fix: add content type header to empty body union rest xml payloads (#1073)

Author: 0marperez

codegen/smithy-aws-kotlin-codegen/src/main/kotlin/aws/sdk/kotlin/codegen/protocols/RestXml.kt

@@ -9,13 +9,16 @@ import aws.sdk.kotlin.codegen.protocols.core.AwsHttpBindingProtocolGenerator
 import aws.sdk.kotlin.codegen.protocols.xml.RestXmlSerdeDescriptorGenerator
 import software.amazon.smithy.aws.traits.protocols.RestXmlTrait
 import software.amazon.smithy.codegen.core.Symbol
-import software.amazon.smithy.kotlin.codegen.core.*
+import software.amazon.smithy.kotlin.codegen.core.KotlinWriter
+import software.amazon.smithy.kotlin.codegen.core.RuntimeTypes
+import software.amazon.smithy.kotlin.codegen.core.withBlock
 import software.amazon.smithy.kotlin.codegen.model.*
 import software.amazon.smithy.kotlin.codegen.rendering.protocol.*
 import software.amazon.smithy.kotlin.codegen.rendering.serde.*
 import software.amazon.smithy.model.Model
 import software.amazon.smithy.model.shapes.*
-import software.amazon.smithy.model.traits.*
+import software.amazon.smithy.model.traits.TimestampFormatTrait
+import software.amazon.smithy.model.traits.XmlNameTrait
 import kotlin.contracts.ExperimentalContracts
 import kotlin.contracts.contract
 
@@ -34,6 +37,20 @@ open class RestXml : AwsHttpBindingProtocolGenerator() {
     override fun getProtocolHttpBindingResolver(model: Model, serviceShape: ServiceShape): HttpBindingResolver =
         HttpTraitResolver(model, serviceShape, ProtocolContentTypes.consistent("application/xml"))
 
+    // See: https://github.com/awslabs/aws-sdk-kotlin/issues/1050
+    override fun renderContentTypeHeader(
+        ctx: ProtocolGenerator.GenerationContext,
+        op: OperationShape,
+        writer: KotlinWriter,
+        resolver: HttpBindingResolver,
+    ) {
+        if (op.payloadIsUnionShape(ctx.model)) {
+            writer.write("builder.headers.setMissing(\"Content-Type\", #S)", resolver.determineRequestContentType(op))
+        } else {
+            super.renderContentTypeHeader(ctx, op, writer, resolver)
+        }
+    }
+
     override fun structuredDataParser(ctx: ProtocolGenerator.GenerationContext): StructuredDataParserGenerator =
         RestXmlParserGenerator(this, defaultTimestampFormat)
 

codegen/smithy-aws-kotlin-codegen/src/main/kotlin/aws/sdk/kotlin/codegen/protocols/core/AwsHttpBindingProtocolGenerator.kt

@@ -67,9 +67,6 @@ abstract class AwsHttpBindingProtocolGenerator : HttpBindingProtocolGenerator()
                 "SDKAppendsGzipAndIgnoresHttpProvidedEncoding_awsJson1_1",
                 "SDKAppendsGzipAndIgnoresHttpProvidedEncoding_awsQuery",
                 "SDKAppendsGzipAndIgnoresHttpProvidedEncoding_ec2Query",
-
-                // FIXME - missing Content-Type on restXml empty payloads, see https://github.com/awslabs/aws-sdk-kotlin/issues/1050
-                "RestXmlHttpPayloadWithUnsetUnion",
             ),
         )