JPEG Network Graphics

import magic
# Libmagic natively detects the JNG magic bytes
print(magic.from_file('image.jng', mime=True)) # Outputs 'image/x-jng'

const fs = require('fs');
// Manually detecting the JNG 8-byte signature
const buffer = Buffer.alloc(8);
const fd = fs.openSync('image.jng', 'r');
fs.readSync(fd, buffer, 0, 8, 0);
fs.closeSync(fd);
const isJNG = buffer[0] === 0x8B && buffer[1] === 0x4A && buffer[2] === 0x4E && buffer[3] === 0x47;
console.log('Is JPEG Network Graphics:', isJNG);

import (
    "bytes"
    "net/http"
)
// Native Go HTTP detection does not recognize JNG. 
// You must explicitly check the signature:
// isJNG := bytes.HasPrefix(buf, []byte{0x8B, 0x4A, 0x4E, 0x47, 0x0D, 0x0A, 0x1A, 0x0A})

$mime = mime_content_type('image.jng');
echo $mime; // Standard setups will often resolve this correctly to 'image/x-jng' via the system magic file