tool.medowar.de/bimi-check.php

<?php
declare(strict_types=1);

/**
 * Looks up a BIMI record (default._bimi.domain), parses its tags, fetches and
 * validates the referenced SVG logo, and checks that DMARC is at enforcement —
 * the precondition mailbox providers require before they will show a BIMI logo.
 */
class BimiChecker
{
    /** Hard cap on how much of the logo/certificate we download. */
    private const MAX_FETCH_BYTES = 256 * 1024;

    /** BIMI logos must be SVG Tiny Portable/Secure and stay under this size. */
    private const MAX_SVG_BYTES = 32 * 1024;

    public function check(string $domain, string $selector): array
    {
        $fqdn = $selector . '._bimi.' . $domain;
        $report = [
            'domain'   => $domain,
            'selector' => $selector,
            'fqdn'     => $fqdn,
            'record'   => null,
            'tags'     => [],
            'logo'     => null,
            'dmarc'    => self::checkDmarc($domain),
            'errors'   => [],
            'warnings' => [],
            'valid'    => false,
        ];

        $record = self::getTxtRecord($fqdn);
        if ($record === null) {
            $report['errors'][] = 'No BIMI TXT record found at ' . $fqdn . '.';
            return $report;
        }
        $report['record'] = $record;

        $tags = self::parseTags($record);
        $report['tags'] = $tags;

        $version = strtoupper($tags['v'] ?? '');
        if ($version === '') {
            $report['errors'][] = 'Missing v= tag — a BIMI record must start with v=BIMI1.';
        } elseif ($version !== 'BIMI1') {
            $report['errors'][] = 'Unexpected v= tag: "' . ($tags['v'] ?? '') . '" (expected "BIMI1").';
        }

        $logoUrl = trim($tags['l'] ?? '');
        if ($logoUrl === '') {
            // An empty l= is a valid "opt out / decline" signal, but usually a mistake.
            $report['warnings'][] = 'l= tag is empty — this domain declines to publish a logo.';
        } elseif (!self::isHttpsUrl($logoUrl)) {
            $report['errors'][] = 'l= must be an https:// URL. Got: ' . $logoUrl;
        } else {
            $report['logo'] = self::inspectLogo($logoUrl);
            foreach ($report['logo']['errors'] as $e) {
                $report['errors'][] = $e;
            }
            foreach ($report['logo']['warnings'] as $w) {
                $report['warnings'][] = $w;
            }
        }

        $authUrl = trim($tags['a'] ?? '');
        if ($authUrl === '') {
            $report['warnings'][] = 'No a= tag — Gmail and Apple Mail require a Verified Mark Certificate (VMC/CMC) to show the logo.';
        } elseif (!self::isHttpsUrl($authUrl)) {
            $report['errors'][] = 'a= must be an https:// URL pointing to a PEM certificate. Got: ' . $authUrl;
        }

        // BIMI only renders when DMARC is enforced. Fold that into the verdict.
        $dmarc = $report['dmarc'];
        if (!$dmarc['found']) {
            $report['errors'][] = 'No DMARC record found — BIMI requires an enforced DMARC policy.';
        } elseif (!$dmarc['enforced']) {
            $report['errors'][] = 'DMARC policy is p=' . ($dmarc['policy'] ?? 'none')
                . ' — BIMI requires p=quarantine or p=reject.';
        } elseif ($dmarc['pct'] !== null && $dmarc['pct'] < 100) {
            $report['warnings'][] = 'DMARC pct=' . $dmarc['pct'] . ' — BIMI needs pct=100 (or no pct tag) to apply to all mail.';
        }

        $report['valid'] = empty($report['errors']);
        return $report;
    }

    /** @return array<string,string> */
    private static function parseTags(string $record): array
    {
        $tags = [];
        foreach (explode(';', $record) as $part) {
            $part = trim($part);
            if ($part === '' || !str_contains($part, '=')) {
                continue;
            }
            [$key, $value] = explode('=', $part, 2);
            $tags[strtolower(trim($key))] = trim($value);
        }
        return $tags;
    }

    /** Downloads the SVG logo and checks the SVG Tiny PS constraints BIMI imposes. */
    private static function inspectLogo(string $url): array
    {
        $logo = [
            'url'      => $url,
            'bytes'    => null,
            'mime'     => null,
            'title'    => null,
            'errors'   => [],
            'warnings' => [],
        ];

        $fetch = self::fetch($url);
        if ($fetch['error'] !== null) {
            $logo['errors'][] = 'Could not fetch logo (' . $url . '): ' . $fetch['error'];
            return $logo;
        }

