Add a method in the JNI API to get direct access information.

For binary content (not compressed), it could be interesting to
directly read the content in the zim file instead of using `kiwix-lib`.

This method returns the needed information to do so (if possible).

src/android/kiwixreader.cpp

@@ -277,6 +277,40 @@ JNIEXPORT jbyteArray JNICALL Java_org_kiwix_kiwixlib_JNIKiwixReader_getContentPa
   return data;
 }
 
+JNIEXPORT jobject JNICALL
+Java_org_kiwix_kiwixlib_JNIKiwixReadear_getDirectAccessInformation(
+    JNIEnv* env, jobject obj, jstring url)
+{
+   jclass classPair = env->FindClass("org/kiwix/kiwixlib/Pair");
+   jmethodID midPairinit = env->GetMethodID(classPair, "<init>", "(D)");
+   jobject pair = env->NewObject(classPair, midPairinit);
+   setPairObjValue("", 0, pair, env);
+
+   std::string cUrl = jni2c(url, env);
+   try {
+    zim::Article article;
+    READER->getArticleObjectByDecodedUrl(kiwix::urlDecode(cUrl), article);
+    if (! article.good()) {
+      return pair;
+    }
+    int loopCounter = 0;
+    while (article.isRedirect() && loopCounter++ < 42) {
+      article = article.getRedirectArticle();
+    }
+    if (loopCounter == 42) {
+      return pair;
+    }
+
+    auto part_info = article.getDirectAccessInformation();
+    setPairObjValue(part_info.first, part_info.second, pair, env);
+  } catch (...) {
+    std::cerr << "Unable to locate direct access information for url " << cUrl
+              << std::endl;
+
+  }
+  return pair;
+}
+
 JNIEXPORT jboolean JNICALL
 Java_org_kiwix_kiwixlib_JNIKiwixReader_searchSuggestions(JNIEnv* env,
                                                          jobject obj,

src/android/meson.build

@@ -7,7 +7,8 @@ kiwix_jni = custom_target('jni',
           'org/kiwix/kiwixlib/JNIKiwixSearcher.java',
           'org/kiwix/kiwixlib/JNIKiwixInt.java',
           'org/kiwix/kiwixlib/JNIKiwixString.java',
-          'org/kiwix/kiwixlib/JNIKiwixBool.java'],
+          'org/kiwix/kiwixlib/JNIKiwixBool.java',
+          'org/kiwix/kiwixlib/Pair.java'],
   output: ['org_kiwix_kiwixlib_JNIKiwix.h',
            'org_kiwix_kiwixlib_JNIKiwixReader.h',
            'org_kiwix_kiwixlib_JNIKiwixSearcher.h',

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

@@ -23,6 +23,7 @@ package org.kiwix.kiwixlib;
 import org.kiwix.kiwixlib.JNIKiwixString;
 import org.kiwix.kiwixlib.JNIKiwixInt;
 import org.kiwix.kiwixlib.JNIKiwixSearcher;
+import org.kiwix.kiwixlib.Pair;
 
 public class JNIKiwixReader
 {
@@ -56,6 +57,24 @@ public class JNIKiwixReader
                                       int len,
                                       JNIKiwixInt size);
 
+  /**
+   * getDirectAccessInformation.
+   *
+   * Return information giving where the content is located in the zim file.
+   *
+   * Some contents (binary content) are stored uncompressed in the zim file.
+   * Knowing this information, it could be interesting to directly open
+   * the zim file (or zim part) and directly read the content from it (and so
+   * bypassing the libzim).
+   *
+   * Return a `Pair` (filename, offset) where the content is located.
+   *
+   * If the content cannot be directly accessed (content is compressed or zim
+   * file is cut in the middle of the content), the filename is an empty string
+   * and offset is zero.
+   */
+  public native Pair getDirectAccessInformation(String url);
+
   public native boolean searchSuggestions(String prefix, int count);
 
   public native boolean getNextSuggestion(JNIKiwixString title);

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

@@ -0,0 +1,26 @@
+/*
+ * Copyright (C) 2017 Matthieu Gautier <mgautier@kymeria.fr>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU  General Public License as published by
+ * the Free Software Foundation; either version 3 of the License, or
+ * any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston,
+ * MA 02110-1301, USA.
+ */
+
+package org.kiwix.kiwixlib;
+
+public class Pair
+{
+  public String filename;
+  public int offset;
+}

src/android/utils.h

@@ -137,4 +137,14 @@ inline void setBoolObjValue(const bool value, const jobject obj, JNIEnv* env)
   env->SetIntField(obj, objFid, c2jni(value));
 }
 
+inline void setPairObjValue(const std::string& filename, const int offset,
+                            const jobject obj, JNIEnv* env)
+{
+  jclass objClass = env->GetObjectClass(obj);
+  jfieldID filenameFid = env->GetFieldID(objClass, "filename", "Ljava/lang/String;");
+  env->SetObjectField(obj, filenameFid, c2jni(filename, env));
+  jfieldID offsetFid = env->GetFieldID(objClass, "offset", "I");
+  env->SetIntField(obj, offsetFid, offset);
+}
+
 #endif // _ANDROID_JNI_UTILS_H