add serde support on meta data

Author: thomas-k-cameron

rust-runtime/aws-smithy-types/src/error/metadata.rs

@@ -6,6 +6,7 @@
 //! Error metadata
 
 use crate::retry::{ErrorKind, ProvideErrorKind};
+use std::borrow::Cow;
 use std::collections::HashMap;
 use std::fmt;
 
@@ -39,11 +40,19 @@ pub const EMPTY_ERROR_METADATA: ErrorMetadata = ErrorMetadata {
 /// For many services, Errors are modeled. However, many services only partially model errors or don't
 /// model errors at all. In these cases, the SDK will return this generic error type to expose the
 /// `code`, `message` and `request_id`.
+#[cfg_attr(
+    all(aws_sdk_unstable, feature = "serde-serialize"),
+    derive(serde::Serialize)
+)]
+#[cfg_attr(
+    all(aws_sdk_unstable, feature = "serde-deserialize"),
+    derive(serde::Deserialize)
+)]
 #[derive(Debug, Eq, PartialEq, Default, Clone)]
 pub struct ErrorMetadata {
     code: Option<String>,
     message: Option<String>,
-    extras: Option<HashMap<&'static str, String>>,
+    extras: Option<HashMap<Cow<'static, str>, String>>,
 }
 
 /// Builder for [`ErrorMetadata`].
@@ -98,7 +107,7 @@ impl Builder {
             .extras
             .as_mut()
             .unwrap()
-            .insert(key, value.into());
+            .insert(Cow::Borrowed(key), value.into());
         self
     }