fix: resolve JSON.parse error in frontend API calls

- Add error handling for JSON encoding in all backend handlers
- Add CORS support to backend server
- Add proxy configuration for frontend development server
- Improve error handling in frontend API calls
- Build frontend to create static files for backend serving
- Add comprehensive error messages and user feedback

Fixes issue where frontend received malformed JSON responses from backend API.

backend/data/test.md

@@ -0,0 +1 @@
+# hi

backend/go.mod

@@ -10,6 +10,7 @@ require (
 
 require (
 	github.com/inconshreveable/mousetrap v1.1.0 // indirect
+	github.com/rs/cors v1.11.1 // indirect
 	github.com/spf13/pflag v1.0.5 // indirect
 	golang.org/x/sys v0.0.0-20220715151400-c0bba94af5f8 // indirect
 )

backend/go.sum

@@ -8,6 +8,8 @@ github.com/inconshreveable/mousetrap v1.1.0 h1:wN+x4NVGpMsO7ErUn/mUI3vEoE6Jt13X2
 github.com/inconshreveable/mousetrap v1.1.0/go.mod h1:vpF70FUmC8bwa3OWnCshd2FqLfsEA9PFc4w1p2J65bw=
 github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
 github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
+github.com/rs/cors v1.11.1 h1:eU3gRzXLRK57F5rKMGMZURNdIG4EoAmX8k94r9wXWHA=
+github.com/rs/cors v1.11.1/go.mod h1:XyqrcTp5zjWr1wsJ8PIRZssZ8b/WMcMf71DJnit4EMU=
 github.com/russross/blackfriday/v2 v2.1.0/go.mod h1:+Rmxgy9KzJVeS9/2gXHxylqXiyQDYRxCVz55jmeOWTM=
 github.com/sirupsen/logrus v1.9.3 h1:dueUQJ1C2q9oE3F7wvmSGAaVtTmUizReu6fjN8uqzbQ=
 github.com/sirupsen/logrus v1.9.3/go.mod h1:naHLuLoDiP4jHNo9R0sCBMtWGeIprob74mVsIT4qYEQ=

backend/internal/handlers/handlers.go

@@ -31,9 +31,13 @@ func (h *Handlers) ListFiles() http.HandlerFunc {
 		}
 
 		w.Header().Set("Content-Type", "application/json")
-		json.NewEncoder(w).Encode(map[string]interface{}{
+		if err := json.NewEncoder(w).Encode(map[string]interface{}{
 			"files": files,
-		})
+		}); err != nil {
+			h.logger.Errorf("Failed to encode response: %v", err)
+			h.writeError(w, http.StatusInternalServerError, "failed to encode response")
+			return
+		}
 	}
 }
 
@@ -62,9 +66,13 @@ func (h *Handlers) CreateFile() http.HandlerFunc {
 		}
 
 		w.Header().Set("Content-Type", "application/json")
-		json.NewEncoder(w).Encode(map[string]string{
+		if err := json.NewEncoder(w).Encode(map[string]string{
 			"message": "file created successfully",
-		})
+		}); err != nil {
+			h.logger.Errorf("Failed to encode response: %v", err)
+			h.writeError(w, http.StatusInternalServerError, "failed to encode response")
+			return
+		}
 	}
 }
 
@@ -86,10 +94,14 @@ func (h *Handlers) GetFile() http.HandlerFunc {
 		}
 
 		w.Header().Set("Content-Type", "application/json")
-		json.NewEncoder(w).Encode(map[string]interface{}{
+		if err := json.NewEncoder(w).Encode(map[string]interface{}{
 			"filename": filename,
 			"content":  string(content),
-		})
+		}); err != nil {
+			h.logger.Errorf("Failed to encode response: %v", err)
+			h.writeError(w, http.StatusInternalServerError, "failed to encode response")
+			return
+		}
 	}
 }
 
@@ -120,9 +132,13 @@ func (h *Handlers) UpdateFile() http.HandlerFunc {
 		}
 
 		w.Header().Set("Content-Type", "application/json")
-		json.NewEncoder(w).Encode(map[string]string{
+		if err := json.NewEncoder(w).Encode(map[string]string{
 			"message": "file updated successfully",
-		})
+		}); err != nil {
+			h.logger.Errorf("Failed to encode response: %v", err)
+			h.writeError(w, http.StatusInternalServerError, "failed to encode response")
+			return
+		}
 	}
 }
 
