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Refactor Pattern 1 & 2: Extract duplicate code into helper functions
- Pattern 2 (High Priority): Extract SDK CallToolResult error returns - Created newErrorCallToolResult() helper in unified.go - Replaced 16 instances of duplicate error pattern - Added unit tests for the helper function - Pattern 1 (Medium Priority): Extract HTTP connection error checking - Created isHTTPConnectionError() helper in connection.go - Replaced 2 instances of duplicate error detection - Added unit tests for the helper function All existing tests pass. Total reduction: ~45 lines of duplicated code. Co-authored-by: lpcox <15877973+lpcox@users.noreply.github.com>
1 parent e9d481e commit 7e7dffc

4 files changed

Lines changed: 123 additions & 22 deletions

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‎internal/mcp/connection.go‎

Lines changed: 14 additions & 6 deletions
Original file line numberDiff line numberDiff line change
@@ -23,6 +23,18 @@ import (
2323

2424
var logConn = logger.New("mcp:connection")
2525

26+
// isHTTPConnectionError checks if an error is a network connection error
27+
// This helper reduces code duplication for checking common connection error patterns
28+
func isHTTPConnectionError(err error) bool {
29+
if err == nil {
30+
return false
31+
}
32+
errMsg := err.Error()
33+
return strings.Contains(errMsg, "connection refused") ||
34+
strings.Contains(errMsg, "no such host") ||
35+
strings.Contains(errMsg, "network is unreachable")
36+
}
37+
2638
// parseSSEResponse extracts JSON data from SSE-formatted response
2739
// SSE format: "event: message\ndata: {json}\n\n"
2840
func parseSSEResponse(body []byte) ([]byte, error) {
@@ -584,9 +596,7 @@ func (c *Connection) initializeHTTPSession() (string, error) {
584596
httpResp, err := c.httpClient.Do(httpReq)
585597
if err != nil {
586598
// Check if it's a connection error (cannot connect at all)
587-
if strings.Contains(err.Error(), "connection refused") ||
588-
strings.Contains(err.Error(), "no such host") ||
589-
strings.Contains(err.Error(), "network is unreachable") {
599+
if isHTTPConnectionError(err) {
590600
return "", fmt.Errorf("cannot connect to HTTP backend at %s: %w", c.httpURL, err)
591601
}
592602
return "", fmt.Errorf("failed to send initialize request to %s: %w", c.httpURL, err)
@@ -698,9 +708,7 @@ func (c *Connection) sendHTTPRequest(ctx context.Context, method string, params
698708
httpResp, err := c.httpClient.Do(httpReq)
699709
if err != nil {
700710
// Check if it's a connection error (cannot connect at all)
701-
if strings.Contains(err.Error(), "connection refused") ||
702-
strings.Contains(err.Error(), "no such host") ||
703-
strings.Contains(err.Error(), "network is unreachable") {
711+
if isHTTPConnectionError(err) {
704712
return nil, fmt.Errorf("cannot connect to HTTP backend at %s: %w", c.httpURL, err)
705713
}
706714
return nil, fmt.Errorf("failed to send HTTP request to %s: %w", c.httpURL, err)

