Autodesk 3D Studio

import magic
# Libmagic may struggle to uniquely identify 3DS and often outputs 'application/octet-stream'
# Checking the 4D 4D chunk header manually:
with open('model.3ds', 'rb') as f:
    is_3ds = f.read(2) == b'\x4D\x4D'
    print('Is 3DS:', is_3ds)

const fs = require('fs');
// Manually detecting the 3DS main chunk ID (0x4D4D)
const buffer = Buffer.alloc(2);
const fd = fs.openSync('model.3ds', 'r');
fs.readSync(fd, buffer, 0, 2, 0);
fs.closeSync(fd);
const is3DS = buffer[0] === 0x4D && buffer[1] === 0x4D;
console.log('Is 3DS File:', is3DS);

import (
    "bytes"
    "net/http"
)
// http.DetectContentType will generally return 'application/octet-stream'.
// You must perform a direct prefix check for the chunk ID.
// is3DS := bytes.HasPrefix(buf, []byte{0x4D, 0x4D})

$mime = mime_content_type('model.3ds');
echo $mime; // Standard setups will often resolve this to 'application/octet-stream' without custom magic byte definitions.