MCP Resource functionality

Author: MegaGrindStone

CHANGELOG.md

@@ -12,6 +12,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Add refresh title feature to refresh chat title from LLM
 - Implement MCP Prompts functionality
 - Add `MCPClient` interface for testing purposes
+- Implement MCP Resource handling
 
 ### Fixed
 

internal/handlers/chat.go

@@ -123,6 +123,37 @@ func (m Main) HandleChats(w http.ResponseWriter, r *http.Request) {
 		userMessages = []models.Message{m.processUserMessage(msg)}
 	}
 
+	// Handle attached resources
+	attachedResourcesJSON := r.FormValue("attached_resources")
+	if attachedResourcesJSON != "" && attachedResourcesJSON != "[]" {
+		var resourceURIs []string
+		if err := json.Unmarshal([]byte(attachedResourcesJSON), &resourceURIs); err != nil {
+			m.logger.Error("Failed to unmarshal attached resources",
+				slog.String("attachedResources", attachedResourcesJSON),
+				slog.String(errLoggerKey, err.Error()))
+			http.Error(w, "Invalid attached resources format", http.StatusBadRequest)
+			return
+		}
+
+		// Process resources and add resource contents to user message
+		if len(resourceURIs) > 0 {
+			resourceContents, err := m.processAttachedResources(r.Context(), resourceURIs)
+			if err != nil {
+				m.logger.Error("Failed to process attached resources",
+					slog.String("resourceURIs", fmt.Sprintf("%v", resourceURIs)),
+					slog.String(errLoggerKey, err.Error()))
+				http.Error(w, err.Error(), http.StatusInternalServerError)
+				return
+			}
+
+			// Add resource contents to the last user message
+			if len(userMessages) > 0 {
+				lastMsgIdx := len(userMessages) - 1
+				userMessages[lastMsgIdx].Contents = append(userMessages[lastMsgIdx].Contents, resourceContents...)
+			}
+		}
+	}
+
 	// Add all user messages to the chat
 	for _, msg := range userMessages {
 		msgID, err := m.store.AddMessage(r.Context(), chatID, msg)
@@ -342,6 +373,33 @@ func (m Main) processUserMessage(message string) models.Message {
 	}
 }
 
+// processAttachedResources processes attached resource URIs from the form data
+// and returns content objects for each resource.
+func (m Main) processAttachedResources(ctx context.Context, resourceURIs []string) ([]models.Content, error) {
+	var contents []models.Content
+
+	for _, uri := range resourceURIs {
+		clientIdx, ok := m.resourcesMap[uri]
+		if !ok {
+			return nil, fmt.Errorf("resource not found: %s", uri)
+		}
+
+		result, err := m.mcpClients[clientIdx].ReadResource(ctx, mcp.ReadResourceParams{
+			URI: uri,
+		})
+		if err != nil {
+			return nil, fmt.Errorf("failed to read resource %s: %w", uri, err)
+		}
+
+		contents = append(contents, models.Content{
+			Type:             models.ContentTypeResource,
+			ResourceContents: result.Contents,
+		})
+	}
+
+	return contents, nil
+}
+
 // renderNewChatResponse renders the complete chatbox for new chats.
 func (m Main) renderNewChatResponse(w http.ResponseWriter, chatID string, messages []models.Message, aiMsgID string) {
 	msgs := make([]message, len(messages))
@@ -593,6 +651,9 @@ func (m Main) chat(chatID string, messages []models.Message) {
 				callTool = true
 				aiMsg.Contents = append(aiMsg.Contents, content)
 				contentIdx++
+			case models.ContentTypeResource:
+				m.logger.Error("Content type resource is not allowed")
+				return
 			case models.ContentTypeToolResult:
 				m.logger.Error("Content type tool results is not allowed")
 				return

internal/handlers/main.go

@@ -47,6 +47,7 @@ type MCPClient interface {
 	PromptServerSupported() bool
 	ListTools(ctx context.Context, params mcp.ListToolsParams) (mcp.ListToolsResult, error)
 	ListResources(ctx context.Context, params mcp.ListResourcesParams) (mcp.ListResourcesResult, error)
+	ReadResource(ctx context.Context, params mcp.ReadResourceParams) (mcp.ReadResourceResult, error)
 	ListPrompts(ctx context.Context, params mcp.ListPromptsParams) (mcp.ListPromptResult, error)
 	GetPrompt(ctx context.Context, params mcp.GetPromptParams) (mcp.GetPromptResult, error)
 	CallTool(ctx context.Context, params mcp.CallToolParams) (mcp.CallToolResult, error)

internal/handlers/main_test.go

@@ -675,6 +675,10 @@ func (m *mockMCPClient) ListResources(_ context.Context, _ mcp.ListResourcesPara
 	return mcp.ListResourcesResult{Resources: m.resources}, nil
 }
 
