压缩 HTTP 的请求和响应

node:zlib 模块可用于实现对 HTTP 定义的 gzip、deflate 和 br 内容编码机制的支持。

HTTP Accept-Encoding 标头在 HTTP 请求中用于识别客户端接受的压缩编码。 Content-Encoding 标头用于标识实际应用于消息的压缩编码。

下面给出的示例经过彻底简化以显示基本概念。 使用 zlib 编码可能很昂贵，结果应该被缓存。 有关 zlib 使用中涉及的速度/内存/压缩权衡的更多信息，请参阅内存使用调整。

// 客户端请求示例
const zlib = require('node:zlib');
const http = require('node:http');
const fs = require('node:fs');
const { pipeline } = require('node:stream');

const request = http.get({ host: 'example.com',
                           path: '/',
                           port: 80,
                           headers: { 'Accept-Encoding': 'br,gzip,deflate' } });
request.on('response', (response) => {
  const output = fs.createWriteStream('example.com_index.html');

  const onError = (err) => {
    if (err) {
      console.error('An error occurred:', err);
      process.exitCode = 1;
    }
  };

  switch (response.headers['content-encoding']) {
    case 'br':
      pipeline(response, zlib.createBrotliDecompress(), output, onError);
      break;
    // 或者，只需使用 zlib.createUnzip() 来处理以下两种情况：
    case 'gzip':
      pipeline(response, zlib.createGunzip(), output, onError);
      break;
    case 'deflate':
      pipeline(response, zlib.createInflate(), output, onError);
      break;
    default:
      pipeline(response, output, onError);
      break;
  }
});

// 服务器示例
// 对每个请求运行 gzip 操作是非常昂贵的。
// 缓存压缩的缓冲区会更有效率。
const zlib = require('node:zlib');
const http = require('node:http');
const fs = require('node:fs');
const { pipeline } = require('node:stream');

http.createServer((request, response) => {
  const raw = fs.createReadStream('index.html');
  // 存储资源的压缩版本和未压缩版本。
  response.setHeader('Vary', 'Accept-Encoding');
  let acceptEncoding = request.headers['accept-encoding'];
  if (!acceptEncoding) {
    acceptEncoding = '';
  }

  const onError = (err) => {
    if (err) {
      // 如果发生错误，则无能为力，
      // 因为服务器已经发送了 200 响应代码，
      // 并且已经向客户端发送了一些数据。
      // 能做的最好的事情
      // 就是立即终止响应并记录错误。
      response.end();
      console.error('An error occurred:', err);
    }
  };

  // 注意：这不是一个符合标准的接受编码解析器。
  // 参见 https://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.3
  if (/\bdeflate\b/.test(acceptEncoding)) {
    response.writeHead(200, { 'Content-Encoding': 'deflate' });
    pipeline(raw, zlib.createDeflate(), response, onError);
  } else if (/\bgzip\b/.test(acceptEncoding)) {
    response.writeHead(200, { 'Content-Encoding': 'gzip' });
    pipeline(raw, zlib.createGzip(), response, onError);
  } else if (/\bbr\b/.test(acceptEncoding)) {
    response.writeHead(200, { 'Content-Encoding': 'br' });
    pipeline(raw, zlib.createBrotliCompress(), response, onError);
  } else {
    response.writeHead(200, {});
    pipeline(raw, response, onError);
  }
}).listen(1337);

默认情况下，zlib 方法在解压缩截断数据时会抛出错误。 但是，如果已知数据不完整，或者希望仅检查压缩文件的开头，则可以通过更改用于解压缩输入的最后一个块的刷新方法来抑制默认错误处理数据：

// 这是上述示例中缓冲区的截断版本
const buffer = Buffer.from('eJzT0yMA', 'base64');

zlib.unzip(
  buffer,
  // 对于 Brotli，相当于 zlib.constants.BROTLI_OPERATION_FLUSH
  { finishFlush: zlib.constants.Z_SYNC_FLUSH },
  (err, buffer) => {
    if (err) {
      console.error('An error occurred:', err);
      process.exitCode = 1;
    }
    console.log(buffer.toString());
  });

这不会改变其他错误抛出情况下的行为，例如当输入数据的格式无效时。 使用此方法，将无法确定输入是否提前结束或缺少完整性检查，因此需要手动检查解压结果是否有效。

The node:zlib module can be used to implement support for the gzip, deflate and br content-encoding mechanisms defined by HTTP.

