Refactor determining server error type when deserializing an @httpPayload (#3752)

Determining the error type when deserializing an `@httpPayload` is a
protocol-specific concern, and as such should not live in
`ServerHttpBoundProtocolGenerator`, which should remain
protocol-agnostic. This commits makes that determination part of the
`ServerProtocol` interface.

As a drive-by improvement, the companion object in
`ServerHttpBoundProtocolGenerator` has also been removed, since its
members have been unused for a long time.

----

_By submitting this pull request, I confirm that you can use, modify,
copy, and redistribute this contribution, under the terms of your
choice._

Author: david-perez

codegen-server/src/main/kotlin/software/amazon/smithy/rust/codegen/server/smithy/generators/http/ServerRequestBindingGenerator.kt

@@ -5,7 +5,6 @@
 
 package software.amazon.smithy.rust.codegen.server.smithy.generators.http
 
-import software.amazon.smithy.codegen.core.Symbol
 import software.amazon.smithy.model.shapes.OperationShape
 import software.amazon.smithy.rust.codegen.core.rustlang.RustType
 import software.amazon.smithy.rust.codegen.core.rustlang.RustWriter
@@ -20,12 +19,12 @@ import software.amazon.smithy.rust.codegen.core.smithy.generators.http.HttpBindi
 import software.amazon.smithy.rust.codegen.core.smithy.generators.http.HttpMessageType
 import software.amazon.smithy.rust.codegen.core.smithy.mapRustType
 import software.amazon.smithy.rust.codegen.core.smithy.protocols.HttpBindingDescriptor
-import software.amazon.smithy.rust.codegen.core.smithy.protocols.Protocol
 import software.amazon.smithy.rust.codegen.server.smithy.ServerCodegenContext
+import software.amazon.smithy.rust.codegen.server.smithy.generators.protocol.ServerProtocol
 import software.amazon.smithy.rust.codegen.server.smithy.targetCanReachConstrainedShape
 
 class ServerRequestBindingGenerator(
-    protocol: Protocol,
+    val protocol: ServerProtocol,
     codegenContext: ServerCodegenContext,
     operationShape: OperationShape,
     additionalHttpBindingCustomizations: List<HttpBindingCustomization> = listOf(),
@@ -50,12 +49,11 @@ class ServerRequestBindingGenerator(
 
     fun generateDeserializePayloadFn(
         binding: HttpBindingDescriptor,
-        errorSymbol: Symbol,
         structuredHandler: RustWriter.(String) -> Unit,
     ): RuntimeType =
         httpBindingGenerator.generateDeserializePayloadFn(
             binding,
-            errorSymbol,
+            protocol.deserializePayloadErrorType(binding).toSymbol(),
             structuredHandler,
             HttpMessageType.REQUEST,
         )

codegen-server/src/main/kotlin/software/amazon/smithy/rust/codegen/server/smithy/generators/protocol/ServerProtocol.kt

@@ -8,6 +8,7 @@ package software.amazon.smithy.rust.codegen.server.smithy.generators.protocol
 import software.amazon.smithy.model.shapes.MemberShape
 import software.amazon.smithy.model.shapes.OperationShape
 import software.amazon.smithy.model.shapes.Shape
+import software.amazon.smithy.model.shapes.StringShape
 import software.amazon.smithy.model.shapes.StructureShape
 import software.amazon.smithy.rust.codegen.core.rustlang.Writable
 import software.amazon.smithy.rust.codegen.core.rustlang.rust
@@ -17,7 +18,9 @@ import software.amazon.smithy.rust.codegen.core.smithy.RuntimeConfig
 import software.amazon.smithy.rust.codegen.core.smithy.RuntimeType
 import software.amazon.smithy.rust.codegen.core.smithy.protocols.AwsJson
 import software.amazon.smithy.rust.codegen.core.smithy.protocols.AwsJsonVersion
+import software.amazon.smithy.rust.codegen.core.smithy.protocols.HttpBindingDescriptor
 import software.amazon.smithy.rust.codegen.core.smithy.protocols.HttpBindingResolver
+import software.amazon.smithy.rust.codegen.core.smithy.protocols.HttpLocation
 import software.amazon.smithy.rust.codegen.core.smithy.protocols.Protocol
 import software.amazon.smithy.rust.codegen.core.smithy.protocols.RestJson
 import software.amazon.smithy.rust.codegen.core.smithy.protocols.RestXml
@@ -70,8 +73,8 @@ interface ServerProtocol : Protocol {
     fun serverRouterRequestSpecType(requestSpecModule: RuntimeType): RuntimeType
 
