Re: Bug#1099935: dnspython: autopkgtest regression on s390x: bad request

On Sun, Mar 16, 2025 at 12:12:08PM +0000, Pranav P wrote:
>I am still continuing my search on the issue.
>It seems that the issue is rising from pylsqpack.
>When the value field in the packet header for HTTP3 GET request contains
>long strings there are problems while encoding (Only in s390x).
>Due to this one of the GET parameters gets jumbled and this results in a bad request.
>I am not able to see the same issue on ls-qpack though.
>I will update any new findings.

Yes, I was just going through this today (I hadn't noticed your emails 
until after I'd spent some time on it) and I found much the same thing.  
I reduced it to the following more manageable test case:

   # amd64
   >>> import pylsqpack
   >>> encoder = pylsqpack.Encoder()
   >>> decoder = pylsqpack.Decoder(4096, 16)
   >>> _, frame = encoder.encode(0, [(b':path', b'/dns-query?dns=AAABAAABAAAAAAAAAAABAAABAAAAAAAAA2RucwZnb29nbGUAAAEAAQ')])
   >>> decoder.feed_header(0, frame)
   (b'', [(b':path', b'/dns-query?dns=AAABAAABAAAAAAAAAAABAAABAAAAAAAAA2RucwZnb29nbGUAAAEAAQ')])

   # s390x
   >>> import pylsqpack
   >>> encoder = pylsqpack.Encoder()
   >>> decoder = pylsqpack.Decoder(4096, 16)
   >>> _, frame = encoder.encode(0, [(b':path', b'/dns-query?dns=AAABAAABAAAAAAAAAAABAAABAAAAAAAAA2RucwZnb29nbGUAAAEAAQ')])
   >>> decoder.feed_header(0, frame)
   (b'', [(b':path', b'd/snq-euyrd?snA=AAABAAABAAAAAAAAAAABAAABAAAAAAAAR2cuZwbn92bnUGAAAEAAQ')])