http: set Content-Type for 202/204 streamable responses (#149)

Fixes: #148
Reviewed-on: https://gitea.com/gitea/gitea-mcp/pulls/149
Reviewed-by: silverwind <2021+silverwind@noreply.gitea.com>
Co-authored-by: Mutex <gitea314@libertyprime.org>
Co-committed-by: Mutex <gitea314@libertyprime.org>

operation/operation_http_headers_test.go

@@ -0,0 +1,77 @@
+package operation
+
+import (
+	"net/http"
+	"net/http/httptest"
+	"testing"
+)
+
+func TestWithNoBodyContentTypeAddsContentTypeForAcceptedAndNoContent(t *testing.T) {
+	tests := []struct {
+		name   string
+		status int
+	}{
+		{
+			name:   "accepted",
+			status: http.StatusAccepted,
+		},
+		{
+			name:   "no_content",
+			status: http.StatusNoContent,
+		},
+	}
+
+	for _, tc := range tests {
+		t.Run(tc.name, func(t *testing.T) {
+			handler := withNoBodyContentType(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+				w.WriteHeader(tc.status)
+			}))
+
+			req := httptest.NewRequest(http.MethodPost, "/mcp", nil)
+			rr := httptest.NewRecorder()
+			handler.ServeHTTP(rr, req)
+
+			if rr.Code != tc.status {
+				t.Fatalf("expected status %d, got %d", tc.status, rr.Code)
+			}
+			if got := rr.Header().Get("Content-Type"); got != "application/json" {
+				t.Fatalf("expected Content-Type application/json, got %q", got)
+			}
+		})
+	}
+}
+
+func TestWithNoBodyContentTypePreservesExistingContentType(t *testing.T) {
+	handler := withNoBodyContentType(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.Header().Set("Content-Type", "text/plain")
+		w.WriteHeader(http.StatusAccepted)
+	}))
+
+	req := httptest.NewRequest(http.MethodPost, "/mcp", nil)
+	rr := httptest.NewRecorder()
+	handler.ServeHTTP(rr, req)
+
+	if rr.Code != http.StatusAccepted {
+		t.Fatalf("expected status %d, got %d", http.StatusAccepted, rr.Code)
+	}
+	if got := rr.Header().Get("Content-Type"); got != "text/plain" {
+		t.Fatalf("expected Content-Type text/plain, got %q", got)
+	}
+}
+
+func TestWithNoBodyContentTypeDoesNotModifyOtherStatusCodes(t *testing.T) {
+	handler := withNoBodyContentType(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.WriteHeader(http.StatusOK)
+	}))
+
+	req := httptest.NewRequest(http.MethodPost, "/mcp", nil)
+	rr := httptest.NewRecorder()
+	handler.ServeHTTP(rr, req)
+
+	if rr.Code != http.StatusOK {
+		t.Fatalf("expected status %d, got %d", http.StatusOK, rr.Code)
+	}
+	if got := rr.Header().Get("Content-Type"); got != "" {
+		t.Fatalf("expected empty Content-Type, got %q", got)
+	}
+}