ktor 对某些数据类抛出 NoTransformationFoundException

Question

我有一个功能分支，我正在其中从休息服务加载数据。对于两个请求，这绝对按预期工作，但对于一个请求，我总是得到 NoTransformationFoundException。

我正在像这样创建 http 客户端：

private val httpClient =
    HttpClient(OkHttp) {
        install(JsonFeature) {
            serializer = GsonSerializer()
        }
    }

在上面你可以看到我正在使用 okhttp 和 gson。为了使问题更容易调试，这里是我的 ktor 依赖项：

compile "io.ktor:ktor-client-okhttp:1.2.6"
compile "io.ktor:ktor-client-json:1.2.6"
compile "io.ktor:ktor-client-gson:1.2.6"

像下面这样的请求对我来说效果很好。以下是相关文档（包括响应 JSON）：

data class Vendors(val vendors: List<Vendor>)

data class Vendor(
    val id: String,
    val name: String,
    val roles: List<String>
)

fun fetchVendors() = runBlocking {
    httpClient.get<Vendors>("https://api.amazonalexa.com/v1/vendors") {
        headers.append("Authorization", "Bearer $accessToken")
    }?.vendors
}

更新：我知道一定有区别：上面的内容类型是application/json

然而，这个调用（获取技能，以及此处的文档）不断失败：

data class Skills(
    val isTruncated: Boolean,
    val skills: List<Skill>
)

data class Skill(
    val apis: List<String>,
    val asin: String,
    val lastUpdated: String,
    val nameByLocale: Map<String, String>,
    val publicationStatus: String,
    val skillId: String,
    val stage: String
)

fun fetchSkills(vendor: String) = runBlocking {
    httpClient.get<Skills>("https://api.amazonalexa.com/v1/skills?vendorId=$vendor") {
        headers.append("Authorization", "Bearer $accessToken")
    }.skills
}

更新：这是响应内容类型：application/json+hal

我不明白为什么一个有效而另一个失败并出现以下异常：

Exception in thread "main" io.ktor.client.call.NoTransformationFoundException: No transformation found: class kotlinx.coroutines.io.ByteBufferChannel -> class my.package.name.Skills
        at io.ktor.client.call.HttpClientCall.receive(HttpClientCall.kt:88)
        at my.package.name.AmazonApi$fetchSkills$1.invokeSuspend(AmazonApi.kt:200)
        at kotlin.coroutines.jvm.internal.BaseContinuationImpl.resumeWith(ContinuationImpl.kt:33)
        at io.ktor.util.pipeline.SuspendFunctionGun.resumeRootWith(PipelineContext.kt:215)
        at io.ktor.util.pipeline.SuspendFunctionGun.loop(PipelineContext.kt:172)
        at io.ktor.util.pipeline.SuspendFunctionGun.access$loop(PipelineContext.kt:67)
        at io.ktor.util.pipeline.SuspendFunctionGun$continuation$1.resumeWith(PipelineContext.kt:122)
        at kotlin.coroutines.jvm.internal.BaseContinuationImpl.resumeWith(ContinuationImpl.kt:46)
        at io.ktor.util.pipeline.SuspendFunctionGun.resumeRootWith(PipelineContext.kt:215)
        at io.ktor.util.pipeline.SuspendFunctionGun.loop(PipelineContext.kt:172)
        at io.ktor.util.pipeline.SuspendFunctionGun.access$loop(PipelineContext.kt:67)
        at io.ktor.util.pipeline.SuspendFunctionGun$continuation$1.resumeWith(PipelineContext.kt:122)
        at kotlin.coroutines.jvm.internal.BaseContinuationImpl.resumeWith(ContinuationImpl.kt:46)
        at io.ktor.util.pipeline.SuspendFunctionGun.resumeRootWith(PipelineContext.kt:215)
        at io.ktor.util.pipeline.SuspendFunctionGun.loop(PipelineContext.kt:172)
        at io.ktor.util.pipeline.SuspendFunctionGun.access$loop(PipelineContext.kt:67)
        at io.ktor.util.pipeline.SuspendFunctionGun$continuation$1.resumeWith(PipelineContext.kt:122)
        at kotlin.coroutines.jvm.internal.BaseContinuationImpl.resumeWith(ContinuationImpl.kt:46)
        at kotlinx.coroutines.DispatchedTask.run(Dispatched.kt:241)
        at kotlinx.coroutines.EventLoopImplBase.processNextEvent(EventLoop.common.kt:270)
        at kotlinx.coroutines.BlockingCoroutine.joinBlocking(Builders.kt:79)
        at kotlinx.coroutines.BuildersKt__BuildersKt.runBlocking(Builders.kt:54)
        at kotlinx.coroutines.BuildersKt.runBlocking(Unknown Source)
        at kotlinx.coroutines.BuildersKt__BuildersKt.runBlocking$default(Builders.kt:36)
        at kotlinx.coroutines.BuildersKt.runBlocking$default(Unknown Source)
        at my.package.name.AmazonApi.fetchSkills(AmazonApi.kt:131)
        at my.package.name.Cli.createProject(Cli.kt:305)
        at my.package.name.Cli.parseArgs(Cli.kt:208)
        at my.package.name.Cli$Companion.main(Cli.kt:508)
        at my.package.name.Cli.main(Cli.kt)

请给我一些如何解决此问题的提示，或者至少如何调试它。顺便说一句，当我使用 String 而不是 Skill 时，我看到了预期的响应 JSON。

Answer 1

根据 GitHub 评论，我可以使用此解决方法：

val httpClient = HttpClient(OkHttp) {
    install(JsonFeature) {
        serializer = GsonSerializer()
        acceptContentTypes += ContentType("application", "json+hal")
    }
}

不过，我仍在寻找更好的解决方案，而不会引起警告。