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     // The user is calculated from the uid in android.os.UserHandle#getUserId(int uid) as "uid / 100000", so we do the same:
  36     uid_t current_uid = getuid();
  37     int android_user_id = current_uid / 100000;
  38     char* android_user_id_string;
  39     if (asprintf(&android_user_id_string, "%d", android_user_id) == -1) {
  40         fprintf(stderr, "asprintf() error");
  41         return;
  42     }
  43
  44     int const extra_args = 15; // Including ending NULL.
  45     char** child_argv = malloc((sizeof(char*)) * (argc + extra_args));
  46
  47     child_argv[0] = "am";
  48     child_argv[1] = "broadcast";
  49     child_argv[2] = "--user";
  50     child_argv[3] = android_user_id_string;
  51     child_argv[4] = "-n";
  52     child_argv[5] = "com.termux.api/.TermuxApiReceiver";
  53     child_argv[6] = "--es";
  54     // Input/output are reversed for the java process (our output is its input):
  55     child_argv[7] = "socket_input";
  56     child_argv[8] = output_address_string;
  57     child_argv[9] = "--es";
  58     child_argv[10] = "socket_output";
  59     child_argv[11] = input_address_string;
  60     child_argv[12] = "--es";
  61     child_argv[13] = "api_method";
  62     child_argv[14] = argv[1];
  63
  64     // Copy the remaining arguments -2 for first binary and second api name:
  65     memcpy(child_argv + extra_args, argv + 2, (argc-1) * sizeof(char*));
  66
  67     // End with NULL:
  68     child_argv[argc + extra_args] = NULL;
  69
  70     // Use an a executable taking care of PATH and LD_LIBRARY_PATH:
  71     char const* const am_executable = "/data/data/com.termux/files/usr/bin/am";
  72     execv(am_executable, child_argv);
  73
  74     perror("execv(\"/system/bin/am\")");
  75     exit(1);
  76 }
  77
  78 void generate_uuid(char* str) {
  79     sprintf(str, "%x%x-%x-%x-%x-%x%x%x",
  80             arc4random(), arc4random(),                // Generates a 64-bit Hex number
  81             (uint32_t) getpid(),           // Generates a 32-bit Hex number
  82             ((arc4random() & 0x0fff) | 0x4000),  // Generates a 32-bit Hex number of the form 4xxx (4 indicates the UUID version)
  83             arc4random() % 0x3fff + 0x8000,      // Generates a 32-bit Hex number in the range [0x8000, 0xbfff]
  84             arc4random(), arc4random(), arc4random());       // Generates a 96-bit Hex number
  85 }
  86
  87 // Thread function which reads from stdin and writes to socket.
  88 void* transmit_stdin_to_socket(void* arg) {
  89     int output_server_socket = *((int*) arg);
  90     struct sockaddr_un remote_addr;
  91     socklen_t addrlen = sizeof(remote_addr);
  92     int output_client_socket = accept(output_server_socket, (struct sockaddr*) &remote_addr, &addrlen);
  93
  94     int len;
  95     char buffer[1024];
  96     while (len = read(STDIN_FILENO, &buffer, sizeof(buffer)-1), len > 0) {
  97         if (write(output_client_socket, buffer, len) < 0) break;
  98     }
  99     // Close output socket on end of input:
 100     close(output_client_socket);
 101     return NULL;
 102 }
 103
 104 // Main thread function which reads from input socket and writes to stdout.
 105 void transmit_socket_to_stdout(int input_socket_fd) {
 106     int len;
 107     char buffer[1024];
 108     while ((len = read(input_socket_fd, &buffer, sizeof(buffer)-1)) > 0) {
 109         buffer[len] = 0;
 110         write(STDOUT_FILENO, buffer, len);
 111     }
 112     if (len < 0) perror("read()");
 113 }
 114
 115 int main(int argc, char** argv) {
 116     // Do not transform children into zombies when they terminate:
 117     struct sigaction sigchld_action = { .sa_handler = SIG_DFL, .sa_flags = SA_RESTART | SA_NOCLDSTOP | SA_NOCLDWAIT };
 118     sigaction(SIGCHLD, &sigchld_action, NULL);
 119
 120     char input_address_string[100];  // This program reads from it.
 121     char output_address_string[100]; // This program writes to it.
 122
 123     generate_uuid(input_address_string);
 124     generate_uuid(output_address_string);
 125
 126     struct sockaddr_un input_address = { .sun_family = AF_UNIX };
 127     struct sockaddr_un output_address = { .sun_family = AF_UNIX };
 128     // Leave struct sockaddr_un.sun_path[0] as 0 and use the UUID string as abstract linux namespace:
 129     strncpy(&input_address.sun_path[1], input_address_string, strlen(input_address_string));
 130     strncpy(&output_address.sun_path[1], output_address_string, strlen(output_address_string));
 131
 132     int input_server_socket = socket(AF_UNIX, SOCK_STREAM|SOCK_CLOEXEC, 0);
 133     if (input_server_socket == -1) { perror("socket()"); return 1; }
 134     int output_server_socket = socket(AF_UNIX, SOCK_STREAM|SOCK_CLOEXEC, 0);
 135     if (output_server_socket == -1) { perror("socket()"); return 1; }
 136
 137     if (bind(input_server_socket, (struct sockaddr*) &input_address, sizeof(sa_family_t) + strlen(input_address_string) + 1) == -1) {
 138         perror("bind(input)");
 139         return 1;
 140     }
 141     if (bind(output_server_socket, (struct sockaddr*) &output_address, sizeof(sa_family_t) + strlen(output_address_string) + 1) == -1) {
 142         perror("bind(output)");
 143         return 1;
 144     }
 145
 146     if (listen(input_server_socket, 1) == -1) { perror("listen()"); return 1; }
 147     if (listen(output_server_socket, 1) == -1) { perror("listen()"); return 1; }
 148
 149     pid_t fork_result = fork();
 150     switch (fork_result) {
 151         case -1: perror("fork()"); return 1;
 152         case 0: exec_am_broadcast(argc, argv, input_address_string, output_address_string); return 0;
 153     }
 154
 155     struct sockaddr_un remote_addr;
 156     socklen_t addrlen = sizeof(remote_addr);
 157     int input_client_socket = accept(input_server_socket, (struct sockaddr*) &remote_addr, &addrlen);
 158
 159     pthread_t transmit_thread;
 160     pthread_create(&transmit_thread, NULL, transmit_stdin_to_socket, &output_server_socket);
 161
 162     transmit_socket_to_stdout(input_client_socket);
 163
 164     return 0;
 165 }
 166