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] 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;
+}
 
 }