mdw@git.distorted.org.uk Git - termux-packages/blob - packages/termux-api/termux-api.c

   1 // termux-api.c - helper binary for calling termux api classes
   2 // Usage: termux-api ${API_METHOD} ${ADDITIONAL_FLAGS}
   3 //        This executes
   4 //          am broadcast com.termux.api/.TermuxApiReceiver --es socket_input ${INPUT_SOCKET}
   5 //                                                        --es socket_output ${OUTPUT_SOCKET}
   6 //                                                        --es ${API_METHOD}
   7 //                                                        ${ADDITIONAL_FLAGS}
   8 //        where ${INPUT_SOCKET} and ${OUTPUT_SOCKET} are addresses to linux abstract namespace sockets,
   9 //        used to pass on stdin to the java implementation and pass back output from java to stdout.
  10 #define _POSIX_SOURCE
  11 #define _GNU_SOURCE
  12 #include <fcntl.h>
  13 #include <pthread.h>
  14 #include <signal.h>
  15 #include <stdbool.h>
  16 #include <stdio.h>
  17 #include <stdlib.h>
  18 #include <string.h>
  19 #include <sys/socket.h>
  20 #include <sys/stat.h>
  21 #include <sys/types.h>
  22 #include <sys/un.h>
  23 #include <time.h>
  24 #include <unistd.h>
  25
  26 // Function which execs "am broadcast ..".
  27 void exec_am_broadcast(int argc, char** argv, char* input_address_string, char* output_address_string)
  28 {
  29         // Redirect stdout to /dev/null (but leave stderr open):
  30         close(STDOUT_FILENO);
  31         open("/dev/null", O_RDONLY);
  32         // Close stdin:
  33         close(STDIN_FILENO);
  34
  35         char const* const file = "/system/bin/am";
  36         // Avoid the system am binary from linking to wrong libraries:
  37         unsetenv("LD_LIBRARY_PATH");
  38
  39         // The user is calculated from the uid in android.os.UserHandle#getUserId(int uid) as "uid / 100000", so we do the same:
  40         uid_t current_uid = getuid();
  41         int android_user_id = current_uid / 100000;
  42         char* android_user_id_string;
  43         if (asprintf(&android_user_id_string, "%d", android_user_id) == -1) {
  44                 fprintf(stderr, "asprintf() error");
  45                 return;
  46         }
  47
  48         int const extra_args = 15; // Including ending NULL.
  49         char** child_argv = malloc((sizeof(char*)) * (argc + extra_args));
  50
  51         child_argv[0] = "am";
  52         child_argv[1] = "broadcast";
  53         child_argv[2] = "--user";
  54         child_argv[3] = android_user_id_string;
  55         child_argv[4] = "-n";
  56         child_argv[5] = "com.termux.api/.TermuxApiReceiver";
  57         child_argv[6] = "--es";
  58         // Input/output are reversed for the java process (our output is its input):
  59         child_argv[7] = "socket_input";
  60         child_argv[8] = output_address_string;
  61         child_argv[9] = "--es";
  62         child_argv[10] = "socket_output";
  63         child_argv[11] = input_address_string;
  64         child_argv[12] = "--es";
  65         child_argv[13] = "api_method";
  66         child_argv[14] = argv[1];
  67
  68         // Copy the remaining arguments -2 for first binary and second api name:
  69         memcpy(child_argv + extra_args, argv + 2, (argc-1) * sizeof(char*));
  70
  71         // End with NULL:
  72         child_argv[argc + extra_args] = NULL;
  73
  74         execv(file, child_argv);
  75         perror("execv(\"/system/bin/am\")");
  76         exit(1);
  77 }
  78
  79 void generate_uuid(char* str) {
  80         sprintf(str, "%x%x-%x-%x-%x-%x%x%x",
  81                         rand(), rand(),                 // Generates a 64-bit Hex number
  82                         (uint32_t) getpid(),                         // Generates a 32-bit Hex number
  83                         ((rand() & 0x0fff) | 0x4000),   // Generates a 32-bit Hex number of the form 4xxx (4 indicates the UUID version)
  84                         rand() % 0x3fff + 0x8000,       // Generates a 32-bit Hex number in the range [0x8000, 0xbfff]
  85                         rand(), rand(), rand());        // Generates a 96-bit Hex number
  86 }
  87
  88 // Thread function which reads from stdin and writes to socket.
