rewrite strip store paths

Old version used sed, which is not inplace and causes
issues when garbage collection triggers during a build.
This patch adds a small rewriter that works in place.

2 files changed, 77 insertions, 0 deletions

diff --git a/strip-store-paths/default.nix b/strip-store-paths/default.nix
new file mode 100644
index 0000000..40fb546
--- /dev/null
+++ b/strip-store-paths/default.nix
@@ -0,0 +1,20 @@
+{ stdenv, zig }:
+
+stdenv.mkDerivation {
+  name = "strip-store-paths";
+  nativeBuildInputs = [ zig ];
+  src = ./strip-store-paths.zig;
+
+  unpackPhase = ''
+    cp $src strip-store-paths.zig
+  '';
+
+  buildPhase = ''
+    export HOME=$TMPDIR
+    zig build-exe -OReleaseFast strip-store-paths.zig
+  '';
+
+  installPhase = ''
+    install -Dm 755 ./strip-store-paths $out/bin/strip-store-paths
+  '';
+}
diff --git a/strip-store-paths/strip-store-paths.zig b/strip-store-paths/strip-store-paths.zig
new file mode 100644
index 0000000..58d7504
--- /dev/null
+++ b/strip-store-paths/strip-store-paths.zig
@@ -0,0 +1,57 @@
+const std = @import("std");
+
+pub const File = struct {
+    ptr: []align(std.mem.page_size) u8,
+    len: u64,
+    allocator: *std.mem.Allocator,
+
+    pub fn init(fd: std.os.fd_t, allocator: *std.mem.Allocator) !File {
+        var stats = try std.os.fstat(fd);
+        var ptr = try std.os.mmap(null,
+                                  @intCast(usize, stats.size),
+                                  std.os.PROT_READ | std.os.PROT_WRITE,
+                                  std.os.MAP_SHARED,
+                                  fd,
+                                  0);
+        return File {
+            .ptr = ptr,
+            .len = @intCast(u64, stats.size),
+            .allocator = allocator
+        };
+    }
+
+    pub fn deinit(self: *File) void {
+        std.os.munmap(self.ptr);
+        self.ptr = undefined;
+        self.len = 0;
+    }
+};
+
+pub fn main() !void {
+    var arena = std.heap.ArenaAllocator.init(std.heap.page_allocator);
+    defer arena.deinit();
+    const allocator = &arena.allocator;
+
+    const args = try std.process.argsAlloc(allocator);
+    if (args.len != 2) {
+        std.debug.print("usage: {s} file\n", .{args[0]});
+        std.os.exit(1);
+    }
+    const path = args[1];
+
+    // mmap input
+    var fd = try std.os.open(path, std.os.O_RDWR, 0);
+    var input = try File.init(fd, allocator);
+    defer input.deinit();
+
+    // search for /nix/store
+    var i: usize = 0;
+    const needle = "/nix/store/";
+    while (std.mem.indexOfPos(u8, input.ptr, i, needle)) |idx| {
+        i = idx + needle.len; 
+        var j = i + 32; // pos of - in a true path
+        if (j < input.len and input.ptr[j] == '-') {
+            std.mem.copy(u8, input.ptr[i..], "00000000000000000000000000000000");
+        }
+    }
+}