Add postgres backend

README.md

@@ -109,6 +109,11 @@ The backend is activated by setting `TP_BACKEND=azure_storage`. Each paste is
 stored as a separate blob which means that this backend supports paste sizes [up to 5TB](https://docs.microsoft.com/en-us/azure/storage/common/storage-scalability-targets).
 Metadata associated with a paste is stored directly on the blob via [custom metadata fields](https://docs.microsoft.com/en-us/azure/storage/blobs/storage-properties-metadata).
 
+### postgres
+This is a backend based on the Postgres database. The backend assumes that you
+have a running Postgres database set up that the application can connect to via
+a connection string. The backend is activated by setting `TP_BACKEND=postgres`.
+
 ## Configuration
 TorPaste can be configured by using `ENV`ironment Variables. The list of available
 variables as well as their actions is below so you can use them to parameterize your
@@ -158,3 +163,8 @@ and how to set up a storage account [here](https://docs.microsoft.com/en-us/azur
   exist, it will be created. *Default:* `torpaste`.
 * `TP_BACKEND_AZURE_STORAGE_TIMEOUT_SECONDS` : Use this variable to set the
   timeout in seconds for all requests to Azure. *Default:* `10`.
+
+#### postgres
+
+* `TP_BACKEND_POSTGRES_DATABASE_CONNECTION` : Use this variable to set the
+  connection string with which to connect to the Postgres database.

backends/postgres.py

@@ -0,0 +1,178 @@
+import psycopg2
+from contextlib import contextmanager
+from functools import wraps
+from itertools import groupby
+from operator import itemgetter
+from os import environ
+
+from backends.exceptions import ErrorException
+
+_ENV_DATABASE_CONNECTION = 'TP_BACKEND_POSTGRES_DATABASE_CONNECTION'
+
+
+class _Db(object):
+    _paramstyle = None
+    _connection = None
+
+    @classmethod
+    @contextmanager
+    def _get_cursor(cls, commit):
+        cursor = cls._connection.cursor()
+
+        yield cursor
+
+        if commit:
+            cls._connection.commit()
+
+    @classmethod
+    def read_cursor(cls):
+        return cls._get_cursor(commit=False)
+
+    @classmethod
+    def write_cursor(cls):
+        return cls._get_cursor(commit=True)
+
+    @classmethod
+    def prepare_sql(cls, sql):
+        return sql.replace('?', cls._paramstyle)
+
+    @classmethod
+    def connect(cls, connection, paramstyle):
+        cls._connection = connection
+        cls._paramstyle = paramstyle
+
+
+def _getenv_required(key):
+    try:
+        return environ[key]
+    except KeyError:
+        raise ErrorException(
+            'Required environment variable %s not set' % key)
+
+
+def _wrap_postgres_exception(func):
+    @wraps(func)
+    def _adapt_exception_types(*args, **kwargs):
+        try:
+            return func(*args, **kwargs)
+        except psycopg2.Error as ex:
+            print(ex)
+            raise ErrorException(
+                'Error while communicating with the Postgres database'
+            ) from ex
+
+    return _adapt_exception_types
+
+
+@_wrap_postgres_exception
+def initialize_backend():
+    _Db.connect(psycopg2.connect(
+        _getenv_required(_ENV_DATABASE_CONNECTION)),
+        paramstyle='%s')
+
+    with _Db.write_cursor() as cursor:
+        cursor.execute('''
+            CREATE TABLE IF NOT EXISTS pastes (
+              id TEXT,
+              content TEXT,
+              PRIMARY KEY (id))
+        ''')
+        cursor.execute('''
+            CREATE TABLE IF NOT EXISTS pastes_metadata (
+              id TEXT,
+              key TEXT,
+              value TEXT,
+              PRIMARY KEY (id, key))
+        ''')
+
+
+@_wrap_postgres_exception
+def new_paste(paste_id, paste_content):
+    with _Db.write_cursor() as cursor:
+        cursor.execute(_Db.prepare_sql('''
+            INSERT INTO pastes (id, content) VALUES (?, ?)
+        '''), [paste_id, paste_content])
+
+
+@_wrap_postgres_exception
+def update_paste_metadata(paste_id, metadata):
+    with _Db.write_cursor() as cursor:
+        cursor.execute(_Db.prepare_sql('''
+            DELETE FROM pastes_metadata WHERE id = ?
+        '''), [paste_id])
+        cursor.executemany(_Db.prepare_sql('''
+            INSERT INTO pastes_metadata VALUES (?, ?, ?)
+        '''), [(paste_id, key, value) for (key, value) in metadata.items()])
+
+
+@_wrap_postgres_exception
+def does_paste_exist(paste_id):
+    with _Db.read_cursor() as cursor:
+        cursor.execute(_Db.prepare_sql('''
+            SELECT 1 FROM pastes WHERE id = ?
+        '''), [paste_id])
+        row = cursor.fetchone()
+    return row is not None
+
+
+@_wrap_postgres_exception
+def get_paste_contents(paste_id):
+    with _Db.read_cursor() as cursor:
+        cursor.execute(_Db.prepare_sql('''
+            SELECT content FROM pastes WHERE id = ?
+        '''), [paste_id])
+        row = cursor.fetchone()
+    return row[0] if row else None
+
+
+@_wrap_postgres_exception
+def get_paste_metadata(paste_id):
+    with _Db.read_cursor() as cursor:
+        cursor.execute(_Db.prepare_sql('''
+            SELECT key, value FROM pastes_metadata WHERE id = ?
+        '''), [paste_id])
+        rows = cursor.fetchall()
+    return {key: value for (key, value) in rows}
+
+
+@_wrap_postgres_exception
+def get_paste_metadata_value(paste_id, key):
+    with _Db.read_cursor() as cursor:
+        cursor.execute(_Db.prepare_sql('''
+            SELECT value FROM pastes_metadata WHERE id = ? AND key = ?
+        '''), [paste_id, key])
+        row = cursor.fetchone()
+    return row[0] if row else None
+
+
+def _filters_match(metadata, filters, fdefaults):
+    for metadata_key, filter_value in filters.items():
+        try:
+            metadata_value = metadata[metadata_key]
+        except KeyError:
+            metadata_value = fdefaults.get(metadata_key)
+
+        if metadata_value != filter_value:
+            return False
+
+    return True
+
+
+def _get_all_paste_ids(filters, fdefaults):
+    with _Db.read_cursor() as cursor:
+        cursor.execute(_Db.prepare_sql('''
+            SELECT id, key, value FROM pastes_metadata
+            UNION
+            SELECT id, '', '' FROM pastes
+        '''))
+        rows = cursor.fetchall()
+
+    for paste_id, rows in groupby(rows, itemgetter(0)):
+        metadata = {key: value for (_, key, value) in rows}
+        if _filters_match(metadata, filters, fdefaults):
+            yield paste_id
+
+
+@_wrap_postgres_exception
+def get_all_paste_ids(filters={}, fdefaults={}):
+    return list(_get_all_paste_ids(filters, fdefaults)) or ['none']

requirements.txt

@@ -1,2 +1,3 @@
 Flask
 azure-storage==0.36.0
+psycopg2==2.7.3.2

torpaste.py

@@ -24,6 +24,7 @@
 COMPATIBLE_BACKENDS = [
     "filesystem",
     "azure_storage",
+    "postgres",
 ]
 
 # Available list of paste visibilities