Allow label to be a comman-separated list on config client

The client will search through a list of labels until it finds one
that succeeds, otherwise fail.

Fixes gh-153

docs/src/main/asciidoc/spring-cloud-config.adoc

@@ -189,7 +189,7 @@ Config Server comes with a Health Indicator that checks if the configured
 for an application named `app`, the `default` profile and the default
 label provided by the `EnvironmentRepository` implementation.
 
-You can configure the Health Indicator to check more appliations
+You can configure the Health Indicator to check more applications
 along with custom profiles and custom labels, e.g.
 
 ----
@@ -419,8 +419,7 @@ an Exception.
 
 === Locating Remote Configuration Resources
 
-The Config Service serves property sources from `/{name}/{env}/{label}`, where the default bindings in the
-client app are
+The Config Service serves property sources from `/{name}/{env}/{label}`, where the default bindings in the client app are
 
 * "name" = `${spring.application.name}`
 * "env" = `${spring.profiles.active}` (actually `Environment.getActiveProfiles()`)
@@ -430,7 +429,11 @@ All of them can be overridden by setting `spring.cloud.config.\*`
 (where `*` is "name", "env" or "label"). The "label" is useful for
 rolling back to previous versions of configuration; with the default
 Config Server implementation it can be a git label, branch name or
-commit id.
+commit id. Label can also be provided as a comma-separated list, in 
+which case the items in the list are tried on-by-one until one succeeds.
+This can be useful when working on a feature branch, for instance,
+when you might want to align the config label with your branch, but 
+make it optional (e.g. `spring.cloud.config.label=myfeature,develop`).
 
 === Security
 

spring-cloud-config-client/src/main/java/org/springframework/cloud/config/client/ConfigServicePropertySourceLocator.java

@@ -31,7 +31,9 @@ import org.springframework.core.env.MapPropertySource;
 import org.springframework.http.HttpEntity;
 import org.springframework.http.HttpMethod;
 import org.springframework.http.HttpRequest;
+import org.springframework.http.HttpStatus;
 import org.springframework.http.MediaType;
+import org.springframework.http.ResponseEntity;
 import org.springframework.http.client.ClientHttpRequestExecution;
 import org.springframework.http.client.ClientHttpRequestInterceptor;
 import org.springframework.http.client.ClientHttpResponse;
@@ -58,7 +60,7 @@ public class ConfigServicePropertySourceLocator implements PropertySourceLocator
 	}
 
 	@Override
-	@Retryable(interceptor="configServerRetryInterceptor")
+	@Retryable(interceptor = "configServerRetryInterceptor")
 	public org.springframework.core.env.PropertySource<?> locate(
 			org.springframework.core.env.Environment environment) {
 		ConfigClientProperties client = defaults.override(environment);
@@ -68,22 +70,24 @@ public class ConfigServicePropertySourceLocator implements PropertySourceLocator
 		Exception error = null;
 		String errorBody = null;
 		try {
-			Object[] args = new String[] { client.getName(), client.getProfile() };
-			String path = "/{name}/{profile}";
+			String[] labels = new String[]{""};
 			if (StringUtils.hasText(client.getLabel())) {
-				args = new String[] { client.getName(), client.getProfile(),
-						client.getLabel() };
-				path = path + "/{label}";
+				labels = StringUtils.commaDelimitedListToStringArray(client.getLabel());
 			}
-			Environment result = restTemplate.exchange(client.getRawUri() + path,
-					HttpMethod.GET, new HttpEntity<Void>((Void) null), Environment.class,
-					args).getBody();
-			for (PropertySource source : result.getPropertySources()) {
-				@SuppressWarnings("unchecked")
-				Map<String, Object> map = (Map<String, Object>) source.getSource();
-				composite.addPropertySource(new MapPropertySource(source.getName(), map));
+			// Try all the labels until one works
+			for (String label : labels) {
+				Environment result = getRemoteEnvironment(restTemplate, client.getRawUri(), client.getName(), client.getProfile(), label.trim());
+				if (result != null) {
+					for (PropertySource source : result.getPropertySources()) {
+						@SuppressWarnings("unchecked")
+						Map<String, Object> map = (Map<String, Object>) source
+								.getSource();
+						composite.addPropertySource(new MapPropertySource(source
+								.getName(), map));
+					}
+					return composite;
+				}
 			}
-			return composite;
 		}
 		catch (HttpServerErrorException e) {
 			error = e;
@@ -101,11 +105,28 @@ public class ConfigServicePropertySourceLocator implements PropertySourceLocator
 					error);
 		}
 		logger.error("Could not locate PropertySource: "
-				+ (errorBody == null ? error.getMessage() : errorBody));
+				+ (errorBody == null ? error==null ? "label not found" : error.getMessage() : errorBody));
 		return null;
 
