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import { countBy } from 'lodash';
import { __ } from '~/locale';
import {
getBaseURL,
relativePathToAbsolute,
setUrlParams,
joinPaths,
} from '~/lib/utils/url_utility';
import { darkModeEnabled } from '~/lib/utils/color_utils';
import { setAttributes, isElementVisible } from '~/lib/utils/dom_utils';
import { createAlert, VARIANT_WARNING } from '~/flash';
import { unrestrictedPages } from './constants';
// Renders diagrams and flowcharts from text using Mermaid in any element with the
// `js-render-mermaid` class.
//
// Example markup:
//
// <pre class="js-render-mermaid">
// graph TD;
// A-- > B;
// A-- > C;
// B-- > D;
// C-- > D;
// </pre>
//
const SANDBOX_FRAME_PATH = '/-/sandbox/mermaid';
// This is an arbitrary number; Can be iterated upon when suitable.
export const MAX_CHAR_LIMIT = 2000;
// Max # of mermaid blocks that can be rendered in a page.
export const MAX_MERMAID_BLOCK_LIMIT = 50;
// Max # of `&` allowed in Chaining of links syntax
const MAX_CHAINING_OF_LINKS_LIMIT = 30;
export const BUFFER_IFRAME_HEIGHT = 10;
export const SANDBOX_ATTRIBUTES = 'allow-scripts allow-popups';
const ALERT_CONTAINER_CLASS = 'mermaid-alert-container';
export const LAZY_ALERT_SHOWN_CLASS = 'lazy-alert-shown';
// Keep a map of mermaid blocks we've already rendered.
const elsProcessingMap = new WeakMap();
let renderedMermaidBlocks = 0;
/**
* Determines whether a given Mermaid diagram is visible.
*
* @param {Element} el The Mermaid DOM node
* @returns
*/
const isVisibleMermaid = (el) => el.closest('details') === null && isElementVisible(el);
function shouldLazyLoadMermaidBlock(source) {
/**
* If source contains `&`, which means that it might
* contain Chaining of links a new syntax in Mermaid.
*/
if (countBy(source)['&'] > MAX_CHAINING_OF_LINKS_LIMIT) {
return true;
}
return false;
}
function fixElementSource(el) {
// Mermaid doesn't like `<br />` tags, so collapse all like tags into `<br>`, which is parsed correctly.
const source = el.textContent?.replace(/<br\s*\/>/g, '<br>');
return { source };
}
export function getSandboxFrameSrc() {
const path = joinPaths(gon.relative_url_root || '', SANDBOX_FRAME_PATH);
if (!darkModeEnabled()) {
return path;
}
const absoluteUrl = relativePathToAbsolute(path, getBaseURL());
return setUrlParams({ darkMode: darkModeEnabled() }, absoluteUrl);
}
function renderMermaidEl(el, source) {
const iframeEl = document.createElement('iframe');
setAttributes(iframeEl, {
src: getSandboxFrameSrc(),
sandbox: SANDBOX_ATTRIBUTES,
frameBorder: 0,
scrolling: 'no',
width: '100%',
});
const wrapper = document.createElement('div');
wrapper.appendChild(iframeEl);
// Hide the markdown but keep it "visible enough" to allow Copy-as-GFM
// https://gitlab.com/gitlab-org/gitlab/-/merge_requests/83202
el.closest('pre').classList.add('gl-sr-only');
el.closest('pre').parentNode.appendChild(wrapper);
// Event Listeners
iframeEl.addEventListener('load', () => {
// Potential risk associated with '*' discussed in below thread
// https://gitlab.com/gitlab-org/gitlab/-/merge_requests/74414#note_735183398
iframeEl.contentWindow.postMessage(source, '*');
});
window.addEventListener(
'message',
(event) => {
if (event.origin !== 'null' || event.source !== iframeEl.contentWindow) {
return;
}
const { h } = event.data;
iframeEl.height = `${h + BUFFER_IFRAME_HEIGHT}px`;
},
false,
);
}
function renderMermaids(els) {
if (!els.length) return;
const pageName = document.querySelector('body').dataset.page;
// A diagram may have been truncated in search results which will cause errors, so abort the render.
if (pageName === 'search:show') return;
let renderedChars = 0;
els.forEach((el) => {
// Skipping all the elements which we've already queued in requestIdleCallback
if (elsProcessingMap.has(el)) {
return;
}
const { source } = fixElementSource(el);
/**
* Restrict the rendering to a certain amount of character
* and mermaid blocks to prevent mermaidjs from hanging
* up the entire thread and causing a DoS.
*/
if (
!unrestrictedPages.includes(pageName) &&
((source && source.length > MAX_CHAR_LIMIT) ||
renderedChars > MAX_CHAR_LIMIT ||
renderedMermaidBlocks >= MAX_MERMAID_BLOCK_LIMIT ||
shouldLazyLoadMermaidBlock(source))
) {
const parent = el.parentNode;
if (!parent.classList.contains(LAZY_ALERT_SHOWN_CLASS)) {
const alertContainer = document.createElement('div');
alertContainer.classList.add(ALERT_CONTAINER_CLASS);
alertContainer.classList.add('gl-mb-5');
parent.after(alertContainer);
createAlert({
message: __(
'Warning: Displaying this diagram might cause performance issues on this page.',
),
variant: VARIANT_WARNING,
parent: parent.parentNode,
containerSelector: `.${ALERT_CONTAINER_CLASS}`,
primaryButton: {
text: __('Display'),
clickHandler: () => {
alertContainer.remove();
renderMermaidEl(el, source);
},
},
});
parent.classList.add(LAZY_ALERT_SHOWN_CLASS);
}
return;
}
renderedChars += source.length;
renderedMermaidBlocks += 1;
const requestId = window.requestIdleCallback(() => {
renderMermaidEl(el, source);
});
elsProcessingMap.set(el, requestId);
});
}
export default function renderMermaid(els) {
if (!els.length) return;
const visibleMermaids = [];
const hiddenMermaids = [];
for (const el of els) {
if (isVisibleMermaid(el)) {
visibleMermaids.push(el);
} else {
hiddenMermaids.push(el);
}
}
renderMermaids(visibleMermaids);
hiddenMermaids.forEach((el) => {
el.closest('details')?.addEventListener(
'toggle',
({ target: details }) => {
if (details.open) {
renderMermaids([...details.querySelectorAll('.js-render-mermaid')]);
}
},
{
once: true,
},
);
});
}
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