (!string2Int(s, info.narSize)) throw Error("number expected");
     }
diff --git a/src/libutil/hash.cc b/src/libutil/hash.cc
index 2087e3464..fcc0b9eb7 100644
--- a/src/libutil/hash.cc
+++ b/src/libutil/hash.cc
@@ -144,7 +144,10 @@ Hash Hash::fromSRI(std::string_view original) {
     return Hash(rest, std::make_pair(parsedType, true));
 }
 
-Hash::Hash(std::string_view s) : Hash(s, std::nullopt) {}
+Hash Hash::parseAnyPrefixed(std::string_view s)
+{
+    return parseAny(s, std::nullopt);
+}
 
 static std::pair<HashType, bool> newFunction(std::string_view & original, std::optional<HashType> optType)
 {
@@ -181,8 +184,11 @@ static std::pair<HashType, bool> newFunction(std::string_view & original, std::o
 }
 
 // mutates the string_view
-Hash::Hash(std::string_view original, std::optional<HashType> optType)
-    : Hash(original, newFunction(original, optType)) {}
+Hash Hash::parseAny(std::string_view original, std::optional<HashType> optType)
+{
+    auto typeAndSRI = newFunction(original, optType);
+    return Hash(original, typeAndSRI);
+}
 
 Hash::Hash(std::string_view rest, std::pair<HashType, bool> typeAndSRI)
     : Hash(typeAndSRI.first)
@@ -249,7 +255,7 @@ Hash newHashAllowEmpty(std::string hashStr, std::optional<HashType> ht)
         warn("found empty hash, assuming '%s'", h.to_string(SRI, true));
         return h;
     } else
-        return Hash(hashStr, ht);
+        return Hash::parseAny(hashStr, ht);
 }
 
 
diff --git a/src/libutil/hash.hh b/src/libutil/hash.hh
index 766009438..3e413a52c 100644
--- a/src/libutil/hash.hh
+++ b/src/libutil/hash.hh
@@ -39,9 +39,11 @@ struct Hash
        Subresource Integrity hash expression). If the 'type' argument
        is not present, then the hash type must be specified in the
        string. */
-    Hash(std::string_view s, std::optional<HashType> type);
+    static Hash parseAny(std::string_view s, std::optional<HashType> type);
     // hash type must be part of string
-    Hash(std::string_view s);
+    static Hash parseAnyPrefixed(std::string_view s);
+    // prefix parsed separately; non SRI hash
+    static Hash parseAnyUnprefixed(std::string_view s, HashType type);
 
     static Hash fromSRI(std::string_view original);
 
diff --git a/src/nix-prefetch-url/nix-prefetch-url.cc b/src/nix-prefetch-url/nix-prefetch-url.cc
index 22410c44c..f752e0448 100644
--- a/src/nix-prefetch-url/nix-prefetch-url.cc
+++ b/src/nix-prefetch-url/nix-prefetch-url.cc
@@ -156,7 +156,7 @@ static int _main(int argc, char * * argv)
         Hash hash(ht), expectedHash(ht);
         std::optional<StorePath> storePath;
         if (args.size() == 2) {
-            expectedHash = Hash(args[1], ht);
+            expectedHash = Hash::parseAny(args[1], ht);
             const auto recursive = unpack ? FileIngestionMethod::Recursive : FileIngestionMethod::Flat;
             storePath = store->makeFixedOutputPath(recursive, expectedHash, name);
             if (store->isValidPath(*storePath))
diff --git a/src/nix-store/nix-store.cc b/src/nix-store/nix-store.cc
index ff04cbefc..cc3b07c31 100644
--- a/src/nix-store/nix-store.cc
+++ b/src/nix-store/nix-store.cc
@@ -208,7 +208,7 @@ static void opPrintFixedPath(Strings opFlags, Strings opArgs)
     string hash = *i++;
     string name = *i++;
 
-    cout << fmt("%s\n", store->printStorePath(store->makeFixedOutputPath(recursive, Hash(hash, hashAlgo), name)));
+    cout << fmt("%s\n", store->printStorePath(store->makeFixedOutputPath(recursive, Hash::parseAny(hash, hashAlgo), name)));
 }
 
 
@@ -950,7 +950,7 @@ static void opServe(Strings opFlags, Strings opArgs)
                 auto deriver = readString(in);
                 if (deriver != "")
                     info.deriver = store->parseStorePath(deriver);
-                info.narHash = Hash(readString(in), htSHA256);
+                info.narHash = Hash::parseAny(readString(in), htSHA256);
                 info.references = readStorePaths<StorePathSet>(*store, in);
                 in >> info.registrationTime >> info.narSize >> info.ultimate;
                 info.sigs = readStrings<StringSet>(in);
diff --git a/src/nix/hash.cc b/src/nix/hash.cc
index b97c6d21f..fb0843ce2 100644
--- a/src/nix/hash.cc
+++ b/src/nix/hash.cc
@@ -103,7 +103,7 @@ struct CmdToBase : Command
     void run() override
     {
         for (auto s : args)
-            logger->stdout(Hash(s, ht).to_string(base, base == SRI));
+            logger->stdout(Hash::parseAny(s, ht).to_string(base, base == SRI));
     }
 };
 

From 343d1569b193e4456e2e5365921371bfd6e37205 Mon Sep 17 00:00:00 2001
From: Carlo Nucera <carlo.nucera@protonmail.com>
Date: Thu, 2 Jul 2020 10:48:47 -0400
Subject: [PATCH 12/30] Fix test suite

---
 src/libutil/hash.cc | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/src/libutil/hash.cc b/src/libutil/hash.cc
index fcc0b9eb7..084d24170 100644
--- a/src/libutil/hash.cc
+++ b/src/libutil/hash.cc
@@ -149,9 +149,9 @@ Hash Hash::parseAnyPrefixed(std::string_view s)
     return parseAny(s, std::nullopt);
 }
 