     /**
-     * In some protocols, such as restJson1,
-     * when there is no modeled body input, content type must not be set and the body must be empty.
+     * In some protocols, such as `restJson1` and `rpcv2Cbor`,
+     * when there is no modeled body input, `content-type` must not be set and the body must be empty.
      * Returns a boolean indicating whether to perform this check.
      */
     fun serverContentTypeCheckNoModeledInput(): Boolean = false
@@ -90,6 +93,19 @@ interface ServerProtocol : Protocol {
     fun runtimeError(runtimeConfig: RuntimeConfig): RuntimeType =
         ServerCargoDependency.smithyHttpServer(runtimeConfig)
             .toType().resolve("protocol::$protocolModulePath::runtime_error::RuntimeError")
+
+    /**
+     * The function that deserializes a payload-bound shape takes as input a byte slab and returns a `Result` holding
+     * the deserialized shape if successful. What error type should we use in case of failure?
+     *
+     * The shape could be payload-bound either because of the `@httpPayload` trait, or because it's part of an event
+     * stream.
+     *
+     * Note that despite the trait (https://smithy.io/2.0/spec/http-bindings.html#httppayload-trait) being able to
+     * target any structure member shape, AWS Protocols only support binding the following shape types to the payload
+     * (and Smithy does indeed enforce this at model build-time): string, blob, structure, union, and document
+     */
+    fun deserializePayloadErrorType(binding: HttpBindingDescriptor): RuntimeType
 }
 
 fun returnSymbolToParseFn(codegenContext: ServerCodegenContext): (Shape) -> ReturnSymbolToParse {
@@ -185,6 +201,18 @@ class ServerAwsJsonProtocol(
     override fun runtimeError(runtimeConfig: RuntimeConfig): RuntimeType =
         ServerCargoDependency.smithyHttpServer(runtimeConfig)
             .toType().resolve("protocol::aws_json::runtime_error::RuntimeError")
+
+    /*
+     * Note that despite the AWS JSON 1.x protocols not supporting the `@httpPayload` trait, event streams are bound
+     * to the payload.
+     */
+    override fun deserializePayloadErrorType(binding: HttpBindingDescriptor): RuntimeType =
+        deserializePayloadErrorType(
+            codegenContext,
+            binding,
+            requestRejection(runtimeConfig),
+            RuntimeType.smithyJson(codegenContext.runtimeConfig).resolve("deserialize::error::DeserializeError"),
+        )
 }
 
 private fun restRouterType(runtimeConfig: RuntimeConfig) =
@@ -227,6 +255,14 @@ class ServerRestJsonProtocol(
     override fun serverRouterRuntimeConstructor() = "new_rest_json_router"
 
     override fun serverContentTypeCheckNoModeledInput() = true
+
+    override fun deserializePayloadErrorType(binding: HttpBindingDescriptor): RuntimeType =
+        deserializePayloadErrorType(
+            codegenContext,
+            binding,
+            requestRejection(runtimeConfig),
+            RuntimeType.smithyJson(codegenContext.runtimeConfig).resolve("deserialize::error::DeserializeError"),
+        )
 }
 
 class ServerRestXmlProtocol(
@@ -252,6 +288,32 @@ class ServerRestXmlProtocol(
     override fun serverRouterRuntimeConstructor() = "new_rest_xml_router"
 
