Use aiohttp for the asynchronous HTTP endpoint and Playwright’s Chromium browser to render the HTML, measure its laid-out height, and create a PDF with that height as a custom page size. Return the resulting bytes with Content-Type: application/pdf. This avoids ordinary Letter or A4 pagination, but it is appropriate only when you want one tall page; for a conventional multipage document, use a standard paper size instead.
How the full-height PDF flow works
aiohttp handles the web request; it does not lay out HTML or create PDFs. For browser-rendered HTML, Playwright supplies that missing rendering step: its page.pdf() method returns a PDF buffer and accepts page dimensions with units, margins, print backgrounds, and other print settings. By default, PDF rendering uses print CSS.
The core sequence is:
- Prepare HTML at a known layout width and remove unwanted default margins.
- Render it in Chromium and wait for the content, fonts, images, and data that affect layout.
- Measure the rendered document height.
- Pass that height and the intended width to
page.pdf(), using zero margins if the page should reach its edges. - Return the bytes from an aiohttp handler as
application/pdf.
The result is a PDF page whose height follows the measured document, rather than a series of standard-size sheets. This is useful for receipts, reports, or long-page exports when one continuous page is wanted. It is not the same as a normal multipage PDF: some viewers and printers handle unusually tall pages poorly, and a long page can be awkward to navigate or print.
Install the dependencies
Install aiohttp and Playwright in the Python environment used by your app, then install Playwright’s Chromium browser:
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python -m pip install aiohttp playwright
python -m playwright install chromiumRun the browser-install command in the same deployment environment as the application. Installing the Python package alone does not install the browser binary.
Runnable aiohttp and Playwright example
This minimal application serves a fixed HTML document at /document.pdf. It keeps one Chromium process open for the application lifetime, creates an isolated browser context for each request, waits for fonts and images before measuring, and closes the context even if rendering fails.
from aiohttp import web
from playwright.async_api import async_playwright
HTML = """<!doctype html>
<html>
<head>
<meta charset="utf-8">
<style>
@page { margin: 0; }
html, body { margin: 0; padding: 0; }
body {
width: 800px;
font-family: Arial, sans-serif;
overflow-wrap: break-word;
}
main { padding: 24px; }
</style>
</head>
<body>
<main>
<h1>Example report</h1>
<p>Rendered HTML content.</p>
</main>
</body>
</html>"""
async def browser_context(app):
playwright = await async_playwright().start()
browser = await playwright.chromium.launch()
app["browser"] = browser
try:
yield
finally:
await browser.close()
await playwright.stop()
async def pdf_handler(request: web.Request) -> web.Response:
browser = request.app["browser"]
context = await browser.new_context(viewport={"width": 800, "height": 1000})
try:
page = await context.new_page()
page.set_default_timeout(15_000)
await page.set_content(HTML, wait_until="domcontentloaded")
# Wait for layout-affecting assets before measuring.
await page.evaluate("""async () => {
await document.fonts.ready;
await Promise.all(Array.from(document.images, img =>
img.decode().catch(() => undefined)
));
}""")
height_px = await page.evaluate(
"Math.ceil(document.documentElement.scrollHeight)"
)
if height_px < 1 or height_px > 20_000:
raise web.HTTPRequestEntityTooLarge(
max_size=20_000, actual_size=height_px
)
pdf_bytes = await page.pdf(
width="800px",
height=f"{height_px + 2}px",
margin={"top": "0px", "right": "0px",
"bottom": "0px", "left": "0px"},
print_background=True,
prefer_css_page_size=False,
)
finally:
await context.close()
return web.Response(
body=pdf_bytes,
content_type="application/pdf",
headers={"Content-Disposition": 'inline; filename="document.pdf"'},
)
app = web.Application()
app.cleanup_ctx.append(browser_context)
app.router.add_get("/document.pdf", pdf_handler)
web.run_app(app, host="127.0.0.1", port=8080)Start the server with python app.py (using the filename in which you saved the code), then open http://127.0.0.1:8080/document.pdf. The example caps measured height at 20,000 CSS pixels as a simple safeguard; choose a limit appropriate to your service and expected documents. If you want a download prompt rather than inline display, use an attachment disposition instead.
The example’s HTML is fixed and trusted. If you accept HTML or URLs from requesters, validate input and restrict what the browser can access; otherwise the renderer can be abused to consume resources or reach internal network services. Do not interpolate arbitrary user input into an HTML template without escaping or sanitizing it.
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Measure the document accurately
Choose a stable width first
Height depends on width: narrower content wraps into more lines and becomes taller. Set the CSS width deliberately, remove browser-default body margins, and use the same width when calling page.pdf(). If the document’s intended design is responsive, choose a viewport and width that match the output you want rather than relying on incidental defaults.
Wait for everything that changes layout
page.set_content() supports readiness milestones including commit, domcontentloaded, load, and networkidle. Pick the earliest one that guarantees the required content is available. For data-driven pages, wait for the application’s own ready selector or promise; for external images and fonts, wait for them explicitly before measuring. A font swap or late-loading image can change line wrapping and height after measurement.
networkidle is not always the best choice: pages with analytics, polling, or other persistent network activity may never reach it. A targeted readiness check is often more dependable. Conversely, a document that loads assets asynchronously can appear ready at domcontentloaded while still missing content, so do not measure solely because that event fired.