-static std::pair<HashType, bool> newFunction(std::string_view & original, std::optional<HashType> optType)
+static std::pair<HashType, bool> newFunction(std::string_view & rest, std::optional<HashType> optType)
 {
-    auto rest = original;
+    auto original = rest;
 
     bool isSRI = false;
 

From 27c8029573ab49ad11c069ef547e3c087c73939f Mon Sep 17 00:00:00 2001
From: Carlo Nucera <carlo.nucera@protonmail.com>
Date: Thu, 2 Jul 2020 10:58:29 -0400
Subject: [PATCH 13/30] Inline newFunction

---
 src/libutil/hash.cc | 25 ++++++++-----------------
 1 file changed, 8 insertions(+), 17 deletions(-)

diff --git a/src/libutil/hash.cc b/src/libutil/hash.cc
index 084d24170..2908a3445 100644
--- a/src/libutil/hash.cc
+++ b/src/libutil/hash.cc
@@ -149,11 +149,12 @@ Hash Hash::parseAnyPrefixed(std::string_view s)
     return parseAny(s, std::nullopt);
 }
 
-static std::pair<HashType, bool> newFunction(std::string_view & rest, std::optional<HashType> optType)
+Hash Hash::parseAny(std::string_view original, std::optional<HashType> optType)
 {
-    auto original = rest;
+    auto rest = original;
 
     bool isSRI = false;
+    HashType hashType;
 
     // Parse the has type before the separater, if there was one.
     std::optional<HashType> optParsedType;
@@ -171,23 +172,13 @@ static std::pair<HashType, bool> newFunction(std::string_view & rest, std::optio
 
     // Either the string or user must provide the type, if they both do they
     // must agree.
-    if (!optParsedType && !optType) {
+    if (!optParsedType && !optType)
         throw BadHash("hash '%s' does not include a type, nor is the type otherwise known from context.", rest);
-    } else {
-        if (optParsedType && optType && *optParsedType != *optType)
-            throw BadHash("hash '%s' should have type '%s'", original, printHashType(*optType));
-        return {
-            optParsedType ? *optParsedType : *optType,
-            isSRI,
-        };
-    }
-}
+    else if (optParsedType && optType && *optParsedType != *optType)
+        throw BadHash("hash '%s' should have type '%s'", original, printHashType(*optType));
 
-// mutates the string_view
-Hash Hash::parseAny(std::string_view original, std::optional<HashType> optType)
-{
-    auto typeAndSRI = newFunction(original, optType);
-    return Hash(original, typeAndSRI);
+    hashType = optParsedType ? *optParsedType : *optType;
+    return Hash(rest, std::make_pair(hashType, isSRI));
 }
 
 Hash::Hash(std::string_view rest, std::pair<HashType, bool> typeAndSRI)

From f61bc45d192809a040a359b22f3dbd0722613af6 Mon Sep 17 00:00:00 2001
From: Carlo Nucera <carlo.nucera@protonmail.com>
Date: Thu, 2 Jul 2020 11:09:04 -0400
Subject: [PATCH 14/30] Get rid of the std::pair

---
 src/libutil/hash.cc | 10 ++++------
 src/libutil/hash.hh |  2 +-
 2 files changed, 5 insertions(+), 7 deletions(-)

diff --git a/src/libutil/hash.cc b/src/libutil/hash.cc
index 2908a3445..2f006ce1e 100644
--- a/src/libutil/hash.cc
+++ b/src/libutil/hash.cc
@@ -141,7 +141,7 @@ Hash Hash::fromSRI(std::string_view original) {
         throw BadHash("hash '%s' is not SRI", original);
     HashType parsedType = parseHashType(*hashRaw);
 
-    return Hash(rest, std::make_pair(parsedType, true));
+    return Hash(rest, parsedType, true);
 }
 
 Hash Hash::parseAnyPrefixed(std::string_view s)
@@ -178,14 +178,12 @@ Hash Hash::parseAny(std::string_view original, std::optional<HashType> optType)
         throw BadHash("hash '%s' should have type '%s'", original, printHashType(*optType));
 
     hashType = optParsedType ? *optParsedType : *optType;
-    return Hash(rest, std::make_pair(hashType, isSRI));
+    return Hash(rest, hashType, isSRI);
 }
 
-Hash::Hash(std::string_view rest, std::pair<HashType, bool> typeAndSRI)
-    : Hash(typeAndSRI.first)
+Hash::Hash(std::string_view rest, HashType type, bool isSRI)
+    : Hash(type)
 {
-    auto [type, isSRI] = std::move(typeAndSRI);
-
     if (!isSRI && rest.size() == base16Len()) {
 
         auto parseHexDigit = [&](char c) {
diff --git a/src/libutil/hash.hh b/src/libutil/hash.hh
index 3e413a52c..4e3591a04 100644
--- a/src/libutil/hash.hh
+++ b/src/libutil/hash.hh
@@ -49,7 +49,7 @@ struct Hash
 
 private:
     // type must be provided, s must not include <type> prefix
-    Hash(std::string_view s, std::pair<HashType, bool> typeAndSRI);
+    Hash(std::string_view s, HashType type, bool isSRI);
 
 public:
     /* Check whether a hash is set. */

From 9462d8a50b5443bc2dac616f94ded9ad37020094 Mon Sep 17 00:00:00 2001
From: Carlo Nucera <carlo.nucera@protonmail.com>
Date: Thu, 2 Jul 2020 11:11:18 -0400
Subject: [PATCH 15/30] Rename fromSRI to parseSRI for constistency

