feat(core): Support truncation for LangChain integration request messages (#18157)

This PR adds [truncation support for LangChain integration request
messages](#18018).
All messages already get normalized to arrays of messages, so here we
need no case distinction for strings.

Adds tests to verify behavior for 1. simple string inputs and 2.
conversations in the form of arrays of strings.

Closes #18018

Author: nicohrubec

dev-packages/node-integration-tests/suites/tracing/langchain/scenario-message-truncation.mjs

@@ -0,0 +1,72 @@
+import { ChatAnthropic } from '@langchain/anthropic';
+import * as Sentry from '@sentry/node';
+import express from 'express';
+
+function startMockAnthropicServer() {
+  const app = express();
+  app.use(express.json());
+
+  app.post('/v1/messages', (req, res) => {
+    const model = req.body.model;
+
+    res.json({
+      id: 'msg_truncation_test',
+      type: 'message',
+      role: 'assistant',
+      content: [
+        {
+          type: 'text',
+          text: 'Response to truncated messages',
+        },
+      ],
+      model: model,
+      stop_reason: 'end_turn',
+      stop_sequence: null,
+      usage: {
+        input_tokens: 10,
+        output_tokens: 15,
+      },
+    });
+  });
+
+  return new Promise(resolve => {
+    const server = app.listen(0, () => {
+      resolve(server);
+    });
+  });
+}
+
+async function run() {
+  const server = await startMockAnthropicServer();
+  const baseUrl = `http://localhost:${server.address().port}`;
+
+  await Sentry.startSpan({ op: 'function', name: 'main' }, async () => {
+    const model = new ChatAnthropic({
+      model: 'claude-3-5-sonnet-20241022',
+      apiKey: 'mock-api-key',
+      clientOptions: {
+        baseURL: baseUrl,
+      },
+    });
+
+    const largeContent1 = 'A'.repeat(15000); // ~15KB
+    const largeContent2 = 'B'.repeat(15000); // ~15KB
+    const largeContent3 = 'C'.repeat(25000); // ~25KB (will be truncated)
+
+    // Create one very large string that gets truncated to only include Cs
+    await model.invoke(largeContent3 + largeContent2);
+
+    // Create an array of messages that gets truncated to only include the last message (result should again contain only Cs)
+    await model.invoke([
+      { role: 'system', content: largeContent1 },
+      { role: 'user', content: largeContent2 },
+      { role: 'user', content: largeContent3 },
+    ]);
+  });
+
+  await Sentry.flush(2000);
+
+  server.close();
+}
+
+run();

dev-packages/node-integration-tests/suites/tracing/langchain/test.ts

@@ -194,4 +194,55 @@ describe('LangChain integration', () => {
       await createRunner().ignore('event').expect({ transaction: EXPECTED_TRANSACTION_TOOL_CALLS }).start().completed();
     });
   });
+
+  const EXPECTED_TRANSACTION_MESSAGE_TRUNCATION = {
+    transaction: 'main',
+    spans: expect.arrayContaining([
+      expect.objectContaining({
+        data: expect.objectContaining({
+          'gen_ai.operation.name': 'chat',
+          'sentry.op': 'gen_ai.chat',
+          'sentry.origin': 'auto.ai.langchain',
+          'gen_ai.system': 'anthropic',
+          'gen_ai.request.model': 'claude-3-5-sonnet-20241022',
+          // Messages should be present and should include truncated string input (contains only Cs)
+          'gen_ai.request.messages': expect.stringMatching(/^\[\{"role":"user","content":"C+"\}\]$/),
+        }),
+        description: 'chat claude-3-5-sonnet-20241022',
+        op: 'gen_ai.chat',
+        origin: 'auto.ai.langchain',
+        status: 'ok',
+      }),
+      expect.objectContaining({
+        data: expect.objectContaining({
+          'gen_ai.operation.name': 'chat',
+          'sentry.op': 'gen_ai.chat',
+          'sentry.origin': 'auto.ai.langchain',
+          'gen_ai.system': 'anthropic',
+          'gen_ai.request.model': 'claude-3-5-sonnet-20241022',
+          // Messages should be present (truncation happened) and should be a JSON array of a single index (contains only Cs)
+          'gen_ai.request.messages': expect.stringMatching(/^\[\{"role":"user","content":"C+"\}\]$/),
+        }),
+        description: 'chat claude-3-5-sonnet-20241022',
+        op: 'gen_ai.chat',
+        origin: 'auto.ai.langchain',
+        status: 'ok',
+      }),
+    ]),
+  };
+
+  createEsmAndCjsTests(
+    __dirname,
+    'scenario-message-truncation.mjs',
+    'instrument-with-pii.mjs',
+    (createRunner, test) => {
+      test('truncates messages when they exceed byte limit', async () => {
+        await createRunner()
+          .ignore('event')
+          .expect({ transaction: EXPECTED_TRANSACTION_MESSAGE_TRUNCATION })
+          .start()
+          .completed();
+      });
+    },
+  );
 });

packages/core/src/utils/langchain/utils.ts

@@ -23,6 +23,7 @@ import {
   GEN_AI_USAGE_OUTPUT_TOKENS_ATTRIBUTE,
   GEN_AI_USAGE_TOTAL_TOKENS_ATTRIBUTE,
 } from '../ai/gen-ai-attributes';
+import { truncateGenAiMessages } from '../ai/messageTruncation';
 import { LANGCHAIN_ORIGIN, ROLE_MAP } from './constants';
 import type { LangChainLLMResult, LangChainMessage, LangChainSerialized } from './types';
 
@@ -281,7 +282,8 @@ export function extractChatModelRequestAttributes(
 
   if (recordInputs && Array.isArray(langChainMessages) && langChainMessages.length > 0) {
     const normalized = normalizeLangChainMessages(langChainMessages.flat());
-    setIfDefined(attrs, GEN_AI_REQUEST_MESSAGES_ATTRIBUTE, asString(normalized));
+    const truncated = truncateGenAiMessages(normalized);
+    setIfDefined(attrs, GEN_AI_REQUEST_MESSAGES_ATTRIBUTE, asString(truncated));
   }
 
   return attrs;