Add docs

Author: gabotechs

src/errors/mod.rs

@@ -11,13 +11,22 @@ mod parquet_error;
 mod parser_error;
 mod schema_error;
 
+/// Encodes a [DataFusionError] into a [tonic::Status] error. The produced error is suitable
+/// to be sent over the wire and decoded by the receiving end, recovering the original
+/// [DataFusionError] across a network boundary with [tonic_status_to_datafusion_error].
 pub fn datafusion_error_to_tonic_status(err: &DataFusionError) -> tonic::Status {
     let err = DataFusionErrorProto::from_datafusion_error(err);
     let err = err.encode_to_vec();
     let status = tonic::Status::with_details(tonic::Code::Internal, "DataFusionError", err.into());
     status
 }
 
+/// Decodes a [DataFusionError] from a [tonic::Status] error. If the provided [tonic::Status]
+/// error was produced with [datafusion_error_to_tonic_status], this function will be able to
+/// recover it even across a network boundary.
+///
+/// The provided [tonic::Status] error might also be something else, like an actual network
+/// failure. This function returns `None` for those cases.
 pub fn tonic_status_to_datafusion_error(status: &tonic::Status) -> Option<DataFusionError> {
     if status.code() != tonic::Code::Internal {
         return None;