feat(tool): add remove error middleware & mcp toolcallresulthander (#147)
Zhj
5 months ago
committed by
GitHub
parent
d099dce571
commit
8c6efe243f
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/*
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* Copyright 2025 CloudWeGo Authors
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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package main
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import (
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"context"
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"fmt"
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"github.com/bytedance/sonic"
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"github.com/cloudwego/eino-ext/components/tool/mcp/officialmcp"
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"github.com/cloudwego/eino/components/tool"
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"github.com/cloudwego/eino/compose"
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"github.com/cloudwego/eino/schema"
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"github.com/modelcontextprotocol/go-sdk/mcp"
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)
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// main function demonstrates how to use the tool call result handler.
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func main() {
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// 1. Initialize context and get tools.
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// The GetTools function is configured to use our custom toolCallResultHandler.
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ctx := context.Background()
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tools, err := GetTools(ctx)
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if err != nil {
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fmt.Println(err)
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return
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}
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// 2. Create a new ToolNode.
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// A ToolNode is a component that can execute tool calls.
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tn, _ := compose.NewToolNode(ctx, &compose.ToolsNodeConfig{
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Tools: tools,
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})
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// 3. Simulate a tool call message from an assistant.
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// This message represents a request to call the 'web_search' tool.
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msg := schema.AssistantMessage("call web_search tool", []schema.ToolCall{
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{
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ID: "1",
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Function: schema.FunctionCall{
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Name: "web_search",
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Arguments: `{"url":"web_url"}`,
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},
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},
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})
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// 4. Invoke the ToolNode.
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// When tn.Invoke is called, it will execute the 'web_search' tool.
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// After the tool returns a result, the toolCallResultHandler will be triggered
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// to process the result before it is returned here.
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result, err := tn.Invoke(ctx, msg)
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if err != nil {
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fmt.Println(err)
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return
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}
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_ = result
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}
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type detailContent struct {
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Summary string
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Details string
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}
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const webSearchTool = "web_search"
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// toolCallResultHandler is a callback function that gets executed after a tool call.
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// It allows for the modification of the tool call's result before it's returned.
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// This can be useful for tailoring the output, or in this case,
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// condensing the result to save on token usage.
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func toolCallResultHandler(ctx context.Context, name string, result *mcp.CallToolResult) (*mcp.CallToolResult, error) {
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// First, check if the tool call resulted in an error.
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if result.IsError {
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marshaledResult, err := sonic.MarshalString(result)
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if err != nil {
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return nil, err
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}
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// If there was an error, return it to be handled upstream.
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return nil, fmt.Errorf("failed to call official mcp tool, mcp server return error: %s", marshaledResult)
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}
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// We're specifically interested in post-processing the 'web_search' tool's output.
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if name == webSearchTool && len(result.Content) > 0 {
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// The output format of the 'web_search' tool is known and consistent.
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// It is expected to return a single content block, which is why we can safely access the first element.
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content := result.Content[0]
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// We also know that the content will be of type TextContent.
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if textContent, ok := content.(*mcp.TextContent); ok {
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detailCt := detailContent{}
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// The Text field contains a JSON string with 'Summary' and 'Details'. We unmarshal it.
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err := sonic.UnmarshalString(textContent.Text, &detailCt)
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if err != nil {
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return nil, err
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}
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// To reduce token consumption for the language model, if the 'Details' are too long (over 1000 chars),
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// we replace the content with the shorter 'Summary'.
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if len(detailCt.Details) > 1000 {
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textContent.Text = detailCt.Summary
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} else {
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textContent.Text = detailCt.Details
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}
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// Update the result content with the potentially modified text.
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result.Content[0] = textContent
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}
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}
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// Return the (possibly modified) result.
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return result, nil
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}
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// GetTools initializes and returns a list of tools.
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// It hooks in the toolCallResultHandler to process the results of any tool calls.
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func GetTools(ctx context.Context) ([]tool.BaseTool, error) {
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// officialmcp.GetTools is used to get the official MCP tools.
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// We provide a custom configuration to it.
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tools, err := officialmcp.GetTools(ctx, &officialmcp.Config{
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// ToolCallResultHandler is a field in the config that takes a function.
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// This function will be called with the result of every tool call.
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ToolCallResultHandler: toolCallResultHandler,
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})
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if err != nil {
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return nil, err
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}
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return tools, nil
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}
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@ -0,0 +1,86 @@
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/*
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* Copyright 2025 CloudWeGo Authors
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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// This example shows how to configure the errorremover middleware on a ToolsNode
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// to catch errors during local tool invocation and return custom information.
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// Run: go run ./components/tool/middlewares/errorremover/example
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package errorremover
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import (
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"context"
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"fmt"
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"github.com/cloudwego/eino/compose"
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"github.com/cloudwego/eino/schema"
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)
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// removeErrorHandler is an error handler function that generates a string
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// describing the error that occurred during a tool call.
