Lua action runs more than once for a TCP request #3496

Detailed Description of the Problem

The Lua script from an action inside a tcp-request content rule runs twice for a single request under some circumstances.

Expected Behavior

The script should run exactly once for a single request.

Steps to Reproduce the Behavior

1. Use the configuration file and Lua script below to setup a TCP mode proxy
2. Make two HTTP requests (within a single TCP request because of keep-alive) against the server with curl -v http://127.0.0.1:8080/1 http://127.0.0.1:8080/2

Only the first HTTP request should be processed by the Lua script (which returns HTTP 204). The second HTTP request should go to the upstream server on port 80.

However, the Lua script runs twice on the first try. It processed both HTTP requests. Presumably because do-resolve takes time. On the second try when the DNS record is cached, or if the do-resolve action is removed, the script runs only once.

Do you have any idea what may have caused this?

Commit 9f1e9ee

If the commit above is reverted, the issue goes away.

Do you have an idea how to solve the issue?

No response

What is your configuration?

global
    lua-load app.lua

listen proxy
    bind :8080
    tcp-request inspect-delay 5s
    tcp-request content lua.app
    tcp-request content do-resolve(txn.ip,default) str('haproxy.org')
    server upstream 127.0.0.1:80

function app(txn)
    core.Debug('lua func')
    repeat
        line = txn.req:getline()
        core.Debug(line)
    until #line <= 2 -- crlf
    txn.res:send('HTTP/1.1 204 No Content\r\n\r\n')
end
core.register_action("app", {"tcp-req"}, app, 0)

Output of haproxy -vv

Linux archlinux 6.18.48-1-lts #1 SMP PREEMPT_DYNAMIC Fri, 28 Aug 2026 11:47:30 +0000 x86_64 GNU/Linux

HAProxy version 3.4.4 2026/08/27 - https://haproxy.org/
Status: long-term supported branch - will stop receiving fixes around Q2 2031.
Known bugs: http://www.haproxy.org/bugs/bugs-3.4.4.html
Running on: Linux 6.18.48-1-lts #1 SMP PREEMPT_DYNAMIC Fri, 28 Aug 2026 11:47:30 +0000 x86_64
Build options :
  TARGET  = linux-glibc
  CC      = cc
  CFLAGS  = -O2 -g -fwrapv -fvect-cost-model=very-cheap -march=x86-64 -mtune=generic -O2 -pipe -fno-plt -fexceptions -Wp,-D_FORTIFY_SOURCE=
3 -Wformat -Werror=format-security -fstack-clash-protection -fcf-protection -fno-omit-frame-pointer -mno-omit-leaf-frame-pointer -g -ffile-
prefix-map=/build/haproxy/src=/usr/src/debug/haproxy -flto=auto -fwrapv
  OPTIONS = USE_GETADDRINFO=1 USE_OPENSSL=1 USE_LUA=1 USE_ZLIB=1 USE_QUIC=1 USE_PROMEX=1 USE_PCRE2=1 USE_PCRE2_JIT=1
  DEBUG   =