Edge proxies such as Cloudflare Workers inject accept-encoding values
(e.g. gzip, br, zstd) into every outbound request. When Headroom
forwarded these headers unchanged to OpenAI or Anthropic, the upstream
could respond with Brotli-encoded content. Because httpx does not
decompress brotli without the optional brotli package, the raw
compressed bytes reached the JSON parser, causing a UnicodeDecodeError
and a 502 response to the client.
Fix: pop accept-encoding before forwarding so httpx negotiates its own
encoding independently. Applied consistently across all four request
header construction sites:
- openai.py: chat completions handler
- openai.py: Responses API handler
- openai.py: generic passthrough handler
- anthropic.py: main messages handler (CCR continuation already had the strip)
Closes#135
Test cases verify:
- Content-Encoding and Content-Length headers are correctly removed
- Response bodies are already decompressed by httpx
- Keeping compression headers causes length mismatch issues
- The fix doesn't break uncompressed responses
These tests will catch regressions of the ZlibError bug.
Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>