---
 src/libfetchers/fetchers.cc | 2 +-
 src/libfetchers/tarball.cc  | 4 ++--
 src/libutil/hash.cc         | 2 +-
 src/libutil/hash.hh         | 2 +-
 4 files changed, 5 insertions(+), 5 deletions(-)

diff --git a/src/libfetchers/fetchers.cc b/src/libfetchers/fetchers.cc
index 91d0d6a1d..b1782feab 100644
--- a/src/libfetchers/fetchers.cc
+++ b/src/libfetchers/fetchers.cc
@@ -35,7 +35,7 @@ std::unique_ptr<Input> inputFromAttrs(const Attrs & attrs)
         auto res = inputScheme->inputFromAttrs(attrs2);
         if (res) {
             if (auto narHash = maybeGetStrAttr(attrs, "narHash"))
-                res->narHash = Hash::fromSRI(*narHash);
+                res->narHash = Hash::parseSRI(*narHash);
             return res;
         }
     }
diff --git a/src/libfetchers/tarball.cc b/src/libfetchers/tarball.cc
index 732fac8c3..6ca51269b 100644
--- a/src/libfetchers/tarball.cc
+++ b/src/libfetchers/tarball.cc
@@ -242,13 +242,13 @@ struct TarballInputScheme : InputScheme
 
         auto hash = input->url.query.find("hash");
         if (hash != input->url.query.end()) {
-            input->hash = Hash::fromSRI(hash->second);
+            input->hash = Hash::parseSRI(hash->second);
             input->url.query.erase(hash);
         }
 
         auto narHash = input->url.query.find("narHash");
         if (narHash != input->url.query.end()) {
-            input->narHash = Hash::fromSRI(narHash->second);
+            input->narHash = Hash::parseSRI(narHash->second);
             input->url.query.erase(narHash);
         }
 
diff --git a/src/libutil/hash.cc b/src/libutil/hash.cc
index 2f006ce1e..a077d40a0 100644
--- a/src/libutil/hash.cc
+++ b/src/libutil/hash.cc
@@ -132,7 +132,7 @@ std::string Hash::to_string(Base base, bool includeType) const
     return s;
 }
 
-Hash Hash::fromSRI(std::string_view original) {
+Hash Hash::parseSRI(std::string_view original) {
     auto rest = original;
 
     // Parse the has type before the separater, if there was one.
diff --git a/src/libutil/hash.hh b/src/libutil/hash.hh
index 4e3591a04..d321cc8e1 100644
--- a/src/libutil/hash.hh
+++ b/src/libutil/hash.hh
@@ -45,7 +45,7 @@ struct Hash
     // prefix parsed separately; non SRI hash
     static Hash parseAnyUnprefixed(std::string_view s, HashType type);
 
-    static Hash fromSRI(std::string_view original);
+    static Hash parseSRI(std::string_view original);
 
 private:
     // type must be provided, s must not include <type> prefix

From 36cbc74689321399aeae26ff506809b8d9b24674 Mon Sep 17 00:00:00 2001
From: Carlo Nucera <carlo.nucera@protonmail.com>
Date: Thu, 2 Jul 2020 11:21:00 -0400
Subject: [PATCH 16/30] Inline and simplify in parseAnyPrefixed

---
 src/libutil/hash.cc | 27 +++++++++++++++++++++++++--
 1 file changed, 25 insertions(+), 2 deletions(-)

diff --git a/src/libutil/hash.cc b/src/libutil/hash.cc
index a077d40a0..75f8f319c 100644
--- a/src/libutil/hash.cc
+++ b/src/libutil/hash.cc
@@ -144,9 +144,32 @@ Hash Hash::parseSRI(std::string_view original) {
     return Hash(rest, parsedType, true);
 }
 
-Hash Hash::parseAnyPrefixed(std::string_view s)
+Hash Hash::parseAnyPrefixed(std::string_view original)
 {
-    return parseAny(s, std::nullopt);
+    auto rest = original;
+
+    bool isSRI = false;
+
+    // Parse the has type before the separater, if there was one.
+    std::optional<HashType> optParsedType;
+    {
+        auto hashRaw = splitPrefix(rest, ':');
+
+        if (!hashRaw) {
+            hashRaw = splitPrefix(rest, '-');
+            if (hashRaw)
+                isSRI = true;
+        }
+        if (hashRaw)
+            optParsedType = parseHashType(*hashRaw);
+    }
+
+    // Either the string or user must provide the type, if they both do they
+    // must agree.
+    if (!optParsedType)
+        throw BadHash("hash '%s' does not include a type.", rest);
+
+    return Hash(rest, *optParsedType, isSRI);
 }
 
 Hash Hash::parseAny(std::string_view original, std::optional<HashType> optType)

From ea48e3a5b5f1051c251184792417326c513bf00f Mon Sep 17 00:00:00 2001
From: Carlo Nucera <carlo.nucera@protonmail.com>
Date: Thu, 2 Jul 2020 11:29:33 -0400
Subject: [PATCH 17/30] Abstract common parsing functionality

---
 src/libutil/hash.cc   | 37 +++----------------------------------
 src/libutil/parser.hh | 22 ++++++++++++++++++++++
 2 files changed, 25 insertions(+), 34 deletions(-)

diff --git a/src/libutil/hash.cc b/src/libutil/hash.cc
index 75f8f319c..7d6b8d96e 100644
--- a/src/libutil/hash.cc
+++ b/src/libutil/hash.cc
@@ -147,22 +147,7 @@ Hash Hash::parseSRI(std::string_view original) {
 Hash Hash::parseAnyPrefixed(std::string_view original)
 {
     auto rest = original;
-
-    bool isSRI = false;
-
-    // Parse the has type before the separater, if there was one.
-    std::optional<HashType> optParsedType;
-    {
-        auto hashRaw = splitPrefix(rest, ':');
-
-        if (!hashRaw) {
-            hashRaw = splitPrefix(rest, '-');
-            if (hashRaw)
-                isSRI = true;
-        }
-        if (hashRaw)
-            optParsedType = parseHashType(*hashRaw);
-    }
+    auto [optParsedType, isSRI] = getParsedTypeAndSRI(rest);
 
