fix(brotli): brotli partial response fix

[SilentEntity]

Description

When there is a chunk in the eof, brotli plugin overwrite the response arg[1]. Which results into partial response.

• Fixes bug: Compression plugin brotli is sending partial response  #11079

Checklist

• I have explained the need for this PR and the problem it solves
• I have explained the changes or the new features added to this PR
• I have added tests corresponding to this change
• I have updated the documentation to reflect this change
• I have verified that this change is backward compatible (If not, please discuss on the APISIX mailing list first)

[shreemaan-abhishek]

#11079 seems like an error raised due to incompatibility between HTTP headers and HTTP version. Could you please explain what the need for this fix?

And test cases are also required.

[SilentEntity]

When client connection is slow, and page is loading in chunks[streaming], the last chuck is getting dropped/overwritten. If one see the code last chuck will contain eof [end of file], and according to the lib brotli-ffi the last chuck should be appended with compressor:finish(). But in the code if the last chunk is present, it's getting overwritten :

local chunk, eof = ngx.arg[1], ngx.arg[2]

if type(chunk) == "string" and chunk ~= "" then
    local encode_chunk = ctx.compressor:compress(chunk)
    ngx.arg[1] = encode_chunk .. ctx.compressor:flush()
end

if eof then
    ngx.arg[1] = ctx.compressor:finish()    <--- Problem

The fix should be to append the compressed ngx.arg[1] in the eof.

if eof then
        -- overwriting the arg[1], results into partial response
        ngx.arg[1] = ngx.arg[1] .. ctx.compressor:finish()   <--- fix

Even if the ngx.arg[1] is not present in eof, it won't impact the last chuck.

Test-case of this case is not producible, it will require network throttling with large upstream payload for real scenario.

[shreemaan-abhishek]

okay makes sense now, thanks for the apt explanation.