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Add page numbers and headers to a PDF in Ruby with Net::HTTP

A multi-page PDF that leaves the printer without page numbers gets shuffled exactly once before someone asks for them. pdf_footer (and its twin pdf_header) take a small HTML template that Chromium prints on every page of the PDF — and inside it, <span class="pageNumber"></span> and friends are substituted with live values at print time.

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/report/42",
    format: "pdf",
    pdf_footer: "<div style=\"font-size:10px;width:100%;text-align:center;color:#555;\">Page <span class=\"pageNumber\"></span> of <span class=\"totalPages\"></span></div>",
})
  http.request(req)
end

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

File.binwrite("numbered.pdf", res.body)

Five class names do the substitution: pageNumber, totalPages, date, title (the page's <title>) and url. Two styling rules save an hour of confusion: set an explicit font-size, because the print engine's default is unreadably small — a template that "does not show up" is almost always just tiny — and set width:100% on the wrapper if you want centering or space-between layouts to work.

Setting a header or footer reserves a 60px margin on that edge for it; a request with neither keeps the exact zero-margin output PDFs have always had, so adding a footer to one report cannot shift the layout of any other. The templates are ignored for png/jpeg, and also when pdf_forms is on — the fillable-forms pipeline measures field positions against a zero-margin page, and a margin would misplace every field. Both templates change the cache fingerprint, so a numbered and an unnumbered render of the same URL are separate cache entries.

Same endpoint, one more trick: if the page you are rendering has a form on it, adding "pdf_forms": true to a PDF render brings it back with real, fillable AcroForm fields — a PDF people can type into, not a picture of one. How that works.

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

Header	Meaning
`X-Cache`	Each distinct header/footer template is its own cache entry.
`X-Quota-Remaining`	Metered renders left this month.

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

Add page numbers and headers to a PDF in Ruby with Net::HTTP

Notes for Net::HTTP

Response headers worth reading

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