Move RGS GraphSyncError into the top-level module

The top-level module is only a few hundred lines, so there's not a
lot of reason to hide the `GraphSyncError` in its own module.
Instead, we simply move it to the top-level `lib.rs`, which doesn't
change the public API as it was previously re-exported at the top
level.

Author: TheBlueMatt

lightning-rapid-gossip-sync/src/error.rs

@@ -72,19 +72,54 @@ extern crate alloc;
 use std::fs::File;
 use core::ops::Deref;
 use core::sync::atomic::{AtomicBool, Ordering};
+use core::fmt::Debug;
+use core::fmt::Formatter;
 
 use lightning::io;
+use lightning::ln::msgs::{DecodeError, LightningError};
 use lightning::routing::gossip::NetworkGraph;
 use lightning::util::logger::Logger;
 
-pub use crate::error::GraphSyncError;
-
-/// Error types that these functions can return
-mod error;
-
 /// Core functionality of this crate
 mod processing;
 
+/// All-encompassing standard error type that processing can return
+pub enum GraphSyncError {
+	/// Error trying to read the update data, typically due to an erroneous data length indication
+	/// that is greater than the actual amount of data provided
+	DecodeError(DecodeError),
+	/// Error applying the patch to the network graph, usually the result of updates that are too
+	/// old or missing prerequisite data to the application of updates out of order
+	LightningError(LightningError),
+}
+
+impl From<lightning::io::Error> for GraphSyncError {
+	fn from(error: lightning::io::Error) -> Self {
+		Self::DecodeError(DecodeError::Io(error.kind()))
+	}
+}
+
+impl From<DecodeError> for GraphSyncError {
+	fn from(error: DecodeError) -> Self {
+		Self::DecodeError(error)
+	}
+}
+
+impl From<LightningError> for GraphSyncError {
+	fn from(error: LightningError) -> Self {
+		Self::LightningError(error)
+	}
+}
+
+impl Debug for GraphSyncError {
+	fn fmt(&self, f: &mut Formatter<'_>) -> core::fmt::Result {
+		match self {
+			GraphSyncError::DecodeError(e) => f.write_fmt(format_args!("DecodeError: {:?}", e)),
+			GraphSyncError::LightningError(e) => f.write_fmt(format_args!("LightningError: {:?}", e))
+		}
+	}
+}
+
 /// The main Rapid Gossip Sync object.
 ///
 /// See [crate-level documentation] for usage.
@@ -167,7 +202,7 @@ mod tests {
 	use lightning::ln::msgs::DecodeError;
 	use lightning::routing::gossip::NetworkGraph;
 	use lightning::util::test_utils::TestLogger;
-	use crate::RapidGossipSync;
+	use crate::{GraphSyncError, RapidGossipSync};
 
 	#[test]
 	fn test_sync_from_file() {
@@ -265,7 +300,7 @@ mod tests {
 		let start = std::time::Instant::now();
 		let sync_result = rapid_sync
 			.sync_network_graph_with_file_path("./res/full_graph.lngossip");
-		if let Err(crate::error::GraphSyncError::DecodeError(DecodeError::Io(io_error))) = &sync_result {
+		if let Err(GraphSyncError::DecodeError(DecodeError::Io(io_error))) = &sync_result {
 			let error_string = format!("Input file lightning-rapid-gossip-sync/res/full_graph.lngossip is missing! Download it from https://bitcoin.ninja/ldk-compressed_graph-285cb27df79-2022-07-21.bin\n\n{:?}", io_error);
 			#[cfg(not(require_route_graph_test))]
 			{

lightning-rapid-gossip-sync/src/lib.rs

@@ -14,8 +14,7 @@ use lightning::{log_debug, log_warn, log_trace, log_given_level, log_gossip};
 use lightning::util::ser::{BigSize, Readable};
 use lightning::io;
 
-use crate::error::GraphSyncError;
-use crate::RapidGossipSync;
+use crate::{GraphSyncError, RapidGossipSync};
 
 #[cfg(all(feature = "std", not(test)))]
 use std::time::{SystemTime, UNIX_EPOCH};
@@ -269,9 +268,8 @@ mod tests {
 	use lightning::routing::gossip::NetworkGraph;
 	use lightning::util::test_utils::TestLogger;
 
-	use crate::error::GraphSyncError;
 	use crate::processing::STALE_RGS_UPDATE_AGE_LIMIT_SECS;
-	use crate::RapidGossipSync;
+	use crate::{GraphSyncError, RapidGossipSync};
 
 	const VALID_RGS_BINARY: [u8; 300] = [
 		76, 68, 75, 1, 111, 226, 140, 10, 182, 241, 179, 114, 193, 166, 162, 70, 174, 99, 247,