feat: add thread message posting (#445)

* feat: add thread message posting

fixes #378 

This enables the slack-orb to post to threads. 
See README updates for details.

README.md

@@ -63,6 +63,51 @@ A comma separated list of regex matchable branch or tag names. Notifications wil
 
 See [usage examples](https://circleci.com/developer/orbs/orb/circleci/slack#usage-examples).
 
+## Thread Messages
+
+Post replies in threads with a special parameter `thread_id`. Including this parameter in the `notify` command reference stores the id of the message in a small portion of bytes in cache. Any subsequent invocation of the command with the same value for `thread_id` will post a reply to the initial message in a thread. Example:
+
+```yaml
+- slack/notify:
+      event: always
+      channel: engineering
+      thread_id: testing
+      custom: |
+        {
+          "blocks": [
+            {
+              "type": "section",
+              "fields": [
+                {
+                  "type": "plain_text",
+                  "text": "*Tests started.*",
+                  "emoji": true
+                }
+              ]
+            }
+          ]
+        }
+- slack/notify:
+      event: always
+      channel: engineering
+      thread_id: testing
+      custom: |
+        {
+          "blocks": [
+            {
+              "type": "section",
+              "fields": [
+                {
+                  "type": "plain_text",
+                  "text": "*Tests finished.*",
+                  "emoji": true
+                }
+              ]
+            }
+          ]
+        }
+```
+
 ---
 
 ## FAQ

src/commands/notify.yml

@@ -77,6 +77,14 @@ parameters:
     type: string
     default: Slack - Sending Notification
     description: Specify a custom step name for this command, if desired
+  thread_id:
+    type: string
+    default: ""
+    description: |
+      When set, the first `notify` with a given `thread_id` will appear as a regular slack message.
+      Any subsequent `notify` usage with the same identifier will be posted within the initial message's thread.
+      `thread_id` should be set to any arbitrary string to help you identify different threads. See examples for more information.
+      Enabling thread messages with this parameter implies using a very small amount of cacheing: ~200 B
 steps:
   - run:
       when: on_fail
@@ -88,6 +96,14 @@ steps:
       name: Slack - Detecting Job Status (PASS)
       command: |
         echo 'export CCI_STATUS="pass"' > /tmp/SLACK_JOB_STATUS
+  - when:
+      condition:
+        not:
+          equal: [ "", <<parameters.thread_id>> ]
+      steps:
+        - restore_cache:
+            keys:
+              - cache-<< parameters.thread_id >>-{{ .Environment.CIRCLE_WORKFLOW_ID }}
   - run:
       when: always
       name: << parameters.step_name >>
@@ -103,6 +119,7 @@ steps:
         SLACK_PARAM_IGNORE_ERRORS: "<<parameters.ignore_errors>>"
         SLACK_PARAM_DEBUG: "<<parameters.debug>>"
         SLACK_PARAM_CIRCLECI_HOST: "<<parameters.circleci_host>>"
+        SLACK_PARAM_THREAD: "<<parameters.thread_id>>"
         SLACK_SCRIPT_NOTIFY: "<<include(scripts/notify.sh)>>"
         SLACK_SCRIPT_UTILS: "<<include(scripts/utils.sh)>>"
         # import pre-built templates using the orb-pack local script include.
@@ -111,3 +128,12 @@ steps:
         basic_on_hold_1: "<<include(message_templates/basic_on_hold_1.json)>>"
         basic_success_1: "<<include(message_templates/basic_success_1.json)>>"
       command: <<include(scripts/main.sh)>>
+  - when:
+      condition:
+        not:
+          equal: [ "", <<parameters.thread_id>> ]
+      steps:
+        - save_cache:
+            key: cache-<< parameters.thread_id >>-{{ .Environment.CIRCLE_WORKFLOW_ID }}
+            paths:
+              - /tmp/SLACK_THREAD_INFO

