fix: only detect file: protocol links

fixes #1

README.md

@@ -21,9 +21,32 @@
 
 **markdownlint-rule-relative-links** is a [markdownlint](https://github.com/DavidAnson/markdownlint) custom rule to validate relative links.
 
-It ensures that relative links that start with `./` or `../` (or not starting with external protocols like `http://` or `https://`) are working and not "dead" which means that it exists in the file system of the project that uses `markdownlint`.
+It ensures that relative links (using `file:` protocol) are working and not "dead" which means that it exists in the file system of the project that uses `markdownlint`.
 
-Related links:
+### Example
+
+File structure:
+
+```txt
+├── abc.txt
+└── awesome.md
+```
+
+With `awesome.md` content:
+
+```md
+[abc](./abc.txt)
+
+[Dead link](./dead.txt)
+```
+
+Running `markdownlint-cli2` with `markdownlint-rule-relative-links` will output:
+
+```sh
+awesome.md:3 relative-links Relative links should be valid [Link "./dead.txt" is dead]
+```
+
+### Related links
 
 - [DavidAnson/markdownlint#253](https://github.com/DavidAnson/markdownlint/issues/253)
 - [DavidAnson/markdownlint#121](https://github.com/DavidAnson/markdownlint/issues/121)

src/index.js

@@ -40,14 +40,6 @@ const addError = (onError, lineNumber, detail, context, range, fixInfo) => {
   })
 }
 
-const EXTERNAL_PROTOCOLS = new Set([
-  'http:',
-  'https:',
-  'mailto:',
-  'tel:',
-  'ftp:'
-])
-
 const customRule = {
   names: ['relative-links'],
   description: 'Relative links should be valid',
@@ -79,11 +71,8 @@ const customRule = {
         if (hrefSrc != null) {
           const url = new URL(hrefSrc, pathToFileURL(params.name))
           url.hash = ''
-          const isRelative =
-            hrefSrc.startsWith('./') ||
-            hrefSrc.startsWith('../') ||
-            !EXTERNAL_PROTOCOLS.has(url.protocol)
-          if (isRelative && !fs.existsSync(url.pathname)) {
+          const isRelative = url.protocol === 'file:'
+          if (isRelative && !fs.existsSync(url)) {
             const detail = `Link "${hrefSrc}" is dead`
             addError(onError, lineNumber, detail)
           }

test/fixtures/Valid.md

@@ -3,3 +3,9 @@
 [basic.js](../basic.test.js)
 
 ![Image](./image.png)
+
+[External https link](https://example.com/)
+
+[External https link 2](https:./external.https)
+
+[External ftp link](ftp:./external.ftp)