fix(decoder): auto-detect gzip magic bytes in GzipParser for APIs without Content-Encoding header

[devin-ai-integration]

Summary

Some APIs (notably Apple App Store Connect /v1/salesReports) return gzip-compressed response bodies without setting the Content-Encoding: gzip header. The existing GzipParser unconditionally assumed gzip input, and create_gzip_decoder() used the inner parser (e.g. CsvParser) as the fallback when headers didn't match — so gzip data without the header was never decompressed, producing 'utf-8' codec can't decode byte 0x8b errors.

Changes:

1. GzipParser.parse() — reads the first 2 bytes and checks for gzip magic bytes (\x1f\x8b). If present, decompresses; otherwise passes data through to the inner parser unchanged.
2. create_gzip_decoder() — uses gzip_parser (with auto-detection) instead of gzip_parser.inner_parser as both the default parser in builder mode and the fallback in production mode.

Resolves https://github.com/airbytehq/oncall/issues/11809:

• https://github.com/airbytehq/oncall/issues/11809

Related: #914, #909, #895, #892

Review & Testing Checklist for Human

• Memory regression for large streaming responses: GzipParser.parse() now calls data.read() to buffer the entire response into a BytesIO. The old code streamed through gzip.GzipFile(fileobj=data) directly. For very large responses in production mode (stream_response=True), this could increase memory usage. Consider whether a streaming-friendly approach (e.g., a peek/wrapper that avoids full buffering) is needed for connectors that transfer large files.
• Double decompression edge case in builder mode: When Content-Encoding: gzip IS present and stream_response=False, the requests library already decompresses response.content. GzipParser then receives decompressed bytes — the magic-byte check should correctly identify this as non-gzip and pass through. However, if decompressed content happens to start with \x1f\x8b bytes, it would be incorrectly re-decompressed. Assess whether this is a realistic risk.
• Recommended manual test: Build a connector against Apple App Store Connect /v1/salesReports (or mock a server returning gzip bytes without Content-Encoding) and confirm the response is correctly decompressed and parsed.

Notes

• This is a CDK-level fix affecting all manifest-only/low-code connectors that use GzipDecoder.
• Not a breaking change — strictly additive behavior (auto-detection is a superset of the old unconditional gzip path).
• 7 new unit tests cover: gzip without headers (CSV, JSONL), non-gzip passthrough (CSV, JSONL), empty data, fallback in by_headers mode, and non-streamed mode. All 40 decoder tests pass locally.

Link to Devin session: https://app.devin.ai/sessions/e68cbb230b3b491aae68837d3dea4f26

[devin-ai-integration]

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[github-actions]

PyTest Results (Fast)

3 941 tests  +7   3 930 ✅ +7   7m 39s ⏱️ +40s
    1 suites ±0      11 💤 ±0 
    1 files   ±0       0 ❌ ±0 

Results for commit 782465a. ± Comparison against base commit acafc75.

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PyTest Results (Full)

3 944 tests  +7   3 932 ✅ +7   11m 9s ⏱️ +20s
    1 suites ±0      12 💤 ±0 
    1 files   ±0       0 ❌ ±0 

Results for commit 782465a. ± Comparison against base commit acafc75.