astro/dist/assets/utils/inferSourceFormat.js

Astro is a modern site builder with web best practices, performance, and DX front-of-mind.

import { removeQueryString } from "@astrojs/internal-helpers/path";
import { DEFAULT_OUTPUT_FORMAT } from "../consts.js";
const DATA_PREFIX = "data:";
/**
* Infer the image format from a source path or URL.
*
* For `data:` URIs the MIME is read up to the first `;` or `,` (whichever comes first),
* so both `data:image/svg+xml;base64,...` and `data:image/svg+xml,<svg>...` work.
* `image/svg+xml` normalizes to `svg`; otherwise the subtype after the slash is returned.
*
* Returns undefined when the format cannot be determined.
*/
export function inferSourceFormat(src) {
	// data: URIs encode the MIME type directly, e.g. "data:image/svg+xml;base64,..."
	// or "data:image/svg+xml,<svg>...</svg>" (no media-type parameter).
	if (src.startsWith(DATA_PREFIX)) {
		const sepIndex = src.indexOf(";");
		const commaIndex = src.indexOf(",");
		const mimeEnd = sepIndex === -1 ? commaIndex : commaIndex === -1 ? sepIndex : Math.min(sepIndex, commaIndex);
		if (mimeEnd === -1) return undefined;
		const mime = src.slice(DATA_PREFIX.length, mimeEnd);
		if (mime === "image/svg+xml") return "svg";
		const sub = mime.split("/")[1];
		return sub || undefined;
	}
	// For regular URLs/paths, extract the extension from the last path segment only.
	// Looking at the whole string would treat dots in hostnames (`example.com`) as extensions.
	try {
		const cleanSrc = removeQueryString(src).split("#")[0];
		const lastSlash = cleanSrc.lastIndexOf("/");
		const basename = lastSlash === -1 ? cleanSrc : cleanSrc.slice(lastSlash + 1);
		const lastDot = basename.lastIndexOf(".");
		if (lastDot === -1) return undefined;
		return basename.slice(lastDot + 1).toLowerCase();
	} catch {
		return undefined;
	}
}
export function resolveDefaultOutputFormat(sourceFormat) {
	return sourceFormat === "svg" ? "svg" : DEFAULT_OUTPUT_FORMAT;
}