     // Either the string or user must provide the type, if they both do they
     // must agree.
@@ -175,23 +160,7 @@ Hash Hash::parseAnyPrefixed(std::string_view original)
 Hash Hash::parseAny(std::string_view original, std::optional<HashType> optType)
 {
     auto rest = original;
-
-    bool isSRI = false;
-    HashType hashType;
-
-    // Parse the has type before the separater, if there was one.
-    std::optional<HashType> optParsedType;
-    {
-        auto hashRaw = splitPrefix(rest, ':');
-
-        if (!hashRaw) {
-            hashRaw = splitPrefix(rest, '-');
-            if (hashRaw)
-                isSRI = true;
-        }
-        if (hashRaw)
-            optParsedType = parseHashType(*hashRaw);
-    }
+    auto [optParsedType, isSRI] = getParsedTypeAndSRI(rest);
 
     // Either the string or user must provide the type, if they both do they
     // must agree.
@@ -200,7 +169,7 @@ Hash Hash::parseAny(std::string_view original, std::optional<HashType> optType)
     else if (optParsedType && optType && *optParsedType != *optType)
         throw BadHash("hash '%s' should have type '%s'", original, printHashType(*optType));
 
-    hashType = optParsedType ? *optParsedType : *optType;
+    HashType hashType = optParsedType ? *optParsedType : *optType;
     return Hash(rest, hashType, isSRI);
 }
 
diff --git a/src/libutil/parser.hh b/src/libutil/parser.hh
index d3bfafe75..d20e4dfc6 100644
--- a/src/libutil/parser.hh
+++ b/src/libutil/parser.hh
@@ -21,4 +21,26 @@ static inline std::optional<std::string_view> splitPrefix(std::string_view & str
     return std::nullopt;
 }
 
+// Mutates the string to eliminate the prefixes when found
+std::pair<std::optional<HashType>, bool> getParsedTypeAndSRI(std::string_view & rest) {
+    bool isSRI = false;
+
+    // Parse the has type before the separater, if there was one.
+    std::optional<HashType> optParsedType;
+    {
+        auto hashRaw = splitPrefix(rest, ':');
+
+        if (!hashRaw) {
+            hashRaw = splitPrefix(rest, '-');
+            if (hashRaw)
+                isSRI = true;
+        }
+        if (hashRaw)
+            optParsedType = parseHashType(*hashRaw);
+    }
+
+    return std::make_pair(optParsedType, isSRI);
+}
+
+
 }

From b6b10b1d4cb1cd487bbb5d2cc063ca743ae79004 Mon Sep 17 00:00:00 2001
From: Carlo Nucera <carlo.nucera@protonmail.com>
Date: Thu, 2 Jul 2020 11:34:40 -0400
Subject: [PATCH 18/30] Write the implementation for parseNonSRIUnprefixed

---
 src/libutil/hash.cc | 5 +++++
 src/libutil/hash.hh | 2 +-
 2 files changed, 6 insertions(+), 1 deletion(-)

diff --git a/src/libutil/hash.cc b/src/libutil/hash.cc
index 7d6b8d96e..1150e74ed 100644
--- a/src/libutil/hash.cc
+++ b/src/libutil/hash.cc
@@ -173,6 +173,11 @@ Hash Hash::parseAny(std::string_view original, std::optional<HashType> optType)
     return Hash(rest, hashType, isSRI);
 }
 
+Hash Hash::parseNonSRIUnprefixed(std::string_view s, HashType type)
+{
+    return Hash(s, type, false);
+}
+
 Hash::Hash(std::string_view rest, HashType type, bool isSRI)
     : Hash(type)
 {
diff --git a/src/libutil/hash.hh b/src/libutil/hash.hh
index d321cc8e1..af11a028d 100644
--- a/src/libutil/hash.hh
+++ b/src/libutil/hash.hh
@@ -43,7 +43,7 @@ struct Hash
     // hash type must be part of string
     static Hash parseAnyPrefixed(std::string_view s);
     // prefix parsed separately; non SRI hash
-    static Hash parseAnyUnprefixed(std::string_view s, HashType type);
+    static Hash parseNonSRIUnprefixed(std::string_view s, HashType type);
 
     static Hash parseSRI(std::string_view original);
 

From 1fc835aa223520f37e4945fa8626a096f170b188 Mon Sep 17 00:00:00 2001
From: Carlo Nucera <carlo.nucera@protonmail.com>
Date: Thu, 2 Jul 2020 11:57:21 -0400
Subject: [PATCH 19/30] Tighten parsing for drv files and pathinfo