src/examples/notify_thread.yml

@@ -0,0 +1,100 @@
+description: |
+  Send a Slack notification to a channel and use the same message to post replies in a thread.
+  `thread_id` parameter holds a thread identifier in case there are multiple notifications in the pipeline
+usage:
+  version: 2.1
+  orbs:
+    slack: circleci/[email protected]
+    node: circleci/node:4.1
+  jobs:
+    test:
+      executor:
+        name: node/default
+      steps:
+        - slack/notify:
+            event: always
+            channel: engineering
+            thread_id: testing
+            custom: |
+              {
+                "blocks": [
+                  {
+                    "type": "section",
+                    "fields": [
+                      {
+                        "type": "plain_text",
+                        "text": "*Tests started.*",
+                        "emoji": true
+                      }
+                    ]
+                  }
+                ]
+              }
+        - slack/notify:
+            event: always
+            channel: engineering
+            thread_id: testing
+            custom: |
+              {
+                "blocks": [
+                  {
+                    "type": "section",
+                    "fields": [
+                      {
+                        "type": "plain_text",
+                        "text": "*Tests finished.*",
+                        "emoji": true
+                      }
+                    ]
+                  }
+                ]
+              }
+    deploy:
+      executor:
+        name: node/default
+      steps:
+        - slack/notify:
+            event: always
+            channel: engineering
+            thread_id: deployment
+            custom: |
+              {
+                "blocks": [
+                  {
+                    "type": "section",
+                    "fields": [
+                      {
+                        "type": "plain_text",
+                        "text": "*Deployment started.*",
+                        "emoji": true
+                      }
+                    ]
+                  }
+                ]
+              }
+        - slack/notify:
+            event: always
+            channel: engineering
+            thread_id: deployment
+            custom: |
+              {
+                "blocks": [
+                  {
+                    "type": "section",
+                    "fields": [
+                      {
+                        "type": "plain_text",
+                        "text": "*Deployment finished.*",
+                        "emoji": true
+                      }
+                    ]
+                  }
+                ]
+              }
+  workflows:
+    deploy_and_notify:
+      jobs:
+        - deploy
+        - test:
+            requires:
+              - deploy

src/scripts/notify.sh

@@ -41,10 +41,34 @@ BuildMessageBody() {
 PostToSlack() {
     # Post once per channel listed by the channel parameter
     #    The channel must be modified in SLACK_MSG_BODY
+    #    If thread_id is used a file containing the initial message `thread_ts` per each channel is persisted
+    #    /tmp/SLACK_THREAD_INFO/<channel_name> will contain:
+    #    <thread_id>=12345.12345
 
     # shellcheck disable=SC2001
     for i in $(eval echo \""$SLACK_PARAM_CHANNEL"\" | sed "s/,/ /g")
     do
+        # replace non-alpha
+        SLACK_PARAM_THREAD=$(echo "$SLACK_PARAM_THREAD" | sed -r 's/[^[:alpha:][:digit:].]/_/g')
+        # check if the invoked `notify` command is intended to post threaded messages &
+        # check for persisted thread info file for each channel listed in channel parameter
+        if [ ! "$SLACK_PARAM_THREAD" = "" ] && [ -f "/tmp/SLACK_THREAD_INFO/$i" ]; then
+            # get the initial message thread_ts targeting the correct channel and thread id
+            # || [ "$?" = "1" ] - this is used to avoid exit status 1 if grep doesn't match anything
+            # shellcheck disable=SC2002
+            SLACK_THREAD_EXPORT=$(grep -m1 "$SLACK_PARAM_THREAD" /tmp/SLACK_THREAD_INFO/"$i" || [ "$?" = "1" ])
+            if [ ! "$SLACK_THREAD_EXPORT" = "" ]; then
+                # if there is an initial message with a thread id, load it into the environment
+                # thread_id=12345.12345
+                eval "$SLACK_THREAD_EXPORT"
+            fi
+            # get the value of the specified thread from the environment
+            # SLACK_THREAD_TS=12345.12345
+            SLACK_THREAD_TS=$(eval "echo \"\$$SLACK_PARAM_THREAD\"")
+            # append the thread_ts to the body for posting the message in the correct thread
+            SLACK_MSG_BODY=$(echo "$SLACK_MSG_BODY" | jq --arg thread_ts "$SLACK_THREAD_TS" '.thread_ts = $thread_ts')
+        fi
+
         echo "Sending to Slack Channel: $i"
         SLACK_MSG_BODY=$(echo "$SLACK_MSG_BODY" | jq --arg channel "$i" '.channel = $channel')
         if [ "$SLACK_PARAM_DEBUG" -eq 1 ]; then
@@ -71,6 +95,17 @@ PostToSlack() {
                 exit 1
             fi
         fi
+
+        # check if the invoked `notify` command is intended to post messages in threads
+        if [ ! "$SLACK_PARAM_THREAD" = "" ]; then
+            # get message thread_ts from response
+            SLACK_THREAD_TS=$(echo "$SLACK_SENT_RESPONSE" | jq '.ts')
+            if [ ! "$SLACK_THREAD_TS" = "null" ] ; then
+                # store the thread_ts in the specified channel for the specified thread_id
+                mkdir -p /tmp/SLACK_THREAD_INFO
+                echo "$SLACK_PARAM_THREAD=$SLACK_THREAD_TS" >> /tmp/SLACK_THREAD_INFO/"$i"
+            fi
+        fi
     done
 }