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feat: Define strongly typed function interface (#186)
Introduces a new Typed signature to the functions framework which provides automatic request deserialization and response serialization.
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59 changes: 59 additions & 0 deletions
59
functions-framework-api/src/main/java/com/google/cloud/functions/TypedFunction.java
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,59 @@ | ||
| // Copyright 2019 Google LLC | ||
| // | ||
| // Licensed under the Apache License, Version 2.0 (the "License"); | ||
| // you may not use this file except in compliance with the License. | ||
| // You may obtain a copy of the License at | ||
| // | ||
| // http://www.apache.org/licenses/LICENSE-2.0 | ||
| // | ||
| // Unless required by applicable law or agreed to in writing, software | ||
| // distributed under the License is distributed on an "AS IS" BASIS, | ||
| // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. | ||
| // See the License for the specific language governing permissions and | ||
| // limitations under the License. | ||
|
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| package com.google.cloud.functions; | ||
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| import java.lang.reflect.Type; | ||
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| /** | ||
| * Represents a Cloud Function with a strongly typed interface that is activated by an HTTP request. | ||
| */ | ||
| @FunctionalInterface | ||
| public interface TypedFunction<RequestT, ResponseT> { | ||
| /** | ||
| * Called to service an incoming HTTP request. This interface is implemented by user code to | ||
| * provide the action for a given HTTP function. If this method throws any exception (including | ||
| * any {@link Error}) then the HTTP response will have a 500 status code. | ||
| * | ||
| * @param arg the payload of the event, deserialized from the original JSON string. | ||
| * @return invocation result or null to indicate the body of the response should be empty. | ||
| * @throws Exception to produce a 500 status code in the HTTP response. | ||
| */ | ||
| public ResponseT apply(RequestT arg) throws Exception; | ||
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| /** | ||
| * Called to get the the format object that handles request decoding and response encoding. If | ||
| * null is returned a default JSON format is used. | ||
| * | ||
| * @return the {@link WireFormat} to use for serialization | ||
| */ | ||
| public default WireFormat getWireFormat() { | ||
| return null; | ||
| } | ||
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| /** | ||
| * Describes how to deserialize request object and serialize response objects for an HTTP | ||
| * invocation. | ||
| */ | ||
| public interface WireFormat { | ||
| /** Serialize is expected to encode the object to the provided HttpResponse. */ | ||
| void serialize(Object object, HttpResponse response) throws Exception; | ||
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| /** | ||
| * Deserialize is expected to read an object of {@code Type} from the HttpRequest. The Type is | ||
| * determined through reflection on the user's function. | ||
| */ | ||
| Object deserialize(HttpRequest request, Type type) throws Exception; | ||
| } | ||
| } |
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165 changes: 165 additions & 0 deletions
165
invoker/core/src/main/java/com/google/cloud/functions/invoker/TypedFunctionExecutor.java
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,165 @@ | ||
| package com.google.cloud.functions.invoker; | ||
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| import com.google.cloud.functions.HttpRequest; | ||
| import com.google.cloud.functions.HttpResponse; | ||
| import com.google.cloud.functions.TypedFunction; | ||
| import com.google.cloud.functions.TypedFunction.WireFormat; | ||
| import com.google.cloud.functions.invoker.http.HttpRequestImpl; | ||
| import com.google.cloud.functions.invoker.http.HttpResponseImpl; | ||
| import com.google.gson.Gson; | ||
| import com.google.gson.GsonBuilder; | ||
| import java.io.BufferedReader; | ||
| import java.io.BufferedWriter; | ||
| import java.lang.reflect.Type; | ||
| import java.util.Arrays; | ||
| import java.util.Optional; | ||
| import java.util.logging.Level; | ||
| import java.util.logging.Logger; | ||
| import javax.servlet.http.HttpServlet; | ||
| import javax.servlet.http.HttpServletRequest; | ||
| import javax.servlet.http.HttpServletResponse; | ||
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| public class TypedFunctionExecutor extends HttpServlet { | ||
| private static final String APPLY_METHOD = "apply"; | ||
| private static final Logger logger = Logger.getLogger("com.google.cloud.functions.invoker"); | ||
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| private final Type argType; | ||
| private final TypedFunction<Object, Object> function; | ||
| private final WireFormat format; | ||
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| private TypedFunctionExecutor( | ||
| Type argType, TypedFunction<Object, Object> func, WireFormat format) { | ||
| this.argType = argType; | ||
| this.function = func; | ||
| this.format = format; | ||
| } | ||
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| public static TypedFunctionExecutor forClass(Class<?> functionClass) { | ||