 	}
 
+	private Environment getRemoteEnvironment(RestTemplate restTemplate, String uri, String name, String profile, String label) {
+		String path = "/{name}/{profile}";
+		Object[] args = new String[] { name, profile };
+		if (StringUtils.hasText(label)) {
+			args = new String[] { name, profile, label };
+			path = path + "/{label}";
+		}
+		ResponseEntity<Environment> response = restTemplate.exchange(uri + path,
+				HttpMethod.GET, new HttpEntity<Void>((Void) null),
+				Environment.class, args);
+		if (response==null || response.getStatusCode()!=HttpStatus.OK) {
+			return null;
+		}
+		Environment result = response.getBody();
+		return result;
+	}
+
 	public void setRestTemplate(RestTemplate restTemplate) {
 		this.restTemplate = restTemplate;
 	}

spring-cloud-config-client/src/test/java/org/springframework/cloud/config/client/ConfigServicePropertySourceLocatorTests.java

@@ -13,8 +13,6 @@ import org.junit.rules.ExpectedException;
 import org.mockito.Matchers;
 import org.mockito.Mockito;
 import org.springframework.boot.test.EnvironmentTestUtils;
-import org.springframework.cloud.config.client.ConfigClientProperties;
-import org.springframework.cloud.config.client.ConfigServicePropertySourceLocator;
 import org.springframework.cloud.config.environment.Environment;
 import org.springframework.core.env.ConfigurableEnvironment;
 import org.springframework.core.env.StandardEnvironment;
@@ -27,6 +25,7 @@ import org.springframework.http.ResponseEntity;
 import org.springframework.http.client.ClientHttpRequest;
 import org.springframework.http.client.ClientHttpRequestFactory;
 import org.springframework.http.client.ClientHttpResponse;
+import org.springframework.web.client.HttpClientErrorException;
 import org.springframework.web.client.HttpServerErrorException;
 import org.springframework.web.client.RestTemplate;
 
@@ -54,13 +53,22 @@ public class ConfigServicePropertySourceLocatorTests {
 	@Test
 	public void sunnyDayWithLabel() {
 		Environment body = new Environment("app", "master");
-		mockRequestResponseWithLabel(new ResponseEntity<Environment>(body,
-				HttpStatus.OK), "v1.0.0");
+		mockRequestResponseWithLabel(
+				new ResponseEntity<Environment>(body, HttpStatus.OK), "v1.0.0");
 		locator.setRestTemplate(restTemplate);
-		EnvironmentTestUtils.addEnvironment(environment, "spring.cloud.config.label:v1.0.0");
+		EnvironmentTestUtils.addEnvironment(environment,
+				"spring.cloud.config.label:v1.0.0");
 		assertNotNull(locator.locate(environment));
 	}
 
+	@Test
+	public void sunnyDayWithNoSuchLabel() {
+		mockRequestResponseWithLabel(new ResponseEntity<Void>((Void) null,
+				HttpStatus.NOT_FOUND), "nosuchlabel");
+		locator.setRestTemplate(restTemplate);
+		assertNull(locator.locate(environment));
+	}
+
 	@Test
 	public void failsQuietly() {
 		mockRequestResponseWithoutLabel(new ResponseEntity<String>("Wah!",
@@ -98,6 +106,35 @@ public class ConfigServicePropertySourceLocatorTests {
 		assertNull(locator.locate(environment));
 	}
 
+	@Test
+	public void failFastWhenNotFound() throws Exception {
+		ClientHttpRequestFactory requestFactory = Mockito
+				.mock(ClientHttpRequestFactory.class);
+		ClientHttpRequest request = Mockito.mock(ClientHttpRequest.class);
+		ClientHttpResponse response = Mockito.mock(ClientHttpResponse.class);
+		Mockito.when(
+				requestFactory.createRequest(Mockito.any(URI.class),
+						Mockito.any(HttpMethod.class))).thenReturn(request);
+		RestTemplate restTemplate = new RestTemplate(requestFactory);
+		ConfigClientProperties defaults = new ConfigClientProperties(environment);
+		defaults.setFailFast(true);
+		locator = new ConfigServicePropertySourceLocator(defaults);
+		Mockito.when(request.getHeaders()).thenReturn(new HttpHeaders());
+		Mockito.when(request.execute()).thenReturn(response);
+		HttpHeaders headers = new HttpHeaders();
+		headers.setContentType(MediaType.APPLICATION_JSON);
+		Mockito.when(response.getHeaders()).thenReturn(headers);
+		Mockito.when(response.getStatusCode()).thenReturn(
+				HttpStatus.NOT_FOUND);
+		Mockito.when(response.getBody()).thenReturn(
+				new ByteArrayInputStream("".getBytes()));
+		locator.setRestTemplate(restTemplate);
+		expected.expectCause(IsInstanceOf
+				.<Throwable> instanceOf(HttpClientErrorException.class));
+		expected.expectMessage("fail fast property is set");
+		assertNull(locator.locate(environment));
+	}
+
 	@SuppressWarnings("unchecked")
 	private void mockRequestResponseWithLabel(ResponseEntity<?> response, String label) {
 		Mockito.when(