Experiment in parsing the extra data that Facebook sends in its User Agent string

parse_fb_ua.js

const fbUserAgentPattern = /\]|(?:[\;\[](?=FB|$]))/;

const parseFbUserAgentOptions = (input) => input.split(fbUserAgentPattern)
  .filter(text => text.startsWith('FB'))
  .reduce(text => {
    const [ name, value ] = text.split('/');
    return { name, value };
  }, result);

const prettifyFbUserAgentOptions = (fbUserAgentOptions) => fbUserAgentOptions.map(({name, value}) => name + ': ' + value).join('\n');

const fb = parseFbUserAgentOptions('Mozilla/5.0 (iPhone; CPU iPhone OS 12_3_1 like Mac OS X) AppleWebKit/605.1.15 (KHTML, like Gecko) Mobile/15E148 [FBAN/FBIOS;FBAV/224.0.0.50.109;FBBV/157638993;FBDV/iPhone9,3;FBMD/iPhone;FBSN/iOS;FBSV/12.3.1;FBSS/2;FBCR/Tele2;FBID/phone;FBLC/sv_SE;FBOP/5;FBRV/0]');
const messenger = parseFbUserAgentOptions('Mozilla/5.0 (iPhone; CPU iPhone OS 12_3_1 like Mac OS X) AppleWebKit/605.1.15 (KHTML, like Gecko) Mobile/15E148 [FBAN/MessengerForiOS;FBDV/iPhone9,3;FBMD/iPhone;FBSN/iOS;FBSV/12.3.1;FBSS/2;FBCR/Tele2;FBID/phone;FBLC/sv_SE;FBOP/5]');

console.log('\Facebook iOS:\n');
console.log(prettifyFbUserAgentOptions(fb));
console.log('\nMessenger iOS:\n');
console.log(prettifyFbUserAgentOptions(messenger));

result.md

Output

Facebook iOS:

• FBAN: FBIOS
• FBAV: 224.0.0.50.109
• FBBV: 157638993
• FBDV: iPhone9,3
• FBMD: iPhone
• FBSN: iOS
• FBSV: 12.3.1
• FBSS: 2
• FBCR: Tele2
• FBID: phone
• FBLC: sv_SE
• FBOP: 5
• FBRV: 0

Messenger iOS:

• FBAN: MessengerForiOS
• FBDV: iPhone9,3
• FBMD: iPhone
• FBSN: iOS
• FBSV: 12.3.1
• FBSS: 2
• FBCR: Tele2
• FBID: phone
• FBLC: sv_SE
• FBOP: 5

Interpretations / guesses

• FBAN: App ideNtifier? F+M
• FBAV: App Version? F
• FBBV: Build Version? F
• FBDV: Device Version? F+M
• FBMD: Machine Device? F+M
• FBSN: System ideNtifier? F+M
• FBSV: System Version? F+M
• FBSS: ? "System *"? F+M (2 in both cases)
• FBCR: Carrier? F+M
• FBLC: Language Code? F+M
• FBOP: ? F+M (5 in both cases)
• FBRV: ? F
• FBID: ? (Type of device? Tablet? Phone? etc)

work_by_others.md

• https://mpulp.mobi/2012/01/17/funky-user-agent-on-facebook-iphone-app/