JNI is wanky. Finally about to return an object from C++ to Java/Kotlin

app/build.gradle

@@ -21,7 +21,8 @@ android {
         testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"
         externalNativeBuild {
             cmake {
-                cppFlags "-std=c++14"
+                arguments "-DANDROID_STL=c++_shared", "-DANDROID=true"
+                cppFlags "-std=c++17"
             }
         }
 

app/src/main/cpp/CMakeLists.txt

@@ -13,6 +13,8 @@ cmake_minimum_required(VERSION 3.4.1)
 
 # set(CMAKE_FIND_ROOT_PATH_MODE_LIBRARY BOTH)
 
+set(CMAKE_CXX11_EXTENSION_COMPILE_OPTION "-std=c++17")
+
 set (SOURCES
         Demo.cpp
         SongRepository.cpp

app/src/main/cpp/Demo.cpp

@@ -20,12 +20,33 @@
 
 #include "model/Song.h"
 #include "model/User.h"
+#include "SongRepository.h"
 #include "Tok.h"
 
 
+model::Song retrieveSong(const std::string&);
+
 std::string fetchToken(const std::string&, const std::string&, const std::string&);
 
 
+model::Song retrieveSong(const std::string& token)
+{
+    repository::SongRepository songRepo;
+    model::Song song;
+    song.id = 2;
+    song.title = "Smooth";
+    song.album = "Amaze";
+    song.artist = "The Herb";
+    song.genre = "Blazing";
+    song.duration = 420;
+    song.year = 420;
+
+    song = songRepo.retrieveSong(token, song.id);
+
+    return song;
+}
+
+
 std::string fetchToken(const std::string& username, const std::string& password,
     const std::string& apiUri)
 {
@@ -57,3 +78,49 @@ Java_com_example_mear_activities_DemoStreamActivity_logUser(
 
     return env->NewStringUTF(token.c_str());
 }
+
+
+extern "C"
+JNIEXPORT jobject
+JNICALL
+Java_com_example_mear_activities_DemoStreamActivity_retrieveSong(
+        JNIEnv *env,
+        jobject thisObj,
+        jstring token
+        )
+{
+    const std::string tok = env->GetStringUTFChars(token, NULL);
+
+    auto song = retrieveSong(tok);
+    std::string bank = "SBI Bank";
+
+    jclass songClass = env->FindClass( "com/example/mear/models/Song");
+    jmethodID jconstructor = env->GetMethodID( songClass,  "<init>", "()V" );
+    jobject songObj = env->NewObject( songClass, jconstructor );
+
+    jmethodID songId = env->GetMethodID( songClass,  "setId", "(I)V" );
+    jmethodID songTitle = env->GetMethodID( songClass,  "setTitle", "(Ljava/lang/String;)V" );
+    jmethodID songAlbum = env->GetMethodID( songClass,  "setAlbum", "(Ljava/lang/String;)V" );
+    jmethodID songArtist = env->GetMethodID( songClass,  "setArtist", "(Ljava/lang/String;)V" );
+    jmethodID songGenre = env->GetMethodID( songClass,  "setGenre", "(Ljava/lang/String;)V" );
+    jmethodID songDuration = env->GetMethodID( songClass,  "setDuration", "(I)V" );
+    jmethodID songYear = env->GetMethodID( songClass,  "setYear", "(I)V" );
+
+    jint id = song.id;
+    jstring title = env->NewStringUTF(song.title.c_str());
+    jstring album = env->NewStringUTF(song.album.c_str());
+    jstring artist = env->NewStringUTF(song.artist.c_str());
+    jstring genre = env->NewStringUTF(song.genre.c_str());
+    jint duration = song.duration;
+    jint year = song.year;
+
+    env->CallVoidMethod( songObj, songId, id );
+    env->CallVoidMethod(songObj, songTitle, title);
+    env->CallVoidMethod(songObj, songAlbum, album);
+    env->CallVoidMethod(songObj, songArtist, artist);
+    env->CallVoidMethod(songObj, songGenre, genre);
+    env->CallVoidMethod(songObj, songDuration, duration);
+    env->CallVoidMethod(songObj, songYear, year);
+
+    return songObj;
+}

app/src/main/cpp/SongRepository.cpp

@@ -4,6 +4,9 @@
 
 #include "SongRepository.h"
 
