feat: add methods for binary content of messages

https://gravitee.atlassian.net/browse/APIM-5260

README.adoc

@@ -190,6 +190,11 @@ content.greeting = 'Hello Universe!'
 return JsonOutput.toJson(content)
 ----
 
+The content of a message can also be accessed directly:
+
+ - as a base64 string with `message.contentAsBase64`
+ - as an array of bytes with `message.contentAsByteArray`
+
 == Errors
 
 === Sandbox

src/main/java/io/gravitee/policy/groovy/model/message/BindableMessage.java

@@ -19,6 +19,7 @@
 import io.gravitee.gateway.api.http.HttpHeaders;
 import io.gravitee.gateway.reactive.api.message.Message;
 import io.gravitee.policy.groovy.model.BindableHttpHeaders;
+import java.util.Base64;
 import java.util.List;
 import java.util.Map;
 import java.util.Set;
@@ -111,6 +112,14 @@ public String getContent() {
         return message.content() == null ? "" : content().toString();
     }
 
+    public String getContentAsBase64() {
+        return message.content() == null ? "" : Base64.getEncoder().encodeToString(message.content().getBytes());
+    }
+
+    public byte[] getContentAsByteArray() {
+        return message.content() == null ? new byte[0] : message.content().getBytes();
+    }
+
     @Override
     public Message content(Buffer content) {
         throw new UnsupportedOperationException("Setting content must be done returning a value and setting `overrideContent` to true");

src/test/java/io/gravitee/policy/groovy/GroovyPolicyTest.java

@@ -35,6 +35,9 @@
 import io.reactivex.rxjava3.core.Maybe;
 import io.reactivex.rxjava3.core.MaybeTransformer;
 import java.io.*;
+import java.nio.charset.StandardCharsets;
+import java.util.Arrays;
+import java.util.Base64;
 import java.util.function.Function;
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Test;
@@ -302,6 +305,24 @@ private static GroovyPolicyConfiguration buildConfig(String script) {
         return GroovyPolicyConfiguration.builder().script(loadScript(script)).readContent(true).build();
     }
 
+    @Test
+    void should_get_message_binary_content_as_base64() {
+        var policy = new GroovyPolicy(buildConfig("get_message_binary_content.groovy"));
+        var message = new DefaultMessage();
+        byte[] isoEncodedCharacter = "é".getBytes(StandardCharsets.ISO_8859_1);
+        message.content(Buffer.buffer(isoEncodedCharacter));
+
+        when(request.onMessage(onMessageCaptor.capture())).thenReturn(Completable.complete());
+        policy.onMessageRequest(ctx).test().assertNoValues();
+
+        onMessageCaptor.getValue().apply(message).test().assertComplete().assertNoErrors();
+
+        assertThat(message.<String>attribute("wronglyBase64EncodedContent"))
+            .isNotEqualTo(Base64.getEncoder().encodeToString(isoEncodedCharacter));
+        assertThat(message.<String>attribute("goodBase64Content")).isEqualTo(Base64.getEncoder().encodeToString(isoEncodedCharacter));
+        assertThat(message.<String>attribute("byteArray")).isEqualTo(Arrays.toString(isoEncodedCharacter));
+    }
+
     private static String loadScript(String file) {
         try {
             return new String(getResourceAsStream(file).readAllBytes());

src/test/resources/io/gravitee/policy/groovy/get_message_binary_content.groovy

@@ -0,0 +1,3 @@
+message.attributes.wronglyBase64EncodedContent = message.content.bytes.encodeBase64().toString()  // final value is not well encoded because of Charset transformation
+message.attributes.goodBase64Content = message.contentAsBase64
+message.attributes.byteArray = message.contentAsByteArray.toString()