1 files changed, 86 insertions, 0 deletions
diff --git a/services/sync/golden_gate/src/error.rs b/services/sync/golden_gate/src/error.rs
new file mode 100644
index 0000000000..9d65df428b
--- /dev/null
+++ b/services/sync/golden_gate/src/error.rs
@@ -0,0 +1,86 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+use std::{error, fmt, result, str::Utf8Error};
+
+use nserror::{nsresult, NS_ERROR_INVALID_ARG, NS_ERROR_UNEXPECTED};
+use serde_json::Error as JsonError;
+
+/// A specialized `Result` type for Golden Gate.
+pub type Result<T> = result::Result<T, Error>;
+
+/// The error type for Golden Gate errors.
+#[derive(Debug)]
+pub enum Error {
+    /// A wrapped XPCOM error.
+    Nsresult(nsresult),
+
+    /// A ferry didn't run on the background task queue.
+    DidNotRun(&'static str),
+
+    /// A string contains invalid UTF-8 or JSON.
+    MalformedString(Box<dyn error::Error + Send + Sync + 'static>),
+}
+
+impl error::Error for Error {
+    fn source(&self) -> Option<&(dyn error::Error + 'static)> {
+        match self {
+            Error::MalformedString(error) => Some(error.as_ref()),
+            _ => None,
+        }
+    }
+}
+
+impl fmt::Display for Error {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        match self {
+            Error::Nsresult(result) => write!(f, "Operation failed with {}", result.error_name()),
+            Error::DidNotRun(what) => write!(f, "Failed to run `{}` on background thread", what),
+            Error::MalformedString(error) => error.fmt(f),
+        }
+    }
+}
+
+impl From<nsresult> for Error {
+    fn from(result: nsresult) -> Error {
+        Error::Nsresult(result)
+    }
+}
+
+impl From<Utf8Error> for Error {
+    fn from(error: Utf8Error) -> Error {
+        Error::MalformedString(error.into())
+    }
+}
+
+impl From<JsonError> for Error {
+    fn from(error: JsonError) -> Error {
+        Error::MalformedString(error.into())
+    }
+}
+
+impl From<Error> for nsresult {
+    fn from(error: Error) -> nsresult {
+        match error {
+            Error::DidNotRun(_) => NS_ERROR_UNEXPECTED,
+            Error::Nsresult(result) => result,
+            Error::MalformedString(_) => NS_ERROR_INVALID_ARG,
+        }
+    }
+}
+
+/// A trait that constrains the type of `BridgedEngine::Error`, such that it can
+/// be used as a trait bound for ferries and tasks. `BridgedEngine` doesn't
+/// constrain its associated `Error` type, but we must, so that we can return
+/// Golden Gate errors alongside `BridgedEngine::Error`s, and pass their
+/// result codes and messages to `mozIBridgedSyncEngine*Callback::HandleError`.
+/// Since tasks share error results between the main and background threads,
+/// errors must also be `Send + Sync`.
+///
+/// This would be cleaner to express as a trait alias, but those aren't stable
+/// yet (see rust-lang/rust#41517). Instead, we define a trait with no methods,
+/// and a blanket implementation for its supertraits.
+pub trait BridgedError: From<Error> + Into<nsresult> + fmt::Display + Send + Sync {}
+
+impl<T> BridgedError for T where T: From<Error> + Into<nsresult> + fmt::Display + Send + Sync {}