Use the measured size with units
Playwright accepts explicit page width and height with units such as pixels, inches, centimeters, or millimeters. The example measures CSS pixels and passes them as pixels, with a small two-pixel allowance to reduce clipping from fractional layout. CSS print pixels are 96 per inch, so another option is to convert a measured height to inches with height_px / 96. Whichever approach you choose, check the resulting PDF with the browser version and fonts used in deployment.
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document.documentElement.scrollHeight is a useful document-level measure, but unusual layouts may need a different root element or a more specific measurement. Fixed-position elements, overflowing children, collapsed margins, and content outside the normal document flow can make a simple height measurement differ from what you expect. Test the actual templates, especially at the bottom edge.
Print CSS, screen CSS, and pagination
By default, page.pdf() uses print media CSS. That may hide navigation, alter colors, or apply print-specific layout rules. If the screen stylesheet is the design you want to preserve, call await page.emulate_media(media="screen") before generating the PDF. Set print_background=True when background colors or images must be included; otherwise they may be omitted from print output.
For an intentionally continuous page, set explicit dimensions and zero margins, and inspect your CSS for page-break rules such as break-before or break-inside. For ordinary printable reports, omit the custom height and specify a standard paper format such as A4 or Letter instead. A standard paper size gives the browser a paginated layout and is usually a better fit for documents readers need to print or navigate page by page.
Return the PDF safely from an aiohttp endpoint
An aiohttp response can send the in-memory PDF buffer directly; there is no need to save it to disk for this pattern. Set content_type="application/pdf" so clients recognize the file. The sample uses an inline content disposition, which allows many browsers to open the document in their PDF viewer. Use an attachment disposition if your product should prompt a download.
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For a production endpoint, add request authentication if documents are private, validate the inputs that determine HTML and rendering options, and set explicit limits on input size, asset loading, rendering time, and computed page height. Log rendering failures without logging sensitive document contents. Reuse a browser process or pool rather than launching Chromium for every request, but isolate request-specific pages and contexts so cookies, storage, and state do not leak between users. Use try/finally cleanup for pages, contexts, and browser lifecycle so failures do not leave resources open.
Choose the renderer that fits the source
| Renderer | Best fit | Trade-off |
|---|---|---|
| Playwright | Modern HTML/CSS or JavaScript where browser rendering fidelity matters; supports explicit PDF dimensions, print settings, and page ranges. | Requires deploying and managing a browser runtime. Use it when browser behavior is part of the output you need. |
| WeasyPrint | Mostly static HTML and CSS that can use its Python API, HTML(...).write_pdf(...), with CSS @page rules and in-memory bytes. |
It is not the browser-JavaScript rendering route described here; choose it when the document can be rendered without that behavior. |
| ReportLab | PDFs built from programmatically placed text, tables, charts, and drawing primitives. | You define the document structure and placement rather than relying on browser HTML layout. |
There is no universal performance winner established for these approaches. Startup cost, asset handling, CSS complexity, JavaScript needs, and throughput vary with your templates and deployment, so benchmark representative documents if performance is important.
Or skip the browser setup
If your goal is to capture an existing website rather than render custom Python HTML, ScreenshotNeo offers a website screenshot API that can return screenshots or PDFs. This example is a screenshot request saved as WebP; it is not a claim that the output is a custom-height PDF. See the ScreenshotNeo API documentation for PDF options and request details.
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Troubleshooting
- The PDF is clipped at the bottom. An image, font, or application data may have finished loading after measurement, or the measured root may not include overflowing content. Wait for the relevant assets or application-ready condition, measure the element that contains the full document, and inspect the last few pixels of the output.
- The PDF is unexpectedly paginated or looks different from the browser. Print media rules or page-break CSS may be affecting the render. Check
@media print,@page, and break properties; use screen media only if that is genuinely the intended design. - Backgrounds or colors are missing. Set
print_background=Trueand check whether print styles alter or suppress those colors. - The request hangs waiting for content. A persistent connection may prevent
networkidlefrom occurring. Use an appropriate earlier milestone and wait for a specific selector, event, or asset readiness condition instead. - Chromium will not launch in deployment. Confirm that the Chromium binary was installed in the same environment as Playwright and that the runtime permits the browser’s required system dependencies. Check the launch exception in server logs.
- Requests slow down or exhaust resources under load. Rendering is resource-intensive. Reuse a browser process, limit concurrent work, cap document dimensions and input sizes, and configure timeouts. Measure representative jobs before setting operational limits.
- Untrusted input triggers internal requests or excessive work. Do not let an unrestricted renderer navigate arbitrary URLs or load arbitrary resources. Validate content and constrain outbound network access in the rendering environment.
Frequently Asked Questions
Will text in a Playwright-generated PDF remain selectable?
Yes. Playwright generates a PDF from the rendered page rather than flattening it into a screenshot image, so ordinary browser-rendered text is generally selectable. Text that is itself part of an image is not.
Can I use this for a PDF made from a URL instead of HTML I already have?
Yes. Navigate a Playwright page to the URL, wait for the page-specific content and assets you need, then measure and call page.pdf(). Treat external navigation as untrusted input unless the endpoint restricts destinations and network access.
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