fix: make SSE buffer size configurable to prevent overflow during multi-round searches (#664) (#665)

* fix: make SSE buffer size configurable to prevent overflow during multi-round searches (Issue #664)

- Add NEXT_PUBLIC_MAX_STREAM_BUFFER_SIZE environment variable for frontend SSE stream buffer
- Default to 1MB for backward compatibility, users can increase to 5-10MB for large searches
- Enhance error message with actual buffer sizes and guidance on configuration
- Add validation schema in env.js with positive integer requirement
- Document configuration in .env.example with clear examples and use cases

* Apply suggestions from code review

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

---------

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

web/.env.example

@@ -41,3 +41,17 @@ NEXT_PUBLIC_API_URL=http://localhost:8000/api
 # Github OAuth Token (optional)
 GITHUB_OAUTH_TOKEN=xxxx
 
+# Stream Buffer Size Configuration (optional)
+# Controls the maximum buffer size for SSE (Server-Sent Events) streams in bytes.
+# Default: 1MB (1048576 bytes)
+# Increase this if you experience buffer overflow errors during large searches.
+# Use cases for increasing:
+# - Performing multi-round web searches with large content results
+# - Handling responses with many search results or images
+# - Systems with sufficient memory to handle larger buffers
+# Examples:
+# - 5MB: NEXT_PUBLIC_MAX_STREAM_BUFFER_SIZE=5242880
+# - 10MB: NEXT_PUBLIC_MAX_STREAM_BUFFER_SIZE=10485760
+# Note: Very large buffers may increase memory usage. Start with 5-10MB if needed.
+# NEXT_PUBLIC_MAX_STREAM_BUFFER_SIZE=1048576
+

web/src/core/sse/fetch-stream.ts

@@ -1,6 +1,8 @@
 // Copyright (c) 2025 Bytedance Ltd. and/or its affiliates
 // SPDX-License-Identifier: MIT
 
+import { env } from "~/env";
+
 import { type StreamEvent } from "./StreamEvent";
 
 export async function* fetchStream(
@@ -28,7 +30,8 @@ export async function* fetchStream(
 
   try {
     let buffer = "";
-    const MAX_BUFFER_SIZE = 1024 * 1024; // 1MB buffer size limit
+    // Use configurable buffer size from environment, default to 1MB (1048576 bytes)
+    const MAX_BUFFER_SIZE = env.NEXT_PUBLIC_MAX_STREAM_BUFFER_SIZE ?? (1024 * 1024);
 
     while (true) {
       const { done, value } = await reader.read();
@@ -47,7 +50,11 @@ export async function* fetchStream(
 
       // Check buffer size to avoid memory overflow
       if (buffer.length > MAX_BUFFER_SIZE) {
-        throw new Error("Buffer overflow - received too much data without proper event boundaries");
+        throw new Error(
+          `Buffer overflow - received ${(buffer.length / 1024 / 1024).toFixed(2)}MB of data without proper event boundaries. ` +
+          `Max buffer size is ${(MAX_BUFFER_SIZE / 1024 / 1024).toFixed(2)}MB. ` +
+          `You can increase this by setting NEXT_PUBLIC_MAX_STREAM_BUFFER_SIZE environment variable.`
+        );
       }
 
       let newlineIndex;

web/src/env.js

@@ -23,6 +23,7 @@ export const env = createEnv({
   client: {
     NEXT_PUBLIC_API_URL: z.string().optional(),
     NEXT_PUBLIC_STATIC_WEBSITE_ONLY: z.boolean().optional(),
+    NEXT_PUBLIC_MAX_STREAM_BUFFER_SIZE: z.coerce.number().int().positive().optional(),
   },
 
   /**
@@ -34,6 +35,7 @@ export const env = createEnv({
     NEXT_PUBLIC_API_URL: process.env.NEXT_PUBLIC_API_URL,
     NEXT_PUBLIC_STATIC_WEBSITE_ONLY:
       process.env.NEXT_PUBLIC_STATIC_WEBSITE_ONLY === "true",
+    NEXT_PUBLIC_MAX_STREAM_BUFFER_SIZE: process.env.NEXT_PUBLIC_MAX_STREAM_BUFFER_SIZE,
     AMPLITUDE_API_KEY: process.env.AMPLITUDE_API_KEY,
     GITHUB_OAUTH_TOKEN: process.env.GITHUB_OAUTH_TOKEN,
   },