A Standard MIDI File is a stream of chunks, and almost every size, count, and length in it is a 4-byte big-endian unsigned integer. Today you build the one helper that reads it - the workhorse the whole parser leans on.
Read a 4-byte big-endian unsigned integer from the front of a byte slice.
Everything in a Standard MIDI File is stored big-endian (most significant byte
first), the same byte order used on the network. A chunk announces its length as a
4-byte field, so before you can walk a file at all you need to turn four bytes into
a number. 0x00 0x00 0x00 0x06 is 0x06, which is 6 - a track chunk whose body
is six bytes long.
This single helper is the backbone of the whole project: chunk lengths, and later the header’s own body length, are all big-endian 32-bit integers. Get it exactly right today - byte 0 shifted left 24, byte 3 not shifted at all - and every later lesson builds on it.
// big-endian: the first byte is the most significantfunc readU32(b []byte) uint32 {return uint32(b[0])<<24 | uint32(b[1])<<16 |uint32(b[2])<<8 | uint32(b[3])}