Android，RPC原理，C语言实现Binder跨进程通信Demo

RPC原理图

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Binder C语言层的Demo演示

新建目录

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把两个文件拷贝到我们的Demo下面

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1.binder_server.c

#include <stdio.h>
#include <stdlib.h>
#include <errno.h>
#include <linux/types.h>
#include <stdbool.h>
#include <string.h>
#include "binder.h"#define LOG_TAG "BinderServer"
#include <log/log.h>#define HELLO_BINDER     1
#define HELLO_BINDER_TO  2//服务就是被调用的函数
void hellobinder(void)
{static int cnt = 0;ALOGW("hello : %d\n", ++cnt);
}int hellobinder_to(char *name)
{static int cnt = 0;ALOGW("hello to %s : %d\n", name, ++cnt);return cnt;
}//回调函数
int hellobinder_service_handler(struct binder_state *bs,struct binder_transaction_data_secctx *txn_secctx,struct binder_io *msg,struct binder_io *reply)
{struct binder_transaction_data *txn = &txn_secctx->transaction_data;/* 根据txn->code知道要调用哪一个函数* 参数, 从msg取出* 返回结果, 把结果放入reply*//* sayhello* sayhello_to*/uint16_t *s;char name[512];size_t len;//uint32_t handle;uint32_t strict_policy;int i;// Equivalent to Parcel::enforceInterface(), reading the RPC// header with the strict mode policy mask and the interface name.// Note that we ignore the strict_policy and don't propagate it// further (since we do no outbound RPCs anyway).strict_policy = bio_get_uint32(msg);//code 用于判断我们需要调用哪一个函数，客户端远程调用哪个服务端函数switch(txn->code) { case HELLO_BINDER:hellobinder();//给reply写一个值为0bio_put_uint32(reply, 0); /* no exception */return 0;case HELLO_BINDER_TO:/* 从msg里取出字符串 */s = bio_get_string16(msg, &len);  //"IHelloService"s = bio_get_string16(msg, &len);  // nameif (s == NULL) {return -1;}for (i = 0; i < len; i++)name[i] = s[i];name[i] = '\0';/* 处理 */i = hellobinder_to(name);/* 把结果放入reply 给回客户端*/bio_put_uint32(reply, 0); /* no exception */bio_put_uint32(reply, i);break;default:fprintf(stderr, "unknown code %d\n", txn->code);return -1;}return 0;
}// 进程的 Binder 回调函数
//binder_transaction_data_secctx主要的数据，msg客户端传递过来的函数的参数，reply返回给客户端的数据
int test_server_handler(struct binder_state *bs,struct binder_transaction_data_secctx *txn_secctx,struct binder_io *msg,struct binder_io *reply)
{//取出数据，struct binder_transaction_data *txn = &txn_secctx->transaction_data;//函数指针，int (*handler)(struct binder_state *bs,struct binder_transaction_data *txn,struct binder_io *msg,struct binder_io *reply);// txn->target.ptr 是 svcmgr_publish 传入的第二个参数handler = (int (*)(struct binder_state *bs,struct binder_transaction_data *txn,struct binder_io *msg,struct binder_io *reply))txn->target.ptr;//调用函数指针，那么就会调用txn->target.ptr;这个指针，那么就是hellobinder_service_handlerreturn handler(bs, txn, msg, ，reply);
}int main(int argc, char **argv)
{struct binder_state *bs;//值为 0uint32_t svcmgr = BINDER_SERVICE_MANAGER;uint32_t handle;int ret;//初始化驱动bs = binder_open("/dev/binder", 128*1024);if (!bs) {fprintf(stderr, "failed to open binder driver\n");return -1;}//添加服务hellobinder_service_handler 是 hello 服务对应的回调函数//bs打开启动返回的一个int值，句柄，svcmgr表示把数据发到这个进程中，是ServiceManager，hello是注册的服务的名字//当我们注册的时候把这个hellobinder_service_handler指针传给驱动，驱动就记住hello服务回调是它，客户端需要调用hello服务的时候ret = svcmgr_publish(bs, svcmgr, "hello", hellobinder_service_handler);if (ret) {fprintf(stderr, "failed to publish hello service\n");return -1;}//test_server_handler  进程的 Binder 回调函数，进入循环服务端就不会挂掉，一直执行//binder收到数据，就解析，解析好就传给test_server_handlerbinder_loop(bs, test_server_handler);return 0;
}

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binder_transaction_data_secctx

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主要的数据结构是在这里

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2.binder_client.c

#include <stdio.h>
#include <stdlib.h>
#include <errno.h>
#include <linux/types.h>
#include <stdbool.h>
#include <string.h>
#include "binder.h"#define HELLO_BINDER     1
#define HELLO_BINDER_TO  2int g_handle = 0;
struct binder_state *g_bs;void sayhello(void)
{unsigned iodata[512/4];struct binder_io msg, reply;/* 构造binder_io *///初始化msg数据，表示的是所调用的服务端函数所需的参数bio_init(&msg, iodata, sizeof(iodata), 4);/* 放入参数 *///把数据写入msg中bio_put_uint32(&msg, 0);  // strict mode headerbio_put_string16_x(&msg, "IHelloService");/* 调用binder_call *///发起远程调用，g_bs是binder_open返回的一个句柄，msg函数的参数，reply服务端返回值，g_handle是hello服务在客户端的一个句柄索引，通过它才能找到对应的服务端，HELLO_BINDER是code，表示要调用服务端的哪个函数if (binder_call(g_bs, &msg, &reply, g_handle, HELLO_BINDER))return ;/* 从reply中解析出返回值 *///解析服务端返回的数据binder_done(g_bs, &msg, &reply);}int main(int argc, char **argv)
{int fd;struct binder_state *bs;uint32_t svcmgr = BINDER_SERVICE_MANAGER;int ret;bs = binder_open("/dev/binder", 128*1024);if (!bs) {fprintf(stderr, "failed to open binder driver\n");return -1;}g_bs = bs;/* get service 查找服务，bs是binder_open的返回值，svcmgr是servicemanager表示数据要发送给它，hello是查找服务的名字*///g_handle句柄，索引g_handle = svcmgr_lookup(bs, svcmgr, "hello");if (!g_handle) {return -1;} //调用服务，发起远程调用sayhello();}

编写bp文件

cc_defaults {name: "bindertestflags",cflags: ["-Wall","-Wextra","-Werror","-Wno-unused-parameter","-Wno-missing-field-initializers","-Wno-unused-parameter","-Wno-unused-variable","-Wno-incompatible-pointer-types","-Wno-sign-compare",],product_variables: {binder32bit: {cflags: ["-DBINDER_IPC_32BIT=1"],},},shared_libs: ["liblog"],
}
//c的可执行程序
cc_binary {name: "binderclient",defaults: ["bindertestflags"],vendor: true, srcs: ["binder_client.c","binder.c",],
}cc_binary {name: "binderserver",defaults: ["bindertestflags"],vendor: true, srcs: ["binder_server.c","binder.c",],
}// cc_binary {
//     name: "myservicemanager",
//     defaults: ["mybindertest_flags"],
//     srcs: [
//         "service_manager.c",
//         "binder.c",
//     ],
//     shared_libs: ["libcutils", "libselinux"],
// }