HEAD response with a JSON content-type throws "Unexpected end of JSON input"

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技术栈
javascript, node.js
领域
backend-api-design

调研方向

Issue 指向 lib/httpClient.js 中的 _handleResponse（第 105–114 行）。阅读它如何选择解析响应体，然后检查 httpClient.head(url) 和 httpClient(url, {method: 'HEAD'}) 的现有测试。当两种形式都能成功解析，且 JSON 内容类型下 response.data 为 undefined 时，即为完成。

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描述

A HEAD request to an endpoint that serves JSON rejects with SyntaxError: Unexpected end of JSON input, even though the request succeeded.

A HEAD response carries the same headers as the GET, including Content-Type: application/json, but has no body. _handleResponse decides whether to parse from the content-type alone, so it calls response.json() on the empty body:

https://github.com/digitalbazaar/http-client/blob/main/lib/httpClient.js#L105-L114

Reproduction

Seen with 4.4.0 on Node 24.

import {createServer} from 'node:http';
import {httpClient} from '@digitalbazaar/http-client';

const server = createServer((req, res) => {
  const body = JSON.stringify({ok: true});
  res.writeHead(200, {
    'content-type': 'application/json',
    'content-length': Buffer.byteLength(body)
  });
  // a HEAD response carries the GET's headers and no body
  res.end(req.method === 'HEAD' ? undefined : body);
});
await new Promise(resolve => server.listen(0, resolve));
const url = `http://localhost:${server.address().port}/`;

console.log('GET ', (await httpClient.get(url)).data);
try {
  console.log('HEAD', (await httpClient.head(url)).status);
} catch(e) {
  console.log('HEAD threw:', e.name, '-', e.message);
}
server.close();

Output:

GET  { ok: true }
HEAD threw: SyntaxError - Unexpected end of JSON input
Expected

The HEAD resolves with the response, and response.data is undefined.

Workaround

Passing parseBody: false avoids it. That only helps a caller that controls the options, which is not the case when the request is made through a wrapper such as ezcap's ZcapClient.request().

Suggested fix

Skip the body parse when the request method is HEAD, both for httpClient.head(url) and for the direct httpClient(url, {method: 'HEAD'}) form. Happy to send a PR.

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