feat(go): add MCP plugin support for resources (#3358)

Author: huangjeff5

go/ai/resource.go

@@ -20,12 +20,69 @@ import (
 	"context"
 	"fmt"
 	"maps"
+	"net/url"
+	"strings"
 
 	"github.com/firebase/genkit/go/core"
 	"github.com/firebase/genkit/go/core/api"
-	coreresource "github.com/firebase/genkit/go/core/resource"
+	"github.com/yosida95/uritemplate/v3"
 )
 
+// normalizeURI normalizes a URI for template matching by removing query parameters,
+// fragments, and trailing slashes from the path.
+func normalizeURI(rawURI string) string {
+	// Parse the URI
+	u, err := url.Parse(rawURI)
+	if err != nil {
+		// If parsing fails, return the original URI
+		return rawURI
+	}
+
+	// Remove query parameters and fragment
+	u.RawQuery = ""
+	u.Fragment = ""
+
+	// Remove trailing slash from path (but not from the root path)
+	if len(u.Path) > 1 && strings.HasSuffix(u.Path, "/") {
+		u.Path = strings.TrimSuffix(u.Path, "/")
+	}
+
+	return u.String()
+}
+
+// matches checks if a URI matches the given URI template.
+func matches(templateStr, uri string) (bool, error) {
+	template, err := uritemplate.New(templateStr)
+	if err != nil {
+		return false, fmt.Errorf("invalid URI template %q: %w", templateStr, err)
+	}
+
+	normalizedURI := normalizeURI(uri)
+	values := template.Match(normalizedURI)
+	return len(values) > 0, nil
+}
+
+// extractVariables extracts variables from a URI using the given URI template.
+func extractVariables(templateStr, uri string) (map[string]string, error) {
+	template, err := uritemplate.New(templateStr)
+	if err != nil {
+		return nil, fmt.Errorf("invalid URI template %q: %w", templateStr, err)
+	}
+
+	normalizedURI := normalizeURI(uri)
+	values := template.Match(normalizedURI)
+	if len(values) == 0 {
+		return nil, fmt.Errorf("URI %q does not match template", uri)
+	}
+
+	// Convert uritemplate.Values to string map
+	result := make(map[string]string)
+	for name, value := range values {
+		result[name] = value.String()
+	}
+	return result, nil
+}
+
 // ResourceInput represents the input to a resource function.
 type ResourceInput struct {
 	URI       string            `json:"uri"`       // The resource URI
@@ -129,11 +186,11 @@ func (r *resource) Matches(uri string) bool {
 
 	// Check template
 	if template, ok := resourceMeta["template"].(string); ok && template != "" {
-		matcher, err := coreresource.NewTemplateMatcher(template)
+		matches, err := matches(template, uri)
 		if err != nil {
 			return false
 		}
-		return matcher.Matches(uri)
+		return matches
 	}
 
 	return false
@@ -156,11 +213,7 @@ func (r *resource) ExtractVariables(uri string) (map[string]string, error) {
 
 	// Extract from template
 	if template, ok := resourceMeta["template"].(string); ok && template != "" {
-		matcher, err := coreresource.NewTemplateMatcher(template)
-		if err != nil {
-			return nil, fmt.Errorf("invalid template %q: %w", template, err)
-		}
-		return matcher.ExtractVariables(uri)
+		return extractVariables(template, uri)
 	}
 
 	return nil, fmt.Errorf("no URI or template found in resource metadata")

go/core/resource/matcher.go

@@ -1022,15 +1022,12 @@ func NewResource(name string, opts *ai.ResourceOptions, fn ai.ResourceFunc) ai.R
 func ListResources(g *Genkit) []ai.Resource {
 	acts := g.reg.ListActions()
 	resources := []ai.Resource{}
-	for _, act := range acts {
-		action := act
+	for _, action := range acts {
 		actionDesc := action.Desc()
 		if actionDesc.Type == api.ActionTypeResource {
-			// Look up the resource wrapper
-			if resourceValue := g.reg.LookupValue(fmt.Sprintf("resource/%s", actionDesc.Name)); resourceValue != nil {
-				if resource, ok := resourceValue.(ai.Resource); ok {
-					resources = append(resources, resource)
-				}
+			resource := ai.LookupResource(g.reg, actionDesc.Name)
+			if resource != nil {
+				resources = append(resources, resource)
 			}
 		}
 	}

go/genkit/genkit.go

@@ -17,7 +17,6 @@ package mcp
 
 import (
 	"fmt"
-	"strings"
 
 	"github.com/mark3labs/mcp-go/mcp"
 )
@@ -32,19 +31,9 @@ func (c *GenkitMCPClient) GetToolNameWithNamespace(toolName string) string {
 	return fmt.Sprintf("%s_%s", c.options.Name, toolName)
 }
 
