aws[patch]: Fix empty content bug

libs/langchain-aws/src/common.ts

@@ -67,18 +67,21 @@ export function convertToConverseMessages(messages: BaseMessage[]): {
   const converseSystem: BedrockSystemContentBlock[] = messages
     .filter((msg) => msg._getType() === "system")
     .map((msg) => {
-      const text = msg.content;
-      if (typeof text !== "string") {
-        throw new Error("System message content must be a string.");
+      if (typeof msg.content === "string") {
+        return { text: msg.content };
+      } else if (msg.content.length === 1 && msg.content[0].type === "text") {
+        return { text: msg.content[0].text };
       }
-      return { text };
+      throw new Error(
+        "System message content must be either a string, or a content array containing a single text object."
+      );
     });
   const converseMessages: BedrockMessage[] = messages
-    .filter((msg) => !["system", "tool", "function"].includes(msg._getType()))
+    .filter((msg) => msg._getType() !== "system")
     .map((msg) => {
       if (msg._getType() === "ai") {
         const castMsg = msg as AIMessage;
-        if (typeof castMsg.content === "string") {
+        if (typeof castMsg.content === "string" && castMsg.content !== "") {
           return {
             role: "assistant",
             content: [
@@ -99,16 +102,21 @@ export function convertToConverseMessages(messages: BaseMessage[]): {
                 },
               })),
             };
-          } else {
+          } else if (Array.isArray(castMsg.content)) {
             const contentBlocks: ContentBlock[] = castMsg.content.map(
               (block) => {
-                if (block.type === "text") {
+                if (block.type === "text" && block.text !== "") {
                   return {
                     text: block.text,
                   };
                 } else {
+                  const blockValues = Object.fromEntries(
+                    Object.values(block).filter(([key]) => key !== "type")
+                  );
                   throw new Error(
-                    `Unsupported content block type: ${block.type}`
+                    `Unsupported content block type: ${
+                      block.type
+                    } with content of ${JSON.stringify(blockValues, null, 2)}`
                   );
                 }
               }
@@ -117,10 +125,14 @@ export function convertToConverseMessages(messages: BaseMessage[]): {
               role: "assistant",
               content: contentBlocks,
             };
+          } else {
+            throw new Error(
+              `Invalid message content: empty string. '${msg._getType()}' must contain non-empty content.`
+            );
           }
         }
       } else if (msg._getType() === "human" || msg._getType() === "generic") {
-        if (typeof msg.content === "string") {
+        if (typeof msg.content === "string" && msg.content !== "") {
           return {
             role: "user",
             content: [
@@ -129,7 +141,7 @@ export function convertToConverseMessages(messages: BaseMessage[]): {
               },
             ],
           };
-        } else {
+        } else if (Array.isArray(msg.content)) {
           const contentBlocks: ContentBlock[] = msg.content.flatMap((block) => {
             if (block.type === "image_url") {
               const base64: string =
@@ -149,12 +161,17 @@ export function convertToConverseMessages(messages: BaseMessage[]): {
             role: "user",
             content: contentBlocks,
           };
+        } else {
+          throw new Error(
+            `Invalid message content: empty string. '${msg._getType()}' must contain non-empty content.`
+          );
         }
       } else if (msg._getType() === "tool") {
         const castMsg = msg as ToolMessage;
         if (typeof castMsg.content === "string") {
           return {
-            role: undefined,
+            // Tool use messages are always from the user
+            role: "user",
             content: [
               {
                 toolResult: {
@@ -170,7 +187,8 @@ export function convertToConverseMessages(messages: BaseMessage[]): {
           };
         } else {
           return {
-            role: undefined,
+            // Tool use messages are always from the user
+            role: "user",
             content: [
               {
                 toolResult: {