‎internal/mcp/connection_test.go‎

Lines changed: 47 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -703,3 +703,50 @@ func TestNewHTTPConnection(t *testing.T) {
703703
assert.Equal(t, httpClient, conn.httpClient, "HTTP client should match")
704704
assert.Equal(t, HTTPTransportStreamable, conn.httpTransportType, "Transport type should match")
705705
}
706+
707+
// TestIsHTTPConnectionError tests the HTTP connection error detection helper
708+
func TestIsHTTPConnectionError(t *testing.T) {
709+
tests := []struct {
710+
name string
711+
err error
712+
expected bool
713+
}{
714+
{
715+
name: "nil error",
716+
err: nil,
717+
expected: false,
718+
},
719+
{
720+
name: "connection refused error",
721+
err: fmt.Errorf("dial tcp: connection refused"),
722+
expected: true,
723+
},
724+
{
725+
name: "no such host error",
726+
err: fmt.Errorf("dial tcp: lookup example.invalid: no such host"),
727+
expected: true,
728+
},
729+
{
730+
name: "network is unreachable error",
731+
err: fmt.Errorf("dial tcp: network is unreachable"),
732+
expected: true,
733+
},
734+
{
735+
name: "other error",
736+
err: fmt.Errorf("some other error"),
737+
expected: false,
738+
},
739+
{
740+
name: "timeout error",
741+
err: fmt.Errorf("context deadline exceeded"),
742+
expected: false,
743+
},
744+
}
745+
746+
for _, tt := range tests {
747+
t.Run(tt.name, func(t *testing.T) {
748+
result := isHTTPConnectionError(tt.err)
749+
assert.Equal(t, tt.expected, result, "isHTTPConnectionError should return %v for %v", tt.expected, tt.err)
750+
})
751+
}
752+
}

‎internal/server/call_tool_result_test.go‎

Lines changed: 39 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -1,6 +1,7 @@
11
package server
22

33
import (
4+
"fmt"
45
"testing"
56

67
sdk "github.com/modelcontextprotocol/go-sdk/mcp"
@@ -151,3 +152,41 @@ func TestConvertToCallToolResult_NilCheck(t *testing.T) {
151152

152153
t.Log("✓ CallToolResult is properly non-nil and structured")
153154
}
155+
156+
// TestNewErrorCallToolResult tests the error CallToolResult helper
157+
func TestNewErrorCallToolResult(t *testing.T) {
158+
tests := []struct {
159+
name string
160+
err error
161+
expectError bool
162+
}{
163+
{
164+
name: "simple error",
165+
err: assert.AnError,
166+
expectError: true,
167+
},
168+
{
169+
name: "formatted error",
170+
err: fmt.Errorf("formatted error: %s", "test"),
171+
expectError: true,
172+
},
173+
}
174+
175+
for _, tt := range tests {
176+
t.Run(tt.name, func(t *testing.T) {
177+
result, data, err := newErrorCallToolResult(tt.err)
178+
179+
// Verify the error is returned
180+
assert.Equal(t, tt.err, err, "Error should be returned as-is")
181+
182+
// Verify data is nil
183+
assert.Nil(t, data, "Data should be nil for error results")
184+
185+
// Verify CallToolResult is properly structured
186+
require.NotNil(t, result, "CallToolResult should not be nil")
187+
assert.True(t, result.IsError, "IsError should be true")
188+
189+
t.Logf("✓ Error CallToolResult properly created with IsError=%v", result.IsError)
190+
})
191+
}
192+
}

‎internal/server/unified.go‎

Lines changed: 23 additions & 16 deletions
Original file line numberDiff line numberDiff line change
@@ -320,7 +320,7 @@ func (us *UnifiedServer) registerToolsFromBackend(serverID string) error {
320320
toolArgs, err := parseToolArguments(req)
321321
if err != nil {
322322
logger.LogError("client", "Failed to unmarshal tool arguments, tool=%s, error=%v", toolNameCopy, err)
323-
return &sdk.CallToolResult{IsError: true}, nil, err
323+
return newErrorCallToolResult(err)
324324
}
325325

326326
// Log the MCP tool call request
@@ -331,7 +331,7 @@ func (us *UnifiedServer) registerToolsFromBackend(serverID string) error {
331331
// Check session is initialized
332332
if err := us.requireSession(ctx); err != nil {
333333
logger.LogError("client", "MCP tool call failed: session not initialized, session=%s, tool=%s", sessionID, toolNameCopy)
334-
return &sdk.CallToolResult{IsError: true}, nil, err
334+
return newErrorCallToolResult(err)
335335
}
336336

