fix: preserve newlines in multipart form data decoding#8144
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Krishnachaitanyakc wants to merge 3 commits intomitmproxy:mainfrom
Open
fix: preserve newlines in multipart form data decoding#8144Krishnachaitanyakc wants to merge 3 commits intomitmproxy:mainfrom
Krishnachaitanyakc wants to merge 3 commits intomitmproxy:mainfrom
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The previous `decode_multipart` implementation used `splitlines()` to parse each part and then joined the body lines with `b""`, which silently stripped all newline characters (`\n`, `\r\n`) from field values. This corrupted any multipart payload whose values contained embedded newlines — including plain text with line breaks and binary file uploads (e.g. JPEG images whose raw bytes happen to include 0x0A / 0x0D). The fix locates the header/body separator (`\r\n\r\n` or `\n\n`) with `bytes.find` and keeps the body as a single contiguous `bytes` object. Only the trailing CRLF (or LF) that RFC 2046 defines as part of the boundary delimiter is stripped; all other newlines inside the body are preserved. Tests are updated to use RFC-compliant CRLF delimiters and new cases are added for embedded newlines, bare-LF newlines, binary content, and encode/decode round-tripping. Fixes mitmproxy#4466
The encoder appended an extra empty-bytes element after each value, producing `value\r\n\r\n` before the next boundary instead of the RFC 2046 compliant `value\r\n`. This caused decode_multipart (which correctly strips only one trailing CRLF) to return values with a spurious `\r\n` suffix, breaking the test_set_multipart_form round-trip test in test_http.py. Remove the extra `hdrs.append(b"")` from the encoder and update the encode/round-trip tests to match the corrected output format.
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@mhils can you please review this? |
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Summary
Fixes #4466 — multipart form data values containing newlines (
\nor\r\n) were silently stripped during decoding, corrupting text fields with line breaks and binary file uploads (e.g. JPEG images).decode_multipartusedbytes.splitlines()to parse each part and then joined body lines withb"", which discarded all newline characters from the body content.splitlines()+ join approach withbytes.find()to locate the header/body separator (\r\n\r\nor\n\n), keeping the body as a single contiguousbytesobject. Only the trailing CRLF/LF that RFC 2046 defines as part of the boundary delimiter is stripped.test_decodeto use RFC-compliant CRLF delimiters and added new test cases for:\r\nand\nbytesTest plan
test_decodepasses with CRLF-delimited payloadstest_decode_with_lfpasses for bare-LF payloadstest_decode_content_preserves_newlinescatches the original bug (valuea\r\nbnot flattened toab)test_decode_binary_contentensures binary data with embedded\r\n/\nbytes is preservedtest_decode_roundtripconfirms encode then decode recovers field namestest_encodestill passes unchanged