Add NoSuchKeyError as possible errorcode

Motivation: Such checks are best performed in backend than
having client checking empty or null value. This is also in-line
with more critical requirement for functioning of NotFound
introduced by MonitorUpdatingPersister Design.
Even though there are some popular KVStore's which do not throw
such exception on keyNotFound such as AWS-DDB (arguably the most popular one),
we can still figure out that key didn't exist if value was
returned as null or by similar means in other stores.

Author: G8XSU

build.rs

@@ -14,7 +14,7 @@ fn main() {
 #[cfg(feature = "genproto")]
 fn generate_protos() {
 	download_file(
-				"https://raw.githubusercontent.com/lightningdevkit/vss-server/e1a88afd61f56d7e8e90a32036ca12389e36fe44/app/src/main/proto/vss.proto",
+				"https://raw.githubusercontent.com/lightningdevkit/vss-server/d8991673f572408b7ea6a62627d9d30f03266876/app/src/main/proto/vss.proto",
 				"src/proto/vss.proto",
 		).unwrap();
 

src/error.rs

@@ -10,9 +10,20 @@ use std::fmt::{Display, Formatter};
 /// information regarding each error code and corresponding use-cases.
 #[derive(Debug)]
 pub enum VssError {
+	/// Refer [`ErrorCode::NoSuchKeyException`].
+	NoSuchKeyError(String),
+
+	/// Refer [`ErrorCode::InvalidRequestException`].
 	InvalidRequestError(String),
+
+	/// Refer [`ErrorCode::ConflictException`].
 	ConflictError(String),
+
+	/// Refer [`ErrorCode::InternalServerException`].
 	InternalServerError(String),
+
+	// There is an unknown error, it could be a client-side bug, unrecognized error-code, network error
+	// or something else.
 	InternalError(String),
 }
 
@@ -33,6 +44,9 @@ impl VssError {
 impl Display for VssError {
 	fn fmt(&self, f: &mut Formatter<'_>) -> std::fmt::Result {
 		match self {
+			VssError::NoSuchKeyError(message) => {
+				write!(f, "Requested key does not exist: {}", message)
+			}
 			VssError::InvalidRequestError(message) => {
 				write!(f, "Request sent to VSS Storage was invalid: {}", message)
 			}
@@ -54,6 +68,7 @@ impl Error for VssError {}
 impl From<ErrorResponse> for VssError {
 	fn from(error_response: ErrorResponse) -> Self {
 		match error_response.error_code() {
+			ErrorCode::NoSuchKeyException => VssError::NoSuchKeyError(error_response.message),
 			ErrorCode::InvalidRequestException => VssError::InvalidRequestError(error_response.message),
 			ErrorCode::ConflictException => VssError::ConflictError(error_response.message),
 			ErrorCode::InternalServerException => VssError::InternalServerError(error_response.message),

src/types.rs

@@ -12,6 +12,9 @@ pub struct GetObjectRequest {
 	pub store_id: ::prost::alloc::string::String,
 	/// `Key` for which the value is to be fetched.
 	///
+	/// If the specified `key` does not exist, returns `ErrorResponse` with `NO_SUCH_KEY_EXCEPTION` as
+	/// `ErrorCode`.
+	///
 	/// Consistency Guarantee:
 	/// Get(read) operations against a `key` are consistent reads and will reflect all previous writes,
 	/// since Put/Write provides read-after-write and read-after-update consistency guarantees.
@@ -298,6 +301,8 @@ pub enum ErrorCode {
 	/// An internal server error occurred, client is probably at no fault and can safely retry this
 	/// error with exponential backoff.
 	InternalServerException = 3,
+	/// NO_SUCH_KEY_EXCEPTION is used when the specified `key` in a `GetObjectRequest` does not exist.
+	NoSuchKeyException = 4,
 }
 impl ErrorCode {
 	/// String value of the enum field names used in the ProtoBuf definition.
@@ -310,6 +315,7 @@ impl ErrorCode {
 			ErrorCode::ConflictException => "CONFLICT_EXCEPTION",
 			ErrorCode::InvalidRequestException => "INVALID_REQUEST_EXCEPTION",
 			ErrorCode::InternalServerException => "INTERNAL_SERVER_EXCEPTION",
+			ErrorCode::NoSuchKeyException => "NO_SUCH_KEY_EXCEPTION",
 		}
 	}
 	/// Creates an enum from field names used in the ProtoBuf definition.
@@ -319,6 +325,7 @@ impl ErrorCode {
 			"CONFLICT_EXCEPTION" => Some(Self::ConflictException),
 			"INVALID_REQUEST_EXCEPTION" => Some(Self::InvalidRequestException),
 			"INTERNAL_SERVER_EXCEPTION" => Some(Self::InternalServerException),
+			"NO_SUCH_KEY_EXCEPTION" => Some(Self::NoSuchKeyException),
 			_ => None,
 		}
 	}

tests/tests.rs

@@ -149,6 +149,30 @@ mod tests {
 		mock_server.expect(1).assert();
 	}
 
+	#[tokio::test]
+	async fn test_no_such_key_err_handling() {
+		let base_url = mockito::server_url();
+		let vss_client = VssClient::new(&base_url);
+
+		// NoSuchKeyError
+		let error_response = ErrorResponse {
+			error_code: ErrorCode::NoSuchKeyException.into(),
+			message: "NoSuchKeyException".to_string(),
+		};
+		let mock_server = mockito::mock("POST", GET_OBJECT_ENDPOINT)
+			.with_status(409)
+			.with_body(&error_response.encode_to_vec())
+			.create();
+
+		let get_result = vss_client
+			.get_object(&GetObjectRequest { store_id: "store".to_string(), key: "non_existent_key".to_string() })
+			.await;
+		assert!(matches!(get_result.unwrap_err(), VssError::NoSuchKeyError { .. }));
+
+		// Verify 1 request hit the server
+		mock_server.expect(1).assert();
+	}
+
 	#[tokio::test]
 	async fn test_invalid_request_err_handling() {
 		let base_url = mockito::server_url();