fix(player): set browser UA + Referer for Netease CDN to stop auto-skip

Netease's m701/m801.music.126.net CDN RST connections from FFmpeg's
default Lavf UA. The bot's frame loop treats an early ffmpeg exit as
trackEnd and advances the queue, which surfaced as songs auto-skipping
mid-playlist. Add a browser UA + music.163.com Referer for these URLs,
extract args into a tested buildFfmpegArgs(), and harden reconnect
flags (delay_max 5 -> 30, plus reconnect_on_network_error /
reconnect_on_http_error). Verified by A/B running ffmpeg against the
same fresh CDN URL: legacy args got 0 bytes + "End of file" reading
HTTP response; fixed args streamed the full track to completion.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

scripts/test_netease_ua_fix.mjs

@@ -0,0 +1,73 @@
+// Empirically tests whether the browser UA + Referer headers fix the
+// connection resets we saw in bot.log against m701/m801.music.126.net.
+//
+// Spawns ffmpeg twice against the SAME fresh Netease CDN URL:
+//   A) old args from before the fix (no headers, -reconnect_delay_max 5)
+//   B) new args from after the fix (browser UA + Referer for music.126.net)
+// and reports bytes received + exit code + stderr-tail for each.
+
+import { spawn } from "node:child_process";
+import { buildFfmpegArgs } from "../dist/audio/player.js";
+
+const url = process.argv[2];
+if (!url) {
+  console.error("usage: node scripts/test_netease_ua_fix.mjs <netease_cdn_url>");
+  process.exit(2);
+}
+
+const FFMPEG = "ffmpeg";
+const TIMEOUT_MS = 15_000;
+
+function legacyArgs(u) {
+  return [
+    "-reconnect", "1",
+    "-reconnect_streamed", "1",
+    "-reconnect_delay_max", "5",
+    "-i", u,
+    "-f", "s16le",
+    "-ar", "48000",
+    "-ac", "2",
+    "-acodec", "pcm_s16le",
+    "-",
+  ];
+}
+
+function runFfmpeg(label, args) {
+  return new Promise((resolve) => {
+    const proc = spawn(FFMPEG, args, { stdio: ["ignore", "pipe", "pipe"] });
+    let bytes = 0;
+    let stderrTail = "";
+    let killed = false;
+
+    proc.stdout.on("data", (chunk) => {
+      bytes += chunk.length;
+    });
+    proc.stderr.on("data", (chunk) => {
+      stderrTail = (stderrTail + chunk.toString()).slice(-1500);
+    });
+
+    const timer = setTimeout(() => {
+      killed = true;
+      proc.kill("SIGTERM");
+    }, TIMEOUT_MS);
+
+    proc.on("exit", (code, signal) => {
+      clearTimeout(timer);
+      resolve({ label, bytes, code, signal, killed, stderrTail });
+    });
+  });
+}
+
+console.log(`URL: ${url}\n`);
+
+const a = await runFfmpeg("A) legacy args (no UA)", legacyArgs(url));
+console.log(`[A] code=${a.code} signal=${a.signal} killed=${a.killed} bytes=${a.bytes}`);
+console.log(`    stderr-tail:\n${a.stderrTail.split("\n").slice(-6).map((l) => "    " + l).join("\n")}\n`);
+
+const b = await runFfmpeg("B) fixed args (browser UA + Referer)", buildFfmpegArgs(url, 0));
+console.log(`[B] code=${b.code} signal=${b.signal} killed=${b.killed} bytes=${b.bytes}`);
+console.log(`    stderr-tail:\n${b.stderrTail.split("\n").slice(-6).map((l) => "    " + l).join("\n")}\n`);
+
+const aFailed = a.bytes === 0 && !a.killed && a.code !== 0;
+const bWorked = b.bytes > 100_000; // got real audio bytes
+console.log(`Verdict: legacy ${aFailed ? "FAILED (no bytes, exit code 1)" : "??"} ; fixed ${bWorked ? "WORKED (received audio)" : "??"}`);

