RFR: 8373727: New XBM images parser regression: only the first line of the bitmap array is parsed

[Victor Dyakov]

On Thu, 8 Jan 2026 17:09:24 GMT, Damon Nguyen <dnguyen at openjdk.org> wrote:

> There were three concerns with the previous changes to `XbmImageDecoder`.
> 1. Only the first line of the bit array was read.
> 2. The regex was incorrect because it used `[]` instead of `()` for some grouping.
> 3. The ordering of the width and height in the xbm file was too strict and had to be width first, then height.
> 
> To fix these issues, I have:
> 1. Used a StringBuilder to append lines of the bit array to parse the entire array at once. This required changing the parsing loop and moving some code.
> 2. Updated the regex to capture starting whitespace, optionally start with `0x`, include all chars/digits/punctuation (minus `,` and `};`) instead of just valid hex digits, and end with either `,` or `};`. This also allows for incorrect hex values such as `0x12345abcde` to be detected since the new regex allows for multiple chars after the `0x` until the next delimiter is found. This is accounted for in the test xbm files.
> 3. Determined width or height based off of ending letters (`th` or `t`). This is similar to https://github.com/openjdk/jdk/blob/jdk-26+10/src/java.desktop/share/classes/sun/awt/image/XbmImageDecoder.java#L109-L112.
> 
> A new method is added to `XBMDecoderTest.java` to better check that the bit array parsing works. This method checks for non-empty pixel data.
> 
> A new xbm file is also added to check for the case where `0xAB+` exists in the bit array. This should be invalid, and the previous regex would allow this to pass. 
> 
> All tests pass with the new changes made here.

@jayathirthrao @prrace  please review

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PR Comment: https://git.openjdk.org/jdk/pull/29120#issuecomment-3729701023