---
 src/libstore/content-address.cc | 4 ++--
 src/libstore/derivations.cc     | 4 ++--
 2 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/src/libstore/content-address.cc b/src/libstore/content-address.cc
index 2d96fb0c0..02ab6710f 100644
--- a/src/libstore/content-address.cc
+++ b/src/libstore/content-address.cc
@@ -68,7 +68,7 @@ ContentAddress parseContentAddress(std::string_view rawCa) {
             throw Error("text content address hash should use %s, but instead uses %s",
                 printHashType(htSHA256), printHashType(hashType));
         return TextHash {
-            .hash = Hash::parseAny(rest, std::move(hashType)),
+            .hash = Hash::parseNonSRIUnprefixed(rest, std::move(hashType)),
         };
     } else if (prefix == "fixed") {
         // Parse method
@@ -80,7 +80,7 @@ ContentAddress parseContentAddress(std::string_view rawCa) {
         HashType hashType = parseHashType_();
         return FixedOutputHash {
             .method = method,
-            .hash = Hash::parseAny(rest, std::move(hashType)),
+            .hash = Hash::parseNonSRIUnprefixed(rest, std::move(hashType)),
         };
     } else
         throw UsageError("content address prefix \"%s\" is unrecognized. Recogonized prefixes are \"text\" or \"fixed\"", prefix);
diff --git a/src/libstore/derivations.cc b/src/libstore/derivations.cc
index 30ce32354..149994e3e 100644
--- a/src/libstore/derivations.cc
+++ b/src/libstore/derivations.cc
@@ -118,7 +118,7 @@ static DerivationOutput parseDerivationOutput(const Store & store, istringstream
         const HashType hashType = parseHashType(hashAlgo);
         fsh = FixedOutputHash {
             .method = std::move(method),
-            .hash = Hash::parseAny(hash, hashType),
+            .hash = Hash::parseNonSRIUnprefixed(hash, hashType),
         };
     }
 
@@ -416,7 +416,7 @@ static DerivationOutput readDerivationOutput(Source & in, const Store & store)
         auto hashType = parseHashType(hashAlgo);
         fsh = FixedOutputHash {
             .method = std::move(method),
-            .hash = Hash::parseAny(hash, hashType),
+            .hash = Hash::parseNonSRIUnprefixed(hash, hashType),
         };
     }
 

From a7cd7425d9341cf8a2c3af80b84cc55e874515c6 Mon Sep 17 00:00:00 2001
From: John Ericson <John.Ericson@Obsidian.Systems>
Date: Thu, 2 Jul 2020 23:10:11 +0000
Subject: [PATCH 20/30] Move `getParsedTypeAndSRI` to a more suitable location

Also mark it static
---
 src/libutil/hash.cc   | 21 +++++++++++++++++++++
 src/libutil/parser.hh | 21 ---------------------
 2 files changed, 21 insertions(+), 21 deletions(-)

diff --git a/src/libutil/hash.cc b/src/libutil/hash.cc
index 1150e74ed..76fa67086 100644
--- a/src/libutil/hash.cc
+++ b/src/libutil/hash.cc
@@ -144,6 +144,27 @@ Hash Hash::parseSRI(std::string_view original) {
     return Hash(rest, parsedType, true);
 }
 
+// Mutates the string to eliminate the prefixes when found
+static std::pair<std::optional<HashType>, bool> getParsedTypeAndSRI(std::string_view & rest) {
+    bool isSRI = false;
+
+    // Parse the has type before the separater, if there was one.
+    std::optional<HashType> optParsedType;
+    {
+        auto hashRaw = splitPrefix(rest, ':');
+
+        if (!hashRaw) {
+            hashRaw = splitPrefix(rest, '-');
+            if (hashRaw)
+                isSRI = true;
+        }
+        if (hashRaw)
+            optParsedType = parseHashType(*hashRaw);
+    }
+
+    return {optParsedType, isSRI};
+}
+
 Hash Hash::parseAnyPrefixed(std::string_view original)
 {
     auto rest = original;
diff --git a/src/libutil/parser.hh b/src/libutil/parser.hh
index d20e4dfc6..a6a83ce89 100644
--- a/src/libutil/parser.hh
+++ b/src/libutil/parser.hh
@@ -21,26 +21,5 @@ static inline std::optional<std::string_view> splitPrefix(std::string_view & str
     return std::nullopt;
 }
 
-// Mutates the string to eliminate the prefixes when found
-std::pair<std::optional<HashType>, bool> getParsedTypeAndSRI(std::string_view & rest) {
-    bool isSRI = false;
-
-    // Parse the has type before the separater, if there was one.
-    std::optional<HashType> optParsedType;
-    {
-        auto hashRaw = splitPrefix(rest, ':');
-
-        if (!hashRaw) {
-            hashRaw = splitPrefix(rest, '-');
-            if (hashRaw)
-                isSRI = true;
-        }
-        if (hashRaw)
-            optParsedType = parseHashType(*hashRaw);
-    }
-
-    return std::make_pair(optParsedType, isSRI);
-}
-
 
 }

From 13796be78dfa9d3a189ea6b482659c56b1301634 Mon Sep 17 00:00:00 2001
From: John Ericson <John.Ericson@Obsidian.Systems>
Date: Thu, 2 Jul 2020 23:16:57 +0000
Subject: [PATCH 21/30] Have `splitPrefix` and `splitPrefixTo` parser helpers

---
 src/libstore/content-address.cc |  8 +++-----
 src/libutil/hash.cc             |  6 +++---
 src/libutil/parser.hh           | 10 +++++++++-
 3 files changed, 15 insertions(+), 9 deletions(-)

diff --git a/src/libstore/content-address.cc b/src/libstore/content-address.cc
index 02ab6710f..470cc62c9 100644
--- a/src/libstore/content-address.cc
+++ b/src/libstore/content-address.cc
@@ -46,14 +46,14 @@ ContentAddress parseContentAddress(std::string_view rawCa) {
 
     std::string_view prefix;
     {
-        auto optPrefix = splitPrefix(rest, ':');
+        auto optPrefix = splitPrefixTo(rest, ':');
         if (!optPrefix)
             throw UsageError("not a content address because it is not in the form \"<prefix>:<rest>\": %s", rawCa);
         prefix = *optPrefix;
     }
 
