Move /src to /subprojects

This will facilitate breaking up Nix into multiple packages for each
component with Meson.

subprojects/libutil/archive.hh

@@ -0,0 +1,91 @@
+#pragma once
+///@file
+
+#include "types.hh"
+#include "serialise.hh"
+#include "fs-sink.hh"
+
+
+namespace nix {
+
+
+/**
+ * dumpPath creates a Nix archive of the specified path.
+ *
+ * @param path the file system data to dump. Dumping is recursive so if
+ * this is a directory we dump it and all its children.
+ *
+ * @param [out] sink The serialised archive is fed into this sink.
+ *
+ * @param filter Can be used to skip certain files.
+ *
+ * The format is as follows:
+ *
+ * ```
+ * IF path points to a REGULAR FILE:
+ *   dump(path) = attrs(
+ *     [ ("type", "regular")
+ *     , ("contents", contents(path))
+ *     ])
+ *
+ * IF path points to a DIRECTORY:
+ *   dump(path) = attrs(
+ *     [ ("type", "directory")
+ *     , ("entries", concat(map(f, sort(entries(path)))))
+ *     ])
+ *     where f(fn) = attrs(
+ *       [ ("name", fn)
+ *       , ("file", dump(path + "/" + fn))
+ *       ])
+ *
+ * where:
+ *
+ *   attrs(as) = concat(map(attr, as)) + encN(0)
+ *   attrs((a, b)) = encS(a) + encS(b)
+ *
+ *   encS(s) = encN(len(s)) + s + (padding until next 64-bit boundary)
+ *
+ *   encN(n) = 64-bit little-endian encoding of n.
+ *
+ *   contents(path) = the contents of a regular file.
+ *
+ *   sort(strings) = lexicographic sort by 8-bit value (strcmp).
+ *
+ *   entries(path) = the entries of a directory, without `.` and
+ *   `..`.
+ *
+ *   `+` denotes string concatenation.
+ * ```
+ */
+void dumpPath(const Path & path, Sink & sink,
+    PathFilter & filter = defaultPathFilter);
+
+/**
+ * Same as dumpPath(), but returns the last modified date of the path.
+ */
+time_t dumpPathAndGetMtime(const Path & path, Sink & sink,
+    PathFilter & filter = defaultPathFilter);
+
+/**
+ * Dump an archive with a single file with these contents.
+ *
+ * @param s Contents of the file.
+ */
+void dumpString(std::string_view s, Sink & sink);
+
+void parseDump(FileSystemObjectSink & sink, Source & source);
+
+void restorePath(const std::filesystem::path & path, Source & source, bool startFsync = false);
+
+/**
+ * Read a NAR from 'source' and write it to 'sink'.
+ */
+void copyNAR(Source & source, Sink & sink);
+
+
+inline constexpr std::string_view narVersionMagic1 = "nix-archive-1";
+
+inline constexpr std::string_view caseHackSuffix = "~nix~case~hack~";
+
+
+}