When you read a chunk of bytes and you need to convert them to a number, node.js has functions like buffer.readInt32BE() and buffer.readInt32LE().
If I only know that the first 4 bytes of a file is an integer, what function should I use if I don't know the endianness of the system? Big endian or little endian?
Doing a fast googling (stackoverflow), in C we can test the endianness doing:
if ( htonl(47) == 47 ) {
// Big endian
} else {
// Little endian.
}
How can we test the endianness in node.js to properly use readInt32BE and readInt32Le?
os.endianness() returns the endianness of the CPU. Possible values are "BE" or "LE".
It was added in Node.js v0.10.0, it is not included in <= v0.8.25.
Totally possible, and even reasonable to do if you are working with typed arrays. I wrote a quick module to check if your system is little endian on node.js:
You should not need to test the endianness of the host system.
You need to investigate which byte-order the buffer is formatted using, and use the correct variant to read it out again.