Add fail-fast on init for missing provider credentials

internal/observability/metrics_middleware.go

@@ -48,15 +48,30 @@ type metricsResponseWriter struct {
 	http.ResponseWriter
 	statusCode   int
 	bytesWritten int
+	wroteHeader  bool
 }
 
 func (w *metricsResponseWriter) WriteHeader(statusCode int) {
+	if w.wroteHeader {
+		return
+	}
+	w.wroteHeader = true
 	w.statusCode = statusCode
 	w.ResponseWriter.WriteHeader(statusCode)
 }
 
 func (w *metricsResponseWriter) Write(b []byte) (int, error) {
+	if !w.wroteHeader {
+		w.wroteHeader = true
+		w.statusCode = http.StatusOK
+	}
 	n, err := w.ResponseWriter.Write(b)
 	w.bytesWritten += n
 	return n, err
 }
+
+func (w *metricsResponseWriter) Flush() {
+	if flusher, ok := w.ResponseWriter.(http.Flusher); ok {
+		flusher.Flush()
+	}
+}

internal/observability/middleware_response_writer_test.go

@@ -0,0 +1,65 @@
+package observability
+
+import (
+	"net/http"
+	"net/http/httptest"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+var _ http.Flusher = (*metricsResponseWriter)(nil)
+var _ http.Flusher = (*statusResponseWriter)(nil)
+
+type testFlusherRecorder struct {
+	*httptest.ResponseRecorder
+	flushCount int
+}
+
+func newTestFlusherRecorder() *testFlusherRecorder {
+	return &testFlusherRecorder{ResponseRecorder: httptest.NewRecorder()}
+}
+
+func (r *testFlusherRecorder) Flush() {
+	r.flushCount++
+}
+
+func TestMetricsResponseWriterWriteHeaderOnlyOnce(t *testing.T) {
+	rec := httptest.NewRecorder()
+	rw := &metricsResponseWriter{ResponseWriter: rec, statusCode: http.StatusOK}
+
+	rw.WriteHeader(http.StatusAccepted)
+	rw.WriteHeader(http.StatusInternalServerError)
+
+	assert.Equal(t, http.StatusAccepted, rec.Code)
+	assert.Equal(t, http.StatusAccepted, rw.statusCode)
+}
+
+func TestMetricsResponseWriterFlushDelegates(t *testing.T) {
+	rec := newTestFlusherRecorder()
+	rw := &metricsResponseWriter{ResponseWriter: rec, statusCode: http.StatusOK}
+
+	rw.Flush()
+
+	assert.Equal(t, 1, rec.flushCount)
+}
+
+func TestStatusResponseWriterWriteHeaderOnlyOnce(t *testing.T) {
+	rec := httptest.NewRecorder()
+	rw := &statusResponseWriter{ResponseWriter: rec, statusCode: http.StatusOK}
+
+	rw.WriteHeader(http.StatusNoContent)
+	rw.WriteHeader(http.StatusInternalServerError)
+
+	assert.Equal(t, http.StatusNoContent, rec.Code)
+	assert.Equal(t, http.StatusNoContent, rw.statusCode)
+}
+
+func TestStatusResponseWriterFlushDelegates(t *testing.T) {
+	rec := newTestFlusherRecorder()
+	rw := &statusResponseWriter{ResponseWriter: rec, statusCode: http.StatusOK}
+
+	rw.Flush()
+
+	assert.Equal(t, 1, rec.flushCount)
+}

internal/observability/tracing_middleware.go

@@ -72,14 +72,29 @@ func TracingMiddleware(next http.Handler, tp *sdktrace.TracerProvider) http.Hand
 // statusResponseWriter wraps http.ResponseWriter to capture the status code.
 type statusResponseWriter struct {
 	http.ResponseWriter
-	statusCode int
+	statusCode  int
+	wroteHeader bool
 }
 
 func (w *statusResponseWriter) WriteHeader(statusCode int) {
+	if w.wroteHeader {
+		return
+	}
+	w.wroteHeader = true
 	w.statusCode = statusCode
 	w.ResponseWriter.WriteHeader(statusCode)
 }
 
 func (w *statusResponseWriter) Write(b []byte) (int, error) {
+	if !w.wroteHeader {
+		w.wroteHeader = true
+		w.statusCode = http.StatusOK
+	}
 	return w.ResponseWriter.Write(b)
 }
+
+func (w *statusResponseWriter) Flush() {
+	if flusher, ok := w.ResponseWriter.(http.Flusher); ok {
+		flusher.Flush()
+	}
+}