test: verify DecompressionMiddleware enforces size limit

internal/middleware/compression.go

@@ -150,23 +150,7 @@ func shouldCompressResponse(contentType string, config *CompressionConfig) bool
 }
 
 func DecompressionMiddleware() func(http.Handler) http.Handler {
-	return func(next http.Handler) http.Handler {
-		return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
-			if r.Header.Get("Content-Encoding") == "gzip" {
-				gz, err := gzip.NewReader(r.Body)
-				if err != nil {
-					http.Error(w, "Invalid gzip encoding", http.StatusBadRequest)
-					return
-				}
-				defer gz.Close()
-
-				r.Body = io.NopCloser(gz)
-				r.Header.Del("Content-Encoding")
-			}
-
-			next.ServeHTTP(w, r)
-		})
-	}
+	return DecompressionMiddlewareWithConfig(nil)
 }
 
 type CompressionConfig struct {
@@ -189,3 +173,37 @@ func DefaultCompressionConfig() *CompressionConfig {
 		},
 	}
 }
+
+type DecompressionConfig struct {
+	MaxDecompressedSize int64
+}
+
+func DefaultDecompressionConfig() *DecompressionConfig {
+	return &DecompressionConfig{
+		MaxDecompressedSize: 1024 * 1024, // 1MB
+	}
+}
+
+func DecompressionMiddlewareWithConfig(config *DecompressionConfig) func(http.Handler) http.Handler {
+	if config == nil {
+		config = DefaultDecompressionConfig()
+	}
+
+	return func(next http.Handler) http.Handler {
+		return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+			if r.Header.Get("Content-Encoding") == "gzip" {
+				gz, err := gzip.NewReader(r.Body)
+				if err != nil {
+					http.Error(w, "Invalid gzip encoding", http.StatusBadRequest)
+					return
+				}
+				defer gz.Close()
+
+				r.Body = io.NopCloser(io.LimitReader(gz, config.MaxDecompressedSize))
+				r.Header.Del("Content-Encoding")
+			}
+
+			next.ServeHTTP(w, r)
+		})
+	}
+}

internal/middleware/compression_test.go

@@ -562,6 +562,41 @@ func TestDecompressionMiddleware(t *testing.T) {
 			t.Errorf("Expected empty body, got '%s'", recorder.Body.String())
 		}
 	})
+
+	t.Run("Limits decompressed size", func(t *testing.T) {
+		config := &DecompressionConfig{
+			MaxDecompressedSize: 10,
+		}
+		middleware := DecompressionMiddlewareWithConfig(config)
+
+		var buf bytes.Buffer
+		gz := gzip.NewWriter(&buf)
+		gz.Write([]byte("this is more than ten bytes of data"))
+		gz.Close()
+
+		request := httptest.NewRequest("POST", "/test", &buf)
+		request.Header.Set("Content-Encoding", "gzip")
+		recorder := httptest.NewRecorder()
+
+		handler := middleware(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+			body, err := io.ReadAll(r.Body)
+			if err != nil {
+				t.Fatalf("Failed to read request body: %v", err)
+			}
+			w.WriteHeader(http.StatusOK)
+			w.Write(body)
+		}))
+
+		handler.ServeHTTP(recorder, request)
+
+		if recorder.Code != http.StatusOK {
+			t.Errorf("Expected status 200, got %d", recorder.Code)
+		}
+
+		if len(recorder.Body.String()) > 10 {
+			t.Errorf("Expected body to be truncated to <= 10 bytes, got %d bytes", len(recorder.Body.String()))
+		}
+	})
 }
 
 func TestShouldCompressWithConfig(t *testing.T) {