Generating and writing binary data to stream in Node.js

Question

I want to generate some binary data in my Node.js application and then write it to an HTTP response for the client to download. My current implementation of the same application is in Python, which achieves this using struct module. For example,

import struct
# ...
s = 'Filename header'
s_binary = struct.pack('15s',s)
# ...

Also, how do I convert numbers into binary in Node.js? The way I do it in Python is:

# To convert a float into four byte binary representation in Python.
import struct
num_binary = struct.pack('f',23.33)

How do I do the same thing in Node.js?

This is so far the best solution I've got - straight port of Python's struct library to Node.js - jspack.

Raynos · Accepted Answer · 2011-01-28 02:47:05Z

1

You can look at Bison. It's like JSON but creates binary data.

answered Jan 28, 2011 at 2:47

Raynos

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icktoofay · Accepted Answer · 2011-01-28 02:50:44Z

1

var s="Filename header";
var s_binary=new Buffer(15);
for(var i=0;i<s_binary.length;i++) {
    s_binary[i]=0;
}
s_binary.write(s);
// Now you can write s_binary to a stream.

answered Jan 28, 2011 at 2:50

icktoofay

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10 Comments

Jayesh Over a year ago

ok this might work. Do you know how to convert numbers into binary? Let me update the question with an example in python.

JasonWoof Over a year ago

good solution. Except you don't need to fill with nulls if you're going to immediately fill the buffer with text.

JasonWoof Over a year ago

you can write buffers to streams, eg from the http example, you can do res.end(myBuffer). To send only the first 8 bytes of the buffer: res.end(myBuffer.slice(0, 8));

icktoofay Over a year ago

@JasonWoof: Actually, it is necessary. The Python code will pad the string with null bytes if the string is less than 15 characters. If left uninitialized in node.js, it will be full of junk bytes.

JasonWoof Over a year ago

but it's not less than 15 characters

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