Allow expected content-type to ignore parameters

Fixes: #3471

CHANGELOG.next.toml

@@ -10,6 +10,15 @@
 # references = ["smithy-rs#920"]
 # meta = { "breaking" = false, "tada" = false, "bug" = false, "target" = "client | server | all"}
 # author = "rcoh"
+
+[[smithy-rs]]
+message = """
+Content-Type header validation now ignores parameter portion of media types.
+"""
+references = ["smithy-rs#3471","smithy-rs#3576"]
+meta = { "breaking" = false, "tada" = false, "bug" = true, target = "server" }
+authors = ["djedward"]
+
 [[aws-sdk-rust]]
 message = """
 Fixes the identity resolver types (`credentials_provider()` and `token_provider()`) from `SdkConfig` to have
@@ -19,7 +28,6 @@ references = ["smithy-rs#3427"]
 meta = { "breaking" = false, "tada" = false, "bug" = true }
 authors = ["aajtodd"]
 
-
 [[smithy-rs]]
 message = """
 `SharedIdentityResolver` now respects an existing cache partition when the `ResolveIdentity` implementation

rust-runtime/aws-smithy-http-server/src/protocol/mod.rs

@@ -107,7 +107,7 @@ fn content_type_header_classifier(
             .parse::<mime::Mime>()
             // `expected_content_type` comes from the codegen.
             .expect("BUG: MIME parsing failed, `expected_content_type` is not valid. Please file a bug report under https://github.com/smithy-lang/smithy-rs/issues");
-        if expected_content_type != found_mime {
+        if expected_content_type != found_mime.essence_str() {
             return Err(MissingContentTypeReason::UnexpectedMimeType {
                 expected_mime: Some(expected_mime),
                 found_mime: Some(found_mime),
@@ -257,6 +257,13 @@ mod tests {
         assert!(matches!(result.unwrap_err(), MissingContentTypeReason::ToStrError(_)));
     }
 
+    #[test]
+    fn valid_content_type_header_classifier_http_params() {
+        let request = req_content_type("application/json; charset=utf-8");
+        let result = content_type_header_classifier_http(&request, EXPECTED_MIME_APPLICATION_JSON);
+        assert!(result.is_ok());
+    }
+
     #[test]
     fn valid_accept_header_classifier_multiple_values() {
         let valid_request = req_accept("text/strings, application/json, invalid");