src/audio/player.test.ts

@@ -0,0 +1,68 @@
+import { describe, it, expect } from "vitest";
+import { buildFfmpegArgs } from "./player.js";
+
+function getHeadersArg(args: string[]): string {
+  const idx = args.indexOf("-headers");
+  if (idx === -1) return "";
+  return args[idx + 1] ?? "";
+}
+
+describe("buildFfmpegArgs", () => {
+  it("includes browser User-Agent and Referer for Netease CDN URLs", () => {
+    const url = "http://m701.music.126.net/some/path/song.mp3?vuutv=abc";
+    const args = buildFfmpegArgs(url, 0);
+    const headers = getHeadersArg(args);
+    expect(headers).toContain("User-Agent:");
+    expect(headers).toContain("Mozilla/5.0");
+    expect(headers).toContain("Referer: https://music.163.com/");
+  });
+
+  it("keeps Bilibili Referer + UA for bilibili URLs", () => {
+    const url = "https://upos-sz-mirrorcoso1.bilivideo.com/foo/bar.mp3";
+    const args = buildFfmpegArgs(url, 0);
+    const headers = getHeadersArg(args);
+    expect(headers).toContain("Referer: https://www.bilibili.com");
+    expect(headers).toContain("User-Agent: Mozilla/5.0");
+  });
+
+  it("does not set custom headers for unknown URLs", () => {
+    const url = "https://example.com/song.mp3";
+    const args = buildFfmpegArgs(url, 0);
+    expect(args).not.toContain("-headers");
+  });
+
+  it("includes resilient reconnect flags for all URLs", () => {
+    const args = buildFfmpegArgs("https://example.com/song.mp3", 0);
+    expect(args).toContain("-reconnect");
+    expect(args).toContain("-reconnect_streamed");
+    expect(args).toContain("-reconnect_delay_max");
+    expect(args).toContain("-reconnect_on_network_error");
+    expect(args).toContain("-reconnect_on_http_error");
+    const idx = args.indexOf("-reconnect_delay_max");
+    expect(Number(args[idx + 1])).toBeGreaterThanOrEqual(30);
+  });
+
+  it("inserts -ss before -i when seekSeconds > 0", () => {
+    const args = buildFfmpegArgs("https://example.com/song.mp3", 42);
+    const ssIdx = args.indexOf("-ss");
+    const iIdx = args.indexOf("-i");
+    expect(ssIdx).toBeGreaterThan(-1);
+    expect(args[ssIdx + 1]).toBe("42");
+    expect(ssIdx).toBeLessThan(iIdx);
+  });
+
+  it("does not insert -ss when seekSeconds is 0", () => {
+    const args = buildFfmpegArgs("https://example.com/song.mp3", 0);
+    expect(args).not.toContain("-ss");
+  });
+
+  it("ends args with the input URL and PCM output spec", () => {
+    const url = "https://example.com/song.mp3";
+    const args = buildFfmpegArgs(url, 0);
+    const iIdx = args.indexOf("-i");
+    expect(args[iIdx + 1]).toBe(url);
+    expect(args).toContain("-f");
+    expect(args).toContain("s16le");
+    expect(args[args.length - 1]).toBe("-");
+  });
+});

src/audio/player.ts

@@ -49,6 +49,37 @@ function getFfmpegCommand(): string {
   return resolvedFfmpeg;
 }
 
+const BROWSER_UA =
+  "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/120.0.0.0 Safari/537.36";
+
+export function buildFfmpegArgs(url: string, seekSeconds: number): string[] {
+  const args: string[] = [];
+
+  if (url.includes("bilivideo") || url.includes("bilibili")) {
+    args.push(
+      "-headers",
+      `Referer: https://www.bilibili.com\r\nUser-Agent: ${BROWSER_UA}\r\n`,
+    );
+  } else if (url.includes("music.126.net") || url.includes("music.163.com")) {
+    args.push(
+      "-headers",
+      `Referer: https://music.163.com/\r\nUser-Agent: ${BROWSER_UA}\r\n`,
+    );
+  }
+
+  args.push(
+    "-reconnect", "1",
+    "-reconnect_streamed", "1",
+    "-reconnect_delay_max", "30",
+    "-reconnect_on_network_error", "1",
+    "-reconnect_on_http_error", "4xx,5xx",
+  );
+  if (seekSeconds > 0) args.push("-ss", String(seekSeconds));
+  args.push("-i", url, "-f", "s16le", "-ar", "48000", "-ac", "2", "-acodec", "pcm_s16le", "-");
+
+  return args;
+}
+
 export interface PlayerEvents {
   frame: (opusFrame: Buffer) => void;
   trackEnd: () => void;
@@ -106,13 +137,7 @@ export class AudioPlayer extends EventEmitter {
       return;
     }
 
-    const args: string[] = [];
+    const args = buildFfmpegArgs(url, seekSeconds);
-    if (url.includes("bilivideo") || url.includes("bilibili")) {
-      args.push("-headers", "Referer: https://www.bilibili.com\r\nUser-Agent: Mozilla/5.0...\r\n");
-    }
-    args.push("-reconnect", "1", "-reconnect_streamed", "1", "-reconnect_delay_max", "5");
-    if (seekSeconds > 0) args.push("-ss", String(seekSeconds));
-    args.push("-i", url, "-f", "s16le", "-ar", "48000", "-ac", "2", "-acodec", "pcm_s16le", "-");
 
     const ffmpegBin = getFfmpegCommand();
     this.ffmpeg = spawn(ffmpegBin, args, { stdio: ["ignore", "pipe", "pipe"] });