Fix Anthropic streaming calls with withStructuredOutput

libs/langchain-anthropic/src/output_parsers.ts

@@ -39,10 +39,27 @@ export class AnthropicToolsOutputParser<
   }
 
   protected async _validateResult(result: unknown): Promise<T> {
+    let parsedResult = result;
+    if (typeof result === "string") {
+      try {
+        parsedResult = JSON.parse(result);
+      } catch (e: any) {
+        throw new OutputParserException(
+          `Failed to parse. Text: "${JSON.stringify(
+            result,
+            null,
+            2
+          )}". Error: ${JSON.stringify(e.message)}`,
+          result
+        );
+      }
+    } else {
+      parsedResult = result;
+    }
     if (this.zodSchema === undefined) {
-      return result as T;
+      return parsedResult as T;
     }
-    const zodParsedResult = await this.zodSchema.safeParseAsync(result);
+    const zodParsedResult = await this.zodSchema.safeParseAsync(parsedResult);
     if (zodParsedResult.success) {
       return zodParsedResult.data;
     } else {
@@ -52,7 +69,7 @@ export class AnthropicToolsOutputParser<
           null,
           2
         )}". Error: ${JSON.stringify(zodParsedResult.error.errors)}`,
-        JSON.stringify(result, null, 2)
+        JSON.stringify(parsedResult, null, 2)
       );
     }
   }

libs/langchain-anthropic/src/tests/chat_models-tools.int.test.ts

@@ -38,7 +38,7 @@ class WeatherTool extends StructuredTool {
 }
 
 const model = new ChatAnthropic({
-  modelName: "claude-3-sonnet-20240229",
+  modelName: "claude-3-haiku-20240307",
   temperature: 0,
 });
 
@@ -440,3 +440,24 @@ test("llm token callbacks can handle tool calls", async () => {
   if (!args) return;
   expect(args).toEqual(JSON.parse(tokens));
 });
+
+test.only("streaming with structured output", async () => {
+  const stream = await model
+    .withStructuredOutput(zodSchema)
+    .stream("weather in london");
+  // Currently, streaming yields a single chunk
+  let finalChunk;
+  for await (const chunk of stream) {
+    finalChunk = chunk;
+  }
+  expect(typeof finalChunk).toEqual("object");
+  const stream2 = await model
+    .withStructuredOutput(zodToJsonSchema(zodSchema))
+    .stream("weather in london");
+  // Currently, streaming yields a single chunk
+  let finalChunk2;
+  for await (const chunk of stream2) {
+    finalChunk2 = chunk;
+  }
+  expect(typeof finalChunk2).toEqual("object");
+});