feat: truncate short description exceeding the byte limit (#143)

* feat: truncate short description exceeding the byte limit

* fix tests

.github/FUNDING.yml

@@ -0,0 +1 @@
+github: peter-evans

.github/dependabot.yml

@@ -4,5 +4,18 @@ updates:
     directory: "/"
     schedule:
       interval: "weekly"
+      day: "sunday"
     labels:
       - "dependencies"
+
+  - package-ecosystem: "npm"
+    directory: "/"
+    schedule:
+      interval: "weekly"
+      day: "sunday"
+    ignore:
+      - dependency-name: "*"
+        update-types: ["version-update:semver-major"]
+    labels:
+      - "dependencies"
+ 

.github/workflows/automerge-dependabot.yml

@@ -0,0 +1,13 @@
+name: Auto-merge Dependabot
+on: pull_request
+
+jobs:
+  automerge:
+    runs-on: ubuntu-latest
+    if: github.actor == 'dependabot[bot]'
+    steps:
+      - uses: peter-evans/enable-pull-request-automerge@v3
+        with:
+          token: ${{ secrets.ACTIONS_BOT_TOKEN }}
+          pull-request-number: ${{ github.event.pull_request.number }}
+          merge-method: squash

.github/workflows/ci.yml

@@ -10,6 +10,11 @@ on:
     paths-ignore:
       - 'README.md'
       - 'docs/**'
+
+permissions:
+  pull-requests: write
+  contents: write
+
 jobs:
   build:
     runs-on: ubuntu-latest
@@ -18,6 +23,7 @@ jobs:
       - uses: actions/setup-node@v3
         with:
           node-version: 16.x
+          cache: npm
       - run: npm ci
       - run: npm run build
       - run: npm run format-check
@@ -88,6 +94,7 @@ jobs:
       - name: Create Pull Request
         uses: peter-evans/create-pull-request@v4
         with:
+          token: ${{ secrets.ACTIONS_BOT_TOKEN }}
           commit-message: 'build: update distribution'
           title: Update distribution
           body: |

.github/workflows/publish-docker.yml

@@ -38,4 +38,4 @@ jobs:
           MAJOR_VERSION=$(echo $VERSION | sed -n "s/^\([0-9]*\).[0-9]*.[0-9]*$/\1/p")
           [[ ${#MAJOR_VERSION} -gt 0 ]] && docker tag $IMAGE_NAME $IMAGE_NAME:$MAJOR_VERSION
 
-          docker push $IMAGE_NAME
+          docker push $IMAGE_NAME --all-tags

.github/workflows/update-major-version.yml

@@ -0,0 +1,31 @@
+name: Update Major Version
+run-name: Update ${{ github.event.inputs.main_version }} to ${{ github.event.inputs.target }}
+
+on:
+  workflow_dispatch:
+    inputs:
+      target:
+        description: The target tag or reference
+        required: true
+      main_version:
+        type: choice
+        description: The major version tag to update
+        options:
+          - v3
+
+jobs:
+  tag:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v3
+      with:
+        token: ${{ secrets.ACTIONS_BOT_TOKEN }}
+        fetch-depth: 0
+    - name: Git config
+      run: |
+        git config user.name actions-bot
+        git config user.email actions-bot@users.noreply.github.com
+    - name: Tag new target
+      run: git tag -f ${{ github.event.inputs.main_version }} ${{ github.event.inputs.target }}
+    - name: Push new tag
+      run: git push origin ${{ github.event.inputs.main_version }} --force

README.md

@@ -25,11 +25,15 @@ This is useful if you `docker push` your images to Docker Hub. It provides an ea
 | `repository` | Docker Hub repository in the format `<namespace>/<name>`. | `github.repository` |
 | `short-description` | Docker Hub repository short description. | |
 | `readme-filepath` | Path to the repository readme. | `./README.md` |
+| `enable-url-completion` | Enables completion of relative URLs to absolute ones. See also [known Issues](#url-completion-known-issues). | `false` |
+| `image-extensions` | File extensions that will be treated as images. | `bmp,gif,jpg,jpeg,png,svg,webp` |
 
 #### Content limits
 
-DockerHub has content limits, which if exceeded will result in the content being automatically truncated.
+DockerHub has content limits.
 The readme content is limited to 25,000 bytes, and `short-description` is limited to 100 characters.
+This action truncates content to prevent the request being rejected.
+If the content has been truncated a warning will be issued in the run log.
 
