Using dataplane API by uncommenting 'program api' and 'userlist haproxy-dataplaneapi' section of config causes crash

[JamesTGrant]

Using dataplane API in versions from 3.0.4 onward causes crash.

Simple to replicate by uncommenting 'program api' and 'userlist haproxy-dataplaneapi' section of the example config (note the VERSION variable in the following link!)
(https://raw.githubusercontent.com/haproxytech/haproxy-docker-ubuntu/refs/tags/$VERSION/3.0/haproxy.cfg)
Not yet found a way to use the dataplane API in versions later than 3.0.3

working in 3.0.3-95a607c
broken in 3.0.4-7a59afa onward

Uncomment these two lines from the haproxy.cfg:

program api
    command /usr/bin/dataplaneapi --host 0.0.0.0 --port 5555 --haproxy-bin /usr/sbin/haproxy --config-file /usr/local/etc/haproxy/haproxy.cfg --reload-cmd "kill -SIGUSR2 1" --restart-cmd "kill -SIGUSR2 1" --reload-delay 5 --userlist haproxy-dataplaneapi
    no option start-on-reload

userlist haproxy-dataplaneapi
  user admin insecure-password mypassword

log output:

[NOTICE]   (1) : New program 'api' (8) forked
[NOTICE]   (1) : New worker (9) forked
[NOTICE]   (1) : Loading success.
[WARNING]  (9) : Server static/static1 is DOWN, reason: Layer4 connection problem, info: "Connection refused", check duration: 0ms. 1 active and 0 backup servers left. 0 sessions active, 0 requeued, 0 remaining in queue.
2024/09/19 13:47:00 maxprocs: Leaving GOMAXPROCS=4: CPU quota undefined
2024/09/19 13:47:00 INFO memory is not limited, skipping package=github.com/KimMachineGun/automemlimit/memlimit
[WARNING]  (9) : Server static/static2 is DOWN, reason: Layer4 connection problem, info: "Connection refused", check duration: 0ms. 0 active and 0 backup servers left. 0 sessions active, 0 requeued, 0 remaining in queue.
[ALERT]    (9) : backend 'static' has no server available!
configuration file /etc/haproxy/dataplaneapi.yaml does not exists, creating one
panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0xb0 pc=0x101ce74]

goroutine 1 [running]:
github.com/haproxytech/dataplaneapi/configuration.(*Configuration).migrateUsers(0xc0003c3608)
        github.com/haproxytech/dataplaneapi/configuration/configuration_deprecated.go:76 +0xf4
github.com/haproxytech/dataplaneapi/configuration.(*Configuration).migrateDeprecatedFields(0xc0003c3608)
        github.com/haproxytech/dataplaneapi/configuration/configuration_deprecated.go:34 +0x12c
github.com/haproxytech/dataplaneapi/configuration.(*Configuration).LoadDataplaneStorageConfig(0xc0003c3608)
        github.com/haproxytech/dataplaneapi/configuration/configuration.go:312 +0x6c
main.startServer(0xc0003c3608, 0xc0003d8140)
        github.com/haproxytech/dataplaneapi/cmd/dataplaneapi/main.go:154 +0x985
main.main()
        github.com/haproxytech/dataplaneapi/cmd/dataplaneapi/main.go:67 +0x59
[NOTICE]   (1) : haproxy version is 3.0.4-7a59afa
[NOTICE]   (1) : path to executable is /usr/local/sbin/haproxy
[ALERT]    (1) : Current program 'api' (8) exited with code 2 (Exit)
[ALERT]    (1) : exit-on-failure: killing every processes with SIGTERM
[ALERT]    (1) : Current worker (9) exited with code 143 (Terminated)
[WARNING]  (1) : All workers exited. Exiting... (2)

Here is a BASH script to reproduce the issue:

#! /bin/bash

# fails with VERSION=3.0.4
# works with VERSION=3.0.3
VERSION=3.0.4

# remove any previous instances
if [ "$(docker ps -a -q -f name=my-running-haproxy)" ]; then
    docker stop my-running-haproxy
    docker rm my-running-haproxy
fi

mkdir -p /tmp/haproxy
rm -fR /tmp/haproxy/*
curl -k -L https://raw.githubusercontent.com/haproxytech/haproxy-docker-ubuntu/refs/tags/$VERSION/3.0/haproxy.cfg -o /tmp/haproxy/haproxy.cfg

dataplaneLines=$(cat <<EOF
 userlist haproxy-dataplaneapi
     user admin insecure-password mypassword

 program api
    command /usr/bin/dataplaneapi --host 0.0.0.0 --port 5555 --haproxy-bin /usr/sbin/haproxy --config-file /usr/local/etc/haproxy/haproxy.cfg --reload-cmd "kill -SIGUSR2 1" --restart-cmd "kill -SIGUSR2 1" --reload-delay 5 --userlist haproxy-dataplaneapi
    no option start-on-reload
EOF
)
printf "%s\n" "$dataplaneLines" >> /tmp/haproxy/haproxy.cfg

docker pull ghcr.io/haproxytech/haproxy-docker-ubuntu:$VERSION
docker run -d --name my-running-haproxy --expose 5555 -v /tmp/haproxy:/usr/local/etc/haproxy:rw haproxytech/haproxy-ubuntu:$VERSION
sleep 5
CONTAINER_ID=$(docker ps -a | grep haproxy | awk '{print $1}')
docker logs $CONTAINER_ID

[dkorunic]

Please if possible open an issue in dataplaneapi issue tracker, but in the meantime I'll ping DPAPI devs right away. Thanks!