podman events --format json returns null via remote api

Issue Description

When running podman events --format json --filter event=start inside a container that uses Podman in remote mode (remote = true with a forwarded Docker socket), container start events are returned as the literal JSON value null instead of a proper event JSON object.

This breaks any tooling that parses event JSON, notably the devcontainers CLI (@devcontainers/cli) which crashes with:

TypeError: Cannot read properties of null (reading 'status')

Steps to reproduce the issue

1. Set up rootless Podman 5.8.1 on a host (Ubuntu 24.04, kernel 6.8)

2. Create a container that uses Podman in remote mode via the host socket:

# Create a container with podman configured for remote mode
podman run -d --name test-remote \
  -v /run/user/$(id -u)/podman/podman.sock:/var/run/docker.sock:ro \
  docker.io/library/debian:bookworm-slim \
  sleep infinity

# Install podman inside the container
podman exec test-remote bash -c 'apt-get update && apt-get install -y podman'

# Configure remote mode
podman exec test-remote bash -c 'mkdir -p /etc/containers && printf "[engine]\nremote = true\n" > /etc/containers/containers.conf'
podman exec test-remote bash -c 'export CONTAINER_HOST=unix:///var/run/docker.sock'

3. Start listening for events from INSIDE the container:

podman exec test-remote podman --url unix:///var/run/docker.sock events --format json --filter event=start &

4. Trigger a container start event from the HOST:

podman run --rm docker.io/library/alpine echo hello

5. Observe the output from step 3 — it prints null instead of a JSON event object.

6. For comparison, run the same command directly on the host (not in remote mode):

podman events --format json --filter event=start &
podman run --rm docker.io/library/alpine echo hello
# This returns proper JSON: {"ID":"...","Status":"start","Type":"container",...}

Describe the results you received

null

Describe the results you expected

A properly structured JSON event object, e.g.:

{
  "ID": "abc123...",
  "Status": "start",
  "Type": "container",
  "Action": "start",
  "Attributes": { ... }
}

podman info output

host:
  arch: amd64
  buildahVersion: 1.43.0
  cgroupControllers:
  - cpuset
  - cpu
  - io
  - memory
  - hugetlb
  - pids
  - rdma
  - misc
  cgroupManager: systemd
  cgroupVersion: v2
  conmon:
    package: conmon_2.1.10+ds1-1build2_amd64
    path: /usr/bin/conmon
    version: 'conmon version 2.1.10, commit: unknown'
  cpuUtilization:
    idlePercent: 88.3
    systemPercent: 2.93
    userPercent: 8.76
  cpus: 4
  databaseBackend: sqlite
  distribution:
    codename: noble
    distribution: ubuntu
    version: "24.04"
  eventLogger: journald
  freeLocks: 2048
  hostname: saurus
  idMappings:
    gidmap: null
    uidmap: null
  kernel: 6.8.0-106-generic
  linkmode: dynamic
  logDriver: journald
  memFree: 10440720384
  memTotal: 16770109440
  networkBackend: netavark
  networkBackendInfo:
    backend: netavark
    defaultNetwork: podman
    dns:
      package: aardvark-dns_1.4.0-5_amd64
      path: /usr/lib/podman/aardvark-dns
      version: aardvark-dns 1.4.0
    package: netavark_1.4.0-4_amd64
    path: /usr/lib/podman/netavark
    version: netavark 1.4.0
  ociRuntime:
    name: crun
    package: crun_100:1.26-1_amd64
    path: /usr/bin/crun
    version: |-
      crun version 1.26
      commit: 3241e671f92c33b0c003cd7de319e4f32add6231
      rundir: /run/user/0/crun
      spec: 1.0.0
      +SYSTEMD +SELINUX +APPARMOR +CAP +SECCOMP +EBPF +YAJL
  os: linux
  pasta:
    executable: /usr/bin/pasta
    package: passt_100:0.0+20260120.386b5f54-1_amd64
    version: |
      pasta 0.0+20260120.386b5f54
      Copyright Red Hat
      GNU General Public License, version 2 or later
        <https://www.gnu.org/licenses/old-licenses/gpl-2.0.html>
      This is free software: you are free to change and redistribute it.
      There is NO WARRANTY, to the extent permitted by law.
  remoteSocket:
    exists: true
    path: /run/podman/podman.sock
  rootlessNetworkCmd: pasta
  security:
    apparmorEnabled: true
    capabilities: CAP_AUDIT_WRITE,CAP_CHOWN,CAP_DAC_OVERRIDE,CAP_FOWNER,CAP_FSETID,CAP_KILL,CAP_MKNOD,CAP_NET_BIND_SERVICE,CAP_NET_RAW,CAP_SETFCAP,CAP_SETGID,CAP_SETPCAP,CAP_SETUID,CAP_SYS_CHROOT
    rootless: false
    seccompEnabled: true
    seccompProfilePath: /usr/share/containers/seccomp.json
    selinuxEnabled: false
  serviceIsRemote: false
  slirp4netns:
    executable: /usr/bin/slirp4netns
    package: slirp4netns_1.2.1-1build2_amd64
    version: |-
      slirp4netns version 1.2.1
      commit: 09e31e92fa3d2a1d3ca261adaeb012c8d75a8194
      libslirp: 4.7.0
      SLIRP_CONFIG_VERSION_MAX: 4
      libseccomp: 2.5.5
  swapFree: 0
  swapTotal: 0
  uptime: 43h 18m 37.00s (Approximately 1.79 days)
  variant: ""
plugins:
  authorization: null
  log:
  - k8s-file
  - none
  - passthrough
  - journald
  network:
  - bridge
  - macvlan
  - ipvlan
  volume:
  - local
registries:
  search:
  - docker.io
store:
  configFile: /usr/share/containers/storage.conf
  containerStore:
    number: 0
    paused: 0
    running: 0
    stopped: 0
  graphDriverName: overlay
  graphOptions: {}
  graphRoot: /var/lib/containers/storage
  graphRootAllocated: 206900281344
  graphRootUsed: 35465482240
  graphStatus:
    Backing Filesystem: extfs
    Native Overlay Diff: "true"
    Supports d_type: "true"
    Supports shifting: "true"
    Supports volatile: "true"
    Using metacopy: "false"
  imageCopyTmpDir: /var/tmp
  imageStore:
    number: 1
  runRoot: /run/containers/storage
  transientStore: false
  volumePath: /var/lib/containers/storage/volumes
version:
  APIVersion: 5.8.1
  Built: 0
  BuiltTime: Thu Jan  1 00:00:00 1970
  GitCommit: ""
  GoVersion: go1.26.0
  Os: linux
  OsArch: linux/amd64
  Version: 5.8.1

Podman in a container

Yes

Privileged Or Rootless

Rootless

Upstream Latest Release

Yes

Additional environment details

Additional environment details

Additional information

This issue specifically affects the Docker-compatible events API when accessed via remote mode. The same podman events --format json command works correctly when run directly on the host (non-remote, same Podman version).

Impact: This breaks the @devcontainers/cli (v0.84.0) which uses podman events --format json --filter event=start to detect container startup. The CLI crashes with TypeError: Cannot read properties of null (reading 'status') because it expects a valid JSON object but receives null.

Workaround: Patch the devcontainer CLI to treat null events as a start signal, since the container is already running after podman run — the events listener is just waiting for confirmation.

The issue does NOT occur with Podman 4.9.3 on the same host with the same socket forwarding setup.