Node.js数据使用Buffer解析原始字节

I'm trying to use Buffer to parse 29 bytes of data that is formatted in odd ways. I've been using the slice() method to carve up the data on these odd boundaries. A sample stream looks like the following in hex (spaces added for clarity)...

我正在尝试使用Buffer来解析以奇数方式格式化的29个字节的数据。我一直在使用slice()方法来分割这些奇数边界上的数据。示例流在十六进制中看起来如下所示(为清晰起见添加了空格)...

01 1d 00 00 01 0a 0a 0b 0b 0c 0c 00 00 04 d2 00 00 00 0e c8 00 00 00 00 00 00 00 cc c4

var raw = '011d0000010a0a0b0b0c0c000004d20000000ec800000000000000ccc4';
buff = new Buffer(raw, 'utf8');
var position = 2;

// message type
var msg_type = buff.slice(position,(position+1)).toString();
position += 1;
console.log('... message type is ' + msg_type);

// event type
var event_type = buff.slice(position,(position+1)).toString();
position += 1;
console.log('... event type is ' + event_type);

// grab more data...

This produces an msg_type=1 and event_type=0. It should be 0 and 1, respectively. All of the slices that follow are wrong.

这会产生msg_type = 1和event_type = 0。它应分别为0和1。随后的所有切片都是错误的。

I'm clearly misunderstanding something with the encoding here. Either during Buffer instantiation or in the toString() extraction.

我显然在这里误解了编码。在Buffer实例化期间或在toString()提取期间。

How can I treat this input stream as a series of hex strings and convert them into binary data that I can operate on?

如何将此输入流视为一系列十六进制字符串并将其转换为可以操作的二进制数据?

Thanks!

2 个解决方案

#1

I think the answer is that your Buffer doesn't represent the object you think it does:

我认为答案是你的缓冲区不代表你认为它做的对象:

> var raw = '01 02 03'
> buff = new Buffer(raw, 'utf8')
<Buffer 30 31 20 30 32 20 30 33>
> buff.slice(0,0)
<Buffer >
> buff.slice(0,1)
<Buffer 30>
> buff.slice(0,2)
<Buffer 30 31>
> buff.slice(0,3)
<Buffer 30 31 20>
> buff.slice(0,0).toString()
''
> buff.slice(0,1).toString()
'0'
> buff.slice(0,2).toString()
'01'
> buff.slice(0,3).toString()
'01 '
> buff.slice(0,4).toString()
'01 0'
> buff.slice(0,5).toString()
'01 02'
> buff.slice(0,6).toString()
'01 02 '
> buff.slice(0,7).toString()
'01 02 0'
> buff.slice(0,8).toString()
'01 02 03'
> buff.length
8

Instead of representing a buffer that is three bytes long, this represents a buffer that is 8 bytes long. As you slice into it, you're getting the individual hexadecimal values of the characters. (Note the space is 20 -- just like the %20 so ubiquitous in URLs.)

它不是表示三个字节长的缓冲区,而是表示一个8字节长的缓冲区。当您切入它时,您将获得字符的各个十六进制值。 (注意空格是20 - 就像%20在URL中无处不在。)

But I have a feeling your var = '01 1d 00...' is just an attempt to populate the buffer with some binary data rather than what's actually happening in your program -- it might be easier to work with a simplified version of how you're actually filling the buffer. Maybe read it out of a file?

但我有一种感觉你的var = '01 1d 00 ...'只是试图用一些二进制数据填充缓冲区而不是程序中实际发生的事情 - 使用简化版本的方法可能更容易你实际上正在填充缓冲区。也许从文件中读出来?

#2

Node's Buffer supports this directly with the hex encoding:

Node的Buffer直接使用十六进制编码支持:

var raw = '011d0000010a0a0b0b0c0c000004d20000000ec800000000000000ccc4';
var buff = new Buffer(raw, 'hex');

#1