Add custom error type to database module

src/backend/error.rs

@@ -0,0 +1,55 @@
+use isahc::http::StatusCode;
+
+/// An error that can happen within the backend.
+#[derive(thiserror::Error, Debug)]
+pub enum Error {
+    #[error("The users login credentials were wrong.")]
+    LoginFailed,
+
+    #[error("The user has to be logged in to perform this action.")]
+    Unauthorized,
+
+    #[error("The user is not allowed to perform this action.")]
+    Forbidden,
+
+    #[error("The server returned an unexpected status code: {0}.")]
+    UnexpectedResponse(StatusCode),
+
+    #[error("A networking error happened.")]
+    NetworkError(#[from] isahc::Error),
+
+    #[error("A networking error happened.")]
+    HttpError(#[from] isahc::http::Error),
+
+    #[error(transparent)]
+    DatabaseError(#[from] crate::backend::DatabaseError),
+
+    #[error("An IO error happened.")]
+    IoError(#[from] std::io::Error),
+
+    #[error("An error happened using the SecretService.")]
+    SecretServiceError(#[from] secret_service::Error),
+
+    #[error("An error happened while serializing or deserializing.")]
+    SerdeError(#[from] serde_json::Error),
+
+    #[error("An error happened in GLib.")]
+    GlibError(#[from] glib::BoolError),
+
+    #[error("A channel was canceled.")]
+    ChannelError(#[from] futures_channel::oneshot::Canceled),
+
+    #[error("Error decoding to UTF8.")]
+    Utf8Error(#[from] std::str::Utf8Error),
+
+    #[error("An error happened: {0}")]
+    Other(&'static str),
+
+    // TODO: Remove this once anyhow has been dropped as a dependency.
+    #[error("An unkown error happened.")]
+    Unknown(#[from] anyhow::Error),
+}
+
+
+pub type Result<T> = std::result::Result<T, Error>;
+