Utils class to get package name, signature in NDK

android_utils.h

//
// Created by vntrong on 10/20/2017.
//

#ifndef ANDROID_UTILS_H
#define ANDROID_UTILS_H

#include <jni.h>
#include <string.h>
#include <string>
#include <stdio.h>
#include <stdlib.h>

char *jstringTostring(JNIEnv *env, jstring jstr) {
    char *rtn = NULL;
    jclass clsstring = env->FindClass("java/lang/String");
    jstring strencode = env->NewStringUTF("utf-8");
    jmethodID mid = env->GetMethodID(clsstring, "getBytes", "(Ljava/lang/String;)[B");
    jbyteArray barr = (jbyteArray) env->CallObjectMethod(jstr, mid, strencode);
    jsize alen = env->GetArrayLength(barr);
    jbyte *ba = env->GetByteArrayElements(barr, JNI_FALSE);
    if (alen > 0) {
        rtn = (char *) malloc(alen + 1);
        memcpy(rtn, ba, alen);
        rtn[alen] = 0;
    }
    env->ReleaseByteArrayElements(barr, ba, 0);
    return rtn;
}

char *getCallerPackageName(JNIEnv *env, jobject obj) {
    jclass cls = env->FindClass("android/content/ContextWrapper");
    //this.getPackageManager();
    jmethodID mid = env->GetMethodID(cls, "getPackageManager",
                                     "()Landroid/content/pm/PackageManager;");
    if (mid == NULL) {
        return "";
    }

    jobject pm = env->CallObjectMethod(obj, mid);
    if (pm == NULL) {
        return "";
    }

    //this.getPackageName();
    mid = env->GetMethodID(cls, "getPackageName", "()Ljava/lang/String;");
    if (mid == NULL) {
        return "";
    }

    jstring packageName = (jstring) env->CallObjectMethod(obj, mid);
    return jstringTostring(env, packageName);
}

char *getCallerSignature(JNIEnv *env, jobject obj) {
    jclass cls = env->FindClass("android/content/ContextWrapper");
    //this.getPackageManager();
    jmethodID mid = env->GetMethodID(cls, "getPackageManager",
                                     "()Landroid/content/pm/PackageManager;");
    if (mid == NULL) {
        return "";
    }

    jobject pm = env->CallObjectMethod(obj, mid);
    if (pm == NULL) {
        return "";
    }

    //this.getPackageName();
    mid = env->GetMethodID(cls, "getPackageName", "()Ljava/lang/String;");
    if (mid == NULL) {
        return "";
    }

    jstring packageName = (jstring) env->CallObjectMethod(obj, mid);
    // packageManager->getPackageInfo(packageName, GET_SIGNATURES);
    cls = env->GetObjectClass(pm);
    mid = env->GetMethodID(cls, "getPackageInfo",
                           "(Ljava/lang/String;I)Landroid/content/pm/PackageInfo;");

    jobject packageInfo = env->CallObjectMethod(pm, mid, packageName, 0x40); //GET_SIGNATURES = 64;

    cls = env->GetObjectClass(packageInfo);
    jfieldID fid = env->GetFieldID(cls, "signatures", "[Landroid/content/pm/Signature;");
    jobjectArray signatures = (jobjectArray) env->GetObjectField(packageInfo, fid);
    jobject sign = env->GetObjectArrayElement(signatures, 0);

    cls = env->GetObjectClass(sign);
    mid = env->GetMethodID(cls, "toCharsString", "()Ljava/lang/String;");
    if (mid == NULL) {
        return "";
    }

    jstring signString = (jstring) env->CallObjectMethod(sign, mid);
    return jstringTostring(env, signString);

}

#endif //ANDROID_UTILS_H