html2pdf

Render an HTML document into a PDF. The source is an HTML string or an http(s) URL (downloaded automatically); output is the PDF as raw bytes.

API

local html2pdf = require("html2pdf")

local pdf, err = html2pdf.render({ html = "<h1>Hello</h1>" })
if err ~= nil then
    return nil, err            -- err.kind / err.message / tostring(err)
end

html2pdf.render(request [, options]) -> pdf, err

• request — a table with exactly one source:
  • { html = "<…>" } — a UTF-8 HTML document string, or
  • { url = "https://…" } — an http(s) URL, downloaded automatically.
• options — an optional table (unknown keys are rejected):
  • page_size — "A4" (default), "Letter", "Legal", "A3", "A5".
  • landscape — boolean, defaults to false.
  • margin_mm — page margin in millimetres, a non-negative number, defaults to 10.
• pdf — the rendered document as PDF bytes (a binary Lua string), or nil on failure.
• err — nil on success, otherwise a structured error.

html2pdf.new(runtime) -> module

Advanced: build an instance with injected runtime dependencies ({ funcs?, http_client? }). See RFC 0001.

Errors

Every failure returns a structured error table with message, kind, and retryable. kind is one of invalid_input, download_failed, render_failed, internal. tostring(err) and string concatenation yield the message.

Limits and safety

• Inputs (the HTML string or downloaded body) are capped at 128 MiB.
• URL fetches use an http(s)-only scheme allow-list, a 30s timeout, and a download size cap; private-IP targets are blocked by the runtime.

Rendering engine

HTML and CSS are rendered by an embedded litehtml engine, with PDF output produced by libharu, both compiled into a single wasm32-wasip2 component. The engine supports real HTML and CSS including flexbox, tables, backgrounds, borders, and list markers.

• Fonts — DejaVu LGC (Sans, Serif, Mono; regular/bold/italic) are embedded in the component, so sans-serif, serif and monospace render out of the box. Text is UTF-8, so Latin accents and common symbols (e.g. á ç ã é € —) render correctly.
• Images — data: URIs in JPEG are drawn; other formats (including PNG) and remote http(s) image references are not resolved.
• Not supported — JavaScript, CSS Grid, and full browser-grade CSS fidelity. This module targets document-grade HTML/CSS (reports, invoices, certificates), not arbitrary web pages.
• Pagination — a single page is produced per call; content taller than the page is clipped.