feat: wait for artifact to become available

.github/workflows/test.yml

@@ -128,3 +128,81 @@ jobs:
             Write-Error "File contents of downloaded artifacts are incorrect"
         }
       shell: pwsh
+
+  # Test "wait-until-available" functionality by running two jobs, one requiring artifacts of another
+  test-wait-producer:
+    name: 'Test: wait (producer)'
+
+    strategy:
+      matrix:
+        runs-on: [ubuntu-latest, macos-latest, windows-latest]
+      fail-fast: false
+
+    runs-on: ${{ matrix.runs-on }}
+
+    steps:
+      # TODO find a better way to ensure the "consumer" job started before the artifact is produced.
+      # Maybe run the download in the background process in the same job and checking it's result after upload-artifact.
+      - run: sleep 300
+
+      # Test "wait until available"end-to-end by uploading two artifacts and then downloading them
+      - name: Create artifacts
+        run: echo "Lorem ipsum dolor sit amet" > file-A.txt
+
+      - uses: actions/upload-artifact@v4
+        with:
+          name: 'Artifact-wait-${{ matrix.runs-on }}'
+          path: file-A.txt
+
+  test-wait-consumer:
+    name: 'Test: wait (consumer)'
+
+    strategy:
+      matrix:
+        runs-on: [ubuntu-latest, macos-latest, windows-latest]
+      fail-fast: false
+
+    runs-on: ${{ matrix.runs-on }}
+
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Setup Node 20
+        uses: actions/setup-node@v4
+        with:
+          node-version: 20.x
+          cache: 'npm'
+
+      - run: npm install
+
+      - run: npm run build
+
+      # Test downloading a single artifact
+      - name: Download artifact A
+        uses: ./
+        with:
+          name: 'Artifact-wait-${{ matrix.runs-on }}'
+          path: some/new/path
+          wait-timeout: 600
+
+      # Test downloading an artifact using tilde expansion
+      - name: Download artifact A
+        uses: ./
+        with:
+          name: 'Artifact-wait-${{ matrix.runs-on }}'
+          path: ~/some/path/with/a/tilde
+          # no need for a timeout here
+
+      - name: Verify successful download
+        run: |
+          $file1 = "some/new/path/file-A.txt"
+          $file2 = "~/some/path/with/a/tilde/file-A.txt"
+          if(!(Test-Path -path $file1) -or !(Test-Path -path $file2))
+          {
+              Write-Error "Expected files do not exist"
+          }
+          if(!((Get-Content $file1) -ceq "Lorem ipsum dolor sit amet") -or !((Get-Content $file2) -ceq "Lorem ipsum dolor sit amet"))
+          {
+              Write-Error "File contents of downloaded artifacts are incorrect"
+          }
+        shell: pwsh

README.md

@@ -233,6 +233,43 @@ steps:
     run-id: 1234
 ```
 
+## Waiting for the artifact to be available
+
+You can specify `wait-timeout` (seconds) to instruct the download-artifact action to retry until the artifact is available.
+This is useful if you want to launch the job before its dependency job has finished, e.g. if the dependant requires some time-consuming steps.
+You can do this by removing the `needs` dependency and relying on the retry logic of download-artifact to fetch the artifact after it's uploaded.
+
+Beware that GitHub actions come with a limited number of runners available, so if your workflow uses up the limt on the "dependant" jobs,
+your artifact-source jobs may never be scheduled.
+
+```yaml
+jobs:
+  producer-job:
+    name: This job produces an artifact
+    steps:
+      # ... do something
+
+      # ... then upload an artifact as usual
+      - uses: actions/upload-artifact@v4
+        with:
+          name: artifact-name
+          path: path/to/artifact
+
+  dependant-job:
+    name: This job has some long running preparation that can run before the artifact is necessary
+    steps:
+      # your long-running steps come first - they're run in parallel with the `producer-job` above (given you have enouth GH actions runners available)
+      run: # e.g. install some large SDK
+
+      # then when you finally need the artifact to be downloaded
+      uses: actions/download-artifact@v4
+      with:
+        name: artifact-name
+        path: output-path
+        # wait for 300 seconds
+        wait-timeout: 300
+```
+
 ## Limitations
 
 ### Permission Loss

action.yml

@@ -32,6 +32,9 @@ inputs:
       If github-token is specified, this is the run that artifacts will be downloaded from.'
     required: false
     default: ${{ github.run_id }}
+  wait-timeout:
+    description: 'Wait for the artifact to become available (timeout in seconds)'
+    required: false
 outputs:
   download-path:
     description: 'Path of artifact download'

src/constants.ts

@@ -5,7 +5,8 @@ export enum Inputs {
   Repository = 'repository',
   RunID = 'run-id',
   Pattern = 'pattern',
-  MergeMultiple = 'merge-multiple'
+  MergeMultiple = 'merge-multiple',
+  WaitTimeout = 'wait-timeout'
 }
 
 export enum Outputs {

src/download-artifact.ts

@@ -23,6 +23,7 @@ async function run(): Promise<void> {
     repository: core.getInput(Inputs.Repository, {required: false}),
     runID: parseInt(core.getInput(Inputs.RunID, {required: false})),
     pattern: core.getInput(Inputs.Pattern, {required: false}),
+    waitTimeout: core.getInput(Inputs.WaitTimeout, {required: false}),
     mergeMultiple: core.getBooleanInput(Inputs.MergeMultiple, {required: false})
   }
 
@@ -60,10 +61,35 @@ async function run(): Promise<void> {
   if (isSingleArtifactDownload) {
     core.info(`Downloading single artifact`)
 
-    const {artifact: targetArtifact} = await artifactClient.getArtifact(
-      inputs.name,
-      options
-    )
+    const downloadFn = () => artifactClient.getArtifact(inputs.name, options)
+
+    const waitAndDownload = async <T>(action: () => T) => {
+      const waitUntil = Date.now() + parseInt(inputs.waitTimeout) * 1000
+      let lastError
+      do {
+        try {
+          return await action()
+        } catch (e) {
+          lastError = e
+          core.info(
+            'Waiting for the artifact to become available... ' +
+              `Remaining time until timeout: ${Math.max(
+                0,
+                Math.floor((waitUntil - Date.now()) / 1000)
+              )} seconds`
+          )
+          await new Promise(f => setTimeout(f, 10000))
+        }
+      } while (Date.now() < waitUntil)
+      throw Error(
+        'Waiting for the artifact has timed out. Latest error was: ' + lastError
+      )
+    }
+
+    const {artifact: targetArtifact} =
+      inputs.waitTimeout === ''
+        ? await downloadFn()
+        : await waitAndDownload(() => downloadFn())
 
     if (!targetArtifact) {
       throw new Error(`Artifact '${inputs.name}' not found`)
@@ -75,6 +101,12 @@ async function run(): Promise<void> {
 
     artifacts = [targetArtifact]
   } else {
+    if (inputs.waitTimeout !== '') {
+      core.warning(
+        `Waiting for multiple artifact (i.e. specifying non-zero wait-timeout: '${inputs.waitTimeout}') is not supported.`
+      )
+    }
+
     const listArtifactResponse = await artifactClient.listArtifacts({
       latest: true,
       ...options