The HTTP Accept-Encoding header is used within an HTTP request to identify the compression encodings accepted by the client. The Content-Encoding header is used to identify the compression encodings actually applied to a message.

The examples given below are drastically simplified to show the basic concept. Using zlib encoding can be expensive, and the results ought to be cached. See Memory usage tuning for more information on the speed/memory/compression tradeoffs involved in zlib usage.

// Client request example
const zlib = require('node:zlib');
const http = require('node:http');
const fs = require('node:fs');
const { pipeline } = require('node:stream');

const request = http.get({ host: 'example.com',
                           path: '/',
                           port: 80,
                           headers: { 'Accept-Encoding': 'br,gzip,deflate' } });
request.on('response', (response) => {
  const output = fs.createWriteStream('example.com_index.html');

  const onError = (err) => {
    if (err) {
      console.error('An error occurred:', err);
      process.exitCode = 1;
    }
  };

  switch (response.headers['content-encoding']) {
    case 'br':
      pipeline(response, zlib.createBrotliDecompress(), output, onError);
      break;
    // Or, just use zlib.createUnzip() to handle both of the following cases:
    case 'gzip':
      pipeline(response, zlib.createGunzip(), output, onError);
      break;
    case 'deflate':
      pipeline(response, zlib.createInflate(), output, onError);
      break;
    default:
      pipeline(response, output, onError);
      break;
  }
});

// server example
// Running a gzip operation on every request is quite expensive.
// It would be much more efficient to cache the compressed buffer.
const zlib = require('node:zlib');
const http = require('node:http');
const fs = require('node:fs');
const { pipeline } = require('node:stream');

http.createServer((request, response) => {
  const raw = fs.createReadStream('index.html');
  // Store both a compressed and an uncompressed version of the resource.
  response.setHeader('Vary', 'Accept-Encoding');
  let acceptEncoding = request.headers['accept-encoding'];
  if (!acceptEncoding) {
    acceptEncoding = '';
  }

  const onError = (err) => {
    if (err) {
      // If an error occurs, there's not much we can do because
      // the server has already sent the 200 response code and
      // some amount of data has already been sent to the client.
      // The best we can do is terminate the response immediately
      // and log the error.
      response.end();
      console.error('An error occurred:', err);
    }
  };

  // Note: This is not a conformant accept-encoding parser.
  // See https://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.3
  if (/\bdeflate\b/.test(acceptEncoding)) {
    response.writeHead(200, { 'Content-Encoding': 'deflate' });
    pipeline(raw, zlib.createDeflate(), response, onError);
  } else if (/\bgzip\b/.test(acceptEncoding)) {
    response.writeHead(200, { 'Content-Encoding': 'gzip' });
    pipeline(raw, zlib.createGzip(), response, onError);
  } else if (/\bbr\b/.test(acceptEncoding)) {
    response.writeHead(200, { 'Content-Encoding': 'br' });
    pipeline(raw, zlib.createBrotliCompress(), response, onError);
  } else {
    response.writeHead(200, {});
    pipeline(raw, response, onError);
  }
}).listen(1337);

By default, the zlib methods will throw an error when decompressing truncated data. However, if it is known that the data is incomplete, or the desire is to inspect only the beginning of a compressed file, it is possible to suppress the default error handling by changing the flushing method that is used to decompress the last chunk of input data:

// This is a truncated version of the buffer from the above examples
const buffer = Buffer.from('eJzT0yMA', 'base64');

zlib.unzip(
  buffer,
  // For Brotli, the equivalent is zlib.constants.BROTLI_OPERATION_FLUSH.
  { finishFlush: zlib.constants.Z_SYNC_FLUSH },
  (err, buffer) => {
    if (err) {
      console.error('An error occurred:', err);
      process.exitCode = 1;
    }
    console.log(buffer.toString());
  });

This will not change the behavior in other error-throwing situations, e.g. when the input data has an invalid format. Using this method, it will not be possible to determine whether the input ended prematurely or lacks the integrity checks, making it necessary to manually check that the decompressed result is valid.