fix: Determine git revision hash once at startup (#113)

This way, the server continues to supply the correct git revision hash
  even if the code changes after startup. Unless overridden by an
  environment variable, simply uses `git rev-parse --short HEAD`. In
  production, uses the environment override because the eventual flask
  process doesn't have the correct permissions to perform the git
  command.

  Resolves #108.

flaskr/__init__.py

@@ -2,18 +2,19 @@
 Init file (creates app and database)
 """
 
-import os
-from flask import Flask, current_app
 import click
+from dotenv import load_dotenv
+from flask import Flask, current_app
 from flask.cli import with_appcontext
 from flask_cors import CORS
 from flask_migrate import Migrate
 from flask_sqlalchemy import SQLAlchemy
 import logging
 from logging.handlers import RotatingFileHandler
+import os
+import subprocess # for calling git
 import sys
 
-from dotenv import load_dotenv
 
 from .config import config
 
@@ -57,7 +58,17 @@ def create_app(environment=None, oeis_scheme='https', oeis_hostport='oeis.org'):
     app.config.from_object(config[environment])
     app.config['oeis_scheme'] = oeis_scheme
     app.config['oeis_hostport'] = oeis_hostport
-
+
+    # Remember the git hash of the code we are running:
+    if 'GIT_REVISION_HASH' in os.environ:
+      app.config['git_revision_hash'] = os.getenv('GIT_REVISION_HASH')
+    else:
+      # hash can be provided by the command
+      #    git rev-parse --short HEAD
+      # thanks to: https://stackoverflow.com/questions/14989858/get-the-current-git-hash-in-a-python-script/
+      app.config['git_revision_hash'] = subprocess.check_output(
+        ['git', 'rev-parse', '--short', 'HEAD'], encoding='utf8').strip()
+
     # Logging
     file_handler = RotatingFileHandler('api.log', maxBytes=10000, backupCount=1)
     file_handler.setLevel(logging.INFO)
@@ -101,4 +112,4 @@ def clear_database_command():
         click.echo("No action taken")
         return
     clear_database()
-    click.echo("Database cleared")
+    click.echo("Database cleared")

flaskr/nscope/views.py

@@ -13,7 +13,6 @@
 from cypari2.convert import gen_to_python
 import re
 import requests
-import subprocess # for calling git
 
 
 executor = Executor()
@@ -327,13 +326,8 @@ def get_oeis_factors(oeis_id, num_elements):
 @bp.route("/api/get_commit", methods=["GET"])
 def get_git_commit():
     """ Returns the short git hash for the current build of backscope
-        as provided by the command
-        git rev-parse --short HEAD
-        thanks to: https://stackoverflow.com/questions/14989858/get-the-current-git-hash-in-a-python-script/
+        (as determined at startup in flaskr/__init__.py)
     """
-    short_hash = subprocess.check_output(['git', 'rev-parse', '--short', 'HEAD'], encoding='utf8')
     return jsonify({
-        'short_commit_hash': short_hash.strip()
+        'short_commit_hash': current_app.config['git_revision_hash']
     })
-
-

server/production.sh

@@ -2,4 +2,5 @@
 cd /home/scope/repos/backscope &&
 source .venv/bin/activate &&
 sh tools/install-requirements.sh &&
+export GIT_REVISION_HASH=$(git rev-parse --short HEAD) &&
 gunicorn --workers 3 --bind unix:/home/scope/repos/backscope/backscope.sock -m 777 wsgi:app