Fix double gzip decompression error in aiohttp transport

[bdraco]

Problem

When using the aiohttp transport with ONVIF cameras that send gzip-compressed responses (e.g., Pelco cameras), users encounter a zlib decompression error:

zlib.error: Error -3 while decompressing data: incorrect header check

This issue started appearing in Home Assistant 2025.7.x after switching from httpx to aiohttp for the ONVIF integration.

Root Cause

The issue occurs because:

1. aiohttp automatically decompresses gzip content when it sees the Content-Encoding: gzip header in the response
2. The header was still being passed to zeep in the converted httpx/requests Response object
3. zeep attempts to decompress again, trying to decompress already-decompressed content, resulting in the zlib error

Solution

This PR removes the Content-Encoding header when converting aiohttp responses to httpx.Response or requests.Response objects, since aiohttp has already handled the decompression.

Changes Made

1. Added _filter_headers() helper method to remove the Content-Encoding header while preserving all other headers (including duplicates)
2. Updated _aiohttp_to_httpx_response() to use the filter
3. Updated _aiohttp_to_requests_response() to use the filter
4. Refactored to eliminate code duplication:
   • Created _post_internal() method to share POST logic between post() and post_xml()
   • post_xml() now directly returns a requests.Response, avoiding unnecessary aiohttp→httpx→requests conversion
   • Removed unused _httpx_to_requests_response() method
5. Added comprehensive tests to verify the fix and ensure duplicate headers are preserved

Testing

Two new tests have been added:

• test_gzip_content_encoding_header_removed: Verifies that the Content-Encoding: gzip header is removed after aiohttp decompresses the content, preventing double decompression attempts
• test_multiple_duplicate_headers_preserved: Ensures that other headers, including duplicates (e.g., multiple Set-Cookie headers), are correctly preserved

All existing tests continue to pass, confirming backward compatibility.

Impact

This fix resolves connectivity issues with ONVIF cameras that send gzip-compressed responses, including:

• Pelco cameras (confirmed via packet capture analysis)
• 2N IP Verso devices
• Any other ONVIF device sending gzip-encoded SOAP responses

Related Issues

• Home Assistant Core Issue I can't add Pelco cameras using the ONVIF integration. home-assistant/core#149829: "I can't add Pelco cameras using the ONVIF integration"

Verification

The fix has been verified with:

• Packet capture analysis showing Pelco cameras send responses with Content-Encoding: gzip
• Test script simulating the exact response pattern from affected cameras
• Comprehensive unit tests covering both the fix and edge cases

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

Files with missing lines	Coverage Δ
onvif/zeep_aiohttp.py	96.62% <100.00%> (-0.22%)	⬇️

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