Ruby LaTeX to PDF API

require 'net/http'
require 'json'
require 'uri'

API_KEY = ENV.fetch('FORMATEX_API_KEY')
API_URL = URI.parse('https://api.formatex.io/v1/compile/sync')

def compile_latex(source, engine: 'pdflatex')
  http          = Net::HTTP.new(API_URL.host, API_URL.port)
  http.use_ssl  = true

  request                  = Net::HTTP::Post.new(API_URL.path)
  request['Authorization'] = "Bearer #{API_KEY}"
  request['Content-Type']  = 'application/json'
  request.body             = { source: source, engine: engine }.to_json

  response = http.request(request)

  raise "API error #{response.code}: #{response.body}" unless response.code == '200'

  response.body
end

latex = <<~LATEX
  \documentclass{article}
  \usepackage{amsmath}
  \begin{document}
  Hello from Ruby! $E = mc^2$
  \end{document}
LATEX

pdf = compile_latex(latex)
File.binwrite('output.pdf', pdf)
puts 'PDF saved to output.pdf'

# app/controllers/documents_controller.rb
require 'net/http'
require 'json'
require 'uri'

class DocumentsController < ApplicationController
  FORMATEX_URL = URI.parse('https://api.formatex.io/v1/compile/sync').freeze

  # POST /documents/compile
  def compile
    source = params.require(:source)
    engine = params.fetch(:engine, 'pdflatex')

    pdf_bytes = call_formatex(source, engine)

    send_data pdf_bytes,
              type:        'application/pdf',
              disposition: 'inline',
              filename:    'document.pdf'
  rescue => e
    render json: { error: e.message }, status: :unprocessable_entity
  end

  private

  def call_formatex(source, engine)
    http           = Net::HTTP.new(FORMATEX_URL.host, FORMATEX_URL.port)
    http.use_ssl   = true
    http.open_timeout = 5
    http.read_timeout = 60

    req                  = Net::HTTP::Post.new(FORMATEX_URL.path)
    req['Authorization'] = "Bearer #{ENV.fetch('FORMATEX_API_KEY')}"
    req['Content-Type']  = 'application/json'
    req.body             = { source: source, engine: engine }.to_json

    res = http.request(req)
    raise "FormaTeX error #{res.code}: #{res.body}" unless res.code == '200'

    res.body
  end
end