log information about sent emails

Author: pietroalbini

src/email.rs

@@ -3,10 +3,12 @@ use std::sync::Mutex;
 
 use crate::util::errors::{server_error, AppResult};
 
+use crate::middleware::log_request::add_custom_metadata;
 use lettre::transport::file::FileTransport;
 use lettre::transport::smtp::authentication::{Credentials, Mechanism};
 use lettre::transport::smtp::SmtpTransport;
 use lettre::{Message, Transport};
+use rand::distributions::{Alphanumeric, DistString};
 
 #[derive(Debug)]
 pub struct Emails {
@@ -94,7 +96,21 @@ or go to https://{domain}/me/pending-invites to manage all of your crate ownersh
     }
 
     fn send(&self, recipient: &str, subject: &str, body: &str) -> AppResult<()> {
+        // The message ID is normally generated by the SMTP server, but if we let it generate the
+        // ID there will be no way for the crates.io application to know the ID of the message it
+        // just sent, as it's not included in the SMTP response.
+        //
+        // Our support staff needs to know the message ID to be able to find misdelivered emails.
+        // Because of that we're generating a random message ID, hoping the SMTP server doesn't
+        // replace it when it relays the message.
+        let message_id = format!(
+            "<{}@{}>",
+            Alphanumeric.sample_string(&mut rand::thread_rng(), 32),
+            crate::config::domain_name(),
+        );
+
         let email = Message::builder()
+            .message_id(Some(message_id.clone()))
             .to(recipient.parse()?)
             .from(self.sender_address().parse()?)
             .subject(subject)
@@ -106,23 +122,42 @@ or go to https://{domain}/me/pending-invites to manage all of your crate ownersh
                 login,
                 password,
             } => {
-                SmtpTransport::relay(server)?
-                    .credentials(Credentials::new(login.clone(), password.clone()))
-                    .authentication(vec![Mechanism::Plain])
-                    .build()
-                    .send(&email)
-                    .map_err(|_| server_error("Error in sending email"))?;
+                add_custom_metadata("email_backend", "smtp");
+
+                SmtpTransport::relay(server)
+                    .and_then(|transport| {
+                        transport
+                            .credentials(Credentials::new(login.clone(), password.clone()))
+                            .authentication(vec![Mechanism::Plain])
+                            .build()
+                            .send(&email)
+                    })
+                    .map_err(|e| {
+                        add_custom_metadata("email_error", e);
+                        server_error("Failed to send the email")
+                    })?;
+
+                add_custom_metadata("email_id", message_id);
             }
             EmailBackend::FileSystem { path } => {
-                FileTransport::new(&path)
-                    .send(&email)
-                    .map_err(|_| server_error("Email file could not be generated"))?;
+                add_custom_metadata("email_backend", "fs");
+
+                let id = FileTransport::new(&path).send(&email).map_err(|err| {
+                    add_custom_metadata("email_error", err);
+                    server_error("Email file could not be generated")
+                })?;
+
+                add_custom_metadata("email_path", path.join(format!("{id}.eml")).display());
+            }
+            EmailBackend::Memory { mails } => {
+                add_custom_metadata("email_backend", "memory");
+
+                mails.lock().unwrap().push(StoredEmail {
+                    to: recipient.into(),
+                    subject: subject.into(),
+                    body: body.into(),
+                });
             }
-            EmailBackend::Memory { mails } => mails.lock().unwrap().push(StoredEmail {
-                to: recipient.into(),
-                subject: subject.into(),
-                body: body.into(),
-            }),
         }
 
         Ok(())