     auto parseHashType_ = [&](){
-        auto hashTypeRaw = splitPrefix(rest, ':');
+        auto hashTypeRaw = splitPrefixTo(rest, ':');
         if (!hashTypeRaw)
             throw UsageError("content address hash must be in form \"<algo>:<hash>\", but found: %s", rawCa);
         HashType hashType = parseHashType(*hashTypeRaw);
@@ -73,10 +73,8 @@ ContentAddress parseContentAddress(std::string_view rawCa) {
     } else if (prefix == "fixed") {
         // Parse method
         auto method = FileIngestionMethod::Flat;
-        if (rest.substr(0, 2) == "r:") {
+        if (splitPrefix(rest, "r:"))
             method = FileIngestionMethod::Recursive;
-            rest = rest.substr(2);
-        }
         HashType hashType = parseHashType_();
         return FixedOutputHash {
             .method = method,
diff --git a/src/libutil/hash.cc b/src/libutil/hash.cc
index 76fa67086..35054462c 100644
--- a/src/libutil/hash.cc
+++ b/src/libutil/hash.cc
@@ -136,7 +136,7 @@ Hash Hash::parseSRI(std::string_view original) {
     auto rest = original;
 
     // Parse the has type before the separater, if there was one.
-    auto hashRaw = splitPrefix(rest, '-');
+    auto hashRaw = splitPrefixTo(rest, '-');
     if (!hashRaw)
         throw BadHash("hash '%s' is not SRI", original);
     HashType parsedType = parseHashType(*hashRaw);
@@ -151,10 +151,10 @@ static std::pair<std::optional<HashType>, bool> getParsedTypeAndSRI(std::string_
     // Parse the has type before the separater, if there was one.
     std::optional<HashType> optParsedType;
     {
-        auto hashRaw = splitPrefix(rest, ':');
+        auto hashRaw = splitPrefixTo(rest, ':');
 
         if (!hashRaw) {
-            hashRaw = splitPrefix(rest, '-');
+            hashRaw = splitPrefixTo(rest, '-');
             if (hashRaw)
                 isSRI = true;
         }
diff --git a/src/libutil/parser.hh b/src/libutil/parser.hh
index a6a83ce89..d19d7d8ed 100644
--- a/src/libutil/parser.hh
+++ b/src/libutil/parser.hh
@@ -3,13 +3,15 @@
 #include <optional>
 #include <string_view>
 
+#include "util.hh"
+
 namespace nix {
 
 // If `separator` is found, we return the portion of the string before the
 // separator, and modify the string argument to contain only the part after the
 // separator. Otherwise, wer return `std::nullopt`, and we leave the argument
 // string alone.
-static inline std::optional<std::string_view> splitPrefix(std::string_view & string, char separator) {
+static inline std::optional<std::string_view> splitPrefixTo(std::string_view & string, char separator) {
     auto sepInstance = string.find(separator);
 
     if (sepInstance != std::string_view::npos) {
@@ -21,5 +23,11 @@ static inline std::optional<std::string_view> splitPrefix(std::string_view & str
     return std::nullopt;
 }
 
+static inline bool splitPrefix(std::string_view & string, std::string_view prefix) {
+    bool res = hasPrefix(string, prefix);
+    if (res)
+        string.remove_prefix(prefix.length());
+    return res;
+}
 
 }

From d291be444bf6e50ba13235be975db4443b162903 Mon Sep 17 00:00:00 2001
From: John Ericson <John.Ericson@Obsidian.Systems>
Date: Fri, 3 Jul 2020 14:49:22 +0000
Subject: [PATCH 22/30] Fix Perl

---
 perl/lib/Nix/Store.xs | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/perl/lib/Nix/Store.xs b/perl/lib/Nix/Store.xs
index 2a2a0d429..595153e36 100644
--- a/perl/lib/Nix/Store.xs
+++ b/perl/lib/Nix/Store.xs
@@ -285,7 +285,7 @@ SV * addToStore(char * srcPath, int recursive, char * algo)
 SV * makeFixedOutputPath(int recursive, char * algo, char * hash, char * name)
     PPCODE:
         try {
-            Hash h(hash, parseHashType(algo));
+            auto h = Hash::parseAny(hash, parseHashType(algo));
             auto method = recursive ? FileIngestionMethod::Recursive : FileIngestionMethod::Flat;
             auto path = store()->makeFixedOutputPath(method, h, name);
             XPUSHs(sv_2mortal(newSVpv(store()->printStorePath(path).c_str(), 0)));

From d4250fef239b28b4a098e70e1deac889616dbb9a Mon Sep 17 00:00:00 2001
From: John Ericson <John.Ericson@Obsidian.Systems>
Date: Fri, 3 Jul 2020 15:17:20 +0000
Subject: [PATCH 23/30] Fix Perl, again...

---
 perl/lib/Nix/Store.xs | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/perl/lib/Nix/Store.xs b/perl/lib/Nix/Store.xs
index 595153e36..97cc4d94e 100644
--- a/perl/lib/Nix/Store.xs
+++ b/perl/lib/Nix/Store.xs
@@ -224,7 +224,7 @@ SV * hashString(char * algo, int base32, char * s)
 SV * convertHash(char * algo, char * s, int toBase32)
     PPCODE:
         try {
-            Hash h(s, parseHashType(algo));
+            auto h = Hash::parseAny(s, parseHashType(algo));
             string s = h.to_string(toBase32 ? Base32 : Base16, false);
             XPUSHs(sv_2mortal(newSVpv(s.c_str(), 0)));
         } catch (Error & e) {

From bf61871271971aa45237fb9ba7fa4c63ae083ff2 Mon Sep 17 00:00:00 2001
From: John Ericson <John.Ericson@Obsidian.Systems>
Date: Mon, 20 Jul 2020 17:42:34 +0000
Subject: [PATCH 24/30] parser.hh -> split.hh

