SDKPojo.sdkFieldNameToField uses Smithy locationName, not memberName

[keithharper]

Describe the bug

The SDKPojo.sdkFieldNameToField() method returns a map that uses Smithy locationName values as keys instead of memberName values. This is inconsistent with the SDK's public API which uses member names.

Looking at the generated code for S3.PutObjectRequest, the issue is clear:

private static final SdkField<String> ACL_FIELD = SdkField
        .<String> builder(MarshallingType.STRING)
        .memberName("ACL")
        ...
        .traits(LocationTrait.builder().location(MarshallLocation.HEADER).locationName("x-amz-acl")
                .unmarshallLocationName("x-amz-acl").build()).build();

private static final Map<String, SdkField<?>> SDK_NAME_TO_FIELD = memberNameToFieldInitializer();

@Override
public final Map<String, SdkField<?>> sdkFieldNameToField() {
    return SDK_NAME_TO_FIELD;
}

private static Map<String, SdkField<?>> memberNameToFieldInitializer() {
    Map<String, SdkField<?>> map = new HashMap<>();
    map.put("x-amz-acl", ACL_FIELD);  // ← Bug: Uses locationName instead of memberName
    ...
    return Collections.unmodifiableMap(map);
}

The map is being populated with "x-amz-acl" (locationName) as the key, but it should use "ACL" (memberName) to be consistent with the public API.

Regression Issue

• Select this option if this issue appears to be a regression.

Expected Behavior

The returned map should have member names as keys (e.g., "ACL" -> ACL_FIELD)

Current Behavior

The returned map has locationName values as keys (e.g., "x-amz-acl" -> ACL_FIELD)

Reproduction Steps

// Example with S3's PutObjectRequest
PutObjectRequest request = PutObjectRequest.builder()
    .bucket("my-bucket")
    .key("my-key")
    .acl(ObjectCannedACL.PUBLIC_READ)
    .build();

Map<String, SdkField<?>> fieldMap = request.sdkFieldNameToField();

// This returns null (but shouldn't):
SdkField<?> aclField = fieldMap.get("ACL");

// This returns the field (but shouldn't be necessary):
SdkField<?> aclField = fieldMap.get("x-amz-acl");

Possible Solution

Change memberNameToFieldInitializer() to use memberName values as keys instead of locationName values.

Additional Information/Context

• This issue appears to be most prevalent in S3 operations where many headers use the x-amz- prefix in their locationName
• Other affected S3 fields include: ContentType, metadata headers, and other x-amz-* headers
• This impacts wrapper libraries and reflection-based utilities that expect field names to match the public API
• The method name itself (sdkFieldNameToField) and the method it calls (memberNameToFieldInitializer) suggest it should map SDK field names (member names), not wire protocol names

AWS Java SDK version used

2.31.45

JDK version used

openjdk version "21.0.1" 2023-10-17 OpenJDK Runtime Environment (build 21.0.1+12-29) OpenJDK 64-Bit Server VM (build 21.0.1+12-29, mixed mode, sharing)

Operating System and version

macOS 14.7.6 (23H626)

[ghadishayban]

If this is deemed an incorrect impl, another non-breaking solution is to offer another method with the correct semantics

[debora-ito]

This impacts wrapper libraries and reflection-based utilities that expect field names to match the public API

@keithharper can you tell us more about your use case? Are you a maintainer of a wrapper library?

[keithharper]

Hello @debora-ito! Yes, I'm developing an internal wrapper library that provides a generic interface over the SDK. The library leverages the SDK's self-describing capabilities through the SdkPojo interface to dynamically handle request/response serialization and deserialization across different AWS services.

Our use case relies heavily on the sdkFields() metadata to automatically map between Clojure data structures and SDK request/response objects. Specifically, we use title-cased keywords in Clojure (like :ACL, :ServerSideEncryption) that correspond to the logical member names in the SDK.

The current behavior where sdkFieldNameToField() returns wire protocol names (like "x-amz-acl") instead of member names (like "ACL") breaks our field mapping logic. This is particularly problematic for S3 operations where many fields have custom header mappings.

We've implemented workarounds to handle this inconsistency, but having the map keyed by member names would restore the proper API contract and make the SDK's reflection capabilities work correctly for cross-language integrations.

[sugmanue]

Hi Keith, probably the name of the method sdkFieldNameToField is a bit misleading, but it's behavior is correct. It was introduced to be able to improve the performance of deserialization, thus we need a fast lookup between the input and the corresponding Pojo field. I understand your use case but this method is serving a different one.

Alternatively, you can iterate over the fields sdkFields and create your own mapping that you then can cache for performance.

[sugmanue]

Just a small follow up

This is inconsistent with the SDK's public API

The SdkPojo class is an internal artifact of the SDK, and not a public API, as denoted by its @SdkProtectedApi annotation. Read more about it here.