 #### Specifying the file path
 
@@ -86,6 +90,7 @@ jobs:
         password: ${{ secrets.DOCKERHUB_PASSWORD }}
         repository: peterevans/dockerhub-description
         short-description: ${{ github.event.repository.description }}
+        enable-url-completion: true
 ```
 
 Updates the Docker Hub repository description whenever a new release is created.
@@ -108,6 +113,38 @@ jobs:
         short-description: ${{ github.event.repository.description }}
 ```
 
+### URL completion known Issues
+
+The completion of relative URLs has some known issues:
+
+1. Relative markdown links in inline-code and code blocks **are also converted**:
+
+   ```markdown
+   [link in inline code](#table-of-content)
+   ```
+
+   will be converted into
+
+   ```markdown
+   [link in inline code](https://github.com/peter-evans/dockerhub-description/blob/main/./README.md#table-of-content)
+   ```
+
+2. Links containing square brackets (`]`) in the text fragment **are not converted**:
+
+   ```markdown
+   [[link text with square brackets]](#table-of-content)
+   ```
+
+3. [Reference-style links/images](https://www.markdownguide.org/basic-syntax/#reference-style-links) **are not converted**.
+
+   ```markdown
+   [table-of-content][toc]
+
+   ...
+
+   [toc]: #table-of-content "Table of content"
+   ```
+
 ## Using the Docker image independently of GitHub Actions
 
 The image can be executed in other environments independently of GitHub Actions.

