Make XML validation optional

[Borewit]

Introduces an optional option, to disable XML validation.

Disabling the XML validation makes SVG recognition a lot faster, at the cost the SVG XML is not validated.

Difference in processing time:

With XML validation:
  Parsed small SVGs, 255 SVG strings in 124.32 milliseconds.
  Parsed large SVG, 1 SVG strings in 636.30 milliseconds.
Without XML validation:
  Parsed small SVGs, 255 SVG strings in 9.79 milliseconds.
  Parsed large SVG, 1 SVG strings in 11.00 milliseconds.

Resulting in about ~12× to ~60× times short processing time.

ToDo:

• Needs a unit test covering use cases with validation disabled

Code I used to measure performance:

import fs from 'node:fs/promises';
import path from 'node:path';
import { fileURLToPath } from 'node:url';
import isSvg from 'is-svg';
import { performance } from 'node:perf_hooks';

const __filename = fileURLToPath(import.meta.url);
const __dirname = path.dirname(__filename);

// Small SVG files, using https://github.com/hampusborgos/country-flags/tree/main/svg
const smallSvgFiles = path.resolve(__dirname, '..', 'country-flags', 'svg'); // Small SVG files
// Large SVG file, using https://upload.wikimedia.org/wikipedia/commons/c/c1/Propane_flame_contours-en.svg
const largeSvgFiles = path.resolve(__dirname, 'svg'); // Large SVG file

async function checkSvgFiles(dir, name, options) {
    try {

        const files = await fs.readdir(dir, { withFileTypes: true });
        let svgFiles = 0;

        const svgStrings = [];

        for (const file of files) {
            if (file.isFile()) {
                const filePath = path.join(dir, file.name);
                const content = await fs.readFile(filePath, 'utf8');
                svgStrings.push(content);


            }
        }

        const start = performance.now();

        for(let svgString of svgStrings) {
            if (isSvg(svgString, options)) {
                ++svgFiles;
            }
        }

        const end = performance.now();
        console.log(`  Parsed ${name}, ${svgFiles} SVG strings in ${(end - start).toFixed(2)} milliseconds.`);
    } catch (err) {
        console.error('Error reading directory:', err);
    }
}

async function runTestSuite(options) {
    await checkSvgFiles(smallSvgFiles, 'small SVGs', options);
    await checkSvgFiles(largeSvgFiles, 'large SVG', options);
}

async function runTests() {
    console.log(`With XML validation:`);
    await runTestSuite();
    console.log(`Without XML validation:`);
    await runTestSuite({xmlValidation: false});
}

runTests();

Resolves #42 (with the note that the actual degradation in performance as described in that issue, I could not reproduce, yet this is significantly reduce parsing time)

[sindresorhus]

Why do we need an option for this? The previous version was fast enough without an option to disable validation. Not clear whether it did validation or not, but it worked fine, so I would prefer to keep it simple if possible.

[Borewit]

Why do we need an option for this? The previous version was fast enough without an option to disable validation. Not clear whether it did validation or not, but it worked fine, so I would prefer to keep it simple if possible.

The previous implementation actually did perform basic XML validation. I had to explicitly enable that in @file-type/xml to maintain backward compatibility with is-svg. For reference, file-type itself does not apply XML validation.

The current implementation, even with validation enabled, is slightly faster than the previous one.

In most use cases, I believe users aren’t concerned with basic XML validation—they just want to check whether the input looks like an SVG. For large SVG files, skipping validation can make a significant difference in performance. The first issue raised since the change, was about performance, so apparently there are users who care. Well, at least one user.

[sindresorhus]

Suggested change

	export type IsSvgOptions = {
	/**
	Enable or disable XML validation, enabled by default
	*/
	xmlValidation?: boolean;
	};
	export type Options = {
	/**
	Whether to validate the SVG as proper XML.
	Turning this off can improve performance.
	@default true
	*/
	validate?: boolean;
	};

[sindresorhus]

Suggested change

	export default function isSvg(string, options) {
	export default function isSvg(string, {validate} = {}) {