[rankendpoint] Add invocation instructions

Also reverted the use of main() that made it incompatible with uwsgi and
flask run.

rankendpoint.py

@@ -1,18 +1,33 @@
+# This script serves an HTTP endpoint that provides the racing scores.
+#
+# Example invocation for testing:
+# $ RANKENDPOINT_DBPATH=/path/to/database.db RANKENDPOINT_ROUTE=/getranks flask --app rankendpoint.py run
+#
+# Example invocation in production (behind a properly configured gateway like nginx):
+# $ RANKENDPOINT_DBPATH=/path/to/database.db RANKENDPOINT_ROUTE=/getranks uwsgi \
+#     -s localhost:3031 --manage-script-name --mount /=rankendpoint:app --plugin python3
+
 from flask import Flask, request
 app = Flask(__name__)
 
 import sqlite3
 import sys
+import os
 
 header = "SUCCESS"
 
-def main(db_path):
-    # Opens database in read-only mode
-    # Checking same thread disabled for now, which is fine since we never modify anything
-    try:
+db_path = os.environ.get('RANKENDPOINT_DBPATH')
+route = os.environ.get('RANKENDPOINT_ROUTE')
+
+if None in (db_path, route):
+    sys.exit('must set RANKENDPOINT_DBPATH and RANKENDPOINT_ROUTE environment variables')
+
+# Opens database in read-only mode
+# Checking same thread disabled for now, which is fine since we never modify anything
+try:
     db = sqlite3.connect('file:{}?mode=ro'.format(db_path), uri=True, check_same_thread=False)
     cur = db.cursor()
-    except Exception as ex:
+except Exception as ex:
     print(ex)
     sys.exit()
 
@@ -85,7 +100,8 @@ def get_score_entries(data, name):
 
     return scores
 
-@app.route('/getranks', methods=['POST'])
+# route should be something like /getranks
+@app.route(f'{route}', methods=['POST'])
 def rankings():
     #print("PCUID:", request.form['PCUID'])
     #print("EP_ID:", request.form['EP_ID'])
@@ -128,9 +144,3 @@ def rankings():
     # and send it off!
     return header + xmlbody
 
-if __name__ == "__main__":
-    if len(sys.argv) < 2:
-        print("Usage: {} <db file>".format(sys.argv[0]))
-    else:
-        main(sys.argv[1])
-