__test__/readme-helper.unit.test.ts

@@ -0,0 +1,335 @@
+import {completeRelativeUrls} from '../src/readme-helper'
+
+describe('complete relative urls tests', () => {
+  const GITHUB_SERVER_URL = process.env['GITHUB_SERVER_URL']
+  const GITHUB_REPOSITORY = process.env['GITHUB_REPOSITORY']
+  const GITHUB_REF_NAME = process.env['GITHUB_REF_NAME']
+
+  const README_FILEPATH = './README.md'
+  const EXPECTED_REPOSITORY_URL = `${GITHUB_SERVER_URL}/${GITHUB_REPOSITORY}`
+  const EXPECTED_BLOB_URL = `${EXPECTED_REPOSITORY_URL}/blob/${GITHUB_REF_NAME}`
+  const EXPECTED_RAW_URL = `${EXPECTED_REPOSITORY_URL}/raw/${GITHUB_REF_NAME}`
+
+  // known issues
+  test('reference-style links/image sources are not converted', async () => {
+    const content = [
+      'table-of-content][toc]',
+      '',
+      '[toc]: #table-of-content "Table of content"'
+    ].join('\n')
+    expect(completeRelativeUrls(content, README_FILEPATH, true, '')).toEqual(
+      content
+    )
+  })
+
+  test('links containing square brackets in the text fragment are not converted', async () => {
+    expect(
+      completeRelativeUrls(
+        '[[text with square brackets]](README.md)',
+        README_FILEPATH,
+        true,
+        ''
+      )
+    ).toEqual('[[text with square brackets]](README.md)')
+  })
+
+  test('links containing square brackets in the text fragment are not converted', async () => {
+    expect(
+      completeRelativeUrls('`[text](README.md)`', README_FILEPATH, true, '')
+    ).toEqual(`\`[text](${EXPECTED_BLOB_URL}/README.md)\``)
+  })
+
+  // misc
+  test('do not change content when disabled', async () => {
+    expect(
+      completeRelativeUrls('[text](README.md)', README_FILEPATH, false, '')
+    ).toEqual('[text](README.md)')
+  })
+
+  test('do not change link with mailto protocol', async () => {
+    expect(
+      completeRelativeUrls(
+        '[text](mailto:mail@example.com)',
+        README_FILEPATH,
+        true,
+        ''
+      )
+    ).toEqual(`[text](mailto:mail@example.com)`)
+  })
+
+  test('do not change link with ftp protocol', async () => {
+    expect(
+      completeRelativeUrls(
+        '[text](ftp://example.com)',
+        README_FILEPATH,
+        true,
+        ''
+      )
+    ).toEqual(`[text](ftp://example.com)`)
+  })
+
+  test('do not change link with http protocol', async () => {
+    expect(
+      completeRelativeUrls(
+        '[text](http://example.com)',
+        README_FILEPATH,
+        true,
+        ''
+      )
+    ).toEqual(`[text](http://example.com)`)
+  })
+
+  test('do not change link with https protocol', async () => {
+    expect(
+      completeRelativeUrls(
+        '[text](https://example.com)',
+        README_FILEPATH,
+        true,
+        ''
+      )
+    ).toEqual(`[text](https://example.com)`)
+  })
+
+  test('do not change link with protocol-like beginning', async () => {
+    expect(
+      completeRelativeUrls(
+        '[text](abc://example.com)',
+        README_FILEPATH,
+        true,
+        ''
+      )
+    ).toEqual(`[text](abc://example.com)`)
+  })
+
+  test('do not change image from absolute source with absolute link', async () => {
+    expect(
+      completeRelativeUrls(
+        '[![alttext](https://example.com/image.svg)](https://example.com/image.svg)',
+        README_FILEPATH,
+        true,
+        'svg'
+      )
+    ).toEqual(
+      `[![alttext](https://example.com/image.svg)](https://example.com/image.svg)`
+    )
+  })
+
+  // anchors
+  test('anchor referencing the current document', async () => {
+    expect(
+      completeRelativeUrls(
+        '[text](#relative-anchor)',
+        README_FILEPATH,
+        true,
+        ''
+      )
+    ).toEqual(`[text](${EXPECTED_BLOB_URL}/README.md#relative-anchor)`)
+  })
+
+  test('anchor referencing the current document with a title', async () => {
+    expect(
+      completeRelativeUrls(
+        '[text](#relative-anchor "the anchor (a title)")',
+        README_FILEPATH,
+        true,
+        ''
+      )
+    ).toEqual(
+      `[text](${EXPECTED_BLOB_URL}/README.md#relative-anchor "the anchor (a title)")`
+    )
+  })
+
+  test('anchor referencing the current document with a title and unicode', async () => {
+    expect(
+      completeRelativeUrls(
+        '[text with 🌬](#relative-anchor "the anchor (a title with 🌬)")',
+        README_FILEPATH,
+        true,
+        ''
+      )
+    ).toEqual(
+      `[text with 🌬](${EXPECTED_BLOB_URL}/README.md#relative-anchor "the anchor (a title with 🌬)")`
+    )
+  })
+
+  test('anchor referencing another document', async () => {
+    expect(
+      completeRelativeUrls(
+        '[text](OTHER.md#absolute-anchor)',
+        README_FILEPATH,
+        true,
+        ''
+      )
+    ).toEqual(`[text](${EXPECTED_BLOB_URL}/OTHER.md#absolute-anchor)`)
