WIP

src/libstore/file-hash.hh

@@ -1,5 +1,6 @@
 #pragma once
 
+#include <variant>
 #include "hash.hh"
 
 namespace nix {
@@ -23,6 +24,22 @@ struct FileSystemHash {
     std::string printMethodAlgo() const;
 };
 
+/*
+  We've accumulated several types of content-addressed paths over the years;
+  fixed-output derivations support multiple hash algorithms and serialisation
+  methods (flat file vs NAR). Thus, ‘ca’ has one of the following forms:
+
+  * ‘text:sha256:<sha256 hash of file contents>’: For paths
+    computed by makeTextPath() / addTextToStore().
+
+  * ‘fixed:<r?>:<ht>:<h>’: For paths computed by
+    makeFixedOutputPath() / addToStore().
+*/
+typedef std::variant<
+    Hash, // for paths computed by makeTextPath() / addTextToStore
+    FileSystemHash // for path computed by makeFixedOutputPath
+> ContentAddress;
+
 /* Compute the prefix to the hash algorithm which indicates how the files were
    ingested. */
 std::string makeFileIngestionPrefix(const FileIngestionMethod m);

src/libstore/path.hh

@@ -1,6 +1,7 @@
 #pragma once
 
 #include "rust-ffi.hh"
+#include "file-hash.hh"
 
 namespace nix {
 
@@ -87,6 +88,15 @@ const size_t storePathHashLen = 32; // i.e. 160 bits
 /* Extension of derivations in the Nix store. */
 const std::string drvExtension = ".drv";
 
+std::string to_string(FileIngestionMethod m) {
+    switch(m) {
+    case FileIngestionMethod::Flat:
+        return "false";
+    case FileIngestionMethod::Recursive:
+        return "true";
+    }
+}
+
 struct StorePathWithOutputs
 {
     StorePath path;

src/libstore/store-api.cc

@@ -467,7 +467,7 @@ void Store::pathInfoToJSON(JSONPlaceholder & jsonOut, const StorePathSet & store
                     jsonRefs.elem(printStorePath(ref));
             }
 
-            if (info->ca != "")
+            if (info->ca)
                 jsonPath.attr("ca", info->ca);
 
             std::pair<uint64_t, uint64_t> closureSizes;

src/libstore/store-api.hh

@@ -19,6 +19,7 @@
 #include <memory>
 #include <string>
 #include <chrono>
+#include <variant>
 
 
 namespace nix {
@@ -110,6 +111,19 @@ struct SubstitutablePathInfo
 
 typedef std::map<StorePath, SubstitutablePathInfo> SubstitutablePathInfos;
 
+template<class... Ts> struct overloaded : Ts... { using Ts::operator()...; };
+template<class... Ts> overloaded(Ts...) -> overloaded<Ts...>;
+
+std::string renderContentAddress(ContentAddress ca) {
+    return std::visit(overloaded {
+        [](Hash hash) {
+            return "text:" + hash.to_string();
+        },
+        [](FileSystemHash fsh) {
+            return makeFixedOutputCA(fsh.method, fsh.hash);
+        }
+    }, ca);
+}
 
 struct ValidPathInfo
 {
@@ -139,21 +153,11 @@ struct ValidPathInfo
        that a particular output path was produced by a derivation; the
        path then implies the contents.)
 
-       Ideally, the content-addressability assertion would just be a
+       Ideally, the content-addressability assertion would just be a Boolean,
-       Boolean, and the store path would be computed from
+       and the store path would be computed from the name component, ‘narHash’
-       the name component, ‘narHash’ and ‘references’. However,
+       and ‘references’. However, we support many types of content addresses.
-       1) we've accumulated several types of content-addressed paths
-       over the years; and 2) fixed-output derivations support
-       multiple hash algorithms and serialisation methods (flat file
-       vs NAR). Thus, ‘ca’ has one of the following forms:
-
-       * ‘text:sha256:<sha256 hash of file contents>’: For paths
-         computed by makeTextPath() / addTextToStore().
-
-       * ‘fixed:<r?>:<ht>:<h>’: For paths computed by
-         makeFixedOutputPath() / addToStore().
     */
-    std::string ca;
+    std::optional<ContentAddress> ca;
 
     bool operator == (const ValidPathInfo & i) const
     {

src/nix-store/nix-store.cc

@@ -856,7 +856,7 @@ static void opServe(Strings opFlags, Strings opArgs)
                         out << info->narSize // downloadSize
                             << info->narSize;
                         if (GET_PROTOCOL_MINOR(clientVersion) >= 4)
-                            out << (info->narHash ? info->narHash.to_string() : "") << info->ca << info->sigs;
+                            out << (info->narHash ? info->narHash.to_string() : "") << renderContentAddress(info->ca) << info->sigs;
                     } catch (InvalidPath &) {
                     }
                 }