quic_record_append: return correct code

[julek-wolfssl]

0-return from quic_record_append is an error. quic_record_complete(qr) || len == 0 is not an error condition. We should return as normal on success.

The issue is that passing in buffers with lengths 1 then 3 causes qr_length (in quic_record_make) to return 0. Then when quic_record_append gets called the len gets consumed by the first if and len == 0 is true. This causes the error return which is not correct behaviour.

Reported in #8156. Reproducing is a bit tricky. I couldn't get the docker to work.

First setup ngtcp2 as described in https://github.com/ngtcp2/ngtcp2/pkgs/container/ngtcp2-interop. The Relevant steps are (I tested with master/main branches of all libs):

$ git clone --depth 1 -b v5.7.4-stable https://github.com/wolfSSL/wolfssl
$ cd wolfssl
$ autoreconf -i
$ # For wolfSSL < v5.6.6, append --enable-quic.
$ ./configure --prefix=$PWD/build \
    --enable-all --enable-aesni --enable-harden --enable-keylog-export \
    --disable-ech
$ make -j$(nproc)
$ make install
$ cd ..
$ git clone --recursive https://github.com/ngtcp2/nghttp3
$ cd nghttp3
$ autoreconf -i
$ ./configure --prefix=$PWD/build --enable-lib-only
$ make -j$(nproc) check
$ make install
$ cd ..
$ git clone --recursive https://github.com/ngtcp2/ngtcp2
$ cd ngtcp2
$ autoreconf -i
$ # For Mac users who have installed libev with MacPorts, append
$ # LIBEV_CFLAGS="-I/opt/local/include" LIBEV_LIBS="-L/opt/local/lib -lev"
$ ./configure PKG_CONFIG_PATH=$PWD/../wolfssl/build/lib/pkgconfig:$PWD/../nghttp3/build/lib/pkgconfig \
    --with-wolfssl
$ make -j$(nproc) check

Download and unzip https://github.com/user-attachments/files/17621329/failing.pcap.zip

From the ngtcp2 dir:

./examples/wsslserver 127.0.0.1 44433 /path/to/wolfssl/certs/server-key.pem /path/to/wolfssl/certs/server-cert.pem

Then run the following python script (failing.pcap has to be available in the running dir) (probably needs to be run as sudo):

from scapy.utils import rdpcap, PcapNgReader
from scapy.all import *
reader = PcapNgReader("failing.pcap")
for i in reader:
    p = i[IP]
    p.dport = 44433
    p.dst = "127.0.0.1"
    p[UDP].chksum=0
    p.display()
    send(p)

Then observe the log line:

I00000000 0xa48accb7b49ec1556ac7111c64d3a4572a81 frm tx 625216795 Initial CONNECTION_CLOSE(0x1c) error_code=CRYPTO_ERROR(0x100) frame_type=0 reason_len=0 reason=[]

You can also use gdb and place a break inside the following section in wolfssl/src/quic.c.

    if (quic_record_complete(qr) || len == 0) {
        return 0;
    }

[julek-wolfssl]

Retest this please