Add method to get value of tag from a book.

Only the `getTagStr` method is available on android because we need a
proper exception handling on wrapping side.

Fix #298

include/book.h

@@ -60,6 +60,8 @@ class Book
   const std::string& getUrl() const { return m_url; }
   const std::string& getName() const { return m_name; }
   const std::string& getTags() const { return m_tags; }
+  std::string getTagStr(const std::string& tagName) const;
+  bool getTagBool(const std::string& tagName) const;
   const std::string& getOrigId() const { return m_origId; }
   const uint64_t& getArticleCount() const { return m_articleCount; }
   const uint64_t& getMediaCount() const { return m_mediaCount; }

src/book.cpp

@@ -23,6 +23,7 @@
 #include "tools/base64.h"
 #include "tools/regexTools.h"
 #include "tools/networkTools.h"
+#include "tools/otherTools.h"
 
 #include <pugixml.hpp>
 
@@ -203,4 +204,12 @@ const std::string& Book::getFavicon() const {
   return m_favicon;
 }
 
+std::string Book::getTagStr(const std::string& tagName) const {
+  return getTagValueFromTagList(convertTags(m_tags), tagName);
+}
+
+bool Book::getTagBool(const std::string& tagName) const {
+  return convertStrToBool(getTagStr(tagName));
+}
+
 }

src/wrapper/java/book.cpp

@@ -66,4 +66,11 @@ GETTER(jstring, getFavicon)
 GETTER(jstring, getFaviconUrl)
 GETTER(jstring, getFaviconMimeType)
 
+METHOD(jstring, Book, getTagStr, jstring tagName) try {
+  auto cRet = Book->getTagStr(jni2c(tagName, env));
+  return c2jni(cRet, env);
+} catch(...) {
+  return c2jni<std::string>("", env);
+}
+
 #undef GETTER

src/wrapper/java/org/kiwix/kiwixlib/Book.java

@@ -20,6 +20,13 @@ public class Book
   public native String getUrl();
   public native String getName();
   public native String getTags();
+  /**
+   * Return the value associated to the tag tagName
+   *
+   * @param tagName the tag name to search for.
+   * @return The value of the tag. If the tag is not found, return empty string.
+   */
+  public native String getTagStr(String tagName);
 
   public native long getArticleCount();
   public native long getMediaCount();