SilentEntity commented on PR #11087:
URL: https://github.com/apache/apisix/pull/11087#issuecomment-2021957243

   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`](https://github.com/GenessyX/brotli-ffi/tree/master) 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.


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