[JNI] Allow android to know that an article is a redirect.

Android need to handle the redirection by doing a redirection in the web
view, not by providing the content of the targeted article.

This is already what we do in kiwix-serve or ios.

The API should be far better by returning a Entry but for now,
we just change the given url if the article is a redirection.

src/android/kiwixreader.cpp

@@ -225,7 +225,7 @@ JNIEXPORT jstring JNICALL Java_org_kiwix_kiwixlib_JNIKiwixReader_getMimeType(
 }
 
 JNIEXPORT jbyteArray JNICALL Java_org_kiwix_kiwixlib_JNIKiwixReader_getContent(
-    JNIEnv* env, jobject obj, jstring url, jobject titleObj, jobject mimeTypeObj, jobject sizeObj)
+    JNIEnv* env, jobject obj, jobject url, jobject titleObj, jobject mimeTypeObj, jobject sizeObj)
 {
   /* Default values */
   setStringObjValue("", titleObj, env);
@@ -234,21 +234,24 @@ JNIEXPORT jbyteArray JNICALL Java_org_kiwix_kiwixlib_JNIKiwixReader_getContent(
   jbyteArray data = env->NewByteArray(0);
 
   /* Retrieve the content */
-  std::string cUrl = jni2c(url, env);
+  std::string cUrl = getStringObjValue(url, env);
   unsigned int cSize = 0;
 
   try {
     auto entry = READER->getEntryFromEncodedPath(cUrl);
+    bool isRedirect = entry.isRedirect();
     entry = entry.getFinalEntry();
     cSize = entry.getSize();
     setIntObjValue(cSize, sizeObj, env);
-
+    setStringObjValue(entry.getMimetype(), mimeTypeObj, env);
+    setStringObjValue(entry.getTitle(), titleObj, env);
+    if (isRedirect) {
+      setStringObjValue(entry.getPath(), url, env);
+    } else {
       data = env->NewByteArray(cSize);
       env->SetByteArrayRegion(
           data, 0, cSize, reinterpret_cast<const jbyte*>(entry.getBlob().data()));
-
-    setStringObjValue(entry.getMimetype(), mimeTypeObj, env);
-    setStringObjValue(entry.getTitle(), titleObj, env);
+    }
   } catch (std::exception& e) {
     __android_log_print(ANDROID_LOG_ERROR, "kiwix", "Unable to get content for url: %s", cUrl.c_str());
     __android_log_print(ANDROID_LOG_ERROR, "kiwix", e.what());

src/android/org/kiwix/kiwixlib/JNIKiwixReader.java

@@ -38,7 +38,21 @@ public class JNIKiwixReader
 
   public native String getMimeType(String url);
 
-  public native byte[] getContent(String url,
+  /**
+   * Get the content of a article.
+   *
+   * Return a byte array of the content of the article.
+   * Set the title, mimeType to the title and mimeType of the article.
+   * Set the size to the size of the returned array.
+   *
+   * If the entry doesn't exist :
+   *  - return a empty byte array
+   *  - set all arguments (except url) to empty/0.
+   * If the entry exist but is a redirection :
+   *  - return an empty byte array
+   *  - set all arguments (including url) to information of the targeted article.
+   */
+  public native byte[] getContent(JNIKiwixString url,
                                   JNIKiwixString title,
                                   JNIKiwixString mimeType,
                                   JNIKiwixInt size);

src/android/utils.h

@@ -114,6 +114,13 @@ inline std::string jni2c(const jstring& val, JNIEnv* env)
 
 inline int jni2c(const jint val) { return (int)val; }
 /* Method to deal with variable passed by reference */
+inline std::string getStringObjValue(const jobject obj, JNIEnv* env)
+{
+  jclass objClass = env->GetObjectClass(obj);
+  jfieldID objFid = env->GetFieldID(objClass, "value", "Ljava/lang/String;");
+  jstring jstr = (jstring)env->GetObjectField(obj, objFid);
+  return jni2c(jstr, env);
+}
 inline void setStringObjValue(const std::string& value,
                               const jobject obj,
                               JNIEnv* env)