Stream live server logs over SSE

platform/api/log_ingest_handlers_test.go

@@ -1,7 +1,10 @@
 package api
 
 import (
+	"bufio"
 	"net/http"
+	"net/http/httptest"
+	"strings"
 	"testing"
 	"time"
 
@@ -35,6 +38,32 @@ func TestLogIngestAPIWorkflow(t *testing.T) {
 	}
 }
 
+func TestLogEventsSSEReplaysHistory(t *testing.T) {
+	router := newTestRouter()
+	hello := createLogIngestAPIFixtures(t, router)
+	batch := validLogBatchRequest(t, hello.SessionToken, 1, 2)
+	assertStatus(t, performJSON(t, router, http.MethodPost, "/api/v1/run/logs/batches", batch), http.StatusOK)
+
+	server := httptest.NewServer(router)
+	defer server.Close()
+	client := server.Client()
+	client.Timeout = 2 * time.Second
+	response, err := client.Get(server.URL + "/api/v1/server-instances/server-1/logs/events?historyLimit=2")
+	if err != nil {
+		t.Fatalf("open log event stream: %v", err)
+	}
+	defer response.Body.Close()
+	if response.StatusCode != http.StatusOK || !strings.HasPrefix(response.Header.Get("Content-Type"), "text/event-stream") {
+		t.Fatalf("unexpected event stream response: status=%d content-type=%q", response.StatusCode, response.Header.Get("Content-Type"))
+	}
+	body := readSSEUntil(t, response, "event: ready")
+	for _, fragment := range []string{"event: stream", "event: log", `"streamId":"log-1"`, `"seq":1`, `"seq":2`} {
+		if !strings.Contains(body, fragment) {
+			t.Fatalf("expected SSE body to contain %q, got:\n%s", fragment, body)
+		}
+	}
+}
+
 func TestLogIngestAPIDuplicateAndErrors(t *testing.T) {
 	router := newTestRouter()
 	hello := createLogIngestAPIFixtures(t, router)
@@ -77,6 +106,20 @@ func createLogIngestAPIFixtures(t *testing.T, router http.Handler) dto.RunContro
 	return hello
 }
 
+func readSSEUntil(t *testing.T, response *http.Response, marker string) string {
+	t.Helper()
+	reader := bufio.NewReader(response.Body)
+	var body strings.Builder
+	for !strings.Contains(body.String(), marker) {
+		line, err := reader.ReadString('\n')
+		if err != nil {
+			t.Fatalf("read event stream: %v\n%s", err, body.String())
+		}
+		body.WriteString(line)
+	}
+	return body.String()
+}
+
 func validLogBatchRequest(t *testing.T, sessionToken string, firstSeq uint64, lastSeq uint64) dto.LogBatchIngestRequest {
 	t.Helper()
 	entries := make([]dto.LogEntryBody, 0, lastSeq-firstSeq+1)