| if (!TypedFunction.class.isAssignableFrom(functionClass)) { | ||
| throw new RuntimeException( | ||
| "Class " | ||
| + functionClass.getName() | ||
| + " does not implement " | ||
| + TypedFunction.class.getName()); | ||
| } | ||
| @SuppressWarnings("unchecked") | ||
| Class<? extends TypedFunction<?, ?>> typedFunctionClass = | ||
| (Class<? extends TypedFunction<?, ?>>) functionClass.asSubclass(TypedFunction.class); | ||
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| Optional<Type> argType = handlerTypeArgument(typedFunctionClass); | ||
| if (argType.isEmpty()) { | ||
| throw new RuntimeException( | ||
| "Class " | ||
| + typedFunctionClass.getName() | ||
| + " does not implement " | ||
| + TypedFunction.class.getName()); | ||
| } | ||
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| TypedFunction<?, ?> typedFunction; | ||
| try { | ||
| typedFunction = typedFunctionClass.getDeclaredConstructor().newInstance(); | ||
| } catch (Exception e) { | ||
| throw new RuntimeException( | ||
| "Class " | ||
| + typedFunctionClass.getName() | ||
| + " must declare a valid default constructor to be usable as a strongly typed" | ||
| + " function. Could not use constructor: " | ||
| + e.toString()); | ||
| } | ||
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| WireFormat format = typedFunction.getWireFormat(); | ||
| if (format == null) { | ||
| format = LazyDefaultFormatHolder.defaultFormat; | ||
| } | ||
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| @SuppressWarnings("unchecked") | ||
| TypedFunctionExecutor executor = | ||
| new TypedFunctionExecutor( | ||
| argType.orElseThrow(), (TypedFunction<Object, Object>) typedFunction, format); | ||
| return executor; | ||
| } | ||
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| /** | ||
| * Returns the {@code ReqT} of a concrete class that implements {@link TypedFunction | ||
| * TypedFunction<ReqT, RespT>}. Returns an empty {@link Optional} if {@code ReqT} can't be | ||
| * determined. | ||
| */ | ||
| static Optional<Type> handlerTypeArgument(Class<? extends TypedFunction<?, ?>> functionClass) { | ||
| return Arrays.stream(functionClass.getMethods()) | ||
| .filter(method -> method.getName().equals(APPLY_METHOD) && method.getParameterCount() == 1) | ||
| .map(method -> method.getGenericParameterTypes()[0]) | ||
| .filter(type -> type != Object.class) | ||
| .findFirst(); | ||
| } | ||
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| /** Executes the user's method, can handle all HTTP type methods. */ | ||
| @Override | ||
| public void service(HttpServletRequest req, HttpServletResponse res) { | ||
| HttpRequestImpl reqImpl = new HttpRequestImpl(req); | ||
| HttpResponseImpl resImpl = new HttpResponseImpl(res); | ||
| ClassLoader oldContextClassLoader = Thread.currentThread().getContextClassLoader(); | ||
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| try { | ||
| Thread.currentThread().setContextClassLoader(function.getClass().getClassLoader()); | ||
| handleRequest(reqImpl, resImpl); | ||
| } finally { | ||
| Thread.currentThread().setContextClassLoader(oldContextClassLoader); | ||
| resImpl.flush(); | ||
| } | ||
| } | ||
|
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| private void handleRequest(HttpRequest req, HttpResponse res) { | ||
| Object reqObj; | ||
| try { | ||
| reqObj = format.deserialize(req, argType); | ||
| } catch (Throwable t) { | ||
| logger.log(Level.SEVERE, "Failed to parse request for " + function.getClass().getName(), t); | ||
| res.setStatusCode(HttpServletResponse.SC_BAD_REQUEST); | ||
| return; | ||
| } | ||
|
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| Object resObj; | ||
| try { | ||
| resObj = function.apply(reqObj); | ||
| } catch (Throwable t) { | ||
| logger.log(Level.SEVERE, "Failed to execute " + function.getClass().getName(), t); | ||
| res.setStatusCode(HttpServletResponse.SC_INTERNAL_SERVER_ERROR); | ||
| return; | ||
| } | ||
|
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| try { | ||
| format.serialize(resObj, res); | ||
| } catch (Throwable t) { | ||
| logger.log( | ||
| Level.SEVERE, "Failed to serialize response for " + function.getClass().getName(), t); | ||
| res.setStatusCode(HttpServletResponse.SC_INTERNAL_SERVER_ERROR); | ||
| return; | ||
| } | ||
| } | ||
|
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| private static class LazyDefaultFormatHolder { | ||
| static final WireFormat defaultFormat = new GsonWireFormat(); | ||
| } | ||
|
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| private static class GsonWireFormat implements TypedFunction.WireFormat { | ||
| private final Gson gson = new GsonBuilder().create(); | ||
|
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| @Override | ||
| public void serialize(Object object, HttpResponse response) throws Exception { | ||
| if (object == null) { | ||
| response.setStatusCode(HttpServletResponse.SC_NO_CONTENT); | ||
| return; | ||
| } | ||
| try (BufferedWriter bodyWriter = response.getWriter()) { | ||
| gson.toJson(object, bodyWriter); | ||
| } | ||
| } | ||
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| @Override | ||
| public Object deserialize(HttpRequest request, Type type) throws Exception { | ||
| try (BufferedReader bodyReader = request.getReader()) { | ||
| return gson.fromJson(bodyReader, type); | ||
| } | ||
| } | ||
| } | ||
| } |
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