[native][backup_client] Handle BackupNotFound in retrieve_latest_back…

…up_info

Summary:
Rust part of [[ https://linear.app/comm/issue/ENG-10039/allow-checking-if-a-user-has-a-backup | ENG-10039 ]]

Depends on D14189

Test Plan:
For:
- user with backup
- without backup
- not existing user

```
lang=javascript
try {
  const result = await retrieveLatestBackupInfo('username123');
  if (result === null) {
    console.log('backup not found');
  } else {
    console.log('backup found', result);
  }
} catch (e) {
  const msg = getMessageForException(e);
  if (msg === 'user_not_found') {
    console.log('user not found');
  } else {
    console.log('error: ' + msg);
  }
}
````

Reviewers: kamil, tomek

Reviewed By: tomek

Subscribers: ashoat

Differential Revision: https://phab.comm.dev/D14190

native/native_rust_library/src/backup.rs

@@ -242,7 +242,11 @@ pub mod ffi {
           .map_err(|err| err.to_string());
 
       let result = match latest_backup_id_response {
-        Ok(result) => result,
+        Ok(Some(result)) => result,
+        Ok(None) => {
+          string_callback("".to_string(), promise_id, "null".to_string());
+          return;
+        }
         Err(error) => {
           string_callback(error, promise_id, "".to_string());
           return;
@@ -321,26 +325,34 @@ pub async fn create_siwe_backup_msg_compaction(
 
 async fn download_latest_backup_info(
   user_identifier: String,
-) -> Result<LatestBackupInfoResponse, Box<dyn Error>> {
+) -> Result<Option<LatestBackupInfoResponse>, Box<dyn Error>> {
   let backup_client = BackupClient::new(BACKUP_SOCKET_ADDR)?;
 
   let latest_backup_descriptor = BackupDescriptor::Latest { user_identifier };
 
-  let backup_info_response = backup_client
+  let backup_info_response = match backup_client
     .download_backup_data(&latest_backup_descriptor, RequestedData::BackupInfo)
-    .await?;
+    .await
+  {
+    Ok(response) => response,
+    Err(err) if err.is_backup_not_found() => return Ok(None),
+    Err(err) if err.is_user_not_found() => {
+      return Err(Box::new(UserNotFoundError))
+    }
+    Err(err) => return Err(err.into()),
+  };
 
   let LatestBackupInfoResponse {
     backup_id,
     user_id,
     siwe_backup_msg,
   } = serde_json::from_slice(&backup_info_response)?;
 
-  Ok(LatestBackupInfoResponse {
+  Ok(Some(LatestBackupInfoResponse {
     backup_id,
     user_id,
     siwe_backup_msg,
-  })
+  }))
 }
 
 async fn download_backup_keys(
@@ -419,6 +431,11 @@ fn get_user_identity_from_secure_store() -> Result<UserIdentity, cxx::Exception>
   })
 }
 
+/// helper struct to generate proper error message string
+#[derive(Debug, derive_more::Error, derive_more::Display)]
+#[display(fmt = "user_not_found")]
+struct UserNotFoundError;
+
 // This struct should match `SIWEBackupData` in `lib/types/backup-types.js`
 #[derive(Debug, Clone, Serialize, Deserialize)]
 #[serde(rename_all = "camelCase")]

shared/backup_client/src/lib.rs

@@ -139,7 +139,6 @@ impl BackupClient {
     let response = request.send().await?;
 
     let result = response.error_for_status()?.bytes().await?.to_vec();
-
     Ok(result)
   }
 }
@@ -398,6 +397,17 @@ pub enum Error {
   Unauthenticated,
   InvalidRequest,
 }
+
+impl Error {
+  pub fn is_user_not_found(&self) -> bool {
+    matches!(self, Self::ReqwestError(err) if err.status() == Some(StatusCode::BAD_REQUEST))
+  }
+
+  pub fn is_backup_not_found(&self) -> bool {
+    matches!(self, Self::ReqwestError(err) if err.status() == Some(StatusCode::NOT_FOUND))
+  }
+}
+
 impl std::error::Error for Error {}
 
 impl From<InvalidHeaderValue> for Error {