        $body = $fetch['body'];
        $logo['bytes'] = strlen($body);
        $logo['mime']  = $fetch['mime'];

        if ($logo['bytes'] > self::MAX_SVG_BYTES) {
            $logo['errors'][] = sprintf(
                'Logo is %.1f KB — BIMI requires the SVG to be under 32 KB.',
                $logo['bytes'] / 1024
            );
        }

        if (!str_contains($body, '<svg')) {
            $logo['errors'][] = 'Logo does not look like an SVG file (no <svg> element found).';
            return $logo;
        }

        // Pull the root <svg> attributes to check the required Tiny PS profile.
        if (preg_match('/<svg\b[^>]*>/is', $body, $m)) {
            $svgTag = $m[0];
            if (!preg_match('/baseProfile\s*=\s*["\']tiny-ps["\']/i', $svgTag)) {
                $logo['errors'][] = 'SVG is missing baseProfile="tiny-ps" — BIMI requires the SVG Tiny Portable/Secure profile.';
            }
            if (!preg_match('/version\s*=\s*["\']1\.2["\']/i', $svgTag)) {
                $logo['warnings'][] = 'SVG root should declare version="1.2" for the Tiny profile.';
            }
            if (preg_match('/\b(x|y|width|height)\s*=/i', $svgTag)) {
                $logo['warnings'][] = 'SVG root should not have x/y/width/height — use a square viewBox instead.';
            }
            if (!preg_match('/viewBox\s*=\s*["\']\s*0\s+0\s+(\d+(?:\.\d+)?)\s+(\d+(?:\.\d+)?)\s*["\']/i', $svgTag, $vb)) {
                $logo['warnings'][] = 'SVG should have a square viewBox starting at "0 0".';
            } elseif (abs((float) $vb[1] - (float) $vb[2]) > 0.01) {
                $logo['warnings'][] = 'viewBox is not square (' . $vb[1] . '×' . $vb[2] . ') — BIMI logos must be square.';
            }
        }

        // Forbidden constructs in the Tiny PS profile.
        if (preg_match('/<script\b/i', $body)) {
            $logo['errors'][] = 'SVG contains a <script> element — scripts are forbidden in BIMI logos.';
        }
        if (preg_match('/<(a|image|use|foreignObject)\b/i', $body, $m)) {
            $logo['errors'][] = 'SVG contains a <' . strtolower($m[1]) . '> element, which is not allowed in the Tiny PS profile.';
        }
        if (preg_match('/xlink:href|(?<![a-z])href\s*=/i', $body)) {
            $logo['warnings'][] = 'SVG references external content (href) — external references are not permitted.';
        }
        if (preg_match('/<(animate|animateTransform|animateMotion|set)\b/i', $body)) {
            $logo['warnings'][] = 'SVG contains animation elements — animation is not allowed.';
        }

        if (preg_match('/<title>(.*?)<\/title>/is', $body, $m)) {
            $logo['title'] = trim(html_entity_decode(strip_tags($m[1])));
        } else {
            $logo['warnings'][] = 'SVG has no <title> element — recommended so the logo has an accessible name.';
        }

        return $logo;
    }

    /** Reads the domain's DMARC record and decides whether it is at enforcement. */
    private static function checkDmarc(string $domain): array
    {
        $record = self::getTxtRecord('_dmarc.' . $domain);
        $out = ['found' => false, 'record' => null, 'policy' => null, 'pct' => null, 'enforced' => false];
        if ($record === null || stripos($record, 'v=DMARC1') === false) {
            return $out;
        }
        $out['found']  = true;
        $out['record'] = $record;

        $tags = self::parseTags($record);
        $out['policy'] = strtolower($tags['p'] ?? 'none');
        if (isset($tags['pct']) && is_numeric($tags['pct'])) {
            $out['pct'] = (int) $tags['pct'];
        }
        $out['enforced'] = in_array($out['policy'], ['quarantine', 'reject'], true);
        return $out;
    }

    private static function isHttpsUrl(string $url): bool
    {
        return (bool) preg_match('#^https://[^\s/]+#i', $url);
    }

    private static function fetch(string $url): array
    {
        $ctx = stream_context_create([
            'http' => [
                'method'        => 'GET',
                'timeout'       => 8,
                'user_agent'    => 'medowar-bimi-check/1.0',
                'max_redirects' => 3,
                'ignore_errors' => true,
            ],
            'ssl' => [
                'verify_peer'      => true,
                'verify_peer_name' => true,
            ],
        ]);

        $stream = @fopen($url, 'rb', false, $ctx);
        if ($stream === false) {
            return ['body' => '', 'mime' => null, 'error' => 'connection failed or TLS error'];
        }

        $meta   = stream_get_meta_data($stream);
        $status = self::statusFromHeaders($meta['wrapper_data'] ?? []);
        $mime   = self::headerValue($meta['wrapper_data'] ?? [], 'content-type');