+#include <curl/curl.h>
+#include <nlohmann/json.hpp>
+
 namespace repository {
     // TODO: implement this
     std::vector<model::Song> SongRepository::fetchSongs(const std::string& token,
@@ -13,4 +16,59 @@ namespace repository {
 
       return songs;
     }
+
+
+    model::Song SongRepository::retrieveSong(const std::string& token, const int id) {
+        std::string uri;
+        uri.append(std::to_string(id));
+        model::Song song;
+
+        CURL *curl;
+        CURLcode res;
+        struct curl_slist *chunk = NULL;
+        curl = curl_easy_init();
+
+        if (!curl) {
+            return song;
+        }
+
+        auto resp = std::make_unique<char[]>(10000);
+
+        std::string authInfo("Authorization: Bearer ");
+        authInfo.append(token);
+        chunk = curl_slist_append(chunk, authInfo.c_str());
+
+        curl_easy_setopt(curl, CURLOPT_URL, uri.c_str());
+        curl_easy_setopt(curl, CURLOPT_HTTPHEADER, chunk);
+        curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, respBodyRetriever);
+        curl_easy_setopt(curl, CURLOPT_WRITEDATA, resp.get());
+        curl_easy_setopt(curl, CURLOPT_SSL_VERIFYPEER, 0L);
+
+        res = curl_easy_perform(curl);
+        curl_easy_cleanup(curl);
+
+        if (res == CURLE_OK) {
+            auto s = nlohmann::json::parse(resp.get());
+            song.id = s["id"].get<int>();
+            song.title = s["title"].get<std::string>();
+            song.album = s["album"].get<std::string>();
+            song.artist = s["artist"].get<std::string>();
+            song.genre = s["genre"].get<std::string>();
+            song.duration = s["duration"].get<int>();
+            song.year = s["year"].get<int>();
+
+            return song;
+        }
+
+        return song;
+    }
+
+
+    size_t SongRepository::respBodyRetriever(void* ptr, size_t size, size_t nmemb, char *e)
+    {
+        std::memcpy(e, ptr, nmemb);
+        e[nmemb] = '\0';
+
+        return nmemb;
+    }
 }

app/src/main/cpp/SongRepository.h

@@ -15,7 +15,10 @@ namespace repository {
     class SongRepository {
     public:
         std::vector<model::Song> fetchSongs(const std::string&, const std::string&);
+
+        model::Song retrieveSong(const std::string&, const int);
     private:
+        static size_t respBodyRetriever(void*, size_t, size_t, char*);
     };
 }
 

app/src/main/cpp/Tok.cpp

@@ -4,6 +4,7 @@
 
 #include "Tok.h"
 
+#include <memory>
 #include <cstring>
 
 #include <curl/curl.h>
@@ -20,7 +21,7 @@ namespace manager {
             return "none";
         }
 
-        char resp[2048];
+        auto resp = std::make_unique<char[]>(10000);
 
         const auto loginUri = fetchLoginUri(uri);
         const auto obj = userJsonString(user);
@@ -28,14 +29,14 @@ namespace manager {
         curl_easy_setopt(curl, CURLOPT_URL, loginUri.c_str());
         curl_easy_setopt(curl, CURLOPT_POSTFIELDS, obj.c_str());
         curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, respBodyRetriever);
-        curl_easy_setopt(curl, CURLOPT_WRITEDATA, resp);
+        curl_easy_setopt(curl, CURLOPT_WRITEDATA, resp.get());
         curl_easy_setopt(curl, CURLOPT_SSL_VERIFYPEER, 0L);
 
         res = curl_easy_perform(curl);
         curl_easy_cleanup(curl);
 
         if (res == CURLE_OK) {
-            auto s = nlohmann::json::parse(resp);
+            auto s = nlohmann::json::parse(resp.get());
             return s["token"].get<std::string>();
         }
 

app/src/main/cpp/Tok.h

@@ -5,6 +5,7 @@
 #ifndef MEAR_TOK_H
 #define MEAR_TOK_H
 
+#include <memory>
 #include <string>
 
 #include "model/User.h"

app/src/main/java/com/example/mear/activities/DemoStreamActivity.kt

@@ -9,6 +9,8 @@ import kotlinx.android.synthetic.main.activity_demo_stream.*
 import kotlinx.android.synthetic.main.content_demo_stream.*
 import org.jetbrains.anko.toast
 
+import com.example.mear.models.Song
+
 class DemoStreamActivity : AppCompatActivity() {
 
     companion object {
@@ -18,7 +20,11 @@ class DemoStreamActivity : AppCompatActivity() {
     }
 
 
+    private var token: String? = null
+
+
     private external fun logUser(usr: String, pass: String, api: String): String
+    private external fun retrieveSong(tok: String): Song
 
 
     override fun onCreate(savedInstanceState: Bundle?) {
@@ -50,8 +56,9 @@ class DemoStreamActivity : AppCompatActivity() {
         var passwordStr = password.text.toString()
         var apiUriStr = apiUri.text.toString()
 
-        var token = logUser(usernameStr, passwordStr, apiUriStr)
-        toast(token).show()
+        token = logUser(usernameStr, passwordStr, apiUriStr)
+        toast(token!!).show()
+        var s = retrieveSong(token!!);
     }
 
     private fun validFields(): Boolean {

app/src/main/java/com/example/mear/models/Song.kt

@@ -0,0 +1,4 @@
+package com.example.mear.models
+
+class Song (var id: Int = 3, var title: String = "", var album: String = "", var artist: String = "",
+            var genre: String = "", var year: Int = 0, var duration: Int = 0)