feat: encrypt notification tokens

src/imap.rs

@@ -41,6 +41,7 @@ use crate::mimeparser;
 use crate::net::proxy::ProxyConfig;
 use crate::net::session::SessionStream;
 use crate::oauth2::get_oauth2_access_token;
+use crate::push::encrypt_device_token;
 use crate::receive_imf::{
     from_field_to_contact_id, get_prefetch_parent_message, receive_imf_inner, ReceivedMsg,
 };
@@ -1559,17 +1560,53 @@ impl Session {
             return Ok(());
         };
 
-        if self.can_metadata() && self.can_push() {
+        let device_token_changed = context
+            .get_config(Config::DeviceToken)
+            .await?
+            .map_or(true, |config_token| device_token != config_token);
+
+        if device_token_changed && self.can_metadata() && self.can_push() {
             let folder = context
                 .get_config(Config::ConfiguredInboxFolder)
                 .await?
                 .context("INBOX is not configured")?;
 
-            self.run_command_and_check_ok(format!(
-                "SETMETADATA \"{folder}\" (/private/devicetoken \"{device_token}\")"
-            ))
-            .await
-            .context("SETMETADATA command failed")?;
+            let encrypted_device_token =
+                encrypt_device_token(&device_token).context("Failed to encrypt device token")?;
+
+            // We expect that the server supporting `XDELTAPUSH` capability
+            // has non-synchronizing literals support as well:
+            // <https://www.rfc-editor.org/rfc/rfc7888>.
+            let encrypted_device_token_len = encrypted_device_token.len();
+
+            if encrypted_device_token_len <= 4096 {
+                self.run_command_and_check_ok(&format_setmetadata(
+                    &folder,
+                    &encrypted_device_token,
+                ))
+                .await
+                .context("SETMETADATA command failed")?;
+
+                // Store device token saved on the server
+                // to prevent storing duplicate tokens.
+                // The server cannot deduplicate on its own
+                // because encryption gives a different
+                // result each time.
+                context
+                    .set_config_internal(Config::DeviceToken, Some(&device_token))
+                    .await?;
+            } else {
+                // If Apple or Google (FCM) gives us a very large token,
+                // do not even try to give it to IMAP servers.
+                //
+                // Limit of 4096 is arbitrarily selected
+                // to be the same as required by LITERAL- IMAP extension.
+                //
+                // Dovecot supports LITERAL+ and non-synchronizing literals
+                // of any length, but there is no reason for tokens
+                // to be that large even after OpenPGP encryption.
+                warn!(context, "Device token is too long for LITERAL-, ignoring.");
+            }
             context.push_subscribed.store(true, Ordering::Relaxed);
         } else if !context.push_subscriber.heartbeat_subscribed().await {
             let context = context.clone();
@@ -1581,6 +1618,13 @@ impl Session {
     }
 }
 
+fn format_setmetadata(folder: &str, device_token: &str) -> String {
+    let device_token_len = device_token.len();
+    format!(
+        "SETMETADATA \"{folder}\" (/private/devicetoken {{{device_token_len}+}}\r\n{device_token})"
+    )
+}
+
 impl Session {
     /// Returns success if we successfully set the flag or we otherwise
     /// think add_flag should not be retried: Disconnection during setting
@@ -2864,4 +2908,16 @@ mod tests {
             vec![("INBOX".to_string(), vec![1, 2, 3], "2:3".to_string())]
         );
     }
+
+    #[test]
+    fn test_setmetadata_device_token() {
+        assert_eq!(
+            format_setmetadata("INBOX", "foobarbaz"),
+            "SETMETADATA \"INBOX\" (/private/devicetoken {9+}\r\nfoobarbaz)"
+        );
+        assert_eq!(
+            format_setmetadata("INBOX", "foo\r\nbar\r\nbaz\r\n"),
+            "SETMETADATA \"INBOX\" (/private/devicetoken {15+}\r\nfoo\r\nbar\r\nbaz\r\n)"
+        );
+    }
 }