Hash 类

• 继承自: <stream.Transform>

Hash 类是用于创建数据的哈希摘要的实用工具。 它可以通过以下两种方式之一使用：

• 作为既可读又可写的流，其中写入数据以在可读端生成计算的哈希摘要，或者
• 使用 hash.update() 和 hash.digest() 方法生成计算的哈希。

crypto.createHash() 方法用于创建 Hash 实例。 Hash 对象不能直接使用 new 关键字创建。

示例：使用 Hash 对象作为流：

const crypto = require('crypto');
const hash = crypto.createHash('sha256');

hash.on('readable', () => {
  // 哈希流只生成
  // 一个元素。
  const data = hash.read();
  if (data) {
    console.log(data.toString('hex'));
    // 打印:
    //   6a2da20943931e9834fc12cfe5bb47bbd9ae43489a30726962b576f4e3993e50
  }
});

hash.write('some data to hash');
hash.end();

示例：使用 Hash 和管道流：

const crypto = require('crypto');
const fs = require('fs');
const hash = crypto.createHash('sha256');

const input = fs.createReadStream('test.js');
input.pipe(hash).setEncoding('hex').pipe(process.stdout);

示例：使用 hash.update() 和 hash.digest() 方法：

const crypto = require('crypto');
const hash = crypto.createHash('sha256');

hash.update('some data to hash');
console.log(hash.digest('hex'));
// 打印:
//   6a2da20943931e9834fc12cfe5bb47bbd9ae43489a30726962b576f4e3993e50

• Extends: <stream.Transform>

The Hash class is a utility for creating hash digests of data. It can be used in one of two ways:

• As a stream that is both readable and writable, where data is written to produce a computed hash digest on the readable side, or
• Using the hash.update() and hash.digest() methods to produce the computed hash.

The crypto.createHash() method is used to create Hash instances. Hash objects are not to be created directly using the new keyword.

Example: Using Hash objects as streams:

const crypto = require('crypto');
const hash = crypto.createHash('sha256');

hash.on('readable', () => {
  // Only one element is going to be produced by the
  // hash stream.
  const data = hash.read();
  if (data) {
    console.log(data.toString('hex'));
    // Prints:
    //   6a2da20943931e9834fc12cfe5bb47bbd9ae43489a30726962b576f4e3993e50
  }
});

hash.write('some data to hash');
hash.end();

Example: Using Hash and piped streams:

const crypto = require('crypto');
const fs = require('fs');
const hash = crypto.createHash('sha256');

const input = fs.createReadStream('test.js');
input.pipe(hash).setEncoding('hex').pipe(process.stdout);

Example: Using the hash.update() and hash.digest() methods:

const crypto = require('crypto');
const hash = crypto.createHash('sha256');

hash.update('some data to hash');
console.log(hash.digest('hex'));
// Prints:
//   6a2da20943931e9834fc12cfe5bb47bbd9ae43489a30726962b576f4e3993e50