Javascript 如何在 Node.js 中逐字节读取二进制文件
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How to read binary files byte by byte in Node.js
提问by Alec Gorge
What is the best way to read part of a binary file in Node.js?
在 Node.js 中读取部分二进制文件的最佳方法是什么？
I am looking to either access specific bytes in the "header" (less than the first 100 bytes) or read the file byte by byte.
我希望访问“标头”中的特定字节（小于前 100 个字节）或逐字节读取文件。
回答by samplebias
Here is an example of fs.read()-ing the first 100 bytes from a file descriptor returned by fs.open():
以下是fs.read()从 返回的文件描述符中-ing 前 100 个字节的示例fs.open()：
var fs = require('fs');
fs.open('file.txt', 'r', function(status, fd) {
if (status) {
console.log(status.message);
return;
}
var buffer = Buffer.alloc(100);
fs.read(fd, buffer, 0, 100, 0, function(err, num) {
console.log(buffer.toString('utf8', 0, num));
});
});
回答by zwitterion
This is another option
这是另一种选择
const fs = require('fs');
const fileName = 'something.bin'
/*
Requirements ex:
Content in 512 bytes chunks.
Send the 512 bytes packet as a 1024 char string, where each byte is sent as a
2 hex digits.
An "addr" field starts from 0 and tracks the offset of the first byte of the
packet.
*/
function chunk(s, maxBytes) {
//! https://nodejs.org/api/buffer.html#buffer_buf_slice_start_end
/*
buf.slice([start[, end]])
start <integer> Where the new Buffer will start. Default: 0.
end <integer> Where the new Buffer will end (not inclusive). Default: buf.length.
Returns: <Buffer>
*/
let buf = Buffer.from(s);
const result = [];
let readBuffer = true
let startChunkByte = 0
let endChunkByte = maxBytes
while(readBuffer) {
// First round
startChunkByte === 0 ? endChunkByte = startChunkByte + maxBytes : ""
//Handle last chunk
endChunkByte >= buf.length ? readBuffer = false : ""
// addr: the position of the first bytes. raw: the chunk of x bytes
result.push({"addr":startChunkByte,"raw":buf.slice(startChunkByte, endChunkByte).toString('hex')});
startChunkByte = endChunkByte
endChunkByte = startChunkByte + maxBytes
}
return result;
}
fs.readFile(fileName, (err, data) => {
if (err) throw err;
// Let's choose 512 bytes chunks
const arrBinChunk = chunk(data, 512)
arrBinChunk.forEach(element => console.log(element))
//Tests - should be able to see 1024, 1024, as per riquerements
arrBinChunk.forEach(element => console.log(element.raw.length))
});