337337
result, data, err := us.callBackendTool(ctx, serverIDCopy, toolNameCopy, toolArgs)
@@ -395,7 +395,7 @@ func (us *UnifiedServer) registerSysTools() error {
395395
toolArgs, err := parseToolArguments(req)
396396
if err != nil {
397397
logger.LogError("client", "Failed to unmarshal sys_init arguments, error=%v", err)
398-
return &sdk.CallToolResult{IsError: true}, nil, err
398+
return newErrorCallToolResult(err)
399399
}
400400

401401
// Extract token from args
@@ -408,7 +408,7 @@ func (us *UnifiedServer) registerSysTools() error {
408408
sessionID := us.getSessionID(ctx)
409409
if sessionID == "" {
410410
logger.LogError("client", "MCP session initialization failed: no session ID provided")
411-
return &sdk.CallToolResult{IsError: true}, nil, fmt.Errorf("no session ID provided")
411+
return newErrorCallToolResult(fmt.Errorf("no session ID provided"))
412412
}
413413

414414
logger.LogInfo("client", "MCP session initialization started, session=%s, has_token=%v", sessionID, token != "")
@@ -436,7 +436,7 @@ func (us *UnifiedServer) registerSysTools() error {
436436
result, err := us.sysServer.HandleRequest("tools/call", json.RawMessage(params))
437437
if err != nil {
438438
logger.LogError("client", "MCP session initialization: sys_init call failed, session=%s, error=%v", sessionID, err)
439-
return &sdk.CallToolResult{IsError: true}, nil, err
439+
return newErrorCallToolResult(err)
440440
}
441441

442442
resultJSON, _ := json.Marshal(result)
@@ -486,7 +486,7 @@ func (us *UnifiedServer) registerSysTools() error {
486486
// Check session is initialized
487487
if err := us.requireSession(ctx); err != nil {
488488
logger.LogError("client", "MCP sys_list_servers failed: session not initialized, session=%s", sessionID)
489-
return &sdk.CallToolResult{IsError: true}, nil, err
489+
return newErrorCallToolResult(err)
490490
}
491491

492492
params, _ := json.Marshal(map[string]interface{}{
@@ -496,7 +496,7 @@ func (us *UnifiedServer) registerSysTools() error {
496496
result, err := us.sysServer.HandleRequest("tools/call", json.RawMessage(params))
497497
if err != nil {
498498
logger.LogError("client", "MCP sys_list_servers error, session=%s, error=%v", sessionID, err)
499-
return &sdk.CallToolResult{IsError: true}, nil, err
499+
return newErrorCallToolResult(err)
500500
}
501501

502502
resultJSON, _ := json.Marshal(result)
@@ -657,7 +657,7 @@ func (us *UnifiedServer) callBackendTool(ctx context.Context, serverID, toolName
657657
resource, operation, err := g.LabelResource(ctx, toolName, args, backendCaller, us.capabilities)
658658
if err != nil {
659659
log.Printf("[DIFC] Guard labeling failed: %v", err)
660-
return &sdk.CallToolResult{IsError: true}, nil, fmt.Errorf("guard labeling failed: %w", err)
660+
return newErrorCallToolResult(fmt.Errorf("guard labeling failed: %w", err))
661661
}
662662

663663
log.Printf("[DIFC] Resource: %s | Operation: %s | Secrecy: %v | Integrity: %v",
@@ -688,33 +688,33 @@ func (us *UnifiedServer) callBackendTool(ctx context.Context, serverID, toolName
688688
sessionID := us.getSessionID(ctx)
689689
conn, err := launcher.GetOrLaunchForSession(us.launcher, serverID, sessionID)
690690
if err != nil {
691-
return &sdk.CallToolResult{IsError: true}, nil, fmt.Errorf("failed to connect: %w", err)
691+
return newErrorCallToolResult(fmt.Errorf("failed to connect: %w", err))
692692
}
693693

