fix: normalize relative img src (#514)

fix #450

Author: brc-dd

src/node/markdown/markdown.ts

@@ -11,6 +11,7 @@ import { hoistPlugin } from './plugins/hoist'
 import { preWrapperPlugin } from './plugins/preWrapper'
 import { linkPlugin } from './plugins/link'
 import { headingPlugin } from './plugins/headings'
+import { imagePlugin } from './plugins/image'
 import { Header } from '../shared'
 import anchor from 'markdown-it-anchor'
 import attrs from 'markdown-it-attrs'
@@ -67,6 +68,7 @@ export const createMarkdownRenderer = (
     .use(hoistPlugin)
     .use(containerPlugin)
     .use(headingPlugin)
+    .use(imagePlugin)
     .use(
       linkPlugin,
       {

src/node/markdown/plugins/image.ts

@@ -0,0 +1,15 @@
+// markdown-it plugin for normalizing image source
+
+import MarkdownIt from 'markdown-it'
+import { EXTERNAL_URL_RE } from '../../shared'
+
+export const imagePlugin = (md: MarkdownIt) => {
+  md.renderer.rules.image = (tokens, idx, options, env, self) => {
+    const token = tokens[idx]
+    const url = token.attrGet('src')
+    if (url && !EXTERNAL_URL_RE.test(url) && !/^\.?\//.test(url)) {
+      token.attrSet('src', './' + url)
+    }
+    return self.renderToken(tokens, idx, options)
+  }
+}