Added a serving sample for dart

serving/samples/helloworld-dart/Dockerfile

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+FROM google/dart-runtime

serving/samples/helloworld-dart/README.md

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+# Hello World - Dart sample
+
+A simple web app written in the [Dart](www.dartlang.org) programming language
+that you can use for testing. It reads in the env variable `TARGET` and prints
+`"Hello $TARGET"`. If `TARGET` is not specified, it will use `"World"` as `TARGET`.
+
+## Prerequisites
+
+* A Kubernetes cluster with Knative installed. Follow the
+  [installation instructions](https://github.com/knative/docs/blob/master/install/README.md) if you need
+  to create one.
+* [Docker](https://www.docker.com) installed and running on your local machine,
+  and a Docker Hub account configured (we'll use it for a container registry).
+* [dart-sdk](https://www.dartlang.org/tools/sdk#install) installed and configured.
+
+## Recreating the sample code
+
+While you can clone all of the code from this directory, it is useful to know how
+to build a hello world Dart application step-by-step. This application can be
+created using the following instructions.
+
+1. Create a new directory and write `pubspec.yaml` as follows:
+
+    ```yaml
+    name: hello_world_dart
+    private: True  # let's not accidentally publish this to pub.dartlang.org
+    description: >-
+      Hello world server example in dart.
+    dependencies:
+      shelf: ^0.7.3
+    environment:
+      sdk: '>=2.0.0 <3.0.0'
+    ```
+
+2. Install dependencies
+
+    ```shell
+    pub get
+    ```
+
+3. Create a new file `bin/main.dart` and write the following code:
+
+    ```dart
+    import 'dart:io';
+
+    import 'package:shelf/shelf.dart';
+    import 'package:shelf/shelf_io.dart';
+
+    void main() {
+      // Find port to listen on from environment variable.
+      var port = int.tryParse(Platform.environment['PORT']);
+
+      // Read $TARGET from environment variable.
+      var target = Platform.environment['TARGET'] ?? 'World';
+
+      // Create handler.
+      var handler = Pipeline().addMiddleware(logRequests()).addHandler((request) {
+        return Response.ok('Hello $target');
+      });
+
+      // Serve handler on given port.
+      serve(handler, InternetAddress.anyIPv4, port).then((server) {
+        print('Serving at http://${server.address.host}:${server.port}');
+      });
+    }
+    ```
+
+4. Create a new file named `Dockerfile`, this file defines instructions for 
+   dockerizing your applications, for dart apps this can be done as follows:
+
+    ```Dockerfile
+    FROM google/dart-runtime
+    ```
+
+5. Create a new file, `service.yaml` and copy the following service definition
+   into the file. Make sure to replace `{username}` with your Docker Hub username.
+
+    ```yaml
+    apiVersion: serving.knative.dev/v1alpha1
+    kind: Service
+    metadata:
+      name: helloworld-dart
+      namespace: default
+    spec:
+      runLatest:
+        configuration:
+          revisionTemplate:
+            spec:
+              container:
+                image: docker.io/{username}/helloworld-dart
+                env:
+                - name: TARGET
+                  value: "Dart Sample v1"
+    ```
+
+## Building and deploying the sample
+
+Once you have recreated the sample code files (or used the files in the sample
+folder) you're ready to build and deploy the sample app.
+
+1. Use Docker to build the sample code into a container. To build and push with
+   Docker Hub, run these commands replacing `{username}` with your
+   Docker Hub username:
+
+    ```shell
+    # Build the container on your local machine
+    docker build -t {username}/helloworld-dart .
+
+    # Push the container to docker registry
+    docker push {username}/helloworld-dart
+    ```
+
+1. After the build has completed and the container is pushed to docker hub, you
+   can deploy the app into your cluster. Ensure that the container image value
+   in `service.yaml` matches the container you built in
+   the previous step. Apply the configuration using `kubectl`:
+
+    ```shell
+    kubectl apply --filename service.yaml
+    ```
+
+1. Now that your service is created, Knative will perform the following steps:
+   * Create a new immutable revision for this version of the app.
+   * Network programming to create a route, ingress, service, and load balance for your app.
+   * Automatically scale your pods up and down (including to zero active pods).
+
+1. To find the IP address for your service, use
+   `kubectl get svc knative-ingressgateway -n istio-system` to get the ingress IP for your
+   cluster. If your cluster is new, it may take sometime for the service to get asssigned
+   an external IP address.
+
+    ```shell
+    kubectl get svc knative-ingressgateway --namespace istio-system
+
+    NAME                     TYPE           CLUSTER-IP     EXTERNAL-IP      PORT(S)                                      AGE
+    knative-ingressgateway   LoadBalancer   10.23.247.74   35.203.155.229   80:32380/TCP,443:32390/TCP,32400:32400/TCP   2d
+
+    ```
+
+1. To find the URL for your service, use
+    ```
+    kubectl get services.serving.knative.dev helloworld-dart  --output=custom-columns=NAME:.metadata.name,DOMAIN:.status.domain
+    NAME                DOMAIN
+    helloworld-dart   helloworld-dart.default.example.com
+    ```
+
+1. Now you can make a request to your app to see the result. Replace
+   `{IP_ADDRESS}` with the address you see returned in the previous step.
+
+    ```shell
+    curl -H "Host: helloworld-dart.default.example.com" http://{IP_ADDRESS}
+    Hello Dart Sample v1
+    ```
+
+## Removing the sample app deployment
+
+To remove the sample app from your cluster, delete the service record:
+
+```shell
+kubectl delete --filename service.yaml
+```
+