+  })
+
+  test('anchor referencing another document with a title', async () => {
+    expect(
+      completeRelativeUrls(
+        '[text](OTHER.md#absolute-anchor "the anchor (a title)")',
+        README_FILEPATH,
+        true,
+        ''
+      )
+    ).toEqual(
+      `[text](${EXPECTED_BLOB_URL}/OTHER.md#absolute-anchor "the anchor (a title)")`
+    )
+  })
+
+  test('anchor with image referencing the current document', async () => {
+    expect(
+      completeRelativeUrls(
+        '[![alttext](image.svg)](#absolute-anchor "the anchor (a title)")',
+        README_FILEPATH,
+        true,
+        'svg'
+      )
+    ).toEqual(
+      `[![alttext](${EXPECTED_RAW_URL}/image.svg)](${EXPECTED_BLOB_URL}/README.md#absolute-anchor "the anchor (a title)")`
+    )
+  })
+
+  test('anchor with image referencing another document', async () => {
+    expect(
+      completeRelativeUrls(
+        '[![alttext](image.svg)](OTHER.md#absolute-anchor "the anchor (a title)")',
+        README_FILEPATH,
+        true,
+        'svg'
+      )
+    ).toEqual(
+      `[![alttext](${EXPECTED_RAW_URL}/image.svg)](${EXPECTED_BLOB_URL}/OTHER.md#absolute-anchor "the anchor (a title)")`
+    )
+  })
+
+  // documents
+  test('text document', async () => {
+    expect(
+      completeRelativeUrls('[text](document.yaml)', README_FILEPATH, true, '')
+    ).toEqual(`[text](${EXPECTED_BLOB_URL}/document.yaml)`)
+  })
+
+  test('pdf document', async () => {
+    expect(
+      completeRelativeUrls('[text](document.pdf)', README_FILEPATH, true, '')
+    ).toEqual(`[text](${EXPECTED_BLOB_URL}/document.pdf)`)
+  })
+
+  test('document with a title', async () => {
+    expect(
+      completeRelativeUrls(
+        '[text](document.pdf "the document (a title)")',
+        README_FILEPATH,
+        true,
+        ''
+      )
+    ).toEqual(
+      `[text](${EXPECTED_BLOB_URL}/document.pdf "the document (a title)")`
+    )
+  })
+
+  test('document with a title and unicode', async () => {
+    expect(
+      completeRelativeUrls(
+        '[text with 🌬](document.pdf "the document (a title with 🌬)")',
+        README_FILEPATH,
+        true,
+        ''
+      )
+    ).toEqual(
+      `[text with 🌬](${EXPECTED_BLOB_URL}/document.pdf "the document (a title with 🌬)")`
+    )
+  })
+
+  // images
+  test('image with supported file extension', async () => {
+    expect(
+      completeRelativeUrls(
+        '![alttext](image.svg)',
+        README_FILEPATH,
+        true,
+        'svg'
+      )
+    ).toEqual(`![alttext](${EXPECTED_RAW_URL}/image.svg)`)
+  })
+
+  test('image with unsupported file extension', async () => {
+    expect(
+      completeRelativeUrls(
+        '![alttext](image.svg)',
+        README_FILEPATH,
+        true,
+        'jpeg'
+      )
+    ).toEqual(`![alttext](${EXPECTED_BLOB_URL}/image.svg)`)
+  })
+
+  test('image without alternate text', async () => {
+    expect(
+      completeRelativeUrls('![](image.svg)', README_FILEPATH, true, 'svg')
+    ).toEqual(`![](${EXPECTED_RAW_URL}/image.svg)`)
+  })
+
+  test('image with a title', async () => {
+    expect(
+      completeRelativeUrls(
+        '![alttext](image.svg "the image (a title)")',
+        README_FILEPATH,
+        true,
+        'svg'
+      )
+    ).toEqual(`![alttext](${EXPECTED_RAW_URL}/image.svg "the image (a title)")`)
+  })
+
+  test('image with relative link', async () => {
+    expect(
+      completeRelativeUrls(
+        '[![alttext](image.svg)](image.svg)',
+        README_FILEPATH,
+        true,
+        'svg'
+      )
+    ).toEqual(
+      `[![alttext](${EXPECTED_RAW_URL}/image.svg)](${EXPECTED_BLOB_URL}/image.svg)`
+    )
+  })
+
+  test('image with a title, unicode and relative link', async () => {
+    expect(
+      completeRelativeUrls(
+        '[![alttext with 🌬](image.🌬.svg "the image.🌬.svg (a title)")](image.🌬.svg)',
+        README_FILEPATH,
+        true,
+        'svg'
+      )
+    ).toEqual(
+      `[![alttext with 🌬](${EXPECTED_RAW_URL}/image.🌬.svg "the image.🌬.svg (a title)")](${EXPECTED_BLOB_URL}/image.🌬.svg)`
+    )
+  })
+
+  test('image from absolute source with relative link', async () => {
+    expect(
+      completeRelativeUrls(
+        '[![alttext](https://example.com/image.svg)](image.svg)',
+        README_FILEPATH,
+        true,
+        'svg'
+      )
+    ).toEqual(
+      `[![alttext](https://example.com/image.svg)](${EXPECTED_BLOB_URL}/image.svg)`
+    )
+  })
+
+  test('image with absolute link', async () => {
+    expect(
+      completeRelativeUrls(
+        '[![alttext](image.svg)](https://example.com/image.svg)',
+        README_FILEPATH,
+        true,
+        'svg'
+      )
+    ).toEqual(
+      `[![alttext](${EXPECTED_RAW_URL}/image.svg)](https://example.com/image.svg)`
+    )
+  })
+})

