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Use the 24-hour render cache to cut costs in PHP with cURL extension

Every response carries an X-Cache header, and it is worth wiring into your logs on day one: HIT means the bytes came from the 24-hour cache — served in milliseconds and not counted against your quota. MISS means a real browser rendered the page and one render was metered.

Below is a complete, runnable PHP program using cURL extension, 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.

<?php
$body = json_encode([
    'url' => "https://your-app.com/report/42",
    'format' => "png",
    'width' => 1280,
]);

$ch = curl_init("https://snapdok.io/v1/render");
$headers = [];
curl_setopt_array($ch, [
    CURLOPT_POST => true,
    CURLOPT_POSTFIELDS => $body,
    CURLOPT_RETURNTRANSFER => true,
    CURLOPT_TIMEOUT => 90,
    CURLOPT_HTTPHEADER => [
        'Authorization: Bearer ' . getenv('SNAPDOK_KEY'),
        'Content-Type: application/json',
    ],
    CURLOPT_HEADERFUNCTION => function ($ch, $line) use (&$headers) {
        $parts = explode(':', $line, 2);
        if (count($parts) === 2) $headers[strtolower(trim($parts[0]))] = trim($parts[1]);
        return strlen($line);
    },
]);

$bytes = curl_exec($ch);
$status = curl_getinfo($ch, CURLINFO_RESPONSE_CODE);
curl_close($ch);

if ($status !== 200) {
    throw new RuntimeException("snapdok error $status: $bytes");
}
file_put_contents('shot.png', $bytes);
echo ($headers['x-cache'] ?? '?') . " // HIT = free, MISS = rendered and metered\n";

The cache key is the normalised request body: URL plus every rendering parameter. Same URL at a different width, format or scale is a different entry; alias spellings (device_scale_factor vs device_scale) are folded together first, so they share an entry. Failed renders are never cached and never metered.

Two design consequences. First, idempotent retries are safe: a queue worker that re-fires the same job inside a day costs nothing extra. Second, if you need a fresh render of a page that just changed under the same URL, vary the request — the pragmatic trick is a throwaway query parameter on the target URL (?v=deploy-id), which changes the fingerprint and forces a MISS. Rate limiting still applies to HITs (it protects the endpoint, not the renderer), so keep an eye on X-RateLimit-Remaining in tight loops.

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 cURL extension

Plain ext-curl, no Composer needed. The details that bite: CURLOPT_RETURNTRANSFER must be set or the bytes are echoed to stdout instead of returned; the HTTP status has to be read explicitly with curl_getinfo() because cURL happily "succeeds" on a 401; and response headers need a CURLOPT_HEADERFUNCTION callback if you want to check things like X-Form-Fields. file_put_contents is binary-safe in PHP — strings are byte arrays — so no "b" flag dance is needed.

Response headers worth reading

Header	Meaning
`X-Cache`	HIT or MISS.
`X-Quota-Remaining`	Metered renders left this month.
`X-RateLimit-Remaining`	Requests left in the current second.

Use the 24-hour render cache to cut costs in PHP with cURL extension

Notes for cURL extension

Response headers worth reading

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