---
 src/libstore/content-address.cc     | 2 +-
 src/libutil/hash.cc                 | 2 +-
 src/libutil/{parser.hh => split.hh} | 0
 3 files changed, 2 insertions(+), 2 deletions(-)
 rename src/libutil/{parser.hh => split.hh} (100%)

diff --git a/src/libstore/content-address.cc b/src/libstore/content-address.cc
index a562f2d23..749551d1a 100644
--- a/src/libstore/content-address.cc
+++ b/src/libstore/content-address.cc
@@ -1,6 +1,6 @@
 #include "args.hh"
 #include "content-address.hh"
-#include "parser.hh"
+#include "split.hh"
 
 namespace nix {
 
diff --git a/src/libutil/hash.cc b/src/libutil/hash.cc
index c7ccb809d..65ba1dc81 100644
--- a/src/libutil/hash.cc
+++ b/src/libutil/hash.cc
@@ -7,7 +7,7 @@
 #include "args.hh"
 #include "hash.hh"
 #include "archive.hh"
-#include "parser.hh"
+#include "split.hh"
 #include "util.hh"
 
 #include <sys/types.h>
diff --git a/src/libutil/parser.hh b/src/libutil/split.hh
similarity index 100%
rename from src/libutil/parser.hh
rename to src/libutil/split.hh

From c58c6165c554d671f87b463c9ab1d47a5d75bbbb Mon Sep 17 00:00:00 2001
From: John Ericson <John.Ericson@Obsidian.Systems>
Date: Mon, 20 Jul 2020 17:43:19 +0000
Subject: [PATCH 25/30] Remove period at the end of the exception message

---
 src/libutil/hash.cc | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/libutil/hash.cc b/src/libutil/hash.cc
index 65ba1dc81..dfb3668f1 100644
--- a/src/libutil/hash.cc
+++ b/src/libutil/hash.cc
@@ -177,7 +177,7 @@ Hash Hash::parseAnyPrefixed(std::string_view original)
     // Either the string or user must provide the type, if they both do they
     // must agree.
     if (!optParsedType)
-        throw BadHash("hash '%s' does not include a type.", rest);
+        throw BadHash("hash '%s' does not include a type", rest);
 
     return Hash(rest, *optParsedType, isSRI);
 }

From 8065c6d1606402e936b048aa75ad98ffdd7c8d60 Mon Sep 17 00:00:00 2001
From: John Ericson <John.Ericson@Obsidian.Systems>
Date: Mon, 27 Jul 2020 20:45:34 +0000
Subject: [PATCH 26/30] Abstract out topo sorting logic

---
 src/libstore/misc.cc     | 51 +++++++++++++---------------------------
 src/libutil/topo-sort.hh | 40 +++++++++++++++++++++++++++++++
 2 files changed, 56 insertions(+), 35 deletions(-)
 create mode 100644 src/libutil/topo-sort.hh

diff --git a/src/libstore/misc.cc b/src/libstore/misc.cc
index c4d22a634..34a14d30d 100644
--- a/src/libstore/misc.cc
+++ b/src/libstore/misc.cc
@@ -4,6 +4,7 @@
 #include "local-store.hh"
 #include "store-api.hh"
 #include "thread-pool.hh"
+#include "topo-sort.hh"
 
 
 namespace nix {
@@ -246,41 +247,21 @@ void Store::queryMissing(const std::vector<StorePathWithOutputs> & targets,
 
 StorePaths Store::topoSortPaths(const StorePathSet & paths)
 {
-    StorePaths sorted;
-    StorePathSet visited, parents;
-
-    std::function<void(const StorePath & path, const StorePath * parent)> dfsVisit;
-
-    dfsVisit = [&](const StorePath & path, const StorePath * parent) {
-        if (parents.count(path))
-            throw BuildError("cycle detected in the references of '%s' from '%s'",
-                printStorePath(path), printStorePath(*parent));
-
-        if (!visited.insert(path).second) return;
-        parents.insert(path);
-
-        StorePathSet references;
-        try {
-            references = queryPathInfo(path)->references;
-        } catch (InvalidPath &) {
-        }
-
-        for (auto & i : references)
-            /* Don't traverse into paths that don't exist.  That can
-               happen due to substitutes for non-existent paths. */
-            if (i != path && paths.count(i))
-                dfsVisit(i, &path);
-
-        sorted.push_back(path);
-        parents.erase(path);
-    };
-
-    for (auto & i : paths)
-        dfsVisit(i, nullptr);
-
-    std::reverse(sorted.begin(), sorted.end());
-
-    return sorted;
+    return topoSort(paths,
+        {[&](const StorePath & path) {
+            StorePathSet references;
+            try {
+                references = queryPathInfo(path)->references;
+            } catch (InvalidPath &) {
+            }
+            return references;
+        }},
+        {[&](const StorePath & path, const StorePath & parent) {
+            return BuildError(
+                "cycle detected in the references of '%s' from '%s'",
+                printStorePath(path),
+                printStorePath(parent));
+        }});
 }
 
 
diff --git a/src/libutil/topo-sort.hh b/src/libutil/topo-sort.hh
new file mode 100644
index 000000000..7a68ff169
--- /dev/null
+++ b/src/libutil/topo-sort.hh
@@ -0,0 +1,40 @@
+#include "error.hh"
+
+namespace nix {
+
+template<typename T>
+std::vector<T> topoSort(std::set<T> items,
+        std::function<std::set<T>(const T &)> getChildren,
+        std::function<Error(const T &, const T &)> makeCycleError)
+{
+    std::vector<T> sorted;
+    std::set<T> visited, parents;
+
+    std::function<void(const T & path, const T * parent)> dfsVisit;
+
+    dfsVisit = [&](const T & path, const T * parent) {
+        if (parents.count(path)) throw makeCycleError(path, *parent);
+
+        if (!visited.insert(path).second) return;
+        parents.insert(path);
+
+        std::set<T> references = getChildren(path);
+
+        for (auto & i : references)
+            /* Don't traverse into items that don't exist in our starting set. */
+            if (i != path && items.count(i))
+                dfsVisit(i, &path);
+
+        sorted.push_back(path);
+        parents.erase(path);
+    };
+
+    for (auto & i : items)
+        dfsVisit(i, nullptr);
+
+    std::reverse(sorted.begin(), sorted.end());
+
+    return sorted;
+}
+
+}