__test__/utils.unit.test.ts

@@ -0,0 +1,10 @@
+import {truncateToBytes} from '../src/utils'
+
+describe('truncate to bytes tests', () => {
+  test('unicode aware truncation to a number of bytes', async () => {
+    expect(truncateToBytes('test string to be truncated', 10)).toEqual(
+      'test strin'
+    )
+    expect(truncateToBytes('😀😁😂🤣😃😄😅', 10)).toEqual('😀😁')
+  })
+})

action.yml

@@ -18,6 +18,14 @@ inputs:
     description: >
       Path to the repository readme
       Default: `./README.md`
+  enable-url-completion:
+    description: >
+      Enables completion of relative URLs to absolute ones
+      Default: `false`
+  image-extensions:
+    description: >
+      File extensions that will be treated as images
+      Default: `bmp,gif,jpg,jpeg,png,svg,webp`
 runs:
   using: 'node16'
   main: 'dist/index.js'

jest.config.js

@@ -9,3 +9,8 @@ module.exports = {
   },
   verbose: true
 }
+process.env = Object.assign(process.env, {
+  GITHUB_SERVER_URL: 'https://github.com',
+  GITHUB_REPOSITORY: 'peter-evans/dockerhub-description',
+  GITHUB_REF_NAME: 'main'
+})

package.json

@@ -9,7 +9,7 @@
     "format": "prettier --write '**/*.ts'",
     "format-check": "prettier --check '**/*.ts'",
     "lint": "eslint src/**/*.ts",
-    "test": "jest --passWithNoTests"
+    "test": "jest"
   },
   "repository": {
     "type": "git",
@@ -27,22 +27,23 @@
   },
   "homepage": "https://github.com/peter-evans/dockerhub-description#readme",
   "dependencies": {
-    "@actions/core": "^1.6.0",
+    "@actions/core": "^1.10.0",
-    "node-fetch": "^2.6.7"
+    "node-fetch": "^2.6.9",
+    "unicode-substring": "^0.1.0"
   },
   "devDependencies": {
     "@types/jest": "^27.0.3",
-    "@types/node": "^16.11.11",
+    "@types/node": "^16.18.23",
-    "@typescript-eslint/parser": "^5.5.0",
+    "@typescript-eslint/parser": "^5.57.0",
-    "@vercel/ncc": "^0.32.0",
+    "@vercel/ncc": "^0.36.1",
-    "eslint": "^8.3.0",
+    "eslint": "^8.37.0",
-    "eslint-plugin-github": "^4.3.5",
+    "eslint-plugin-github": "^4.7.0",
-    "eslint-plugin-jest": "^25.3.0",
+    "eslint-plugin-jest": "^25.7.0",
-    "jest": "^27.4.3",
+    "jest": "^27.5.1",
-    "jest-circus": "^27.4.2",
+    "jest-circus": "^27.5.1",
     "js-yaml": "^4.1.0",
-    "prettier": "^2.5.0",
+    "prettier": "^2.8.7",
-    "ts-jest": "^27.0.7",
+    "ts-jest": "^27.1.5",
-    "typescript": "^4.5.2"
+    "typescript": "^4.9.5"
   }
 }

src/dockerhub-helper.ts

@@ -1,8 +1,6 @@
 import * as core from '@actions/core'
 import * as fetch from 'node-fetch'
 
