simplify SamplingMessage

Author: ochafik

src/types.test.ts

@@ -9,8 +9,6 @@ import {
     ToolUseContentSchema,
     ToolResultContentSchema,
     ToolChoiceSchema,
-    UserMessageSchema,
-    AssistantMessageSchema,
     SamplingMessageSchema,
     CreateMessageRequestSchema,
     CreateMessageResultSchema,
@@ -455,18 +453,20 @@ describe('Types', () => {
         });
     });
 
-    describe("UserMessage and AssistantMessage", () => {
+    describe("SamplingMessage content types", () => {
         test("should validate user message with text", () => {
             const userMessage = {
                 role: "user",
                 content: { type: "text", text: "What's the weather?" }
             };
 
-            const result = UserMessageSchema.safeParse(userMessage);
+            const result = SamplingMessageSchema.safeParse(userMessage);
             expect(result.success).toBe(true);
             if (result.success) {
                 expect(result.data.role).toBe("user");
-                expect(result.data.content.type).toBe("text");
+                if (!Array.isArray(result.data.content)) {
+                    expect(result.data.content.type).toBe("text");
+                }
             }
         });
 
@@ -476,13 +476,13 @@ describe('Types', () => {
                 content: {
                     type: "tool_result",
                     toolUseId: "call_123",
-                    content: { temperature: 72 }
+                    content: []
                 }
             };
 
-            const result = UserMessageSchema.safeParse(userMessage);
+            const result = SamplingMessageSchema.safeParse(userMessage);
             expect(result.success).toBe(true);
-            if (result.success) {
+            if (result.success && !Array.isArray(result.data.content)) {
                 expect(result.data.content.type).toBe("tool_result");
             }
         });
@@ -493,7 +493,7 @@ describe('Types', () => {
                 content: { type: "text", text: "I'll check the weather for you." }
             };
 
-            const result = AssistantMessageSchema.safeParse(assistantMessage);
+            const result = SamplingMessageSchema.safeParse(assistantMessage);
             expect(result.success).toBe(true);
             if (result.success) {
                 expect(result.data.role).toBe("assistant");
@@ -511,29 +511,28 @@ describe('Types', () => {
                 }
             };
 
-            const result = AssistantMessageSchema.safeParse(assistantMessage);
+            const result = SamplingMessageSchema.safeParse(assistantMessage);
             expect(result.success).toBe(true);
-            if (result.success) {
+            if (result.success && !Array.isArray(result.data.content)) {
                 expect(result.data.content.type).toBe("tool_use");
             }
         });
 
-        test("should fail validation for assistant with tool result", () => {
-            const invalidMessage = {
+        test("should validate any content type for any role", () => {
+            // The simplified schema allows any content type for any role
+            const assistantWithToolResult = {
                 role: "assistant",
                 content: {
                     type: "tool_result",
                     toolUseId: "call_123",
-                    content: {}
+                    content: []
                 }
             };
 
-            const result = AssistantMessageSchema.safeParse(invalidMessage);
-            expect(result.success).toBe(false);
-        });
+            const result1 = SamplingMessageSchema.safeParse(assistantWithToolResult);
+            expect(result1.success).toBe(true);
 
-        test("should fail validation for user with tool call", () => {
-            const invalidMessage = {
+            const userWithToolUse = {
                 role: "user",
                 content: {
                     type: "tool_use",
@@ -543,8 +542,8 @@ describe('Types', () => {
                 }
             };
 
-            const result = UserMessageSchema.safeParse(invalidMessage);
-            expect(result.success).toBe(false);
+            const result2 = SamplingMessageSchema.safeParse(userWithToolUse);
+            expect(result2.success).toBe(true);
         });
     });
 

src/types.ts

@@ -1181,6 +1181,7 @@ export const ToolChoiceSchema = z
          * Controls when tools are used:
          * - "auto": Model decides whether to use tools (default)
          * - "required": Model MUST use at least one tool before completing
+         * - "none": Model MUST NOT use any tools
          */
         mode: z.optional(z.enum(["auto", "required", "none"])),
         /**
@@ -1212,59 +1213,33 @@ export const ToolResultContentSchema = z
     })
     .passthrough();
 
