fix: set Content-Type header on empty bodies with Ktor if canonical request includes it (#630)

Author: ianbotsf

runtime/protocol/http-client-engines/http-client-engine-ktor/common/src/aws/smithy/kotlin/runtime/http/engine/ktor/KtorRequestAdapter.kt

@@ -7,7 +7,6 @@ package aws.smithy.kotlin.runtime.http.engine.ktor
 import aws.smithy.kotlin.runtime.http.HttpBody
 import aws.smithy.kotlin.runtime.http.request.HttpRequest
 import aws.smithy.kotlin.runtime.http.request.HttpRequestBuilder
-import io.ktor.client.utils.EmptyContent
 import io.ktor.http.*
 import io.ktor.http.content.ByteArrayContent
 import io.ktor.http.content.OutgoingContent
@@ -45,18 +44,23 @@ internal class KtorRequestAdapter(
         // strip content type header which Ktor doesn't allow set this way for some reason
         val contentHeaders = builder.headers["Content-Type"]
         builder.headers.remove("Content-Type")
-        val contentType: ContentType? = contentHeaders?.let { ContentType.parse(it) }
+        val contentType: ContentType? = contentHeaders?.let(ContentType::parse)
 
         // convert the request body
-        when (val body = sdkRequest.body) {
-            is HttpBody.Empty -> builder.body = EmptyContent
-            is HttpBody.Bytes -> builder.body = ByteArrayContent(body.bytes(), contentType)
-            is HttpBody.Streaming -> builder.body = proxyRequestStream(body, contentType)
+        builder.body = when (val body = sdkRequest.body) {
+            is HttpBody.Empty -> emptyContent(contentType)
+            is HttpBody.Bytes -> ByteArrayContent(body.bytes(), contentType)
+            is HttpBody.Streaming -> proxyRequestStream(body, contentType)
         }
 
         return builder
     }
 
+    private fun emptyContent(contentType: ContentType?) = object : OutgoingContent.NoContent() {
+        override val contentLength: Long = 0
+        override val contentType = contentType
+    }
+
     @OptIn(ExperimentalStdlibApi::class)
     private fun proxyRequestStream(body: HttpBody.Streaming, contentType: ContentType?): OutgoingContent {
         val source = body.readFrom()

runtime/protocol/http-client-engines/http-client-engine-ktor/common/test/aws/smithy/kotlin/runtime/http/engine/ktor/KtorRequestAdapterTest.kt

@@ -16,9 +16,7 @@ import io.ktor.utils.io.*
 import io.ktor.utils.io.core.*
 import kotlinx.coroutines.*
 import kotlinx.coroutines.test.runTest
-import kotlin.test.Test
-import kotlin.test.assertEquals
-import kotlin.test.assertTrue
+import kotlin.test.*
 import io.ktor.content.ByteArrayContent as KtorByteArrayContent
 
 @OptIn(ExperimentalCoroutinesApi::class)
@@ -29,7 +27,11 @@ class KtorRequestAdapterTest {
         sdkBuilder.url { host = "test.aws.com" }
         sdkBuilder.header("Content-Type", "application/json")
         val actual = KtorRequestAdapter(sdkBuilder, coroutineContext).toBuilder()
-        actual.headers.contains("Content-Type").shouldBeFalse()
+        assertFalse("Content-Type" in actual.headers)
+
+        val body = actual.body
+        assertIs<OutgoingContent.NoContent>(body)
+        assertEquals(ContentType.parse("application/json"), body.contentType)
     }
 
     @Test

runtime/protocol/http-client-engines/test-suite/common/test/aws/smithy/kotlin/runtime/http/test/UploadTest.kt

@@ -11,6 +11,7 @@ import aws.smithy.kotlin.runtime.http.HttpMethod
 import aws.smithy.kotlin.runtime.http.HttpStatusCode
 import aws.smithy.kotlin.runtime.http.content.ByteArrayContent
 import aws.smithy.kotlin.runtime.http.request.HttpRequest
+import aws.smithy.kotlin.runtime.http.request.headers
 import aws.smithy.kotlin.runtime.http.request.url
 import aws.smithy.kotlin.runtime.http.response.complete
 import aws.smithy.kotlin.runtime.http.test.util.AbstractEngineTest
@@ -112,4 +113,28 @@ class UploadTest : AbstractEngineTest() {
             assertEquals(sha, call.response.headers["content-sha256"], "sha mismatch for upload on ${client.engine}")
         }
     }
+
+    @Test
+    fun testUploadEmptyWithContentTypes() = testEngines {
+        // test that empty bodies with a specified Content-Type actually include Content-Type in the request
+        // see https://github.com/awslabs/aws-sdk-kotlin/issues/588
+        test { env, client ->
+            val req = HttpRequest {
+                method = HttpMethod.POST
+                headers {
+                    append("Content-Type", "application/xml")
+                }
+                url(env.testServer)
+                url.path = "/upload/content"
+                body = HttpBody.Empty
+            }
+
+            val call = client.call(req)
+            call.complete()
+            assertEquals(HttpStatusCode.OK, call.response.status)
+
+            val reqContentType = call.response.headers["request-content-type"]
+            assertEquals("application/xml", reqContentType, "No Content-Type set on ${client.engine}")
+        }
+    }
 }

runtime/protocol/http-client-engines/test-suite/jvm/src/aws/smithy/kotlin/runtime/http/test/suite/Uploads.kt

@@ -31,6 +31,7 @@ internal fun Application.uploadTests() {
                 }
 
                 call.response.header("content-sha256", contentSha.digest().encodeToHex())
+                call.request.headers["Content-Type"]?.let { call.response.header("request-content-type", it) }
                 call.respond(HttpStatusCode.OK)
             }
         }