fix(langchain): Fix structured parser with triple backticks, adds tests

langchain/src/output_parsers/structured.ts

@@ -106,10 +106,14 @@ ${JSON.stringify(zodToJsonSchema(this.schema))}
         : text.trim();
       return await this.schema.parseAsync(JSON.parse(json));
     } catch (e) {
-      throw new OutputParserException(
-        `Failed to parse. Text: "${text}". Error: ${e}`,
-        text
-      );
+      try {
+        return await this.schema.parseAsync(JSON.parse(text.trim()));
+      } catch (e2) {
+        throw new OutputParserException(
+          `Failed to parse. Text: "${text}". Error: ${e2}`,
+          text
+        );
+      }
     }
   }
 }

langchain/src/output_parsers/tests/structured.test.ts

@@ -0,0 +1,101 @@
+import { expect, test } from "@jest/globals";
+import { z } from "zod";
+import { StructuredOutputParser } from "../structured.js";
+
+test("StructuredOutputParser handles valid JSON wrapped in triple backticks", async () => {
+  const parser = StructuredOutputParser.fromZodSchema(
+    z.object({
+      name: z.string().describe("Human name"),
+      age: z.number().describe("Human age"),
+    })
+  );
+  const text = '```json\n{"name": "John Doe", "age": 30}```';
+
+  const result = await parser.parse(text);
+
+  expect(result).toHaveProperty("name", "John Doe");
+  expect(result).toHaveProperty("age", 30);
+});
+
+test("StructuredOutputParser handles JSON without triple backticks", async () => {
+  const parser = StructuredOutputParser.fromZodSchema(
+    z.object({
+      name: z.string().describe("Human name"),
+      age: z.number().describe("Human age"),
+    })
+  );
+  const text = '{"name": "John Doe", "age": 30}';
+
+  const result = await parser.parse(text);
+
+  expect(result).toHaveProperty("name", "John Doe");
+  expect(result).toHaveProperty("age", 30);
+});
+
+test("StructuredOutputParser throws error for invalid JSON wrapped in triple backticks", async () => {
+  const parser = StructuredOutputParser.fromZodSchema(
+    z.object({
+      name: z.string().describe("Human name"),
+      age: z.number().describe("Human age"),
+    })
+  );
+  // Invalid JSON
+  const text = '```json\n{"name": "John Doe", "age": }```';
+
+  await expect(parser.parse(text)).rejects.toThrow("Failed to parse");
+});
+
+test("StructuredOutputParser throws error for normal text without triple backticks", async () => {
+  const parser = StructuredOutputParser.fromZodSchema(
+    z.object({
+      name: z.string().describe("Human name"),
+      age: z.number().describe("Human age"),
+    })
+  );
+  // Invalid JSON
+  const text = "This is just a plain text without JSON.";
+
+  await expect(parser.parse(text)).rejects.toThrow("Failed to parse");
+});
+
+test("StructuredOutputParser handles JSON with backticks inside text but not at the start", async () => {
+  const parser = StructuredOutputParser.fromZodSchema(
+    z.object({
+      name: z.string().describe("Human name"),
+      age: z.number().describe("Human age"),
+    })
+  );
+  const text = 'Some random text ```json\n{"name": "John Doe", "age": 30}```';
+  const result = await parser.parse(text);
+
+  expect(result).toHaveProperty("name", "John Doe");
+  expect(result).toHaveProperty("age", 30);
+});
+
+test("StructuredOutputParser handles JSON with backticks inside JSON", async () => {
+  const parser = StructuredOutputParser.fromZodSchema(
+    z.object({
+      name: z.string().describe("Human name"),
+      age: z.number().describe("Human age"),
+    })
+  );
+  const text = '{"name": "John ```Doe```", "age": 30}';
+
+  const result = await parser.parse(text);
+
+  expect(result).toHaveProperty("name", "John ```Doe```");
+  expect(result).toHaveProperty("age", 30);
+});
+
+test("StructuredOutputParser throws error for JSON with backticks both inside and outside the JSON", async () => {
+  const parser = StructuredOutputParser.fromZodSchema(
+    z.object({
+      name: z.string().describe("Human name"),
+      age: z.number().describe("Human age"),
+    })
+  );
+  const text =
+    'Some random text ```json\n{"name": "John ```Doe```", "age": 30}```';
+
+  await expect(parser.parse(text)).rejects.toThrow("Failed to parse");
+});