Split multiplart email sending into a dedicated handler (#9977)

Co-authored-by: Andrew Morgan <1342360+anoadragon453@users.noreply.github.com>

synapse/handlers/send_email.py

@@ -0,0 +1,98 @@
+# Copyright 2021 The Matrix.org C.I.C. Foundation
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import email.utils
+import logging
+from email.mime.multipart import MIMEMultipart
+from email.mime.text import MIMEText
+from typing import TYPE_CHECKING
+
+from synapse.logging.context import make_deferred_yieldable
+
+if TYPE_CHECKING:
+    from synapse.server import HomeServer
+
+logger = logging.getLogger(__name__)
+
+
+class SendEmailHandler:
+    def __init__(self, hs: "HomeServer"):
+        self.hs = hs
+
+        self._sendmail = hs.get_sendmail()
+        self._reactor = hs.get_reactor()
+
+        self._from = hs.config.email.email_notif_from
+        self._smtp_host = hs.config.email.email_smtp_host
+        self._smtp_port = hs.config.email.email_smtp_port
+        self._smtp_user = hs.config.email.email_smtp_user
+        self._smtp_pass = hs.config.email.email_smtp_pass
+        self._require_transport_security = hs.config.email.require_transport_security
+
+    async def send_email(
+        self,
+        email_address: str,
+        subject: str,
+        app_name: str,
+        html: str,
+        text: str,
+    ) -> None:
+        """Send a multipart email with the given information.
+
+        Args:
+            email_address: The address to send the email to.
+            subject: The email's subject.
+            app_name: The app name to include in the From header.
+            html: The HTML content to include in the email.
+            text: The plain text content to include in the email.
+        """
+        try:
+            from_string = self._from % {"app": app_name}
+        except (KeyError, TypeError):
+            from_string = self._from
+
+        raw_from = email.utils.parseaddr(from_string)[1]
+        raw_to = email.utils.parseaddr(email_address)[1]
+
+        if raw_to == "":
+            raise RuntimeError("Invalid 'to' address")
+
+        html_part = MIMEText(html, "html", "utf8")
+        text_part = MIMEText(text, "plain", "utf8")
+
+        multipart_msg = MIMEMultipart("alternative")
+        multipart_msg["Subject"] = subject
+        multipart_msg["From"] = from_string
+        multipart_msg["To"] = email_address
+        multipart_msg["Date"] = email.utils.formatdate()
+        multipart_msg["Message-ID"] = email.utils.make_msgid()
+        multipart_msg.attach(text_part)
+        multipart_msg.attach(html_part)
+
+        logger.info("Sending email to %s" % email_address)
+
+        await make_deferred_yieldable(
+            self._sendmail(
+                self._smtp_host,
+                raw_from,
+                raw_to,
+                multipart_msg.as_string().encode("utf8"),
+                reactor=self._reactor,
+                port=self._smtp_port,
+                requireAuthentication=self._smtp_user is not None,
+                username=self._smtp_user,
+                password=self._smtp_pass,
+                requireTransportSecurity=self._require_transport_security,
+            )
+        )