     override fun serverContentTypeCheckNoModeledInput() = true
+
+    override fun deserializePayloadErrorType(binding: HttpBindingDescriptor): RuntimeType =
+        deserializePayloadErrorType(
+            codegenContext,
+            binding,
+            requestRejection(runtimeConfig),
+            RuntimeType.smithyXml(runtimeConfig).resolve("decode::XmlDecodeError"),
+        )
+}
+
+/** Just a common function to keep things DRY. **/
+fun deserializePayloadErrorType(
+    codegenContext: CodegenContext,
+    binding: HttpBindingDescriptor,
+    requestRejection: RuntimeType,
+    protocolSerializationFormatError: RuntimeType,
+): RuntimeType {
+    check(binding.location == HttpLocation.PAYLOAD)
+
+    if (codegenContext.model.expectShape(binding.member.target) is StringShape) {
+        // The only way deserializing a string can fail is if the HTTP body does not contain valid UTF-8.
+        // TODO(https://github.com/smithy-lang/smithy-rs/issues/3750): we're returning an incorrect `RequestRejection` variant here.
+        return requestRejection
+    }
+
+    return protocolSerializationFormatError
 }
 
 /**

codegen-server/src/main/kotlin/software/amazon/smithy/rust/codegen/server/smithy/protocols/ServerHttpBoundProtocolGenerator.kt

@@ -5,10 +5,6 @@
 
 package software.amazon.smithy.rust.codegen.server.smithy.protocols
 
-import software.amazon.smithy.aws.traits.protocols.AwsJson1_0Trait
-import software.amazon.smithy.aws.traits.protocols.AwsJson1_1Trait
-import software.amazon.smithy.aws.traits.protocols.RestJson1Trait
-import software.amazon.smithy.aws.traits.protocols.RestXmlTrait
 import software.amazon.smithy.codegen.core.Symbol
 import software.amazon.smithy.model.knowledge.HttpBindingIndex
 import software.amazon.smithy.model.node.ExpectationNotMetException
@@ -20,7 +16,6 @@ import software.amazon.smithy.model.shapes.MemberShape
 import software.amazon.smithy.model.shapes.NumberShape
 import software.amazon.smithy.model.shapes.OperationShape
 import software.amazon.smithy.model.shapes.Shape
-import software.amazon.smithy.model.shapes.StringShape
 import software.amazon.smithy.model.shapes.StructureShape
 import software.amazon.smithy.model.traits.ErrorTrait
 import software.amazon.smithy.model.traits.HttpErrorTrait
@@ -124,13 +119,7 @@ class ServerHttpBoundProtocolGenerator(
 ) : ServerProtocolGenerator(
         protocol,
         ServerHttpBoundProtocolTraitImplGenerator(codegenContext, protocol, customizations, additionalHttpBindingCustomizations),
-    ) {
-    // Define suffixes for operation input / output / error wrappers
-    companion object {
-        const val OPERATION_INPUT_WRAPPER_SUFFIX = "OperationInputWrapper"
-        const val OPERATION_OUTPUT_WRAPPER_SUFFIX = "OperationOutputWrapper"
-    }
-}
+    )
 
