Description

This PR fixes/supports raw mode of Deflate compression.

Details

When request with Accept-Encoding: deflate HTTP header, some CDNs may have an unusual behavior, which responds with the content compressed in raw Deflate mode with Content-Encoding: deflate header. This causes aria2 abort download with error message libz::inflate() failed. cause:incorrect header check.

As zlib Manual described:

EXTERN int ZEXPORT inflateInit2(z_streamp strm,
                                int  windowBits);

... It should be in the range 8..15 for this version of the library.
...
windowBits can also be –8..–15 for raw inflate. In this case, -windowBits determines the window size. inflate() will then process raw deflate data, not looking for a zlib or gzip header, not generating a check value, and not looking for any check values for comparison at the end of the stream.
...
windowBits can also be greater than 15 for optional gzip decoding.

This PR tries to fix this issue by try decompress the content twice. The first trial is in normal mode, which is same as the old behavior. If the first trial fails, it will try re-initialiaze GZipDecodingStreamFilter class with windowBits = -15. Then, if the second trial is failed, aria2 will abort download, same as the old behavior.

Related URLs / Issues

• This PR fixes libz::inflate() failed. cause:incorrect header check #1436
• One of the sample URL: https://comment.bilibili.com/771495675.xml

Test Result

On my laptop the fix passed test with make -j2 check:

PASS: aria2c
============================================================================
Testsuite summary for aria2 1.37.0
============================================================================
# TOTAL: 1
# PASS:  1
# SKIP:  0
# XFAIL: 0
# FAIL:  0
# XPASS: 0
# ERROR: 0
============================================================================

However, a new test file compressed in raw Deflate mode might be needed to add more coverage to this case. Please reach me if I need further actions.