694694
response, err := conn.SendRequestWithServerID(ctx, "tools/call", map[string]interface{}{
695695
"name": toolName,
696696
"arguments": args,
697697
}, serverID)
698698
if err != nil {
699-
return &sdk.CallToolResult{IsError: true}, nil, err
699+
return newErrorCallToolResult(err)
700700
}
701701

702702
// Check if the backend returned an error
703703
if response.Error != nil {
704-
return &sdk.CallToolResult{IsError: true}, nil, fmt.Errorf("backend error: code=%d, message=%s", response.Error.Code, response.Error.Message)
704+
return newErrorCallToolResult(fmt.Errorf("backend error: code=%d, message=%s", response.Error.Code, response.Error.Message))
705705
}
706706

707707
// Parse the backend result
708708
var backendResult interface{}
709709
if err := json.Unmarshal(response.Result, &backendResult); err != nil {
710-
return &sdk.CallToolResult{IsError: true}, nil, fmt.Errorf("failed to parse result: %w", err)
710+
return newErrorCallToolResult(fmt.Errorf("failed to parse result: %w", err))
711711
}
712712

713713
// **Phase 4: Guard labels the response data (for fine-grained filtering)**
714714
labeledData, err := g.LabelResponse(ctx, toolName, backendResult, backendCaller, us.capabilities)
715715
if err != nil {
716716
log.Printf("[DIFC] Response labeling failed: %v", err)
717-
return &sdk.CallToolResult{IsError: true}, nil, fmt.Errorf("response labeling failed: %w", err)
717+
return newErrorCallToolResult(fmt.Errorf("response labeling failed: %w", err))
718718
}
719719

720720
// **Phase 5: Reference Monitor performs fine-grained filtering (if applicable)**
@@ -735,13 +735,13 @@ func (us *UnifiedServer) callBackendTool(ctx context.Context, serverID, toolName
735735
// Convert filtered data to result
736736
finalResult, err = filtered.ToResult()
737737
if err != nil {
738-
return &sdk.CallToolResult{IsError: true}, nil, fmt.Errorf("failed to convert filtered data: %w", err)
738+
return newErrorCallToolResult(fmt.Errorf("failed to convert filtered data: %w", err))
739739
}
740740
} else {
741741
// Simple labeled data - already passed coarse-grained check
742742
finalResult, err = labeledData.ToResult()
743743
if err != nil {
744-
return &sdk.CallToolResult{IsError: true}, nil, fmt.Errorf("failed to convert labeled data: %w", err)
744+
return newErrorCallToolResult(fmt.Errorf("failed to convert labeled data: %w", err))
745745
}
746746
}
747747

@@ -767,7 +767,7 @@ func (us *UnifiedServer) callBackendTool(ctx context.Context, serverID, toolName
767767
// Convert finalResult to SDK CallToolResult format
768768
callResult, err := convertToCallToolResult(finalResult)
769769
if err != nil {
770-
return &sdk.CallToolResult{IsError: true}, nil, fmt.Errorf("failed to convert result: %w", err)
770+
return newErrorCallToolResult(fmt.Errorf("failed to convert result: %w", err))
771771
}
772772

773773
return callResult, finalResult, nil
@@ -779,6 +779,13 @@ func (us *UnifiedServer) Run(transport sdk.Transport) error {
779779
return us.server.Run(us.ctx, transport)
780780
}
781781

782+
// newErrorCallToolResult creates a standard error CallToolResult
783+
// This helper reduces code duplication for error returns following the pattern:
784+
// return &sdk.CallToolResult{IsError: true}, nil, err
785+
func newErrorCallToolResult(err error) (*sdk.CallToolResult, interface{}, error) {
786+
return &sdk.CallToolResult{IsError: true}, nil, err
787+
}
788+
782789
// parseToolArguments extracts and unmarshals tool arguments from a CallToolRequest
783790
// Returns the parsed arguments as a map, or an error if parsing fails
784791
func parseToolArguments(req *sdk.CallToolRequest) (map[string]interface{}, error) {

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