std.tar: support pax headers and gnulong_{name,link}

tar.zig:
* add HeaderIterator() type and convert pipeToFileSystem() to use it.
* add initial support for options.executable_bit_only.
* initial windows support:
  * skip symlinks which require admin rights
  * workaround file.updateTimes() panic by truncating file times
* add tests parseNumeric and parsePaxTime ported from
  https://go.dev/src/archive/tar/strconv_test.go.

lib/std/compress/tar/testdata/
* copy a subset of tar files from
  https://go.dev/src/archive/tar/testdata
* gzip them all with -9. results in around 95% file size reduction

reader_test.zig:
* validate headers against files from testdata/. a port of
  https://go.dev/src/archive/tar/reader_test.go.

test_decompress.zig:
* runs tar.pipeToFileSystem() on valid testdata/ files.

Author: travisstaloch

lib/std/compress.zig

@@ -46,4 +46,5 @@ test {
     _ = xz;
     _ = zlib;
     _ = zstd;
+    _ = @import("compress/tar.zig");
 }

lib/std/compress/tar.zig

@@ -0,0 +1,4 @@
+test "std.tar" {
+    _ = @import("tar/reader_test.zig");
+    _ = @import("tar/test_decompress.zig");
+}

lib/std/compress/tar/reader_test.zig

@@ -0,0 +1,13 @@
+const std = @import("std");
+/// testing helper for decompressing a .gz file. returns an io.fixedBufferStream
+/// with the decompressed data.  caller owns the returned FixedBufferStream.buffer
+pub fn decompressGz(
+    comptime file_name: []const u8,
+    alloc: std.mem.Allocator,
+) !std.io.FixedBufferStream([]u8) {
+    var fbs = std.io.fixedBufferStream(@embedFile(file_name));
+    var decompressor = try std.compress.gzip.decompress(alloc, fbs.reader());
+    defer decompressor.deinit();
+    const decompressed = try decompressor.reader().readAllAlloc(alloc, 1024 * 32);
+    return std.io.fixedBufferStream(decompressed);
+}

lib/std/compress/tar/test_common.zig

@@ -0,0 +1,54 @@
+const std = @import("std");
+const mem = std.mem;
+const tar = std.tar;
+const testing = std.testing;
+const talloc = testing.allocator;
+const builtin = @import("builtin");
+const test_common = @import("test_common.zig");
+
+test "tar decompress testdata" {
+    // skip if wine and debug mode due to 'incorrect alignment'
+    // TODO re-enable after https://github.com/ziglang/zig/issues/14036 is solved
+    if (builtin.os.tag == .windows and builtin.mode == .Debug)
+        return error.SkipZigTest;
+
+    const test_files = [_][]const u8{
+        "xattrs.tar",
+        "gnu-long-nul.tar",
+        "v7.tar",
+        "pax-bad-hdr-file.tar",
+        "pax-global-records.tar",
+        "star.tar",
+        "pax-multi-hdrs.tar",
+        "gnu.tar",
+        "gnu-utf8.tar",
+        "trailing-slash.tar",
+        "pax.tar",
+        "nil-uid.tar",
+        "ustar-file-devs.tar",
+        "pax-pos-size-file.tar",
+        "hardlink.tar",
+        "pax-records.tar",
+        "gnu-multi-hdrs.tar",
+    };
+
+    var cache_dir = testing.tmpDir(.{});
+    defer cache_dir.cleanup();
+
+    inline for (test_files) |test_file| {
+        var fbs = try test_common.decompressGz("testdata/" ++ test_file ++ ".gz", talloc);
+        defer talloc.free(fbs.buffer);
+        {
+            var output_dir = try cache_dir.dir.makeOpenPath(test_file, .{});
+            defer output_dir.close();
+            try tar.pipeToFileSystem(output_dir, fbs.reader(), .{ .mode_mode = .ignore });
+        }
+        try cache_dir.dir.deleteTree(test_file);
+        fbs.reset();
+        {
+            var output_dir = try cache_dir.dir.makeOpenPath(test_file, .{});
+            defer output_dir.close();
+            try tar.pipeToFileSystem(output_dir, fbs.reader(), .{ .mode_mode = .executable_bit_only });
+        }
+    }
+}