@@ -143,16 +159,23 @@ func (h *Handlers) DeleteFile() http.HandlerFunc {
 		}
 
 		w.Header().Set("Content-Type", "application/json")
-		json.NewEncoder(w).Encode(map[string]string{
+		if err := json.NewEncoder(w).Encode(map[string]string{
 			"message": "file deleted successfully",
-		})
+		}); err != nil {
+			h.logger.Errorf("Failed to encode response: %v", err)
+			h.writeError(w, http.StatusInternalServerError, "failed to encode response")
+			return
+		}
 	}
 }
 
 func (h *Handlers) writeError(w http.ResponseWriter, status int, message string) {
 	w.Header().Set("Content-Type", "application/json")
 	w.WriteHeader(status)
-	json.NewEncoder(w).Encode(map[string]string{
+	if err := json.NewEncoder(w).Encode(map[string]string{
 		"error": message,
-	})
+	}); err != nil {
+		h.logger.Errorf("Failed to encode error response: %v", err)
+		w.Write([]byte(`{"error": "failed to encode error response"}`))
+	}
 }

backend/internal/server/server.go

@@ -10,6 +10,7 @@ import (
 	"markdown-editor/internal/logger"
 	"markdown-editor/internal/storage"
 	"github.com/gorilla/mux"
+	"github.com/rs/cors"
 	"github.com/sirupsen/logrus"
 )
 
@@ -73,6 +74,15 @@ func (s *Server) setupRoutes() {
 		frontendDir = frontendDirEnv
 	}
 	s.router.PathPrefix("/").Handler(http.FileServer(http.Dir(frontendDir)))
+
+	// Enable CORS
+	cors := cors.New(cors.Options{
+		AllowedOrigins:   []string{"http://localhost:3000", "http://localhost:8080"},
+		AllowedMethods:   []string{"GET", "POST", "PUT", "DELETE", "OPTIONS"},
+		AllowedHeaders:   []string{"Content-Type", "Authorization"},
+		AllowCredentials: true,
+	})
+	s.router.Use(cors.Handler)
 }
 
 func (s *Server) serve() error {

backend/test/test_api.sh

@@ -0,0 +1,28 @@
+#!/nix/store/ypgcdmzzlgnrmdcsq72c3dxz651jg9zc-bash-5.3p3/bin/bash
+
+# Start the server in the background
+./markdown-editor --data-dir ./test/data --port 8081 --host 127.0.0.1 &
+SERVER_PID=$!
+
+# Give the server time to start
+sleep 2
+
+# Test the /api/files endpoint
+echo "Testing GET /api/files..."
+response=$(curl -s http://127.0.0.1:8081/api/files)
+echo "Response: $response"
+echo ""
+
+# Test if it's valid JSON
+if echo "$response" | python3 -m json.tool > /dev/null 2>&1; then
+    echo "✓ Response is valid JSON"
+else
+    echo "✗ Response is NOT valid JSON"
+    echo "Response was: $response"
+fi
+
+# Kill the server
+kill $SERVER_PID 2>/dev/null
+wait $SERVER_PID 2>/dev/null
+
+echo "Test completed"

backend/test/test_api_detailed.sh

@@ -0,0 +1,35 @@
+#!/nix/store/ypgcdmzzlgnrmdcsq72c3dxz651jg9zc-bash-5.3p3/bin/bash
+
+# Start the server in the background
+./markdown-editor --data-dir ./test/data --port 8082 --host 127.0.0.1 &
+SERVER_PID=$!
+
+# Give the server time to start
+sleep 2
+
+# Test the /api/files endpoint
+echo "Testing GET /api/files..."
+response=$(curl -s -i http://127.0.0.1:8082/api/files)
+echo "$response"
+echo ""
+
+# Extract just the body (skip headers)
+body=$(echo "$response" | awk 'NR>1 && $0 !~ /^[A-Za-z]/ {print; next} /^[A-Za-z]/ {exit}')
+echo "Body: '$body'"
+echo ""
+
+# Test if it's valid JSON
+echo "Checking if response is valid JSON..."
+if echo "$body" | node -e "console.log(JSON.parse(require('fs').readFileSync(0, 'utf8')))" > /dev/null 2>&1; then
+    echo "✓ Response is valid JSON"
+    echo "$body" | node -e "console.log(JSON.parse(require('fs').readFileSync(0, 'utf8')))"
+else
+    echo "✗ Response is NOT valid JSON"
+    echo "Response was: '$body'"
+fi
+
+# Kill the server
+kill $SERVER_PID 2>/dev/null
+wait $SERVER_PID 2>/dev/null
+
+echo "Test completed"