From e3a2154f5ac91a5cbab5d0715984972e1dd7d40d Mon Sep 17 00:00:00 2001
From: John Ericson <John.Ericson@Obsidian.Systems>
Date: Fri, 31 Jul 2020 01:07:59 +0000
Subject: [PATCH 27/30] Fix indentation

---
 src/libfetchers/mercurial.cc | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/libfetchers/mercurial.cc b/src/libfetchers/mercurial.cc
index aee42e136..3e76ffc4d 100644
--- a/src/libfetchers/mercurial.cc
+++ b/src/libfetchers/mercurial.cc
@@ -209,7 +209,7 @@ struct MercurialInputScheme : InputScheme
         });
 
         if (auto res = getCache()->lookup(store, mutableAttrs)) {
-                    auto rev2 = Hash::parseAny(getStrAttr(res->first, "rev"), htSHA1);
+            auto rev2 = Hash::parseAny(getStrAttr(res->first, "rev"), htSHA1);
             if (!input.getRev() || input.getRev() == rev2) {
                 input.attrs.insert_or_assign("rev", rev2.gitRev());
                 return makeResult(res->first, std::move(res->second));

From 3cbee1e840ea1beff566555f1221b2791091e20c Mon Sep 17 00:00:00 2001
From: John Ericson <John.Ericson@Obsidian.Systems>
Date: Sat, 1 Aug 2020 15:26:57 +0000
Subject: [PATCH 28/30] Convert to C-style comments

---
 src/libutil/hash.hh | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/src/libutil/hash.hh b/src/libutil/hash.hh
index d4badbab3..ffc397ce0 100644
--- a/src/libutil/hash.hh
+++ b/src/libutil/hash.hh
@@ -42,9 +42,9 @@ struct Hash
        is not present, then the hash type must be specified in the
        string. */
     static Hash parseAny(std::string_view s, std::optional<HashType> type);
-    // hash type must be part of string
+    /* hash type must be part of string */
     static Hash parseAnyPrefixed(std::string_view s);
-    // prefix parsed separately; non SRI hash
+    /* prefix parsed separately; non SRI hash */
     static Hash parseNonSRIUnprefixed(std::string_view s, HashType type);
 
     static Hash parseSRI(std::string_view original);

From bc165e28aee689a45535afda8012c9b63f87b24c Mon Sep 17 00:00:00 2001
From: John Ericson <John.Ericson@Obsidian.Systems>
Date: Sat, 1 Aug 2020 15:32:20 +0000
Subject: [PATCH 29/30] Embelish documentation of new Hash functions

---
 src/libutil/hash.hh | 13 +++++++++----
 1 file changed, 9 insertions(+), 4 deletions(-)

diff --git a/src/libutil/hash.hh b/src/libutil/hash.hh
index ffc397ce0..00ce7bb6f 100644
--- a/src/libutil/hash.hh
+++ b/src/libutil/hash.hh
@@ -36,21 +36,26 @@ struct Hash
     /* Create a zero-filled hash object. */
     Hash(HashType type);
 
-    /* Initialize the hash from a string representation, in the format
+    /* Parse the hash from a string representation in the format
        "[<type>:]<base16|base32|base64>" or "<type>-<base64>" (a
        Subresource Integrity hash expression). If the 'type' argument
        is not present, then the hash type must be specified in the
        string. */
     static Hash parseAny(std::string_view s, std::optional<HashType> type);
-    /* hash type must be part of string */
+
+    /* Parse a hash from a string representation like the above, except the
+       type prefix is mandatory is there is no separate arguement. */
     static Hash parseAnyPrefixed(std::string_view s);
-    /* prefix parsed separately; non SRI hash */
+
+    /* Parse a plain hash that musst not have any prefix indicating the type.
+       The type is passed in to disambiguate. */
     static Hash parseNonSRIUnprefixed(std::string_view s, HashType type);
 
     static Hash parseSRI(std::string_view original);
 
 private:
-    // type must be provided, s must not include <type> prefix
+    /* The type must be provided, the string view must not include <type>
+       prefix. `isSRI` helps disambigate the various base-* encodings. */
     Hash(std::string_view s, HashType type, bool isSRI);
 
 public:

From c4ada76e860a595e3f034b89f27374ce79513d9f Mon Sep 17 00:00:00 2001
From: John Ericson <John.Ericson@Obsidian.Systems>
Date: Sat, 1 Aug 2020 16:22:50 +0000
Subject: [PATCH 30/30] Fix error message and avoid recalculation

---
 src/libfetchers/fetchers.cc | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/src/libfetchers/fetchers.cc b/src/libfetchers/fetchers.cc
index 08b83b0db..9c69fc564 100644
--- a/src/libfetchers/fetchers.cc
+++ b/src/libfetchers/fetchers.cc
@@ -203,8 +203,8 @@ std::optional<Hash> Input::getNarHash() const
     if (auto s = maybeGetStrAttr(attrs, "narHash")) {
         auto hash = s->empty() ? Hash(htSHA256) : Hash::parseSRI(*s);
         if (hash.type != htSHA256)
-            throw UsageError("narHash must be specified with SRI notation");
-        return newHashAllowEmpty(*s, htSHA256);
+            throw UsageError("narHash must use SHA-256");
+        return hash;
     }
     return {};
 }