-export const UserMessageContentSchema = z.discriminatedUnion("type", [
-  TextContentSchema,
-  ImageContentSchema,
-  AudioContentSchema,
-  ToolResultContentSchema,
-]);
-
 /**
- * A message from the user (server) in a sampling conversation.
+ * Content block types allowed in sampling messages.
+ * This includes text, image, audio, tool use requests, and tool results.
  */
-export const UserMessageSchema = z
-  .object({
-    role: z.literal("user"),
-    content: z.union([UserMessageContentSchema, z.array(UserMessageContentSchema)]),
-    /**
-     * See [MCP specification](https://github.com/modelcontextprotocol/modelcontextprotocol/blob/47339c03c143bb4ec01a26e721a1b8fe66634ebe/docs/specification/draft/basic/index.mdx#general-fields)
-     * for notes on _meta usage.
-     */
-    _meta: z.optional(z.object({}).passthrough()),
-  })
-  .passthrough();
-
-export const AssistantMessageContentSchema = z.discriminatedUnion("type", [
+export const SamplingMessageContentBlockSchema = z.discriminatedUnion("type", [
   TextContentSchema,
   ImageContentSchema,
   AudioContentSchema,
   ToolUseContentSchema,
+  ToolResultContentSchema,
 ]);
 
-/**
- * A message from the assistant (LLM) in a sampling conversation.
- */
-export const AssistantMessageSchema = z
-  .object({
-    role: z.literal("assistant"),
-    content: z.union([AssistantMessageContentSchema, z.array(AssistantMessageContentSchema)]),
-    /**
-     * See [MCP specification](https://github.com/modelcontextprotocol/modelcontextprotocol/blob/47339c03c143bb4ec01a26e721a1b8fe66634ebe/docs/specification/draft/basic/index.mdx#general-fields)
-     * for notes on _meta usage.
-     */
-    _meta: z.optional(z.object({}).passthrough()),
-  })
-  .passthrough();
-
 /**
  * Describes a message issued to or received from an LLM API.
- * This is a discriminated union of UserMessage and AssistantMessage, where
- * each role has its own set of allowed content types.
  */
-export const SamplingMessageSchema = z.discriminatedUnion("role", [
-  UserMessageSchema,
-  AssistantMessageSchema,
-]);
+export const SamplingMessageSchema = z.object({
+  role: z.enum(['user', 'assistant']),
+  content: z.union([
+    SamplingMessageContentBlockSchema,
+    z.array(SamplingMessageContentBlockSchema)
+  ]),
+  /**
+   * See [MCP specification](https://github.com/modelcontextprotocol/modelcontextprotocol/blob/47339c03c143bb4ec01a26e721a1b8fe66634ebe/docs/specification/draft/basic/index.mdx#general-fields)
+   * for notes on _meta usage.
+   */
+  _meta: z.optional(z.object({}).passthrough()),
+}).passthrough();
 
 /**
  * Parameters for a `sampling/createMessage` request.
@@ -1341,7 +1316,10 @@ export const CreateMessageResultSchema = ResultSchema.extend({
     /**
      * Response content. May be ToolUseContent if stopReason is "toolUse".
      */
-    content: z.union([AssistantMessageContentSchema, z.array(AssistantMessageContentSchema)]),
+    content: z.union([
+        SamplingMessageContentBlockSchema,
+        z.array(SamplingMessageContentBlockSchema)
+    ]),
 });
 
 /* Elicitation */
@@ -1798,16 +1776,13 @@ export type LoggingMessageNotification = Infer<typeof LoggingMessageNotification
 
 /* Sampling */
 export type ToolChoice = Infer<typeof ToolChoiceSchema>;
-export type UserMessage = Infer<typeof UserMessageSchema>;
-export type AssistantMessage = Infer<typeof AssistantMessageSchema>;
 export type ModelHint = Infer<typeof ModelHintSchema>;
 export type ModelPreferences = Infer<typeof ModelPreferencesSchema>;
+export type SamplingMessageContentBlock = Infer<typeof SamplingMessageContentBlockSchema>;
 export type SamplingMessage = Infer<typeof SamplingMessageSchema>;
 export type CreateMessageRequestParams = Infer<typeof CreateMessageRequestParamsSchema>;
 export type CreateMessageRequest = Infer<typeof CreateMessageRequestSchema>;
 export type CreateMessageResult = Infer<typeof CreateMessageResultSchema>;
-export type AssistantMessageContent = Infer<typeof AssistantMessageContentSchema>;
-export type UserMessageContent = Infer<typeof UserMessageContentSchema>;
 
 /* Elicitation */
 export type BooleanSchema = Infer<typeof BooleanSchemaSchema>;