From 7b8891fdc74f1d2156cae5e73c73bad991131218 Mon Sep 17 00:00:00 2001
From: Brace Sproul <braceasproul@gmail.com>
Date: Thu, 18 Jul 2024 14:44:56 -0700
Subject: [PATCH] aws[patch]: Fix error when processing empty string chunk
 conent (#6137)

* aws[patch]: Fix error when processing empty string chunk conent

* chore: lint files
---
 libs/langchain-aws/src/common.ts              | 11 ++---
 .../src/tests/chat_models.test.ts             | 40 ++++++++++++++++++-
 2 files changed, 45 insertions(+), 6 deletions(-)

diff --git a/libs/langchain-aws/src/common.ts b/libs/langchain-aws/src/common.ts
index e9dd95759b59..94630eda4a26 100644
--- a/libs/langchain-aws/src/common.ts
+++ b/libs/langchain-aws/src/common.ts
@@ -381,7 +381,7 @@ export function handleConverseStreamContentBlockDelta(
   if (!contentBlockDelta.delta) {
     throw new Error("No delta found in content block.");
   }
-  if (contentBlockDelta.delta.text) {
+  if (typeof contentBlockDelta.delta.text === "string") {
     return new ChatGenerationChunk({
       text: contentBlockDelta.delta.text,
       message: new AIMessageChunk({
@@ -404,11 +404,12 @@ export function handleConverseStreamContentBlockDelta(
       }),
     });
   } else {
-    const unsupportedField = Object.entries(contentBlockDelta.delta).filter(
-      ([_, value]) => !!value
-    );
     throw new Error(
-      `Unsupported content block type: ${unsupportedField[0][0]}`
+      `Unsupported content block type(s): ${JSON.stringify(
+        contentBlockDelta.delta,
+        null,
+        2
+      )}`
     );
   }
 }
diff --git a/libs/langchain-aws/src/tests/chat_models.test.ts b/libs/langchain-aws/src/tests/chat_models.test.ts
index 55c9bdc9713a..e944468f8e1c 100644
--- a/libs/langchain-aws/src/tests/chat_models.test.ts
+++ b/libs/langchain-aws/src/tests/chat_models.test.ts
@@ -3,8 +3,13 @@ import {
   HumanMessage,
   AIMessage,
   ToolMessage,
+  AIMessageChunk,
 } from "@langchain/core/messages";
-import { convertToConverseMessages } from "../common.js";
+import { concat } from "@langchain/core/utils/stream";
+import {
+  convertToConverseMessages,
+  handleConverseStreamContentBlockDelta,
+} from "../common.js";
 
 test("convertToConverseMessages works", () => {
   const messages = [
@@ -71,3 +76,36 @@ test("convertToConverseMessages works", () => {
     url: "https://weather.com",
   });
 });
+
+test("Streaming supports empty string chunks", async () => {
+  const contentBlocks = [
+    {
+      contentBlockIndex: 0,
+      delta: {
+        text: "Hello ",
+      },
+    },
+    {
+      contentBlockIndex: 0,
+      delta: {
+        text: "",
+      },
+    },
+    {
+      contentBlockIndex: 0,
+      delta: {
+        text: "world!",
+      },
+    },
+  ];
+
+  let finalChunk: AIMessageChunk | undefined;
+  for (const block of contentBlocks) {
+    const chunk = handleConverseStreamContentBlockDelta(block).message;
+    finalChunk = !finalChunk ? chunk : concat(finalChunk, chunk);
+  }
+
+  expect(finalChunk).toBeDefined();
+  if (!finalChunk) return;
+  expect(finalChunk.content).toBe("Hello world!");
+});