Add docs and updates for background function support

rename fuction-sample-gcp to function-sample-gcp-http

refdoc polish

background sample polish

Resolves #525
Update pub/sub bg function to use base64 encoding

spring-cloud-function-samples/function-sample-gcp-http/src/main/java/com/example/CloudFunctionMain.java

@@ -0,0 +1,36 @@
+/*
+ * Copyright 2020-2020 the original author or authors.
+ *
+ * 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
+ *
+ *      https://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.
+ */
+
+package com.example;
+
+import java.util.function.Function;
+
+import org.springframework.boot.SpringApplication;
+import org.springframework.boot.autoconfigure.SpringBootApplication;
+import org.springframework.context.annotation.Bean;
+
+@SpringBootApplication
+public class CloudFunctionMain {
+
+	public static void main(String[] args) {
+		SpringApplication.run(CloudFunctionMain.class, args);
+	}
+
+	@Bean
+	public Function<String, String> function() {
+		return value -> value.toUpperCase();
+	}
+}

spring-cloud-function-samples/function-sample-gcp-http/src/main/resources/META-INF/MANIFEST.MF

@@ -0,0 +1 @@
+Main-Class: com.example.CloudFunctionMain

spring-cloud-function-samples/function-sample-gcp-http/src/test/java/com/example/FunctionSampleGcpIntegrationTest.java

@@ -0,0 +1,90 @@
+/*
+ * Copyright 2020-2020 the original author or authors.
+ *
+ * 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
+ *
+ *      https://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.
+ */
+
+package com.example;
+
+import java.io.BufferedReader;
+import java.io.IOException;
+import java.io.InputStream;
+import java.io.InputStreamReader;
+import java.util.concurrent.CountDownLatch;
+import java.util.concurrent.Executors;
+import java.util.concurrent.TimeUnit;
+
+import org.junit.Test;
+
+import org.springframework.boot.test.web.client.TestRestTemplate;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.fail;
+
+public class FunctionSampleGcpIntegrationTest {
+
+	private TestRestTemplate rest = new TestRestTemplate();
+
+	private CountDownLatch startedSuccessfully = new CountDownLatch(1);
+
+	@Test
+	public void testSample() throws IOException {
+		Process process = new ProcessBuilder("./../../mvnw", "function:run").start();
+
+		try {
+			Executors.defaultThreadFactory().newThread(new OutputCapture(process.getErrorStream())).start();
+			Executors.defaultThreadFactory().newThread(new OutputCapture(process.getInputStream())).start();
+
+			if (startedSuccessfully.await(10, TimeUnit.SECONDS)) {
+				String result = rest.postForObject("http://localhost:8080/", "Hello", String.class);
+				assertThat(result).isEqualTo("\"HELLO\"");
+			}
+			else {
+				fail("Failed to start the function.");
+			}
+		}
+		catch (InterruptedException e) {
+			e.printStackTrace();
+		}
+		finally {
+			process.destroy();
+		}
+	}
+
+	class OutputCapture implements Runnable {
+
+		private InputStream inputStream;
+
+		OutputCapture(InputStream inputStream) {
+			this.inputStream = inputStream;
+		}
+
+		@Override
+		public void run() {
+			try (BufferedReader reader = new BufferedReader(new InputStreamReader(inputStream))) {
+				String line;
+				while ((line = reader.readLine()) != null) {
+					System.out.println(line);
+					if (line.equals("INFO: URL: http://localhost:8080/")) {
+						startedSuccessfully.countDown();
+					}
+				}
+			}
+			catch (IOException e) {
+				e.printStackTrace();
+			}
+		}
+
+	}
+
+}