-const DESCRIPTION_MAX_CHARS = 100
-
 export async function getToken(
   username: string,
   password: string
@@ -36,7 +34,7 @@ export async function updateRepositoryDescription(
     full_description: fullDescription
   }
   if (description) {
-    body['description'] = description.slice(0, DESCRIPTION_MAX_CHARS)
+    body['description'] = description
   }
   await fetch(`https://hub.docker.com/v2/repositories/${repository}`, {
     method: 'patch',

src/input-helper.ts

@@ -1,6 +1,5 @@
 import * as core from '@actions/core'
-
+import * as readmeHelper from './readme-helper'
-const README_FILEPATH_DEFAULT = './README.md'
 
 interface Inputs {
   username: string
@@ -8,6 +7,8 @@ interface Inputs {
   repository: string
   shortDescription: string
   readmeFilepath: string
+  enableUrlCompletion: boolean
+  imageExtensions: string
 }
 
 export function getInputs(): Inputs {
@@ -16,7 +17,9 @@ export function getInputs(): Inputs {
     password: core.getInput('password'),
     repository: core.getInput('repository'),
     shortDescription: core.getInput('short-description'),
-    readmeFilepath: core.getInput('readme-filepath')
+    readmeFilepath: core.getInput('readme-filepath'),
+    enableUrlCompletion: Boolean(core.getInput('enable-url-completion')),
+    imageExtensions: core.getInput('image-extensions')
   }
 
   // Environment variable input alternatives and their aliases
@@ -50,16 +53,31 @@ export function getInputs(): Inputs {
     inputs.readmeFilepath = process.env['README_FILEPATH']
   }
 
+  if (!inputs.enableUrlCompletion && process.env['ENABLE_URL_COMPLETION']) {
+    inputs.enableUrlCompletion = Boolean(process.env['ENABLE_URL_COMPLETION'])
+  }
+
+  if (!inputs.imageExtensions && process.env['IMAGE_EXTENSIONS']) {
+    inputs.imageExtensions = process.env['IMAGE_EXTENSIONS']
+  }
+
   // Set defaults
   if (!inputs.readmeFilepath) {
-    inputs.readmeFilepath = README_FILEPATH_DEFAULT
+    inputs.readmeFilepath = readmeHelper.README_FILEPATH_DEFAULT
+  }
+  if (!inputs.enableUrlCompletion) {
+    inputs.enableUrlCompletion = readmeHelper.ENABLE_URL_COMPLETION_DEFAULT
+  }
+  if (!inputs.imageExtensions) {
+    inputs.imageExtensions = readmeHelper.IMAGE_EXTENSIONS_DEFAULT
   }
   if (!inputs.repository && process.env['GITHUB_REPOSITORY']) {
     inputs.repository = process.env['GITHUB_REPOSITORY']
   }
 
-  // Docker repositories must be all lower case
+  // Enforce lower case, where needed
   inputs.repository = inputs.repository.toLowerCase()
+  inputs.imageExtensions = inputs.imageExtensions.toLowerCase()
 
   return inputs
 }

src/main.ts

@@ -1,9 +1,12 @@
 import * as core from '@actions/core'
 import * as inputHelper from './input-helper'
 import * as dockerhubHelper from './dockerhub-helper'
-import * as fs from 'fs'
+import * as readmeHelper from './readme-helper'
+import * as utils from './utils'
 import {inspect} from 'util'
 
+const SHORT_DESCRIPTION_MAX_BYTES = 100
+
 async function run(): Promise<void> {
   try {
     const inputs = inputHelper.getInputs()
@@ -12,9 +15,24 @@ async function run(): Promise<void> {
     inputHelper.validateInputs(inputs)
 