-// ContentToText extracts text content from MCP Content
-func ContentToText(contentList []mcp.Content) string {
-	var textParts []string
-	for _, contentItem := range contentList {
-		if textContent, ok := contentItem.(mcp.TextContent); ok && textContent.Type == "text" {
-			textParts = append(textParts, textContent.Text)
-		} else if erContent, ok := contentItem.(mcp.EmbeddedResource); ok {
-			if trc, ok := erContent.Resource.(mcp.TextResourceContents); ok {
-				textParts = append(textParts, trc.Text)
-			}
-		}
-	}
-	return strings.Join(textParts, "")
+// GetResourceNameWithNamespace returns a resource name prefixed with the client's namespace
+func (c *GenkitMCPClient) GetResourceNameWithNamespace(resourceName string) string {
+	return fmt.Sprintf("%s_%s", c.options.Name, resourceName)
 }
 
 // ExtractTextFromContent extracts text content from MCP Content

go/plugins/mcp/common.go

@@ -0,0 +1,37 @@
+// Copyright 2025 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package main
+
+import (
+	"context"
+
+	"github.com/firebase/genkit/go/ai"
+	"github.com/firebase/genkit/go/genkit"
+	"github.com/firebase/genkit/go/plugins/mcp"
+)
+
+func main() {
+	g := genkit.Init(context.Background())
+	genkit.DefineResource(g, "test-docs", &ai.ResourceOptions{
+		Template: "file://test/{filename}",
+	}, func(ctx context.Context, input *ai.ResourceInput) (*ai.ResourceOutput, error) {
+		return &ai.ResourceOutput{
+			Content: []*ai.Part{ai.NewTextPart("test content")},
+		}, nil
+	})
+
+	server := mcp.NewMCPServer(g, mcp.MCPServerOptions{Name: "test"})
+	server.ServeStdio()
+}

go/plugins/mcp/fixtures/basic_server/basic_server.go

@@ -0,0 +1,42 @@
+// Copyright 2025 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package main
+
+import (
+	"context"
+	"fmt"
+
+	"github.com/firebase/genkit/go/ai"
+	"github.com/firebase/genkit/go/genkit"
+	"github.com/firebase/genkit/go/plugins/mcp"
+)
+
+func main() {
+	g := genkit.Init(context.Background())
+
+	// Resource that provides different content based on filename
+	genkit.DefineResource(g, "content-provider", &ai.ResourceOptions{
+		Template: "file://data/{filename}",
+	}, func(ctx context.Context, input *ai.ResourceInput) (*ai.ResourceOutput, error) {
+		filename := input.Variables["filename"]
+		content := fmt.Sprintf("CONTENT_FROM_SERVER: This is %s with important data.", filename)
+		return &ai.ResourceOutput{
+			Content: []*ai.Part{ai.NewTextPart(content)},
+		}, nil
+	})
+
+	server := mcp.NewMCPServer(g, mcp.MCPServerOptions{Name: "content-server"})
+	server.ServeStdio()
+}

go/plugins/mcp/fixtures/content_server/content_server.go

@@ -0,0 +1,36 @@
+// Copyright 2025 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package main
+
+import (
+	"context"
+
+	"github.com/firebase/genkit/go/ai"
+	"github.com/firebase/genkit/go/genkit"
+	"github.com/firebase/genkit/go/plugins/mcp"
+)
+
+func main() {
+	g := genkit.Init(context.Background())
+	genkit.DefineResource(g, "company-policy", &ai.ResourceOptions{
+		Template: "docs://policy/{section}",
+	}, func(ctx context.Context, input *ai.ResourceInput) (*ai.ResourceOutput, error) {
+		return &ai.ResourceOutput{
+			Content: []*ai.Part{ai.NewTextPart("VACATION_POLICY: Employees get 20 days vacation per year.")},
+		}, nil
+	})
+	server := mcp.NewMCPServer(g, mcp.MCPServerOptions{Name: "test"})
+	server.ServeStdio()
+}

go/plugins/mcp/fixtures/policy_server/policy_server.go

@@ -0,0 +1,36 @@
+// Copyright 2025 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package main
+
+import (
+	"context"
+
+	"github.com/firebase/genkit/go/ai"
+	"github.com/firebase/genkit/go/genkit"
+	"github.com/firebase/genkit/go/plugins/mcp"
+)
+
+func main() {
+	g := genkit.Init(context.Background())
+	genkit.DefineResource(g, "server-a-docs", &ai.ResourceOptions{
+		Template: "a://docs/{file}",
+	}, func(ctx context.Context, input *ai.ResourceInput) (*ai.ResourceOutput, error) {
+		return &ai.ResourceOutput{
+			Content: []*ai.Part{ai.NewTextPart("Content from Server A")},
+		}, nil
+	})
+	server := mcp.NewMCPServer(g, mcp.MCPServerOptions{Name: "server-a"})
+	server.ServeStdio()
+}