libs/langchain-aws/src/tests/chat_models.int.test.ts

@@ -1,7 +1,13 @@
 /* eslint-disable no-process-env */
 
 import { test, expect } from "@jest/globals";
-import { AIMessageChunk, HumanMessage } from "@langchain/core/messages";
+import {
+  AIMessage,
+  AIMessageChunk,
+  HumanMessage,
+  SystemMessage,
+  ToolMessage,
+} from "@langchain/core/messages";
 import { tool } from "@langchain/core/tools";
 import { z } from "zod";
 import { ChatBedrockConverse } from "../chat_models.js";
@@ -319,3 +325,46 @@ test("Test ChatBedrockConverse tool_choice works", async () => {
   expect(result.tool_calls?.[0].name).toBe("get_weather");
   expect(result.tool_calls?.[0].id).toBeDefined();
 });
+
+test("Model can handle empty content messages", async () => {
+  const model = new ChatBedrockConverse({
+    ...baseConstructorArgs,
+  });
+
+  const retrieverTool = tool((_) => "Success", {
+    name: "retrieverTool",
+    schema: z.object({
+      url: z.string().describe("The URL to fetch"),
+    }),
+    description: "A tool to fetch data from a URL",
+  });
+
+  const messages = [
+    new SystemMessage("You're an advanced AI assistant."),
+    new HumanMessage(
+      "What's the weather like today in Berkeley, CA? Use weather.com to check."
+    ),
+    new AIMessage({
+      content: "",
+      tool_calls: [
+        {
+          name: "retrieverTool",
+          args: {
+            url: "https://weather.com",
+          },
+          id: "123_retriever_tool",
+        },
+      ],
+    }),
+    new ToolMessage({
+      tool_call_id: "123_retriever_tool",
+      content: "The weather in Berkeley, CA is 70 degrees and sunny.",
+    }),
+  ];
+
+  const result = await model.bindTools([retrieverTool]).invoke(messages);
+
+  expect(result.content).toBeDefined();
+  expect(typeof result.content).toBe("string");
+  expect(result.content.length).toBeGreaterThan(1);
+});

libs/langchain-aws/src/tests/chat_models.test.ts

@@ -0,0 +1,73 @@
+import {
+  SystemMessage,
+  HumanMessage,
+  AIMessage,
+  ToolMessage,
+} from "@langchain/core/messages";
+import { convertToConverseMessages } from "../common.js";
+
+test("convertToConverseMessages works", () => {
+  const messages = [
+    new SystemMessage("You're an advanced AI assistant."),
+    new HumanMessage(
+      "What's the weather like today in Berkeley, CA? Use weather.com to check."
+    ),
+    new AIMessage({
+      content: "",
+      tool_calls: [
+        {
+          name: "retrieverTool",
+          args: {
+            url: "https://weather.com",
+          },
+          id: "123_retriever_tool",
+        },
+      ],
+    }),
+    new ToolMessage({
+      tool_call_id: "123_retriever_tool",
+      content: "The weather in Berkeley, CA is 70 degrees and sunny.",
+    }),
+  ];
+
+  const { converseMessages, converseSystem } =
+    convertToConverseMessages(messages);
+
+  expect(converseSystem).toHaveLength(1);
+  expect(converseSystem[0].text).toBe("You're an advanced AI assistant.");
+
+  expect(converseMessages).toHaveLength(3);
+
+  const userMsgs = converseMessages.filter((msg) => msg.role === "user");
+  // Length of two because of the first user question, and tool use
+  // messages will have the user role.
+  expect(userMsgs).toHaveLength(2);
+  const textUserMsg = userMsgs.find((msg) => msg.content?.[0].text);
+  expect(textUserMsg?.content?.[0].text).toBe(
+    "What's the weather like today in Berkeley, CA? Use weather.com to check."
+  );
+
+  const toolUseUserMsg = userMsgs.find((msg) => msg.content?.[0].toolResult);
+  expect(toolUseUserMsg).toBeDefined();
+  expect(toolUseUserMsg?.content).toHaveLength(1);
+  if (!toolUseUserMsg?.content?.length) return;
+
+  const toolResultContent = toolUseUserMsg.content[0];
+  expect(toolResultContent).toBeDefined();
+  expect(toolResultContent.toolResult?.toolUseId).toBe("123_retriever_tool");
+  expect(toolResultContent.toolResult?.content?.[0].text).toBe(
+    "The weather in Berkeley, CA is 70 degrees and sunny."
+  );
+
+  const assistantMsg = converseMessages.find((msg) => msg.role === "assistant");
+  expect(assistantMsg).toBeDefined();
+  if (!assistantMsg) return;
+
+  const toolUseContent = assistantMsg.content?.find((c) => "toolUse" in c);
+  expect(toolUseContent).toBeDefined();
+  expect(toolUseContent?.toolUse?.name).toBe("retrieverTool");
+  expect(toolUseContent?.toolUse?.toolUseId).toBe("123_retriever_tool");
+  expect(toolUseContent?.toolUse?.input).toEqual({
+    url: "https://weather.com",
+  });
+});