introduce NewToolResultErrorWithErr and update docs (#140)

deviantony · web-flow · commit 37ac814a6010 · 2025-04-16T20:52:02.000+03:00
* introduce NewToolResultErrorWithErr and update docs

* rename to NewToolResultErrorFromErr
diff --git a/README.md b/README.md
@@ -163,7 +163,7 @@ func main() {
             result = x * y
         case "divide":
             if y == 0 {
-                return nil, errors.New("Cannot divide by zero")
+                return mcp.NewToolResultError("cannot divide by zero"), nil
             }
             result = x / y
         }
@@ -325,7 +325,7 @@ s.AddTool(calculatorTool, func(ctx context.Context, request mcp.CallToolRequest)
         result = x * y
     case "divide":
         if y == 0 {
-            return nil, errors.New("Division by zero is not allowed")
+            return mcp.NewToolResultError("cannot divide by zero"), nil
         }
         result = x / y
     }
@@ -370,20 +370,20 @@ s.AddTool(httpTool, func(ctx context.Context, request mcp.CallToolRequest) (*mcp
         req, err = http.NewRequest(method, url, nil)
     }
     if err != nil {
-        return nil, fmt.Errorf("Failed to create request: %v", err)
+        return mcp.NewToolResultErrorFromErr("unable to create request", err), nil
     }
 
     client := &http.Client{}
     resp, err := client.Do(req)
     if err != nil {
-        return nil, fmt.Errorf("Request failed: %v", err)
+        return mcp.NewToolResultErrorFromErr("unable to execute request", err), nil
     }
     defer resp.Body.Close()
 
     // Return response
     respBody, err := io.ReadAll(resp.Body)
     if err != nil {
-        return nil, fmt.Errorf("Failed to read response: %v", err)
+        return mcp.NewToolResultErrorFromErr("unable to read request response", err), nil
     }
 
     return mcp.NewToolResultText(fmt.Sprintf("Status: %d\nBody: %s", resp.StatusCode, string(respBody))), nil
diff --git a/mcp/utils.go b/mcp/utils.go
@@ -266,6 +266,24 @@ func NewToolResultError(text string) *CallToolResult {
 	}
 }
 
+// NewToolResultErrorFromErr creates a new CallToolResult with an error message.
+// If an error is provided, its details will be appended to the text message.
+// Any errors that originate from the tool SHOULD be reported inside the result object.
+func NewToolResultErrorFromErr(text string, err error) *CallToolResult {
+	if err != nil {
+		text = fmt.Sprintf("%s: %v", text, err)
+	}
+	return &CallToolResult{
+		Content: []Content{
+			TextContent{
+				Type: "text",
+				Text: text,
+			},
+		},
+		IsError: true,
+	}
+}
+
 // NewListResourcesResult creates a new ListResourcesResult
 func NewListResourcesResult(
 	resources []Resource,

Original file line number	Diff line number	Diff line change
`@@ -163,7 +163,7 @@ func main() {`
`163`	`163`	`result = x * y`
`164`	`164`	`case "divide":`
`165`	`165`	`if y == 0 {`
`166`		`- return nil, errors.New("Cannot divide by zero")`
	`166`	`+ return mcp.NewToolResultError("cannot divide by zero"), nil`
`167`	`167`	`}`
`168`	`168`	`result = x / y`
`169`	`169`	`}`
`@@ -325,7 +325,7 @@ s.AddTool(calculatorTool, func(ctx context.Context, request mcp.CallToolRequest)`
`325`	`325`	`result = x * y`
`326`	`326`	`case "divide":`
`327`	`327`	`if y == 0 {`
`328`		`- return nil, errors.New("Division by zero is not allowed")`
	`328`	`+ return mcp.NewToolResultError("cannot divide by zero"), nil`
`329`	`329`	`}`
`330`	`330`	`result = x / y`
`331`	`331`	`}`
`@@ -370,20 +370,20 @@ s.AddTool(httpTool, func(ctx context.Context, request mcp.CallToolRequest) (*mcp`
`370`	`370`	`req, err = http.NewRequest(method, url, nil)`
`371`	`371`	`}`
`372`	`372`	`if err != nil {`
`373`		`- return nil, fmt.Errorf("Failed to create request: %v", err)`
	`373`	`+ return mcp.NewToolResultErrorFromErr("unable to create request", err), nil`
`374`	`374`	`}`
`375`	`375`
`376`	`376`	`client := &http.Client{}`
`377`	`377`	`resp, err := client.Do(req)`
`378`	`378`	`if err != nil {`
`379`		`- return nil, fmt.Errorf("Request failed: %v", err)`
	`379`	`+ return mcp.NewToolResultErrorFromErr("unable to execute request", err), nil`
`380`	`380`	`}`
`381`	`381`	`defer resp.Body.Close()`
`382`	`382`
`383`	`383`	`// Return response`
`384`	`384`	`respBody, err := io.ReadAll(resp.Body)`
`385`	`385`	`if err != nil {`
`386`		`- return nil, fmt.Errorf("Failed to read response: %v", err)`
	`386`	`+ return mcp.NewToolResultErrorFromErr("unable to read request response", err), nil`
`387`	`387`	`}`
`388`	`388`
`389`	`389`	`return mcp.NewToolResultText(fmt.Sprintf("Status: %d\nBody: %s", resp.StatusCode, string(respBody))), nil`