From 2591d21e94803c9fda53decc2c2b81fdd17aa65d Mon Sep 17 00:00:00 2001
From: Tim Kuehn <tikue@google.com>
Date: Thu, 23 Sep 2021 13:57:43 -0700
Subject: [PATCH] Update release notes to mention io::Error =

---
 RELEASES.md | 22 ++++++++++++++++++++++
 1 file changed, 22 insertions(+)

diff --git a/RELEASES.md b/RELEASES.md
index e2e42f5..f061b4e 100644
--- a/RELEASES.md
+++ b/RELEASES.md
@@ -2,6 +2,28 @@
 
 ### Breaking Changes
 
+### RPC error type is changing
+
+RPC return types are changing from `Result<Response, io::Error>` to `Result<Response,
+tarpc::client::RpcError>`.
+
+Becaue tarpc is a library, not an application, it should strive to
+use structured errors in its API so that users have maximal flexibility
+in how they handle errors. io::Error makes that hard, because it is a
+kitchen-sink error type.
+
+RPCs in particular only have 3 classes of errors:
+
+- The connection breaks.
+- The request expires.
+- The server decides not to process the request.
+
+RPC responses can also contain application-specific errors, but from the
+perspective of the RPC library, those are opaque to the framework, classified
+as successful responsees.
+
+### Open Telemetry
+
 The Opentelemetry dependency is updated to version 0.16.x.
 
 ## 0.27.0 (2021-09-22)