+func (m *mockMCPClient) ReadResource(_ context.Context, _ mcp.ReadResourceParams) (mcp.ReadResourceResult, error) {
+	return mcp.ReadResourceResult{}, nil
+}
+
 func (m *mockMCPClient) ListPrompts(_ context.Context, _ mcp.ListPromptsParams) (mcp.ListPromptResult, error) {
 	if m.err != nil {
 		return mcp.ListPromptResult{}, m.err

internal/models/chat.go

@@ -7,6 +7,7 @@ import (
 	"strings"
 	"time"
 
+	"github.com/MegaGrindStone/go-mcp"
 	"github.com/yuin/goldmark"
 	highlighting "github.com/yuin/goldmark-highlighting"
 	"github.com/yuin/goldmark/extension"
@@ -37,6 +38,9 @@ type Content struct {
 	// Text would be filled if Type is ContentTypeText.
 	Text string
 
+	// ResourceContents would be filled if Type is ContentTypeResource.
+	ResourceContents []mcp.ResourceContents
+
 	// ToolName would be filled if Type is ContentTypeCallTool.
 	ToolName string
 	// ToolInput would be filled if Type is ContentTypeCallTool.
@@ -59,20 +63,31 @@ type Role string
 type ContentType string
 
 const (
-	// RoleUser represents a user message. A message with this role would only contain text content.
+	// RoleUser represents a user message. A message with this role would only contain text or resource content.
 	RoleUser Role = "user"
-	// RoleAssistant represents an assistant message. A message with this role would contain text content
-	// and potentially other types of content.
+	// RoleAssistant represents an assistant message. A message with this role would contain
+	// all types of content but resource.
 	RoleAssistant Role = "assistant"
 
 	// ContentTypeText represents text content.
 	ContentTypeText ContentType = "text"
+	// ContentTypeResource represents a resource content.
+	ContentTypeResource ContentType = "resource"
 	// ContentTypeCallTool represents a call to a tool.
 	ContentTypeCallTool ContentType = "call_tool"
 	// ContentTypeToolResult represents the result of a tool call.
 	ContentTypeToolResult ContentType = "tool_result"
 )
 
+var mimeTypeToLanguage = map[string]string{
+	"text/x-go":        "go",
+	"text/golang":      "go",
+	"application/json": "json",
+	"text/javascript":  "javascript",
+	"text/html":        "html",
+	"text/css":         "css",
+}
+
 // RenderContents renders contents into a markdown string.
 func RenderContents(contents []Content) (string, error) {
 	var sb strings.Builder
@@ -83,6 +98,41 @@ func RenderContents(contents []Content) (string, error) {
 				continue
 			}
 			sb.WriteString(content.Text)
+		case ContentTypeResource:
+			if len(content.ResourceContents) == 0 {
+				continue
+			}
+			for _, resource := range content.ResourceContents {
+				sb.WriteString("  \n\n<details>\n")
+				sb.WriteString(fmt.Sprintf("<summary>Resource: %s</summary>\n\n", resource.URI))
+
+				if resource.MimeType != "" {
+					sb.WriteString(fmt.Sprintf("MIME Type: `%s`\n\n", resource.MimeType))
+				}
+
+				if resource.Text != "" {
+					// Use map for language determination
+					language := "text"
+					if lang, exists := mimeTypeToLanguage[resource.MimeType]; exists {
+						language = lang
+					}
+
+					sb.WriteString(fmt.Sprintf("```%s\n%s\n```\n", language, resource.Text))
+				} else if resource.Blob != "" {
+					// Handle binary content
+					if strings.HasPrefix(resource.MimeType, "image/") {
+						// Display images inline
+						sb.WriteString(fmt.Sprintf("<img src=\"data:%s;base64,%s\" alt=\"%s\" />\n",
+							resource.MimeType, resource.Blob, resource.URI))
+					} else {
+						// Provide download link for other binary content
+						sb.WriteString(fmt.Sprintf("<a href=\"data:%s;base64,%s\" download=\"%s\">Download %s</a>\n",
+							resource.MimeType, resource.Blob, resource.URI, resource.URI))
+					}
+				}
+
+				sb.WriteString("\n</details>  \n\n")
+			}
 		case ContentTypeCallTool:
 			sb.WriteString("  \n\n<details>\n")
 			sb.WriteString(fmt.Sprintf("<summary>Calling Tool: %s</summary>\n\n", content.ToolName))