Create new file-hash files

src/libstore/file-hash.hh

@@ -0,0 +1,34 @@
+#pragma once
+
+#include "hash.hh"
+
+namespace nix {
+
+enum struct FileIngestionMethod : uint8_t {
+    Flat = false,
+    Recursive = true
+};
+
+/// Pair of a hash, and how the file system was ingested
+struct FileSystemHash {
+    FileIngestionMethod method;
+    Hash hash;
+    FileSystemHash(FileIngestionMethod method, Hash hash)
+        : method(std::move(method))
+        , hash(std::move(hash))
+    { }
+    FileSystemHash(const FileSystemHash &) = default;
+    FileSystemHash(FileSystemHash &&) = default;
+    FileSystemHash & operator = (const FileSystemHash &) = default;
+    std::string printMethodAlgo() const;
+};
+
+/* Compute the prefix to the hash algorithm which indicates how the files were
+   ingested. */
+std::string makeFileIngestionPrefix(const FileIngestionMethod m);
+
+/* Compute the content-addressability assertion (ValidPathInfo::ca)
+   for paths created by makeFixedOutputPath() / addToStore(). */
+std::string makeFixedOutputCA(FileIngestionMethod method, const Hash & hash);
+
+}