feat: Support thread_ts parameter to post the new message as a thread…

… reply to another

Closes slackapi#187

README.md

@@ -209,6 +209,65 @@ Please note that **the message update step does not accept a channel name.** Set
     SLACK_BOT_TOKEN: ${{ secrets.SLACK_BOT_TOKEN }}
 ```
 
+#### Post as a reply to a message
+
+If you would like to log the real-time updates, you can post new messages as thread replies to the message your build job posted in the subsequent steps. In order to do this, the steps after the first message posting can have `thread-ts: ${{ steps.slack.outputs.ts }}` in their settings. With this, the step creates a new message in the thread of the already posted channel message.
+
+Please note that **the reply message step does not accept a channel name.** Set a channel ID for the steps for the actions that update messages.
+
+```yaml
+- id: slack
+  uses: slackapi/[email protected]
+  with:
+    # The following message update step does not accept a channel name.
+    # Setting a channel ID here for consistency is highly recommended.
+    channel-id: "CHANNEL_ID"
+    payload: |
+      {
+        "text": "Deployment started (In Progress)",
+        "attachments": [
+          {
+            "pretext": "Deployment started",
+            "color": "dbab09",
+            "fields": [
+              {
+                "title": "Status",
+                "short": true,
+                "value": "In Progress"
+              }
+            ]
+          }
+        ]
+      }
+  env:
+    SLACK_BOT_TOKEN: ${{ secrets.SLACK_BOT_TOKEN }}
+- uses: slackapi/[email protected]
+  with:
+    # Unlike the step posting a new message, this step does not accept a channel name.
+    # Please use a channel ID, not a name here.
+    channel-id: "CHANNEL_ID"
+    thread-ts: ${{ steps.slack.outputs.ts }}
+    payload: |
+      {
+        "text": "Deployment finished (Completed)",
+        "attachments": [
+          {
+            "pretext": "Deployment finished",
+            "color": "28a745",
+            "fields": [
+              {
+                "title": "Status",
+                "short": true,
+                "value": "Completed"
+              }
+            ]
+          }
+        ]
+      }
+  env:
+    SLACK_BOT_TOKEN: ${{ secrets.SLACK_BOT_TOKEN }}
+```
+
 ### Technique 3: Slack Incoming Webhook
 
 This approach allows your GitHub Actions job to post a message to a Slack channel or direct message by utilizing [Incoming Webhooks](https://api.slack.com/messaging/webhooks).

action.yml

@@ -20,6 +20,9 @@ inputs:
   update-ts: # The timestamp of a previous message posted to update it instead of posting a new message
     description: 'The timestamp of a previous message posted. It will update the existing message instead of posting a new message'
     required: false
+  thread-ts: # The timestamp of a previous message posted to post a new message as a thread reply to the existing message
+    description: 'The timestamp of a previous message posted. It will post the new message as a thread reply to the existing message'
+    required: false
 outputs:
   time: # id of output
     description: 'The time'

src/slack-send.js

@@ -76,14 +76,25 @@ module.exports = async function slackSend(core) {
       }
 
       if (message.length > 0 || payload) {
-        const ts = core.getInput('update-ts');
+        const updateTs = core.getInput('update-ts');
+        const threadTs = core.getInput('thread-ts');
         await Promise.all(channelIds.split(',').map(async (channelId) => {
-          if (ts) {
-          // update message
-            webResponse = await web.chat.update({ ts, channel: channelId.trim(), text: message, ...(payload || {}) });
+          if (updateTs) {
+            // update message
+            webResponse = await web.chat.update({
+              ts: updateTs,
+              channel: channelId.trim(),
+              text: message,
+              ...(payload || {}),
+            });
           } else {
-          // post message
-            webResponse = await web.chat.postMessage({ channel: channelId.trim(), text: message, ...(payload || {}) });
+            // post message
+            webResponse = await web.chat.postMessage({
+              thread_ts: threadTs,
+              channel: channelId.trim(),
+              text: message,
+              ...(payload || {}),
+            });
           }
         }));
       } else {

test/slack-send-test.js

@@ -68,6 +68,22 @@ describe('slack-send', () => {
         assert.equal(chatArgs.text, 'who let the dogs out?', 'Correct message provided to postMessage');
       });
 
+      it('should send a reply-message using the postMessage API', async () => {
+        fakeCore.getInput.withArgs('slack-message').returns('who let the dogs out?');
+        fakeCore.getInput.withArgs('channel-id').returns('C123456');
+        fakeCore.getInput.withArgs('thread-ts').returns('123123');
+        await slackSend(fakeCore);
+        assert.equal(fakeCore.setOutput.firstCall.firstArg, 'ts', 'Output name set to ts');
+        assert.equal(fakeCore.setOutput.secondCall.firstArg, 'thread_ts', 'Output name set to thread_ts');
+        assert(fakeCore.setOutput.secondCall.lastArg.length > 0, 'Time output a non-zero-length string');
+        assert.equal(fakeCore.setOutput.lastCall.firstArg, 'time', 'Output name set to time');
+        assert(fakeCore.setOutput.lastCall.lastArg.length > 0, 'Time output a non-zero-length string');
+        const chatArgs = ChatStub.postMessage.lastCall.firstArg;
+        assert.equal(chatArgs.channel, 'C123456', 'Correct channel provided to postMessage');
+        assert.equal(chatArgs.thread_ts, '123123', 'Correct thread_ts provided to postMessage');
+        assert.equal(chatArgs.text, 'who let the dogs out?', 'Correct message provided to postMessage');
+      });
+
       it('should send a message using the update API', async () => {
         fakeCore.getInput.withArgs('slack-message').returns('who let the dogs out?');
         fakeCore.getInput.withArgs('channel-id').returns('C123456');