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func removeErrorHandler(ctx context.Context, in *compose.ToolInput, err error) string {
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// Formats the error message to include the tool name and the specific error content.
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return fmt.Sprintf("Failed to call tool '%s', error message: '%s'", in.Name, err.Error())
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}
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// Invokable creates a middleware endpoint for non-streaming (invokable) tools.
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// It intercepts the tool's execution. If the tool returns an error, it calls the
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// error handler and returns its result as a successful ToolOutput,
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// effectively suppressing the original error.
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func Invokable(next compose.InvokableToolEndpoint) compose.InvokableToolEndpoint {
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return func(ctx context.Context, in *compose.ToolInput) (*compose.ToolOutput, error) {
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// Proceed with the next middleware or the actual tool execution.
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output, err := next(ctx, in)
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// If an error occurs during execution.
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if err != nil {
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// Generate a custom error message using removeErrorHandler.
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result := removeErrorHandler(ctx, in, err)
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// Wrap the custom message in a successful ToolOutput and return it,
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// with the error itself set to nil.
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return &compose.ToolOutput{Result: result}, nil
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}
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// If there was no error, return the original output.
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return output, nil
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}
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}
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// Streamable creates a middleware endpoint for streaming tools.
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// It intercepts the tool's execution. If the tool returns an error, it calls the
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// error handler and returns its result as a new stream containing a single successful item.
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// This effectively replaces the error with a successful stream output.
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func Streamable(next compose.StreamableToolEndpoint) compose.StreamableToolEndpoint {
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return func(ctx context.Context, in *compose.ToolInput) (*compose.StreamToolOutput, error) {
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// Proceed with the next middleware or the actual tool execution.
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streamOutput, err := next(ctx, in)
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// If an error occurs during execution.
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if err != nil {
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// Generate a custom error message using removeErrorHandler.
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result := removeErrorHandler(ctx, in, err)
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// Return the new stream as a successful output.
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return &compose.StreamToolOutput{Result: schema.StreamReaderFromArray([]string{result})}, nil
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}
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// If there was no error, return the original stream output.
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return streamOutput, nil
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}
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}
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// Middleware constructs and returns a compose.ToolMiddleware.
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// This middleware is designed to catch errors from tool executions and replace them
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// with a custom, successful output.
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func Middleware() compose.ToolMiddleware {
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return compose.ToolMiddleware{Invokable: Invokable, Streamable: Streamable}
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}
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/*
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* Copyright 2025 CloudWeGo Authors
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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// This example shows how to configure the jsonfix middleware on a ToolsNode
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// to repair invalid JSON arguments before invoking a local tool.
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// Run: go run ./components/tool/middlewares/jsonfix/example
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package main
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import (
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"context"
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"fmt"
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"github.com/cloudwego/eino/components/tool"
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"github.com/cloudwego/eino/components/tool/utils"
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"github.com/cloudwego/eino/compose"
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"github.com/cloudwego/eino/schema"
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"github.com/cloudwego/eino-examples/components/tool/middlewares/errorremover"
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)
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type WebSearch struct {
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URL string `json:"url"`
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}
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func main() {
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ctx := context.Background()
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// 1. Create a mock "web_search" tool.
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// This tool is designed to always return an error to demonstrate the middleware's functionality.
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searcher, _ := utils.InferTool("web_search", "search content for web url", func(ctx context.Context, in *WebSearch) (string, error) {
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// The tool call always fails.
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return "", fmt.Errorf("not found web url")
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})
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// 2. Create a compose.ToolNode and inject the remove_error middleware.
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// This middleware will intercept the tool execution lifecycle.
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//
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// IMPORTANT: Middleware order is critical. To catch errors from any subsequent
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// middleware or from the tool itself, `remove_error.Middleware()` must be placed
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// at the beginning of the `ToolCallMiddlewares` slice. Any middleware placed
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// before it will not have its errors handled by this mechanism due to the
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// sequential nature of middleware execution.
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tn, _ := compose.NewToolNode(ctx, &compose.ToolsNodeConfig{
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Tools: []tool.BaseTool{searcher},
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ToolCallMiddlewares: []compose.ToolMiddleware{errorremover.Middleware()}, // Inject the remove_error middleware.
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})
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msg := schema.AssistantMessage("", []schema.ToolCall{
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{
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ID: "1",
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Function: schema.FunctionCall{
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Name: "web_search",
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Arguments: `{"url":"web_url"}`,
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},
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},
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})
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// 4. Simulate a tool call.
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// Although the underlying 'web_search' tool fails, the 'Invoke' call will succeed.
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// This is because the middleware catches the error and replaces the output with the result from the registered handler.
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outs, err := tn.Invoke(ctx, msg)
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if err != nil {
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fmt.Println("error:", err)
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return
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}
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// 5. Print the result.
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// The output content will be the string returned by the error handler, not the original error message.
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for _, o := range outs {
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fmt.Println("tool:", o.ToolName, "id:", o.ToolCallID, "content:", o.Content)
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}
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}
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