     // Fetch the readme content
-    const readmeContent = await fs.promises.readFile(inputs.readmeFilepath, {
+    core.info('Reading description source file')
-      encoding: 'utf8'
+    const readmeContent = await readmeHelper.getReadmeContent(
-    })
+      inputs.readmeFilepath,
+      inputs.enableUrlCompletion,
+      inputs.imageExtensions
+    )
+    core.debug(readmeContent)
+
+    // Truncate the short description if it is too long
+    const truncatedShortDescription = utils.truncateToBytes(
+      inputs.shortDescription,
+      SHORT_DESCRIPTION_MAX_BYTES
+    )
+    if (truncatedShortDescription.length !== inputs.shortDescription.length) {
+      core.warning(
+        `The short description exceeds DockerHub's limit and has been truncated to ${SHORT_DESCRIPTION_MAX_BYTES} bytes.`
+      )
+    }
 
     // Acquire a token for the Docker Hub API
     core.info('Acquiring token')
@@ -31,9 +49,9 @@ async function run(): Promise<void> {
       readmeContent
     )
     core.info('Request successful')
-  } catch (error: any) {
+  } catch (error) {
     core.debug(inspect(error))
-    core.setFailed(error.message)
+    core.setFailed(utils.getErrorMessage(error))
   }
 }
 