  89 void* transmit_stdin_to_socket(void* arg) {
  90         int output_server_socket = *((int*) arg);
  91         struct sockaddr_un remote_addr;
  92         socklen_t addrlen = sizeof(remote_addr);
  93         int output_client_socket = accept(output_server_socket, (struct sockaddr*) &remote_addr, &addrlen);
  94
  95         int len;
  96         char buffer[1024];
  97         while (len = read(STDIN_FILENO, &buffer, sizeof(buffer)-1), len > 0) {
  98                 if (write(output_client_socket, buffer, len) < 0) break;
  99         }
 100         // Close output socket on end of input:
 101         close(output_client_socket);
 102         return NULL;
 103 }
 104
 105 // Main thread function which reads from input socket and writes to stdout.
 106 void transmit_socket_to_stdout(int input_socket_fd) {
 107         int len;
 108         char buffer[1024];
 109         while ((len = read(input_socket_fd, &buffer, sizeof(buffer)-1)) > 0) {
 110                 buffer[len] = 0;
 111                 write(STDOUT_FILENO, buffer, len);
 112         }
 113         if (len < 0) perror("read()");
 114 }
 115
 116 int main(int argc, char** argv) {
 117         // Do not transform children into zombies when they terminate:
 118         struct sigaction sigchld_action = { .sa_handler = SIG_DFL, .sa_flags = SA_RESTART | SA_NOCLDSTOP | SA_NOCLDWAIT };
 119         sigaction(SIGCHLD, &sigchld_action, NULL);
 120
 121         char input_address_string[100];  // This program reads from it.
 122         char output_address_string[100]; // This program writes to it.
 123
 124         // Seed the random number generator:
 125         struct timeval time;
 126         gettimeofday(&time,NULL);
 127         srand((time.tv_sec * 1000) + (time.tv_usec / 1000));
 128
 129         generate_uuid(input_address_string);
 130         generate_uuid(output_address_string);
 131
 132         struct sockaddr_un input_address = { .sun_family = AF_UNIX };
 133         struct sockaddr_un output_address = { .sun_family = AF_UNIX };
 134         // Leave struct sockaddr_un.sun_path[0] as 0 and use the UUID string as abstract linux namespace:
 135         strncpy(&input_address.sun_path[1], input_address_string, strlen(input_address_string));
 136         strncpy(&output_address.sun_path[1], output_address_string, strlen(output_address_string));
 137
 138         int input_server_socket = socket(AF_UNIX, SOCK_STREAM|SOCK_CLOEXEC, 0);
 139         if (input_server_socket == -1) { perror("socket()"); return 1; }
 140         int output_server_socket = socket(AF_UNIX, SOCK_STREAM|SOCK_CLOEXEC, 0);
 141         if (output_server_socket == -1) { perror("socket()"); return 1; }
 142
 143         if (bind(input_server_socket, (struct sockaddr*) &input_address, sizeof(sa_family_t) + strlen(input_address_string) + 1) == -1) {
 144                 perror("bind(input)");
 145                 return 1;
 146         }
 147         if (bind(output_server_socket, (struct sockaddr*) &output_address, sizeof(sa_family_t) + strlen(output_address_string) + 1) == -1) {
 148                 perror("bind(output)");
 149                 return 1;
 150         }
 151
 152         if (listen(input_server_socket, 1) == -1) { perror("listen()"); return 1; }
 153         if (listen(output_server_socket, 1) == -1) { perror("listen()"); return 1; }
 154
 155         pid_t fork_result = fork();
 156         switch (fork_result) {
 157                 case -1: perror("fork()"); return 1;
 158                 case 0: exec_am_broadcast(argc, argv, input_address_string, output_address_string); return 0;
 159         }
 160
 161         struct sockaddr_un remote_addr;
 162         socklen_t addrlen = sizeof(remote_addr);
 163         int input_client_socket = accept(input_server_socket, (struct sockaddr*) &remote_addr, &addrlen);
 164
 165         pthread_t transmit_thread;
 166         pthread_create(&transmit_thread, NULL, transmit_stdin_to_socket, &output_server_socket);
 167
 168         transmit_socket_to_stdout(input_client_socket);
 169
 170         return 0;
 171 }
 172