Commit efd227eca2e2013b4e540ab2ba44664668a5253b | zig

author	Ryan Liptak <squeek502@hotmail.com> 2026-08-19 17:42:45-07:00
committer	Ryan Liptak <squeek502@hotmail.com> 2026-08-20 08:29:34+02:00
log	efd227eca2e2013b4e540ab2ba44664668a5253b
tree	9fe50c3ea6d6e86b3ddffa7508b6a96fd35b2d18
parent	7988f79528e2105a83bc00b91866b639b181dd51

File.Reader.seekBy: Fix erroneously tossing the buffer in streaming mode

The discard already handles updating the state, so the toss was redundant in the best case and would erroneously drop data in the worst case.

Closes #36568

2 files changed, 9 insertions(+), 4 deletions(-)

lib
- std
  - Io
    File
    Reader.zig
  - fs
    test.zig

lib/std/Io/File/Reader.zig-1

...	@@ -154,7 +154,6 @@ pub fn seekBy(r: *Reader, offset: i64) SeekError!void {	...	@@ -154,7 +154,6 @@ pub fn seekBy(r: *Reader, offset: i64) SeekError!void {
154	return err;	154	return err;
155	};	155	};
156	}	156	}
157	r.interface.tossBuffered();
158	},	157	},
159	.failure => return r.seek_err.?,	158	.failure => return r.seek_err.?,
160	}	159	}

lib/std/fs/test.zig+9-3

 @@ -2409,13 +2409,19 @@ test "seekBy" {
     try tmp_dir.dir.writeFile(io, .{ .sub_path = "blah.txt", .data = "let's test seekBy" });
     const f = try tmp_dir.dir.openFile(io, "blah.txt", .{ .mode = .read_only });
     defer f.close(io);
-    var reader = f.readerStreaming(io, &.{});
+    var buf: [10]u8 = undefined;
+    var reader = f.readerStreaming(io, &buf);
+    // Seek without any buffered data
+    try reader.seekBy(2);
+    // Seek when the buffered data is sufficient to satisfy the seek amount
+    try reader.interface.fill(2);
     try reader.seekBy(2);
     var buffer: [20]u8 = undefined;
     const n = try reader.interface.readSliceShort(&buffer);
-    try expectEqual(15, n);
+    try expectEqual(13, n);
-    try expectEqualStrings("t's test seekBy", buffer[0..15]);
+    try expectEqualStrings("s test seekBy", buffer[0..n]);
 }
 test "seekTo flushes buffered data" {