Resolve content-type from file extension

README.md

@@ -59,7 +59,7 @@ jobs:
           upload_url: ${{ steps.create_release.outputs.upload_url }} # This pulls from the CREATE RELEASE step above, referencing it's ID to get its outputs object, which include a `upload_url`. See this blog post for more info: https://jasonet.co/posts/new-features-of-github-actions/#passing-data-to-future-steps 
           asset_path: ./my-artifact.zip
           asset_name: my-artifact.zip
-          asset_content_type: application/zip
+          # asset_content_type: application/zip # Optional, will be derived from file extension
 ```
 
 This will upload a release artifact to an existing release, outputting the `browser_download_url` for the asset which could be handled by a third party service, or by GitHub Actions for additional uses. For more information, see the GitHub Documentation for the [upload a release asset](https://developer.github.com/v3/repos/releases/#upload-a-release-asset) endpoint. 

package.json

@@ -23,7 +23,8 @@
   "dependencies": {
     "@actions/core": "^1.0.0",
     "@actions/exec": "^1.0.0",
-    "@actions/github": "^1.0.0"
+    "@actions/github": "^1.0.0",
+    "mime": "^2.4.4"
   },
   "devDependencies": {
     "@zeit/ncc": "^0.20.4",

src/upload-release-asset.js

@@ -1,6 +1,7 @@
 const core = require('@actions/core');
 const { GitHub } = require('@actions/github');
 const fs = require('fs');
+const mime = require('mime');
 
 async function run() {
   try {
@@ -11,13 +12,24 @@ async function run() {
     const uploadUrl = core.getInput('upload_url', { required: true });
     const assetPath = core.getInput('asset_path', { required: true });
     const assetName = core.getInput('asset_name', { required: true });
-    const assetContentType = core.getInput('asset_content_type', { required: true });
+    const assetContentType = core.getInput('asset_content_type', { required: false });
+    let contentType;
+
+    if (assetContentType) {
+      contentType = assetContentType;
+    } else {
+      contentType = mime.getType(assetPath);
+
+      if (!contentType) {
+        throw new Error('Mime type could not be resolved from file extension');
+      }
+    }
 
     // Determine content-length for header to upload asset
     const contentLength = filePath => fs.statSync(filePath).size;
 
     // Setup headers for API call, see Octokit Documentation: https://octokit.github.io/rest.js/#octokit-routes-repos-upload-release-asset for more information
-    const headers = { 'content-type': assetContentType, 'content-length': contentLength(assetPath) };
+    const headers = { 'content-type': contentType, 'content-length': contentLength(assetPath) };
 
     // Upload a release asset
     // API Documentation: https://developer.github.com/v3/repos/releases/#upload-a-release-asset

tests/upload-release-asset.test.js

@@ -96,4 +96,38 @@ describe('Upload Release Asset', () => {
     expect(core.setFailed).toHaveBeenCalledWith('Error uploading release asset');
     expect(core.setOutput).toHaveBeenCalledTimes(0);
   });
+
+  test('Mime type is resolved from file extension', async () => {
+    core.getInput = jest
+      .fn()
+      .mockReturnValueOnce('upload_url')
+      .mockReturnValueOnce('asset_path.zip')
+      .mockReturnValueOnce('asset_name');
+
+    await run();
+
+    expect(uploadReleaseAsset).toHaveBeenCalledWith({
+      url: 'upload_url',
+      headers: { 'content-type': 'application/zip', 'content-length': 527 },
+      name: 'asset_name',
+      file: content
+    });
+  });
+
+  test('Action fails if mime type could not be resolved', async () => {
+    core.getInput = jest
+      .fn()
+      .mockReturnValueOnce('upload_url')
+      .mockReturnValueOnce('asset_path')
+      .mockReturnValueOnce('asset_name');
+
+    core.setOutput = jest.fn();
+
+    core.setFailed = jest.fn();
+
+    await run();
+
+    expect(core.setFailed).toHaveBeenCalledWith('Mime type could not be resolved from file extension');
+    expect(core.setOutput).toHaveBeenCalledTimes(0);
+  });
 });