        $body = @stream_get_contents($stream, self::MAX_FETCH_BYTES);
        fclose($stream);

        if ($status !== null && $status >= 400) {
            return ['body' => '', 'mime' => $mime, 'error' => 'HTTP ' . $status];
        }
        if ($body === false || $body === '') {
            return ['body' => '', 'mime' => $mime, 'error' => 'empty response'];
        }
        return ['body' => $body, 'mime' => $mime, 'error' => null];
    }

    /** @param array<int,string> $headers */
    private static function statusFromHeaders(array $headers): ?int
    {
        foreach ($headers as $h) {
            if (preg_match('#^HTTP/\S+\s+(\d{3})#', $h, $m)) {
                $status = (int) $m[1];
            }
        }
        return $status ?? null;
    }

    /** @param array<int,string> $headers */
    private static function headerValue(array $headers, string $name): ?string
    {
        foreach ($headers as $h) {
            if (stripos($h, $name . ':') === 0) {
                return trim(substr($h, strlen($name) + 1));
            }
        }
        return null;
    }

    private static function getTxtRecord(string $fqdn): ?string
    {
        foreach ((@dns_get_record($fqdn, DNS_TXT) ?: []) as $r) {
            $txt = $r['txt'] ?? (isset($r['entries']) ? implode('', $r['entries']) : '');
            if ($txt !== '') {
                return $txt;
            }
        }
        return null;
    }
}

$domain   = trim((string) ($_GET['domain'] ?? ''));
$selector = trim((string) ($_GET['selector'] ?? ''));
$report   = null;
$inputError = null;

if ($selector === '') {
    $selector = 'default';
}

if ($domain !== '') {
    // Accept a bare hostname; strip scheme/path if a URL was pasted.
    $domain = preg_replace('#^\w+://#', '', $domain);
    $domain = explode('/', $domain)[0];
    $domain = strtolower(trim($domain));

    if (!preg_match('/^(?=.{1,253}$)([a-z0-9](-?[a-z0-9])*\.)+[a-z]{2,}$/', $domain)) {
        $inputError = 'Please enter a valid domain name (e.g. example.com).';
    } elseif (!preg_match('/^[a-zA-Z0-9]([a-zA-Z0-9._-]{0,127})?$/', $selector)) {
        $inputError = 'Please enter a valid selector (letters, digits, dot, dash, underscore).';
    } else {
        $report = (new BimiChecker())->check($domain, $selector);
    }
}

$h = 'htmlspecialchars';
?>
<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>BIMI Record Checker</title>
    <style>
        body {
            font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif;
            max-width: 1000px;
            margin: 40px auto;
            padding: 0 20px;
            background: #f5f5f5;
            color: #333;
        }
        h1 { color: #333; }
        .info { background: #e3f2fd; padding: 15px; border-radius: 5px; margin-bottom: 20px; }
        form.lookup { margin-bottom: 20px; display: flex; gap: 10px; flex-wrap: wrap; }
        input[type=text] {
            flex: 1; min-width: 180px; padding: 10px; font-size: 15px;
            border: 1px solid #ccc; border-radius: 5px;
        }
        input[name=selector] { flex: 0 0 200px; min-width: 140px; }
        .btn {
            display: inline-block; padding: 10px 20px; background: #2196F3; color: white;
            text-decoration: none; border-radius: 5px; border: none; cursor: pointer; font-size: 15px;
        }
        .btn:hover { background: #1976D2; }
        .error { background: #ffebee; color: #c62828; padding: 10px; border-radius: 5px; margin: 10px 0; }
        .warning {
            background: #fff8e1; color: #e65100; padding: 10px; border-radius: 5px;
            margin: 10px 0; border-left: 5px solid #ff9800;
        }
        .verdict {
            display: flex; align-items: center; gap: 12px; padding: 16px 20px; border-radius: 6px;
            font-size: 17px; font-weight: 600; margin: 20px 0 10px;
        }
        .verdict.ok   { background: #e8f5e9; color: #2e7d32; border-left: 6px solid #43a047; }
        .verdict.fail { background: #ffebee; color: #c62828; border-left: 6px solid #e53935; }
        .record {
            background: #263238; color: #aed581; padding: 8px 12px; border-radius: 4px;
            font-family: monospace; font-size: 13px; word-break: break-all; margin: 10px 0;
        }
        .logo-preview {
            display: flex; align-items: center; gap: 16px; background: white; padding: 14px;
            border-radius: 6px; box-shadow: 0 1px 3px rgba(0,0,0,0.1); margin: 12px 0;
        }
        .logo-preview img {
            width: 64px; height: 64px; border-radius: 50%; border: 1px solid #eee;
            background: #fafafa; object-fit: contain;
        }
        .logo-preview .meta { font-size: 13px; color: #555; }
        table { width: 100%; border-collapse: collapse; background: white; box-shadow: 0 1px 3px rgba(0,0,0,0.1); margin-top: 10px; }
        th, td { padding: 8px 12px; text-align: left; border-bottom: 1px solid #eee; font-size: 13px; }
        th { background: #fafafa; color: #555; font-weight: 600; }
        td.mono, .mono { font-family: monospace; word-break: break-all; }
        h2 { color: #333; margin-top: 30px; }
        .empty { text-align: center; color: #999; padding: 40px; }
    </style>
</head>
<body>
    <h1>🎨 BIMI Record Checker</h1>

