How to properly include an http C library into an Android Project? - c

Question

I am making an Android Project and I am trying to make a post request using HTTPS to a server. To make the post request I am requires to use JNI so I need to implement this in C.
My idea was to use a library that I could include into my project as i have done with the minizip library here.
I found this library here that seemed to me light engough and could server my purpose. I included in the folder c as you can also see below the files ca_cert.h, https.c and https.h along with the folder mbedtls exactly as is found on the github project.
├── app.iml
├── build.gradle
├── CMakeLists.txt
└── src
├── androidTest
│   └── java
│   └── etc
├── main
│   ├── AndroidManifest.xml
│   ├── c
│   │   ├── ca_cert.h
│   │   ├── https.c
│   │   ├── https.h
│   │   ├── mbedtls
│   │   │   ├── etc
│   │   ├── native-lib.c
│   │   ├── pathfinder.c
│   │   ├── pathfinder.h
│   │   ├── post_data.c
│   │   ├── post_data.h
│   │   ├── third
│   ├── java
│   │   └── etc
│   └── res
│   ├── etc
└── test
└── java
└── etc
As you can see in the tree structure above I have a CMakeLists.txt in the root directory and in src/main/c/ you will see the files and the folder i took from the the https library mentioned.
The contents of the CMakeLists.txt are the following
cmake_minimum_required(VERSION 3.4.1)
add_library( # Sets the name of the library.
native-lib
# Sets the library as a shared library.
SHARED
# Provides a relative path to your source file(s).
src/main/c/native-lib.c
src/main/c/ca_cert.h
src/main/c/https.h
)
include_directories(native-lib SHARED src/main/c/mbedtls/include)
#add_definitions(-DHAVE_ZLIB)
find_library( PRE_BUILD_ANDROID_LIB android)
find_library( log-lib log)
find_library(z-lib z)
target_link_libraries( native-lib
${PRE_BUILD_ANDROID_LIB}
${log-lib}
${z-lib}
)
I am missing something though for sure cause when i attempt to run a simple example like the following
JNIEXPORT jint JNICALL
Java_example_example_do_post(
JNIEnv *env,
jobject this ) {
NSV_LOGE("post_data starts\n");
char *url;
char data[1024], response[4096];
int i, ret, size;
HTTP_INFO hi1, hi2;
// Init http session. verify: check the server CA cert.
http_init(&hi1, FALSE);
http_init(&hi2, TRUE);
url = "http://httpbin.org/get?message=https_client";
ret = http_get(&hi1, url, response, sizeof(response));
return 0;
}
I get
../../../../src/main/c/native-lib.c:56: error: undefined reference to 'http_init'
../../../../src/main/c/native-lib.c:57: error: undefined reference to 'http_init'
../../../../src/main/c/native-lib.c:61: error: undefined reference to 'http_get'
clang: error: linker command failed with exit code 1 (use -v to see invocation)

Answer 1

Replace
src/main/c/ca_cert.h
src/main/c/https.h
with
src/main/c/https.c
in CMakeLists.txt.