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Merge pull request #1674 from lightpanda-io/atob-unpadded-base64

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accept must accept unpadded data in atob
This commit is contained in:
Karl Seguin
2026-02-28 07:00:00 +08:00
committed by GitHub
parent 88baff96d0 6857b74623
commit 7d8688a130
2 changed files with 31 additions and 2 deletions
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10
src/browser/tests/window/window.html
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@@ -75,6 +75,16 @@
testing.expectEqual('abc', atob('YWJj'));
testing.expectEqual('0123456789', atob('MDEyMzQ1Njc4OQ=='));
testing.expectEqual('The quick brown fox jumps over the lazy dog', atob('VGhlIHF1aWNrIGJyb3duIGZveCBqdW1wcyBvdmVyIHRoZSBsYXp5IGRvZw=='));
// atob must accept unpadded base64 (forgiving-base64 decode per HTML spec)
testing.expectEqual('a', atob('YQ')); // 2 chars, len%4==2, needs '=='
testing.expectEqual('ab', atob('YWI')); // 3 chars, len%4==3, needs '='
testing.expectEqual('ceil', atob('Y2VpbA')); // 6 chars, len%4==2, needs '=='
// length % 4 == 1 must still throw
testing.expectError('Error: InvalidCharacterError', () => {
atob('Y');
});
</script>
<script id=btoa_atob_roundtrip>

23
src/browser/webapi/Window.zig
View File

@@ -396,9 +396,28 @@ pub fn btoa(_: *const Window, input: []const u8, page: *Page) ![]const u8 {
pub fn atob(_: *const Window, input: []const u8, page: *Page) ![]const u8 {
const trimmed = std.mem.trim(u8, input, &std.ascii.whitespace);
const decoded_len = std.base64.standard.Decoder.calcSizeForSlice(trimmed) catch return error.InvalidCharacterError;
// Per HTML spec "forgiving-base64 decode" algorithm:
// https://infra.spec.whatwg.org/#forgiving-base64-decode
const padded: []const u8 = switch (trimmed.len % 4) {
1 => return error.InvalidCharacterError,
2 => blk: {
const buf = try page.call_arena.alloc(u8, trimmed.len + 2);
@memcpy(buf[0..trimmed.len], trimmed);
buf[trimmed.len] = '=';
buf[trimmed.len + 1] = '=';
break :blk buf;
},
3 => blk: {
const buf = try page.call_arena.alloc(u8, trimmed.len + 1);
@memcpy(buf[0..trimmed.len], trimmed);
buf[trimmed.len] = '=';
break :blk buf;
},
else => trimmed,
};
const decoded_len = std.base64.standard.Decoder.calcSizeForSlice(padded) catch return error.InvalidCharacterError;
const decoded = try page.call_arena.alloc(u8, decoded_len);
std.base64.standard.Decoder.decode(decoded, trimmed) catch return error.InvalidCharacterError;
std.base64.standard.Decoder.decode(decoded, padded) catch return error.InvalidCharacterError;
return decoded;
}