Extract duplicate HTTP connection error detection into helper function

internal/mcp/connection.go

@@ -37,6 +37,17 @@ func parseSSEResponse(body []byte) ([]byte, error) {
 	return nil, fmt.Errorf("no data field found in SSE response")
 }
 
+// isConnectionError checks if an error indicates a connection failure
+func isConnectionError(err error) bool {
+	if err == nil {
+		return false
+	}
+	errStr := err.Error()
+	return strings.Contains(errStr, "connection refused") ||
+		strings.Contains(errStr, "no such host") ||
+		strings.Contains(errStr, "network is unreachable")
+}
+
 // ContextKey for session ID
 type ContextKey string
 
@@ -584,9 +595,7 @@ func (c *Connection) initializeHTTPSession() (string, error) {
 	httpResp, err := c.httpClient.Do(httpReq)
 	if err != nil {
 		// Check if it's a connection error (cannot connect at all)
-		if strings.Contains(err.Error(), "connection refused") ||
-			strings.Contains(err.Error(), "no such host") ||
-			strings.Contains(err.Error(), "network is unreachable") {
+		if isConnectionError(err) {
 			return "", fmt.Errorf("cannot connect to HTTP backend at %s: %w", c.httpURL, err)
 		}
 		return "", fmt.Errorf("failed to send initialize request to %s: %w", c.httpURL, err)
@@ -698,9 +707,7 @@ func (c *Connection) sendHTTPRequest(ctx context.Context, method string, params
 	httpResp, err := c.httpClient.Do(httpReq)
 	if err != nil {
 		// Check if it's a connection error (cannot connect at all)
-		if strings.Contains(err.Error(), "connection refused") ||
-			strings.Contains(err.Error(), "no such host") ||
-			strings.Contains(err.Error(), "network is unreachable") {
+		if isConnectionError(err) {
 			return nil, fmt.Errorf("cannot connect to HTTP backend at %s: %w", c.httpURL, err)
 		}
 		return nil, fmt.Errorf("failed to send HTTP request to %s: %w", c.httpURL, err)

internal/mcp/connection_test.go

@@ -703,3 +703,60 @@ func TestNewHTTPConnection(t *testing.T) {
 	assert.Equal(t, httpClient, conn.httpClient, "HTTP client should match")
 	assert.Equal(t, HTTPTransportStreamable, conn.httpTransportType, "Transport type should match")
 }
+
+// TestIsConnectionError tests the isConnectionError helper function
+func TestIsConnectionError(t *testing.T) {
+	tests := []struct {
+		name     string
+		err      error
+		expected bool
+	}{
+		{
+			name:     "nil error",
+			err:      nil,
+			expected: false,
+		},
+		{
+			name:     "connection refused error",
+			err:      fmt.Errorf("dial tcp: connection refused"),
+			expected: true,
+		},
+		{
+			name:     "no such host error",
+			err:      fmt.Errorf("dial tcp: lookup example.com: no such host"),
+			expected: true,
+		},
+		{
+			name:     "network is unreachable error",
+			err:      fmt.Errorf("dial tcp: connect: network is unreachable"),
+			expected: true,
+		},
+		{
+			name:     "connection refused in wrapped error",
+			err:      fmt.Errorf("failed to connect: %w", fmt.Errorf("connection refused")),
+			expected: true,
+		},
+		{
+			name:     "other error",
+			err:      fmt.Errorf("some other error"),
+			expected: false,
+		},
+		{
+			name:     "timeout error",
+			err:      fmt.Errorf("context deadline exceeded"),
+			expected: false,
+		},
+		{
+			name:     "EOF error",
+			err:      fmt.Errorf("unexpected EOF"),
+			expected: false,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			result := isConnectionError(tt.err)
+			assert.Equal(t, tt.expected, result, "isConnectionError(%v) should return %v", tt.err, tt.expected)
+		})
+	}
+}