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Allow block attributes strings to terminate in \ character #71291

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Merged
sirreal merged 6 commits into from
Sep 4, 2025
Merged

Allow block attributes strings to terminate in \ character #71291

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1497e77
Add failing test
sirreal Aug 20, 2025
72a01cc
Fix \ and \" attribute escape combinations
sirreal Aug 21, 2025
95ad0eb
Simplify regexp
sirreal Aug 21, 2025
6975f7f
Improve comment
sirreal Sep 1, 2025
0b829a3
Use alternate fix by unescaping `\\` first
sirreal Sep 1, 2025
e6d7683
Replace escaped `\\` first.
sirreal Sep 1, 2025
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22 changes: 12 additions & 10 deletions packages/blocks/src/api/serializer.js
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Original file line number Diff line number Diff line change
Expand Up @@ -281,19 +281,21 @@ export function getCommentAttributes( blockType, attributes ) {
export function serializeAttributes( attributes ) {
return (
JSON.stringify( attributes )
// Replace escaped `\` characters with the unicode escape sequence.
.replaceAll( '\\\\', '\\u005c' )
Comment on lines +284 to +285
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@sirreal sirreal Sep 1, 2025 •
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@dmsnell I'd love to get your opinion on this (and WordPress/wordpress-develop#9558). Initially, I was worried about block invalidation, but if the block was serialized (validly, in a way that can be deserialized) I think there's actually some flexibility because the attribute values are compared not their string representation.

Initially, I maintained the same escaping only addressing the problem of incorrect replacement of syntactic JSON " string delimiter. That approach yielded a very complex regular expression with negative lookbehind and placeholder replacement:

gutenberg/packages/blocks/src/api/serializer.js

Lines 301 to 307 in 6975f7f

* - "\"" -> "\u0022"
* - "\\" -> "\\"
* - "\\\"" -> "\\\u0022"
*
* See https://developer.wordpress.org/reference/functions/wp_kses_stripslashes/
*/
.replace( /(?<!\\)(\\\\)*\\"/g, '$1\\u0022' )

Instead, I decided to replace escaped backslashes first (\\ to \u005c) and later replace escaped doubled quotes (\" to \u0022). This can be achieved with simple string replacements and no regular expressions.

A simpler approach is possible in PHP to fix the \" replacement by using JSON_HEX_QUOT flag when encoding. However, the updated approach to replace escaped backslashes is easy to match. See WordPress/wordpress-develop#9558.

This is from a long time ago, but feedback is welcome if you have any @aduth (via #6619).

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@dmsnell dmsnell Sep 1, 2025

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I will give some thought to it, but it may not come before next week. I have a lot of catch-up from WCUS

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@dmsnell dmsnell Sep 2, 2025

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if the block was serialized (validly, in a way that can be deserialized) I think there's actually some flexibility because the attribute values are compared not their string representation.

This should be accurate. There is even more flexibility than that too, because some block attributes are normalized before comparison for validation (e.g. CSS class names, extra HTML attributes, whitespace).


// Don't break HTML comments.
.replace( /--/g, '\\u002d\\u002d' )
.replaceAll( '--', '\\u002d\\u002d' )

// Don't break non-standard-compliant tools.
.replace( /</g, '\\u003c' )
.replace( />/g, '\\u003e' )
.replace( /&/g, '\\u0026' )

// Bypass server stripslashes behavior which would unescape stringify's
// escaping of quotation mark.
//
// See: https://developer.wordpress.org/reference/functions/wp_kses_stripslashes/
.replace( /\\"/g, '\\u0022' )
.replaceAll( '<', '\\u003c' )
.replaceAll( '>', '\\u003e' )
.replaceAll( '&', '\\u0026' )

// Replace escaped quotes (`\"`) to prevent problems with wp_kses_stripsplashes.
// This simple replacement is safe because `\\` has already been replaced.
// `\"` is not a JSON string quote like `"\\"`.
.replaceAll( '\\"', '\\u0022' )
);
}

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12 changes: 12 additions & 0 deletions packages/blocks/src/api/test/serializer.js
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Original file line number Diff line number Diff line change
Expand Up @@ -204,6 +204,18 @@ describe( 'block serializer', () => {
'{"a":"\\u0022 and \\u0022"}'
);
} );

it( 'should handle backslash and quote combinations', () => {
const orig = {
bs: '\\',
bsQuote: '\\"',
bsQuoteBs: '\\"\\',
};
expect( JSON.parse( serializeAttributes( orig ) ) ).toEqual( orig );
expect( serializeAttributes( orig ) ).toBe(
'{"bs":"\\u005c","bsQuote":"\\u005c\\u0022","bsQuoteBs":"\\u005c\\u0022\\u005c"}'
);
} );
} );

describe( 'getCommentDelimitedContent()', () => {
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