From 5ca021456e8d23ed13a51da9698b9b66e90d8ec2 Mon Sep 17 00:00:00 2001
From: Carl Worth <cworth@cworth.org>
Date: Tue, 29 Sep 2020 09:59:42 -0700
Subject: [PATCH] Abstract out two slack-related functions

The two new functions are slack_is_valid_request and slack_send_reply.
These functions provide some shared code for dealing with slack to
avoid code duplication.

These functions also provide a debug mode (that doesn't use slack at
all). This is a convenience for testing the implementation of slash
commands in a local "make run" session without needing to touch Slack
endpoints at all. (Instead, all requests are considered valid and
slack replies are simply printed to stdout.)
---
 turbot.py | 69 ++++++++++++++++++++++++++++++++++++++++---------------
 1 file changed, 50 insertions(+), 19 deletions(-)

diff --git a/turbot.py b/turbot.py
index 5095d2a..2b9462f 100755
--- a/turbot.py
+++ b/turbot.py
@@ -19,6 +19,52 @@ slack_events = SlackEventAdapter(slack_signing_secret, "/slack/events", app)
 signature_verifier = SignatureVerifier(slack_signing_secret)
 slack_client = WebClient(slack_bot_token)
 
+def slack_is_valid_request(request):
+    """Returns true if request actually came from Slack.
+
+    By means of checking the requests signature together with the slack
+    signing key.
+
+    Note: If flask is in debug mode, this function will always return true."""
+
+    if app.debug:
+        return True
+
+    data = request.get_data()
+    headers = request.headers
+
+    return signature_verifier.is_valid_request(data, headers)
+
+def slack_send_reply(request, text):
+    """Send a Slack message as a reply to a specified request.
+
+    If the request is associated with a direct message, the reply is
+    made by using the "response_url" from the request. Otherwise, the
+    reply will be sent to the channel associated with the request.
+
+    Note: If flask is in debug mode, this function will just print the
+    text to stdout."""
+
+    channel_name = request.form.get('channel_name')
+    response_url = request.form.get('response_url')
+    channel = request.form.get('channel_id')
+
+    if (app.debug):
+        print("Sending message to channel '{}': {}".format(channel, text))
+        return
+
+    if (channel_name == "directmessage"):
+        resp = requests.post(response_url,
+                             json = {"text": text},
+                             headers = {"Content-type": "application/json"})
+        if (resp.status_code != 200):
+            app.logger.error("Error posting request to Slack: " + resp.text)
+    else:
+        try:
+            slack_client.chat_postMessage(channel=channel, text=text)
+        except SlackApiError as e:
+            app.logger.error("Slack API error: " + e.response["error"])
+
 def rot_string(str, n=13):
     """Return a rotated version of a string
 
@@ -54,16 +100,10 @@ def rot():
     in a direct message that it is not a member of. Otherwise, if the slash
     command was issued in a channel, the bot will reply in that channel."""
 
-    data = request.get_data()
-    headers = request.headers
-    response_url = request.form.get('response_url')
-    channel_name = request.form.get('channel_name')
-    channel = request.form.get('channel_id')
-    query = request.form.get('text')
-
-    if not signature_verifier.is_valid_request(data, headers):
+    if not slack_is_valid_request(request):
         return make_response("invalid request", 403)
 
+    query = request.form.get('text')
     match = re.match(r'^([0-9]+|\*) (.*)$', query)
     if (match):
         try:
@@ -87,17 +127,8 @@ def rot():
 
     reply += "```"
 
-    if (channel_name == "directmessage"):
-        resp = requests.post(response_url,
-                             json = {"text": reply},
-                             headers = {"Content-type": "application/json"})
-        if (resp.status_code != 200):
-            app.logger.error("Error posting request to Slack: " + resp.text)
-    else:
-        try:
-            slack_client.chat_postMessage(channel=channel, text=reply)
-        except SlackApiError as e:
-            app.logger.error("Slack API error: " + e.response["error"])
+    slack_send_reply(request, reply)
+
     return ""
 
 @slack_events.on("error")
-- 
2.45.2