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Wait for a JavaScript-rendered form, then make it fillable in Ruby with Net::HTTP

React, Vue and friends render forms after the initial HTML arrives — so a too-eager render captures a spinner where the form should be, and a pdf_forms pass finds zero controls to convert. The fix is two request parameters, no code changes on your site: "wait_until": "networkidle" holds the render until the page stops fetching, and delay adds a fixed settling pause after that.

Below is a complete, runnable Ruby program using Net::HTTP, no third-party dependency needed. It reads your API key from the SNAPDOK_KEY environment variable — free keys take about thirty seconds and need no card.

require "json"
require "net/http"
require "uri"

uri = URI("https://snapdok.io/v1/render")

res = Net::HTTP.start(uri.host, uri.port, use_ssl: true, read_timeout: 90) do |http|
  req = Net::HTTP::Post.new(uri)
  req["Authorization"] = "Bearer #{ENV.fetch("SNAPDOK_KEY")}"
  req["Content-Type"] = "application/json"
  req.body = JSON.generate({
    url: "https://your-app.com/apply",
    format: "pdf",
    pdf_forms: true,
    wait_until: "networkidle",
    delay: 500,
})
  http.request(req)
end

raise "snapdok error #{res.code}: #{res.body}" unless res.is_a?(Net::HTTPSuccess)

File.binwrite("spa-form.pdf", res.body)
puts "#{res["X-Form-Fields"]}  # 0 here usually means you rendered too early"

wait_until accepts four stages, in order of patience: commit (bytes started arriving), domcontentloaded, load (the default), and networkidle (no network requests for a quiet period — the right choice for SPAs that hydrate after load). delay is an extra wait in milliseconds after that stage is reached: use a few hundred ms for forms that animate in, or that fetch their field list from an API after mount.

The feedback loop is X-Form-Fields: if it comes back 0 on a page you know has a form, the form was not in the DOM yet (or it is inside an iframe, which is never converted). Bump delay, or check the form is rendered server-side. Raise timeout (navigation cap, ms) for genuinely slow apps rather than looping retries — a failed render is never charged, but it is slower than one patient render.

Notes for Net::HTTP

Stdlib only — no gems. The traps Net::HTTP is famous for, all handled in the sample: TLS is not automatic (set use_ssl: true or you will POST in the clear to port 80 and get a redirect); the default read_timeout of 60 s is close enough to real render times that raising it is wise; and the response body is a binary-ready String, but write it with File.binwrite — plain File.write on Windows would mangle line-ending bytes in the PDF. Check is_a?(Net::HTTPSuccess): Net::HTTP never raises on HTTP error statuses.

Response headers worth reading

HeaderMeaning
X-Form-Fields0 on a form page = rendered before the form existed.
X-Demo-Duration-MsHow long the render took (demo route).
X-CacheCached responses replay instantly.

Full parameter reference: the docs. Hard numbers on caps and timeouts: limits.

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