backend/test_api.sh

@@ -0,0 +1,82 @@
+#!/nix/store/ypgcdmzzlgnrmdcsq72c3dxz651jg9zc-bash-5.3p3/bin/bash
+
+# Create test data directory
+mkdir -p test/data
+
+# Start the server in the background
+./markdown-editor --data-dir test/data --port 8080 --host 127.0.0.1 > /tmp/server.log 2>&1 &
+SERVER_PID=$!
+
+# Wait for server to start
+echo "Waiting for server to start..."
+sleep 3
+
+# Check if server is running
+if ! ps -p $SERVER_PID > /dev/null; then
+    echo "Server failed to start"
+    cat /tmp/server.log
+    exit 1
+fi
+
+echo "Server is running (PID: $SERVER_PID)"
+echo "Testing API endpoints..."
+echo ""
+
+# Test 1: GET /api/files (empty)
+echo "Test 1: GET /api/files (no files)"
+response=$(curl -s http://127.0.0.1:8080/api/files)
+echo "Response: $response"
+if echo "$response" | grep -q '"files"'; then
+    echo "✓ Response contains 'files' key"
+else
+    echo "✗ Response does not contain 'files' key"
+fi
+echo ""
+
+# Test 2: Create a file
+echo "Test 2: POST /api/files (create test.md)"
+response=$(curl -s -X POST http://127.0.0.1:8080/api/files \
+    -H "Content-Type: application/json" \
+    -d '{"filename":"test.md","content":"# Test Content"}')
+echo "Response: $response"
+if echo "$response" | grep -q '"message"'; then
+    echo "✓ Response contains 'message' key"
+else
+    echo "✗ Response does not contain 'message' key"
+fi
+echo ""
+
+# Test 3: GET /api/files (with file)
+echo "Test 3: GET /api/files (with file)"
+response=$(curl -s http://127.0.0.1:8080/api/files)
+echo "Response: $response"
+if echo "$response" | grep -q '"files"'; then
+    echo "✓ Response contains 'files' key"
+    if echo "$response" | grep -q '"test.md"'; then
+        echo "✓ Response contains 'test.md'"
+    else
+        echo "✗ Response does not contain 'test.md'"
+    fi
+else
+    echo "✗ Response does not contain 'files' key"
+fi
+echo ""
+
+# Test 4: GET /api/files/test.md
+echo "Test 4: GET /api/files/test.md"
+response=$(curl -s http://127.0.0.1:8080/api/files/test.md)
+echo "Response: $response"
+if echo "$response" | grep -q '"content"'; then
+    echo "✓ Response contains 'content' key"
+else
+    echo "✗ Response does not contain 'content' key"
+fi
+echo ""
+
+# Kill the server
+echo "Stopping server..."
+kill $SERVER_PID
+wait $SERVER_PID 2>/dev/null
+
+echo ""
+echo "All tests completed!"

frontend/src/App.tsx

@@ -23,10 +23,14 @@ const App: React.FC = () => {
   const fetchFiles = async () => {
     try {
       const response = await fetch('/api/files');
+      if (!response.ok) {
+        throw new Error(`HTTP error! status: ${response.status}`);
+      }
       const data = await response.json();
       setFiles(data.files || []);
     } catch (error) {
       console.error('Error fetching files:', error);
+      // Optionally show an error message to the user
     }
   };
 
@@ -45,19 +49,27 @@ const App: React.FC = () => {
         }),
       });
 
-      if (response.ok) {
+      if (!response.ok) {
-        setNewFilename('');
+        const errorData = await response.json();
-        setNewContent('');
+        alert(`Error creating file: ${errorData.error || 'Unknown error'}`);
-        fetchFiles();
+        return;
       }
+
+      setNewFilename('');
+      setNewContent('');
+      fetchFiles();
     } catch (error) {
       console.error('Error creating file:', error);
+      alert('Error creating file. Please check console for details.');
     }
   };
 
   const handleOpenFile = async (filename: string) => {
     try {
       const response = await fetch(`/api/files/${filename}`);
+      if (!response.ok) {
+        throw new Error(`HTTP error! status: ${response.status}`);
+      }
       const data = await response.json();
       setCurrentFile({
         filename,
@@ -83,11 +95,16 @@ const App: React.FC = () => {
         }),
       });
 
-      if (response.ok) {
+      if (!response.ok) {
-        alert('File saved successfully!');
+        const errorData = await response.json();
+        alert(`Error saving file: ${errorData.error || 'Unknown error'}`);
+        return;
       }
+
+      alert('File saved successfully!');
     } catch (error) {
       console.error('Error saving file:', error);
+      alert('Error saving file. Please check console for details.');
     }
   };
 
@@ -99,14 +116,19 @@ const App: React.FC = () => {
         method: 'DELETE',
       });
 
-      if (response.ok) {
+      if (!response.ok) {
-        fetchFiles();
+        const errorData = await response.json();
-        if (currentFile?.filename === filename) {
+        alert(`Error deleting file: ${errorData.error || 'Unknown error'}`);
-          setCurrentFile(null);
+        return;
-        }
+      }
+
+      fetchFiles();
+      if (currentFile?.filename === filename) {
+        setCurrentFile(null);
       }
     } catch (error) {
       console.error('Error deleting file:', error);
+      alert('Error deleting file. Please check console for details.');
     }
   };
 

frontend/src/setupProxy.js

@@ -0,0 +1,11 @@
+const { createProxyMiddleware } = require('http-proxy-middleware');
+
+module.exports = function(app) {
+  app.use(
+    '/api',
+    createProxyMiddleware({
+      target: 'http://localhost:8080',
+      changeOrigin: true,
+    })
+  );
+};