Fails to retrieve the first piece of data when downloading partial content with `RetryAgent`

[vitalygashkov]

Bug Description

When trying to download the file in parts (using RetryAgent), the download of the first part (when first byte of range is equal to zero) fails due to a content-range mismatch error inside RetryHandler onHeaders method.

Reproducible By

Here's a simple example of reproducing the issue:

const { setGlobalDispatcher, RetryAgent, Agent, request } = require('undici');

setGlobalDispatcher(new RetryAgent(new Agent()));

const start = 0;
const end = 26664011;
const size = end - start + 1;
const url =
  'https://cdn.bitmovin.com/content/assets/art-of-motion-dash-hls-progressive/MI201109210084_mpeg-4_hd_high_1080p25_10mbits.mp4';
const options = { headers: { Range: `bytes=${start}-${end}` } };

request(url, options)
  .then((response) => {
    const contentLength = Number(response.headers['content-length']);
    console.log(contentLength === size);
  })
  .catch((e) => {
    console.log(e.message === 'content-range mismatch'); // true
  });

Expected Behavior

I expect the request to successfully execute and return the first piece of data. If you remove RetryAgent from the code example above, the request will succeed:

const { setGlobalDispatcher, Agent, request } = require('undici');

setGlobalDispatcher(new Agent());

const start = 0;
const end = 26664011;
const size = end - start + 1;
const url =
  'https://cdn.bitmovin.com/content/assets/art-of-motion-dash-hls-progressive/MI201109210084_mpeg-4_hd_high_1080p25_10mbits.mp4';
const options = { headers: { Range: `bytes=${start}-${end}` } };

request(url, options)
  .then((response) => {
    const contentLength = Number(response.headers['content-length']);
    console.log(contentLength === size); // true
  })
  .catch((e) => {
    console.log(e.message === 'content-range mismatch');
  });

Logs & Screenshots

AssertionError [ERR_ASSERTION]: content-range mismatch
    at RetryHandler.onHeaders (/Users/user/project/node_modules/undici/lib/handler/retry-handler.js:248:9)
    at Request.onHeaders (/Users/user/project/node_modules/undici/lib/core/request.js:243:29)
    at Parser.onHeadersComplete (/Users/user/project/node_modules/undici/lib/dispatcher/client-h1.js:507:27)
    at wasm_on_headers_complete (/Users/user/project/node_modules/undici/lib/dispatcher/client-h1.js:121:30)
    at wasm://wasm/0003626a:wasm-function[11]:0x494
    at wasm://wasm/0003626a:wasm-function[51]:0x1003
    at wasm://wasm/0003626a:wasm-function[68]:0x6e8e
    at wasm://wasm/0003626a:wasm-function[67]:0x1568
    at wasm://wasm/0003626a:wasm-function[21]:0x552
    at Parser.execute (/Users/user/project/node_modules/undici/lib/dispatcher/client-h1.js:262:22) {
  generatedMessage: false,
  code: 'ERR_ASSERTION',
  actual: false,
  expected: true,
  operator: '=='
}

Environment

macOS Sonoma 14.3.1 (23D60)
Node v20.11.1

[metcoder95]

Opened a PR for it