    <div class="info">
        Looks up the <strong>BIMI</strong> TXT record for a domain
        (<code>selector._bimi.domain</code>, default selector <code>default</code>),
        parses its tags, fetches the SVG logo to validate the SVG&nbsp;Tiny&nbsp;PS profile,
        and confirms <strong>DMARC</strong> is enforced — the precondition for a logo to display.
    </div>

    <form class="lookup" method="GET">
        <input type="text" name="domain" placeholder="example.com" value="<?= $h($domain) ?>" autofocus>
        <input type="text" name="selector" placeholder="selector (default)" value="<?= $h($report ? $report['selector'] : ($_GET['selector'] ?? '')) ?>">
        <button type="submit" class="btn">🔍 Check BIMI</button>
    </form>

    <?php if ($inputError): ?>
        <div class="error"><?= $h($inputError) ?></div>
    <?php endif; ?>

    <?php if ($report !== null): ?>
        <?php if ($report['valid']): ?>
            <div class="verdict ok">✅ <?= $h($report['fqdn']) ?> — valid, displayable BIMI record.</div>
        <?php else: ?>
            <div class="verdict fail">❌ <?= $h($report['fqdn']) ?> — BIMI record is missing or will not display.</div>
        <?php endif; ?>

        <?php foreach ($report['errors'] as $e): ?>
            <div class="error">❌ <?= $h($e) ?></div>
        <?php endforeach; ?>
        <?php foreach ($report['warnings'] as $w): ?>
            <div class="warning">⚠️ <?= $h($w) ?></div>
        <?php endforeach; ?>

        <?php if ($report['record'] !== null): ?>
            <h2>BIMI record</h2>
            <div class="record"><?= $h($report['record']) ?></div>

            <?php if ($report['logo'] !== null && $report['logo']['bytes'] !== null): ?>
                <div class="logo-preview">
                    <img src="<?= $h($report['logo']['url']) ?>" alt="BIMI logo" loading="lazy">
                    <div class="meta">
                        <strong><?= $h($report['logo']['title'] ?? 'Logo') ?></strong><br>
                        <?= number_format($report['logo']['bytes'] / 1024, 1) ?> KB
                        <?= $report['logo']['mime'] ? '· ' . $h($report['logo']['mime']) : '' ?><br>
                        <span class="mono"><?= $h($report['logo']['url']) ?></span>
                    </div>
                </div>
            <?php endif; ?>

            <table>
                <thead><tr><th>Tag</th><th>Meaning</th><th>Value</th></tr></thead>
                <tbody>
                    <?php
                    $meanings = ['v' => 'Version', 'l' => 'Logo URL (SVG)', 'a' => 'Authority (VMC/CMC)'];
                    foreach ($report['tags'] as $tag => $value):
                    ?>
                        <tr>
                            <td class="mono"><?= $h($tag) ?></td>
                            <td><?= $h($meanings[$tag] ?? '—') ?></td>
                            <td class="mono"><?= $value === '' ? '<em>(empty)</em>' : $h($value) ?></td>
                        </tr>
                    <?php endforeach; ?>
                </tbody>
            </table>
        <?php endif; ?>

        <h2>DMARC prerequisite</h2>
        <?php if ($report['dmarc']['found']): ?>
            <div class="record"><?= $h($report['dmarc']['record']) ?></div>
            <p style="font-size:14px;color:#555;">
                Policy <strong>p=<?= $h($report['dmarc']['policy'] ?? 'none') ?></strong><?php
                    if ($report['dmarc']['pct'] !== null) echo ', pct=' . (int) $report['dmarc']['pct'];
                ?> —
                <?= $report['dmarc']['enforced'] ? 'meets the BIMI enforcement requirement.' : 'not enforced; BIMI will not display.' ?>
            </p>
        <?php else: ?>
            <div class="empty">No DMARC record found at _dmarc.<?= $h($report['domain']) ?>.</div>
        <?php endif; ?>
    <?php endif; ?>
</body>
</html>