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feat: preserve file mode and owner on write (if possible)

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closes #18
This commit is contained in:
CJ van den Berg 2026-04-14 16:40:37 +02:00
parent 8c0cfb96d2
commit 1769342e23
Signed by: neurocyte
GPG key ID: 8EB1E1BB660E3FB9
1 changed files with 28 additions and 5 deletions
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33
src/buffer/Buffer.zig
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@ -1610,14 +1610,37 @@ pub fn store_to_existing_file_const(self: *const Self, file_path_: []const u8) S
file_path = link;
}
var atomic = blk: {
var write_buffer: [4096]u8 = undefined;
const stat = cwd().statFile(file_path) catch
break :blk try cwd().atomicFile(file_path, .{ .write_buffer = &write_buffer });
break :blk try cwd().atomicFile(file_path, .{ .mode = stat.mode, .write_buffer = &write_buffer });
var write_buffer: [4096]u8 = undefined;
if (builtin.os.tag == .windows) {
// windows uses ACLs for ownership so we preserve mode only
var atomic = blk: {
const stat = cwd().statFile(file_path) catch
break :blk try cwd().atomicFile(file_path, .{ .write_buffer = &write_buffer });
break :blk try cwd().atomicFile(file_path, .{ .mode = stat.mode, .write_buffer = &write_buffer });
};
defer atomic.deinit();
try self.store_to_file_const(&atomic.file_writer.interface);
return atomic.finish();
}
// use fstat to get uid/gid, which std.fs.File.Stat omits.
const orig_stat: ?std.posix.Stat = blk: {
const f = cwd().openFile(file_path, .{}) catch break :blk null;
defer f.close();
break :blk std.posix.fstat(f.handle) catch null;
};
const mode: std.fs.File.Mode = if (orig_stat) |s| s.mode else std.fs.File.default_mode;
var atomic = try cwd().atomicFile(file_path, .{ .mode = mode, .write_buffer = &write_buffer });
defer atomic.deinit();
try self.store_to_file_const(&atomic.file_writer.interface);
// fchmod bypasses the process umask preserving the exact original mode
// fchown restores original owner/group
// EPERM is silently ignored when we lack sufficient privileges
if (orig_stat) |s| {
atomic.file_writer.file.chmod(s.mode) catch {};
std.posix.fchown(atomic.file_writer.file.handle, s.uid, s.gid) catch {};
}
try atomic.finish();
}