fix: only set Content-Type when appropriate

codegen/smithy-aws-kotlin-codegen/src/main/kotlin/aws/sdk/kotlin/codegen/protocols/RestJson1.kt

@@ -51,11 +51,14 @@ class RestJson1 : JsonHttpBindingProtocolGenerator() {
             // explicit payload member as the sole payload
             val memberName = httpPayload.member.defaultName()
             val target = ctx.model.expectShape(httpPayload.member.target)
-            if (target is StructureShape) {
-                writer.withBlock("if (input.#L == null) {", "}", memberName) {
+            writer.withBlock("if (input.#L == null) {", "}", memberName) {
+                if (target is StructureShape) {
                     addImport(RuntimeTypes.Http.ByteArrayContent)
                     write("builder.body = #T(#S.encodeToByteArray())", RuntimeTypes.Http.ByteArrayContent, "{}")
                 }
+                // Content-Type still needs to be set for non-structured payloads
+                // https://github.com/awslabs/smithy/blob/main/smithy-aws-protocol-tests/model/restJson1/http-content-type.smithy#L174
+                write("builder.headers.setMissing(\"Content-Type\", #S)", resolver.determineRequestContentType(op))
             }
         }
     }

gradle.properties

@@ -12,7 +12,7 @@ sdkVersion=0.14.3-SNAPSHOT
 smithyVersion=1.17.0
 smithyGradleVersion=0.5.3
 # smithy-kotlin codegen and runtime are versioned together
-smithyKotlinVersion=0.8.2
+smithyKotlinVersion=0.8.3-SNAPSHOT
 
 # kotlin
 kotlinVersion=1.6.10

services/s3/model/s3-tests.smithy

@@ -63,3 +63,38 @@ apply PutObject @httpRequestTests([
         }
     }
 ])
+
+apply CreateBucket @httpRequestTests([
+    {
+        id: "CreateBucketNoBody",
+        documentation: "Validates https://github.com/awslabs/aws-sdk-kotlin/issues/567 (empty body)",
+        protocol: "aws.protocols#restXml",
+        method: "PUT",
+        uri: "/mybucket",
+        host: "s3.us-west-2.amazonaws.com",
+        body: "",
+        forbidHeaders: ["Content-Type", "Content-Length"],
+        params: {
+            Bucket: "mybucket",
+        }
+    },
+    {
+        id: "CreateBucketWithBody",
+        documentation: "This test case validates https://github.com/awslabs/aws-sdk-kotlin/issues/567 (non-empty body)",
+        protocol: "aws.protocols#restXml",
+        method: "PUT",
+        uri: "/mybucket",
+        host: "s3.us-west-2.amazonaws.com",
+        body: "<CreateBucketConfiguration xmlns=\"http://s3.amazonaws.com/doc/2006-03-01/\"><LocationConstraint>us-east-2</LocationConstraint></CreateBucketConfiguration>",
+        headers: {
+            "Content-Type": "application/xml",
+            "Content-Length": "153"
+        },
+        params: {
+            Bucket: "mybucket",
+            CreateBucketConfiguration: {
+                LocationConstraint: "us-east-2"
+            }
+        }
+    }
+])