feat: Reset compose state if error is recoverable

Previously if anything went wrong in the messaging host, we only showed
a notification to the user and the user was stuck with a greyed out
ExtEditorR button.

However in some cases, the error may be fixed by updating ExtEditorR's
and/or the editor's configurations, e.g.

- Host cannot create the temporary EML file
- Host cannot write to the temporary EML file
- Host cannot start the editor

Now when such an error arises, we re-enable ExtEditorR's button and
clear out all received messages for the compose window (which should be
empty in the first place).

For other errors, we keep the button greyed out to avoid overwriting any
data. And there are also errors like version mismatch where users have
to reload ExtEditorR.

extension/background.js

@@ -126,6 +126,10 @@ async function nativeMessagingListener(response) {
   console.debug(`${manifest.short_name} received: `, response)
   if (response.title && response.message) {
     await createBasicNotification('', response.title, response.message)
+    if (response.reset === true) {
+      delete receivedPerTab[response.tab.id]  // maybe do a safety check? but how can we recover?
+      await messenger.composeAction.enable(response.tab.id)
+    }
   } else {
     response.composeDetails.attachments = []
 

src/main.rs

@@ -25,6 +25,8 @@ fn handle(request: Exchange, temp_filename: &Path) -> Result<(), messaging::Erro
         } else {
             return Err(messaging::Error{
                 tab: request.tab.clone(),
+                reset: false,  // users may want to enable bypass_version_check *and* reload
+                               // ExtEditorR to recover
                 title: "ExtEditorR version mismatch!".to_owned(),
                 message: format!(
                     "Thunderbird extension is {} while native messaging host is {}. The request has been discarded.",
@@ -38,13 +40,15 @@ fn handle(request: Exchange, temp_filename: &Path) -> Result<(), messaging::Erro
     {
         let mut temp_file = fs::File::create(temp_filename).map_err(|e| messaging::Error {
             tab: request.tab.clone(),
+            reset: true,
             title: "ExtEditorR failed to create temporary file".to_owned(),
             message: e.to_string(),
         })?;
         request
             .to_eml(&mut temp_file)
             .map_err(|e| messaging::Error {
                 tab: request.tab.clone(),
+                reset: true,
                 title: "ExtEditorR failed to write to temporary file".to_owned(),
                 message: e.to_string(),
             })?;
@@ -71,6 +75,7 @@ fn handle(request: Exchange, temp_filename: &Path) -> Result<(), messaging::Erro
         .output()
         .map_err(|e| messaging::Error {
             tab: request.tab.clone(),
+            reset: true,
             title: "ExtEditorR failed to start editor".to_owned(),
             message: e.to_string(),
         })?;
@@ -80,6 +85,7 @@ fn handle(request: Exchange, temp_filename: &Path) -> Result<(), messaging::Erro
             .to_string();
         return Err(messaging::Error {
             tab: request.tab,
+            reset: false,
             title: "ExtEditorR encountered error from external editor".to_owned(),
             message: util::error_message_with_path(stderr, temp_filename),
         });
@@ -90,6 +96,7 @@ fn handle(request: Exchange, temp_filename: &Path) -> Result<(), messaging::Erro
     {
         let temp_file = fs::File::open(temp_filename).map_err(|e| messaging::Error {
             tab: response.tab.clone(),
+            reset: false,
             title: "ExtEditorR failed to read from temporary file".to_owned(),
             message: util::error_message_with_path(e, temp_filename),
         })?;
@@ -99,6 +106,7 @@ fn handle(request: Exchange, temp_filename: &Path) -> Result<(), messaging::Erro
             .merge_from_eml(&mut reader, messaging::MAX_BODY_LENGTH)
             .map_err(|e| messaging::Error {
                 tab: response.tab.clone(),
+                reset: false,
                 title: "ExtEditorR failed to process temporary file".to_owned(),
                 message: util::error_message_with_path(e, temp_filename),
             })?;

src/model/messaging.rs

@@ -222,6 +222,7 @@ impl Exchange {
 #[derive(Clone, Debug, Deserialize, Serialize)]
 pub struct Error {
     pub tab: Tab,
+    pub reset: bool,
     pub title: String,
     pub message: String,
 }