src/readme-helper.ts

@@ -0,0 +1,185 @@
+import * as core from '@actions/core'
+import * as fs from 'fs'
+import * as utils from './utils'
+
+export const README_FILEPATH_DEFAULT = './README.md'
+export const IMAGE_EXTENSIONS_DEFAULT = 'bmp,gif,jpg,jpeg,png,svg,webp'
+export const ENABLE_URL_COMPLETION_DEFAULT = false
+
+const TITLE_REGEX = `(?: +"[^"]+")?`
+const REPOSITORY_URL = `${process.env['GITHUB_SERVER_URL']}/${process.env['GITHUB_REPOSITORY']}`
+const BLOB_PREFIX = `${REPOSITORY_URL}/blob/${process.env['GITHUB_REF_NAME']}/`
+const RAW_PREFIX = `${REPOSITORY_URL}/raw/${process.env['GITHUB_REF_NAME']}/`
+
+const MAX_BYTES = 25000
+
+type Rule = {
+  /**
+   * all left of the relative url belonging to the markdown image/link
+   */
+  left: RegExp
+  /**
+   * relative url
+   */
+  url: RegExp
+  /**
+   * part to prefix the relative url with (excluding github repository url)
+   */
+  absUrlPrefix: string
+}
+
+export async function getReadmeContent(
+  readmeFilepath: string,
+  enableUrlCompletion: boolean,
+  imageExtensions: string
+): Promise<string> {
+  // Fetch the readme content
+  let readmeContent = await fs.promises.readFile(readmeFilepath, {
+    encoding: 'utf8'
+  })
+
+  readmeContent = completeRelativeUrls(
+    readmeContent,
+    readmeFilepath,
+    enableUrlCompletion,
+    imageExtensions
+  )
+
+  const truncatedReadmeContent = utils.truncateToBytes(readmeContent, MAX_BYTES)
+  if (truncatedReadmeContent.length !== readmeContent.length) {
+    core.warning(
+      `The README content exceeds DockerHub's limit and has been truncated to ${MAX_BYTES} bytes.`
+    )
+  }
+
+  return truncatedReadmeContent
+}
+
+export function completeRelativeUrls(
+  readmeContent: string,
+  readmeFilepath: string,
+  enableUrlCompletion: boolean,
+  imageExtensions: string
+): string {
+  if (enableUrlCompletion) {
+    readmeFilepath = readmeFilepath.replace(/^[.][/]/, '')
+
+    // Make relative urls absolute
+    const rules = [
+      ...getRelativeReadmeAnchorsRules(readmeFilepath),
+      ...getRelativeImageUrlRules(imageExtensions),
+      ...getRelativeUrlRules()
+    ]
+
+    readmeContent = applyRules(rules, readmeContent)
+  }
+
+  return readmeContent
+}
+
+function applyRules(rules: Rule[], readmeContent: string): string {
+  rules.forEach(rule => {
+    const combinedRegex = `${rule.left.source}[(]${rule.url.source}[)]`
+    core.debug(`rule: ${combinedRegex}`)
+
+    const replacement = `$<left>(${rule.absUrlPrefix}$<url>)`
+    core.debug(`replacement: ${replacement}`)
+
+    readmeContent = readmeContent.replace(
+      new RegExp(combinedRegex, 'giu'),
+      replacement
+    )
+  })
+
+  return readmeContent
+}
+
+// has to be applied first to avoid wrong results
+function getRelativeReadmeAnchorsRules(readmeFilepath: string): Rule[] {
+  const prefix = `${BLOB_PREFIX}${readmeFilepath}`
+
+  // matches e.g.:
+  //    #table-of-content
+  //    #table-of-content "the anchor (a title)"
+  const url = new RegExp(`(?<url>#[^)]+${TITLE_REGEX})`)
+
+  const rules: Rule[] = [
+    // matches e.g.:
+    //    [#table-of-content](#table-of-content)
+    //    [#table-of-content](#table-of-content "the anchor (a title)")
+    {
+      left: /(?<left>\[[^\]]+\])/,
+      url: url,
+      absUrlPrefix: prefix
+    },
+
+    // matches e.g.:
+    //    [![media/image.svg](media/image.svg)](#table-of-content)
+    //    [![media/image.svg](media/image.svg "title a")](#table-of-content "title b")
+    {
+      left: /(?<left>\[!\[[^\]]*\]\([^)]+\)\])/,
+      url: url,
+      absUrlPrefix: prefix
+    }
+  ]
+
+  return rules
+}
+
+function getRelativeImageUrlRules(imageExtensions: string): Rule[] {
+  const extensionsRegex = imageExtensions.replace(/,/g, '|')
+  // matches e.g.:
+  //    media/image.svg
+  //    media/image.svg "with title"
+  const url = new RegExp(
+    `(?<url>[^:)]+[.](?:${extensionsRegex})${TITLE_REGEX})`
+  )
+
+  const rules: Rule[] = [
+    // matches e.g.:
+    //    ![media/image.svg](media/image.svg)
+    //    ![media/image.svg](media/image.svg "with title")
+    {
+      left: /(?<left>!\[[^\]]*\])/,
+      url: url,
+      absUrlPrefix: RAW_PREFIX
+    }
+  ]
+
+  return rules
+}
+
+function getRelativeUrlRules(): Rule[] {
+  // matches e.g.:
+  //    .releaserc.yaml
+  //    README.md#table-of-content "title b"
+  //    .releaserc.yaml "the .releaserc.yaml file (a title)"
+  const url = new RegExp(`(?<url>[^:)]+${TITLE_REGEX})`)
+
+  const rules: Rule[] = [
+    // matches e.g.:
+    //    [.releaserc.yaml](.releaserc.yaml)
+    //    [.releaserc.yaml](.releaserc.yaml "the .releaserc.yaml file (a title)")
+    {
+      left: /(?<left>\[[^\]]+\])/,
+      url: url,
+      absUrlPrefix: BLOB_PREFIX
+    },
+
+    // matches e.g.:
+    //    [![media/image.svg](media/image.svg)](media/image.svg)
+    //    [![media/image.svg](media/image.svg)](README.md#table-of-content "title b")
+    //    [![media/image.svg](media/image.svg "title a")](media/image.svg)
+    //    [![media/image.svg](media/image.svg "title a")](media/image.svg "title b")
+    //    [![media/image.svg](media/image.svg "title a")](README.md#table-of-content "title b")
+    {
+      left: new RegExp(
+        `(?<left>\\[!\\[[^\\]]*\\]\\([^)]+${TITLE_REGEX}\\)\\])`
+      ),
+      url: url,
+      absUrlPrefix: BLOB_PREFIX
+    }
+  ]
+
+  return rules
+}

src/utils.ts

@@ -0,0 +1,14 @@
+import unicodeSubstring = require('unicode-substring')
+
+export function getErrorMessage(error: unknown) {
+  if (error instanceof Error) return error.message
+  return String(error)
+}
+
+export function truncateToBytes(s: string, n: number): string {
+  let len = n
+  while (Buffer.byteLength(s) > n) {
+    s = unicodeSubstring(s, 0, len--)
+  }
+  return s
+}