API: kill: return 409 on invalid state

If the container isn't running, make sure to return 409 as specified in
the Docker API [1] and the Podman reference.

[1] https://docs.docker.com/engine/api/v1.43/#tag/Container/operation/ContainerKill

Fixes: containers#19368
Signed-off-by: Valentin Rothberg <vrothberg@redhat.com>

pkg/api/handlers/compat/containers.go

@@ -243,6 +243,11 @@ func KillContainer(w http.ResponseWriter, r *http.Request) {
 	}
 
 	if len(report) > 0 && report[0].Err != nil {
+		if errors.Is(report[0].Err, define.ErrCtrStateInvalid) ||
+			errors.Is(report[0].Err, define.ErrCtrStopped) {
+			utils.Error(w, http.StatusConflict, report[0].Err)
+			return
+		}
 		utils.InternalServerError(w, report[0].Err)
 		return
 	}

test/apiv2/20-containers.at

@@ -32,7 +32,10 @@ t POST "containers/foo/attach?logs=true&stream=false" 200 \
   $'\001\031'$mytext
 t POST "containers/foo/kill" 204
 
-podman run -v /tmp:/tmp $IMAGE true
+podman create --replace --name=foo -v /tmp:/tmp $IMAGE true
+# cannot kill non-running container
+t POST "containers/foo/kill" 409
+t POST "libpod/containers/foo/kill" 409
 
 t GET libpod/containers/json 200 length=0