 class ServerHttpBoundProtocolPayloadGenerator(
     codegenContext: CodegenContext,
@@ -697,8 +686,6 @@ class ServerHttpBoundProtocolTraitImplGenerator(
         inputShape: StructureShape,
         bindings: List<HttpBindingDescriptor>,
     ) {
-        val httpBindingGenerator =
-            ServerRequestBindingGenerator(protocol, codegenContext, operationShape, additionalHttpBindingCustomizations)
         val structuredDataParser = protocol.structuredDataParser()
         Attribute.AllowUnusedMut.render(this)
         rust(
@@ -740,7 +727,7 @@ class ServerHttpBoundProtocolTraitImplGenerator(
         for (binding in bindings) {
             val member = binding.member
             val parsedValue =
-                serverRenderBindingParser(binding, operationShape, httpBindingGenerator, structuredDataParser)
+                serverRenderBindingParser(binding, operationShape, httpBindingGenerator(operationShape), structuredDataParser)
             val valueToSet =
                 if (symbolProvider.toSymbol(binding.member).isOptional()) {
                     "Some(value)"
@@ -801,13 +788,8 @@ class ServerHttpBoundProtocolTraitImplGenerator(
                 val structureShapeHandler: RustWriter.(String) -> Unit = { body ->
                     rust("#T($body)", structuredDataParser.payloadParser(binding.member))
                 }
-                val errorSymbol = getDeserializePayloadErrorSymbol(binding)
                 val deserializer =
-                    httpBindingGenerator.generateDeserializePayloadFn(
-                        binding,
-                        errorSymbol,
-                        structuredHandler = structureShapeHandler,
-                    )
+                    httpBindingGenerator.generateDeserializePayloadFn(binding, structuredHandler = structureShapeHandler)
                 return writable {
                     if (binding.member.isStreaming(model)) {
                         rustTemplate(
@@ -1196,9 +1178,7 @@ class ServerHttpBoundProtocolTraitImplGenerator(
         binding: HttpBindingDescriptor,
         operationShape: OperationShape,
     ) {
-        val httpBindingGenerator =
-            ServerRequestBindingGenerator(protocol, codegenContext, operationShape, additionalHttpBindingCustomizations)
-        val deserializer = httpBindingGenerator.generateDeserializeHeaderFn(binding)
+        val deserializer = httpBindingGenerator(operationShape).generateDeserializeHeaderFn(binding)
         writer.rustTemplate(
             """
             #{deserializer}(&headers)?
@@ -1215,8 +1195,7 @@ class ServerHttpBoundProtocolTraitImplGenerator(
     ) {
         check(binding.location == HttpLocation.PREFIX_HEADERS)
 
-        val httpBindingGenerator = ServerRequestBindingGenerator(protocol, codegenContext, operationShape)
-        val deserializer = httpBindingGenerator.generateDeserializePrefixHeadersFn(binding)
+        val deserializer = httpBindingGenerator(operationShape).generateDeserializePrefixHeadersFn(binding)
         writer.rustTemplate(
             """
             #{deserializer}(&headers)?
@@ -1300,33 +1279,13 @@ class ServerHttpBoundProtocolTraitImplGenerator(
         }
     }
 
-    /**
-     * Returns the error type of the function that deserializes a non-streaming HTTP payload (a byte slab) into the
-     * shape targeted by the `httpPayload` trait.
-     */
-    private fun getDeserializePayloadErrorSymbol(binding: HttpBindingDescriptor): Symbol {
-        check(binding.location == HttpLocation.PAYLOAD)
-
-        if (model.expectShape(binding.member.target) is StringShape) {
-            return protocol.requestRejection(runtimeConfig).toSymbol()
-        }
-        return when (codegenContext.protocol) {
-            RestJson1Trait.ID, AwsJson1_0Trait.ID, AwsJson1_1Trait.ID -> {
-                RuntimeType.smithyJson(runtimeConfig).resolve("deserialize::error::DeserializeError").toSymbol()
-            }
-            RestXmlTrait.ID -> {
-                RuntimeType.smithyXml(runtimeConfig).resolve("decode::XmlDecodeError").toSymbol()
-            }
-            else -> {
-                TODO("Protocol ${codegenContext.protocol} not supported yet")
-            }
-        }
-    }
-
     private fun streamingBodyTraitBounds(operationShape: OperationShape) =
         if (operationShape.inputShape(model).hasStreamingMember(model)) {
             "\n B: Into<#{SmithyTypes}::byte_stream::ByteStream>,"
         } else {
             ""
         }
+
+    private fun httpBindingGenerator(operationShape: OperationShape) =
+        ServerRequestBindingGenerator(protocol, codegenContext, operationShape, additionalHttpBindingCustomizations)
 }