serving/samples/helloworld-dart/bin/server.dart

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+import 'dart:io';
+
+import 'package:shelf/shelf.dart';
+import 'package:shelf/shelf_io.dart';
+
+void main() {
+  // Find port to listen on from environment variable.
+  var port = int.tryParse(Platform.environment['PORT']);
+
+  // Read $TARGET from environment variable.
+  var target = Platform.environment['TARGET'] ?? 'World';
+
+  // Create handler.
+  var handler = Pipeline().addMiddleware(logRequests()).addHandler((request) {
+    return Response.ok('Hello $target');
+  });
+
+  // Serve handler on given port.
+  serve(handler, InternetAddress.anyIPv4, port).then((server) {
+    print('Serving at http://${server.address.host}:${server.port}');
+  });
+}

serving/samples/helloworld-dart/pubspec.lock

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+# Generated by pub
+# See https://www.dartlang.org/tools/pub/glossary#lockfile
+packages:
+  async:
+    dependency: transitive
+    description:
+      name: async
+      url: "https://pub.dartlang.org"
+    source: hosted
+    version: "2.0.8"
+  charcode:
+    dependency: transitive
+    description:
+      name: charcode
+      url: "https://pub.dartlang.org"
+    source: hosted
+    version: "1.1.2"
+  collection:
+    dependency: transitive
+    description:
+      name: collection
+      url: "https://pub.dartlang.org"
+    source: hosted
+    version: "1.14.11"
+  http_parser:
+    dependency: transitive
+    description:
+      name: http_parser
+      url: "https://pub.dartlang.org"
+    source: hosted
+    version: "3.1.3"
+  meta:
+    dependency: transitive
+    description:
+      name: meta
+      url: "https://pub.dartlang.org"
+    source: hosted
+    version: "1.1.6"
+  path:
+    dependency: transitive
+    description:
+      name: path
+      url: "https://pub.dartlang.org"
+    source: hosted
+    version: "1.6.2"
+  shelf:
+    dependency: "direct main"
+    description:
+      name: shelf
+      url: "https://pub.dartlang.org"
+    source: hosted
+    version: "0.7.3+3"
+  source_span:
+    dependency: transitive
+    description:
+      name: source_span
+      url: "https://pub.dartlang.org"
+    source: hosted
+    version: "1.4.1"
+  stack_trace:
+    dependency: transitive
+    description:
+      name: stack_trace
+      url: "https://pub.dartlang.org"
+    source: hosted
+    version: "1.9.3"
+  stream_channel:
+    dependency: transitive
+    description:
+      name: stream_channel
+      url: "https://pub.dartlang.org"
+    source: hosted
+    version: "1.6.8"
+  string_scanner:
+    dependency: transitive
+    description:
+      name: string_scanner
+      url: "https://pub.dartlang.org"
+    source: hosted
+    version: "1.0.4"
+  typed_data:
+    dependency: transitive
+    description:
+      name: typed_data
+      url: "https://pub.dartlang.org"
+    source: hosted
+    version: "1.1.6"
+sdks:
+  dart: ">=2.0.0 <3.0.0"

serving/samples/helloworld-dart/pubspec.yaml

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+name: hello_world_dart
+private: True  # let's not accidentally publish this to pub.dartlang.org
+dependencies:
+  shelf: ^0.7.3
+environment:
+  sdk: '>=2.0.0 <3.0.0'

serving/samples/helloworld-dart/service.yaml

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+apiVersion: serving.knative.dev/v1alpha1
+  kind: Service
+  metadata:
+    name: helloworld-dart
+    namespace: default
+  spec:
+    runLatest:
+      configuration:
+        revisionTemplate:
+          spec:
+            container:
+              image: docker.io/{username}/helloworld-dart
+              env:
+              - name: TARGET
+                value: "Dart Sample v1"