tracing: add notification support

Applications consuming pfp may want to pass through the computed
tracing status to other subsystem. This change adds better
support for this usecase:

1. add an explicit point which marks the Status done (completed, sealed)
   and ready to be passed around as such. Even this simple addition
   can be good already for documentation and clarity
2. add minimal infrastructure for notification, leveraging channels.

Signed-off-by: Francesco Romani <[email protected]>

notify.go

@@ -0,0 +1,43 @@
+/*
+ * Copyright 2023 Red Hat, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package podfingerprint
+
+var completionSink chan<- Status
+
+// SetCompletionSink sets the process-global completion destination
+func SetCompletionSink(ch chan<- Status) {
+	completionSink = ch
+}
+
+// MarkCompleted sets a podfingerprint Status as completed.
+// When a Status is completed, it means the Status and its fingerprint is considered sealed,
+// so from now on only idempotent, non-state altering actions (like Repr(), Sign(), Check())
+// are expected to be performed. Applications which use the Tracing fingerprint can use this
+// function to clearly signal this completion point and as another option to pass the Status
+// to other subssystems.
+func MarkCompleted(st Status) error {
+	if completionSink == nil { // nothing to do
+		return nil
+	}
+	completionSink <- st.Clone()
+	return nil
+}
+
+// CleanCompletionSink should be used only in testing
+func CleanCompletionSink() {
+	completionSink = nil
+}

notify_test.go

@@ -0,0 +1,92 @@
+/*
+ * Copyright 2023 Red Hat, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package podfingerprint
+
+import (
+	"testing"
+)
+
+func TestMarkCompleted(t *testing.T) {
+	type testCase struct {
+		name          string
+		sink          chan Status
+		status        Status
+		expectedError error
+	}
+
+	testCases := []testCase{
+		{
+			name: "no completion sink",
+			status: Status{
+				NodeName: "test-node-0",
+				Pods: []NamespacedName{
+					{
+						Namespace: "ns-1",
+						Name:      "pod-1",
+					},
+					{
+						Namespace: "ns-2",
+						Name:      "pod-2",
+					},
+					{
+						Namespace: "ns-2",
+						Name:      "pod-3",
+					},
+				},
+				FingerprintExpected: "pfp0v001807d932586d44a8a",
+				FingerprintComputed: "pfp0v001807d932586d44a8a",
+			},
+			sink: nil, // explicit
+		},
+		{
+			name: "with completion sink",
+			status: Status{
+				NodeName: "test-node-0",
+				Pods: []NamespacedName{
+					{
+						Namespace: "ns-1",
+						Name:      "pod-1",
+					},
+					{
+						Namespace: "ns-2",
+						Name:      "pod-2",
+					},
+					{
+						Namespace: "ns-2",
+						Name:      "pod-3",
+					},
+				},
+				FingerprintExpected: "pfp0v001807d932586d44a8a",
+				FingerprintComputed: "pfp0v001807d932586d44a8a",
+			},
+			sink: make(chan Status, 5), // anything > 1 is fine
+		},
+	}
+
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			SetCompletionSink(tc.sink)
+			err := MarkCompleted(tc.status)
+			if err != tc.expectedError {
+				t.Errorf("got error=%v expected=%v", err, tc.expectedError)
+			}
+			if tc.sink != nil && len(tc.sink) != 1 {
+				t.Errorf("unexpected data in sink: %d", len(tc.sink))
+			}
+		})
+	}
+}

tools/pfp/main.go

@@ -40,7 +40,7 @@ func main() {
 	flag.Parse()
 
 	var fp Fingerprinter
-	var st podfingerprint.Status
+	st := podfingerprint.MakeStatus("STDIN")
 	if *withTrace {
 		fp = podfingerprint.NewTracingFingerprint(0, &st)
 	} else {
@@ -59,7 +59,11 @@ func main() {
 		}
 		fp.Add(fields[0], fields[1])
 	}
-	fmt.Println(fp.Sign())
+	pfp := fp.Sign()
+	if *withTrace {
+		podfingerprint.MarkCompleted(st)
+	}
+	fmt.Println(pfp)
 
 	if *withTrace {
 		json.NewEncoder(os.Stderr).Encode(st)