JNI Generator

Generate Kotlin JNI bindings for C headers. Features:

• Generate Kotlin data classes for C structs.
• Generate Kotlin bindings for C functions.
• Supports multiple C header files.

Usage

git clone https://github.com/agabor/JNIGenerator.git
cd JNIGenerator
mkdir generated
cd JNIGenerator
dotnet run -- template/config.json

Edit template/config.json to

• set path to C headers
• set outputh pathes
• set Kotlin package name(s)
• set API calss name

To customize ouput, you can edit the Scriban templates located in the templates folder.

Examle Input

#ifndef MESSAGE_H
#define MESSAGE_H

struct Message {
    char* subject;
    char* text;
};

int sendMessage(struct Message message);

#endif

Examle Output

Message.kt

//Generated code. Do not edit!

package com.jnigen.model

data class Message (var subject: String = String(), var text: String = String())

JniApi.kt

//Generated code. Do not edit!

package com.jnigen

import com.jnigen.model.*

class JniApi {

    external fun sendMessage(message: Message): Int
    companion object {
        init {
            System.loadLibrary("native-lib")
        }
    }
}

jni-wrapper.c

You can find the generated example JNI code here: https://github.com/agabor/JNIGenerator/blob/master/example-output/jni-wrapper.c

Rules

Structs

Structs in the following form are supported:

struct Message {
    int isUrgent;
    char* subject;
    char* text;
};

It is important that the opening bracket ({) is written in the same line as the struct.

typedefed structs (and other typedefs) are not supported:

typedef struct Message {
    int isUrgent;
    char* subject;
    char* text;
} Message;

Pointers

Pointers are interpreted as arrays, char pointers are interpreted as strings. With the exception of char* do not return raw pointers from functions, and do not use them as parameters. Pointers (arrays) must always be wrapped in structs, and must have a corresponding length variable. This length variable must:

• be of type int,
• must be named the same as the array with the "Length" suffix,
• must be directly before the array variable. example:

struct Contact {
    char* name;
    char* email;
};
struct Message {
    int isUrgent;
    char* subject;
    char* text;
    struct Contact sender;
    int addresseesLength;
    struct Contact* addressees;
};

Constant length arrays

Alternatively, if you have an array with constant length, you can indicate it with a comment:

struct Message {
    int isUrgent;
    char* subject;
    char* text;
    struct Contact sender;
    int addresseesLength;
    struct Contact* addressees;//array-length:5
};

Exclusion from JNI

You might exclude a function or a struct from the JNI by puttinga //no-jni comment directy behind it. Excluding a struct:

struct Message {
    int isUrgent;
    char* subject;
    char* text;
};//no-jni

Excluding a function:

void sendMessage(struct Message message);//no-jni