fix SIP body truncation with AudioCodes SBC

[loreste]

What happened

The CRLF normalizer (added for sipgo#292 bare-LF compat) was normalizing the entire UDP packet — headers and body. When an AudioCodes SBC sends a multipart SIPREC INVITE with bare \n line endings in the body, the normalizer expands those to \r\n, making the body longer than the Content-Length header says. sipgo then reads only Content-Length bytes, chopping the body mid-XML. The multipart reader hits EOF before finding the rs-metadata part and the call gets rejected.

What this fixes

normalizeCRLF now finds the header/body separator first and only normalizes the header section. The body passes through byte-for-byte, so Content-Length stays accurate and the multipart parser gets the full payload.

• Added findHeaderBodySplit() — handles all four separator variants (\r\n\r\n, \n\n, \r\n\n, \n\r\n)
• Renamed the raw normalizer to normalizeCRLFBytes (internal)
• Zero-copy fast path when all line endings are already \r\n

Tests

• AudioCodes end-to-end reproduction: builds a bare-LF SIPREC multipart packet, normalizes it, verifies Content-Length matches body length, then parses both SDP and rs-metadata parts through Go's multipart reader
• Binary body safety: raw 0x0a bytes in body aren't mistaken for line endings
• 100-line XML body: large metadata body preserved byte-for-byte
• All separator variants: CRLF+CRLF, LF+LF, CRLF+LF, LF+CRLF
• Real UDP socket test: sends through crlfPacketConn and checks body integrity
• 97 sip / 63 siprec / 81 integration tests pass

Closes #44

Summary by CodeRabbit

• Bug Fixes
  • Corrected line-ending normalization so SIP message bodies remain unchanged.
  • Prevented Content-Length mismatches and body-size errors when headers use inconsistent line endings.
  • Improved handling of multipart, binary, large, UDP, and TCP SIP messages.
  • Preserved messages that already use standard CRLF line endings without unnecessary changes.

[coderabbitai]

Caution

Review failed

The pull request is closed.

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Advanced

Run ID: 745a1e93-7f63-4a86-8a3f-960446d2fa32

📥 Commits

Reviewing files that changed from the base of the PR and between 6aeee2f and 7a1389d.

📒 Files selected for processing (2)

• pkg/sip/crlf_normalizer.go
• pkg/sip/crlf_normalizer_test.go

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📝 Walkthrough

Walkthrough

The CRLF normalizer now detects the SIP header/body boundary, normalizes bare line feeds in headers only, and preserves body bytes. Tests cover multipart, binary, UDP, separator, passthrough, and benchmark cases.

Changes

SIP CRLF normalization

Layer / File(s)	Summary
Header and body normalization pkg/sip/crlf_normalizer.go	The normalizer finds header/body separators, converts header line endings to CRLF, preserves the body, and updates UDP and TCP wrapper comments.
Normalization regression coverage pkg/sip/crlf_normalizer_test.go	Tests validate separator variants, multipart and binary body preservation, Content-Length consistency, UDP behavior, unchanged CRLF input, and normalization performance.

Estimated code review effort: 3 (Moderate) | ~20 minutes

Severity of issue fixed: Medium

✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch fix/body-truncation-crlf-normalizer

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