langchain-ai · benjamincburns · Apr 30, 2025 · Apr 29, 2025 · Apr 30, 2025 · Apr 30, 2025
diff --git a/langchain-core/src/output_parsers/tests/json.test.ts b/langchain-core/src/output_parsers/tests/json.test.ts
@@ -1,10 +1,29 @@
-import { test, expect } from "@jest/globals";
+import { describe, test, expect } from "@jest/globals";
 import { ChatPromptTemplate } from "../../prompts/chat.js";
 import { RunnableSequence } from "../../runnables/base.js";
 import { RunnablePassthrough } from "../../runnables/passthrough.js";
 import { FakeStreamingLLM } from "../../utils/testing/index.js";
 import { JsonOutputParser } from "../json.js";
 
+async function acc(iter: AsyncGenerator<object>): Promise<object[]> {
+  const acc = [];
+  for await (const chunk of iter) {
+    acc.push(chunk);
+  }
+  return acc;
+}
+
+async function* streamChunks(chunks: string[]): AsyncGenerator<string> {
+  for (const chunk of chunks) {
+    yield chunk;
+    await new Promise<void>((resolve) => {
+      void setTimeout(() => {
+        resolve();
+      }, 0);
+    });
+  }
+}
+
 const STREAMED_TOKENS = `
 {
 
@@ -244,13 +263,64 @@ const EXPECTED_STREAMED_JSON_DIFF = [
   [{ op: "replace", path: "/audience/1", value: "So funny" }],
 ];
 
-async function acc(iter: AsyncGenerator<object>): Promise<object[]> {
-  const acc = [];
-  for await (const chunk of iter) {
-    acc.push(chunk);
+const MARKDOWN_STREAM_TEST_CASES = [
+  {
+    name: "Markdown with split code block",
+    input: ['```json\n{"', 'countries": [{"n', 'ame": "China"}]}', "\n```"],
+    expected: [{ countries: [{ name: "China" }] }],
+  },
+  {
+    name: "Markdown without json identifier, split",
+    input: ['```\n{"', 'key": "val', '"}\n```'],
+    expected: [{ key: "val" }],
+  },
+  {
+    name: "Ignores text after closing markdown backticks",
+    input: ["```json\n", '{ "data": 123 }', "\n```", " Some extra text"],
+    expected: [{ data: 123 }],
+  },
+];
+
+describe("Markdown Streaming Scenarios", () => {
+  for (const testCase of MARKDOWN_STREAM_TEST_CASES) {
+    test(testCase.name, async () => {
+      const parser = new JsonOutputParser();
+      const result = await acc(
+        parser.transform(streamChunks(testCase.input), {})
+      );
+      expect(result).toEqual(testCase.expected);
+    });
   }
-  return acc;
-}
+});
+
+test("Handles markdown with text around code block", async () => {
+  const input = [
+    "Explanation:\n```json\n{",
+    '"answer": 42',
+    "}\n```\nConclusion",
+  ];
+
+  const expected = [{}, { answer: 42 }];
+
+  const parser = new JsonOutputParser();
+  const result = await acc(parser.transform(streamChunks(input), {}));
+  expect(result).toEqual(expected);
+});
+
+test("Handles multiple code blocks in single chunk", async () => {
+  const input = ['```json\n{"a":1}\n```\n```json\n{"b":2}\n```'];
+
+  const parser = new JsonOutputParser();
+  const result = await acc(
+    parser.transform(
+      (async function* () {
+        yield input[0];
+      })(),
+      {}
+    )
+  );
+  expect(result).toEqual([{ a: 1 }]);
+});
 
 test("JSONOutputParser parses streamed JSON", async () => {
   async function* generator() {

diff --git a/langchain-core/src/utils/json.ts b/langchain-core/src/utils/json.ts
@@ -1,12 +1,29 @@
 export function parseJsonMarkdown(s: string, parser = parsePartialJson) {
   // eslint-disable-next-line no-param-reassign
   s = s.trim();
-  const match = /```(json)?(.*)```/s.exec(s);
-  if (!match) {
+
+  const firstFenceIndex = s.indexOf("```");
+  if (firstFenceIndex === -1) {
     return parser(s);
-  } else {
-    return parser(match[2]);
   }
+
+  let contentAfterFence = s.substring(firstFenceIndex + 3);
+
+  if (contentAfterFence.startsWith("json\n")) {
+    contentAfterFence = contentAfterFence.substring(5);
+  } else if (contentAfterFence.startsWith("json")) {
+    contentAfterFence = contentAfterFence.substring(4);
+  } else if (contentAfterFence.startsWith("\n")) {
+    contentAfterFence = contentAfterFence.substring(1);
+  }
+
+  const closingFenceIndex = contentAfterFence.indexOf("```");
+  let finalContent = contentAfterFence;
+  if (closingFenceIndex !== -1) {
+    finalContent = contentAfterFence.substring(0, closingFenceIndex);
+  }
+
+  return parser(finalContent.trim());
 }
 
 // Adapted from https://github.com/KillianLucas/open-interpreter/blob/main/interpreter/core/llm/utils/parse_partial_json.py