fix: use StringDecoder for cipher string encoding remainder buffering#949
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fix: use StringDecoder for cipher string encoding remainder buffering#949
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Restores StringDecoder usage (removed during Nitro rewrite in #573) to properly handle base64/utf8 remainder bytes across update() and final() calls. Without this, base64-encoding each chunk independently produces premature padding, causing string concat to differ from Buffer concat for inputs >= 16 bytes (one AES block). Fixes #945
Prevent silent data corruption when different output encodings are passed to update() and final(). Matches Node.js cipher behavior which asserts the encoding cannot change once a StringDecoder is initialized.
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🤖 End-to-End Test Results - AndroidStatus: ✅ Passed 📸 Final Test ScreenshotScreenshot automatically captured from End-to-End tests and will expire in 30 days This comment is automatically updated on each test run. |
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Summary
Fixes incorrect cipher output when using string encoding (e.g.,
'base64') withupdate()+final()string concatenation.As reported by @vic614, longer inputs where the encrypted byte count isn't divisible by 3 produce different base64 output when using string concat vs Buffer concat. The root cause:
Buffer.toString('base64')encodes each chunk independently, producing trailing=padding mid-stream that corrupts the concatenated result.Changes
ab2str()withStringDecoderin cipherupdate()andfinal()—StringDecoder.write()buffers incomplete base64 groups across calls, andStringDecoder.end()flushes the remainder with proper padding. This matches Node.js's own cipher implementation.update()andfinal()on the same cipher instance, preventing silent data corruption.string_decoderdependency (already in the dep tree viareadable-stream).32 % 3 = 2remainder)16 % 3 = 1remainder)Testing
Run the cipher test suite in the example app. The 3 new tests validate that Buffer concat and string concat produce identical results for various input sizes.
Fixes #945