API: container logs flush status code

API clients expect the status code quickly otherwise they can time out.
If we do not flush we may not write the header immediately and only when
futher logs are send.

Fixes containers#23712

Signed-off-by: Paul Holzinger <[email protected]>

pkg/api/handlers/compat/containers_logs.go

@@ -106,6 +106,13 @@ func LogsFromContainer(w http.ResponseWriter, r *http.Request) {
 
 	w.WriteHeader(http.StatusOK)
 
+	flush := func() {
+		if flusher, ok := w.(http.Flusher); ok {
+			flusher.Flush()
+		}
+	}
+	flush()
+
 	var frame strings.Builder
 	header := make([]byte, 8)
 
@@ -167,8 +174,6 @@ func LogsFromContainer(w http.ResponseWriter, r *http.Request) {
 		if _, err := io.WriteString(w, frame.String()); err != nil {
 			log.Errorf("unable to write frame string: %q", err)
 		}
-		if flusher, ok := w.(http.Flusher); ok {
-			flusher.Flush()
-		}
+		flush()
 	}
 }

test/apiv2/20-containers.at

@@ -150,6 +150,13 @@ podman run --name $CTRNAME -d $IMAGE sleep 25
 t GET containers/$CTRNAME/top?stream=false 200 \
   .Processes.[0].[6]="00:00:00" \
   .Processes.[0].[7]="sleep 25"
+
+# check logs output, IMPORTANT the container should write no logs to reproduce #23712
+APIV2_TEST_EXPECT_TIMEOUT=1 t GET "containers/${CTRNAME}/logs?follow=true&stdout=true&stderr=true" 999
+is "" "$(<$WORKDIR/curl.result.out)" "Container MUST NOT log output"
+like "$(<$WORKDIR/curl.headers.out)" ".*HTTP.* 200 OK.*" \
+     "Received headers from /container/<id>/logs"
+
 podman rm -f -t0 $CTRNAME
 
 CTRNAME=test123