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// termux-api.c - helper binary for calling termux api classes
// Usage: termux-api ${API_METHOD} ${ADDITIONAL_FLAGS}
// This executes
// am broadcast com.termux.api/.TermuxApiReceiver --es socket_input ${INPUT_SOCKET}
// --es socket_output ${OUTPUT_SOCKET}
// --es ${API_METHOD}
// ${ADDITIONAL_FLAGS}
// where ${INPUT_SOCKET} and ${OUTPUT_SOCKET} are addresses to linux abstract namespace sockets,
// used to pass on stdin to the java implementation and pass back output from java to stdout.
#define _POSIX_SOURCE
#define _GNU_SOURCE
#include <fcntl.h>
#include <pthread.h>
#include <signal.h>
#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/socket.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <sys/un.h>
#include <time.h>
#include <unistd.h>
// Function which execs "am broadcast ..".
_Noreturn void exec_am_broadcast(int argc, char** argv, char* input_address_string, char* output_address_string)
{
// Redirect stdout to /dev/null (but leave stderr open):
close(STDOUT_FILENO);
open("/dev/null", O_RDONLY);
// Close stdin:
close(STDIN_FILENO);
int const extra_args = 15; // Including ending NULL.
char** child_argv = malloc((sizeof(char*)) * (argc + extra_args));
child_argv[0] = "am";
child_argv[1] = "broadcast";
child_argv[2] = "--user";
child_argv[3] = "0";
child_argv[4] = "-n";
child_argv[5] = "com.termux.api/.TermuxApiReceiver";
child_argv[6] = "--es";
// Input/output are reversed for the java process (our output is its input):
child_argv[7] = "socket_input";
child_argv[8] = output_address_string;
child_argv[9] = "--es";
child_argv[10] = "socket_output";
child_argv[11] = input_address_string;
child_argv[12] = "--es";
child_argv[13] = "api_method";
child_argv[14] = argv[1];
// Copy the remaining arguments -2 for first binary and second api name:
memcpy(child_argv + extra_args, argv + 2, (argc-1) * sizeof(char*));
// End with NULL:
child_argv[argc + extra_args] = NULL;
// Use an a executable taking care of PATH and LD_LIBRARY_PATH:
execv("/data/data/com.termux/files/usr/bin/am", child_argv);
perror("execv(\"/data/data/com.termux/files/usr/bin/am\")");
exit(1);
}
void generate_uuid(char* str) {
sprintf(str, "%x%x-%x-%x-%x-%x%x%x",
arc4random(), arc4random(), // Generates a 64-bit Hex number
(uint32_t) getpid(), // Generates a 32-bit Hex number
((arc4random() & 0x0fff) | 0x4000), // Generates a 32-bit Hex number of the form 4xxx (4 indicates the UUID version)
arc4random() % 0x3fff + 0x8000, // Generates a 32-bit Hex number in the range [0x8000, 0xbfff]
arc4random(), arc4random(), arc4random()); // Generates a 96-bit Hex number
}
// Thread function which reads from stdin and writes to socket.
void* transmit_stdin_to_socket(void* arg) {
int output_server_socket = *((int*) arg);
struct sockaddr_un remote_addr;
socklen_t addrlen = sizeof(remote_addr);
int output_client_socket = accept(output_server_socket, (struct sockaddr*) &remote_addr, &addrlen);
ssize_t len;
char buffer[1024];
while (len = read(STDIN_FILENO, &buffer, sizeof(buffer)), len > 0) {
if (write(output_client_socket, buffer, len) < 0) break;
}
// Close output socket on end of input:
close(output_client_socket);
return NULL;
}
// Main thread function which reads from input socket and writes to stdout.
void transmit_socket_to_stdout(int input_socket_fd) {
ssize_t len;
char buffer[1024];
while ((len = read(input_socket_fd, &buffer, sizeof(buffer))) > 0) {
write(STDOUT_FILENO, buffer, len);
}
if (len < 0) perror("read()");
}
int main(int argc, char** argv) {
// Do not transform children into zombies when they terminate:
struct sigaction sigchld_action = { .sa_handler = SIG_DFL, .sa_flags = SA_RESTART | SA_NOCLDSTOP | SA_NOCLDWAIT };
sigaction(SIGCHLD, &sigchld_action, NULL);
char input_address_string[100]; // This program reads from it.
char output_address_string[100]; // This program writes to it.
generate_uuid(input_address_string);
generate_uuid(output_address_string);
struct sockaddr_un input_address = { .sun_family = AF_UNIX };
struct sockaddr_un output_address = { .sun_family = AF_UNIX };
// Leave struct sockaddr_un.sun_path[0] as 0 and use the UUID string as abstract linux namespace:
strncpy(&input_address.sun_path[1], input_address_string, strlen(input_address_string));
strncpy(&output_address.sun_path[1], output_address_string, strlen(output_address_string));
int input_server_socket = socket(AF_UNIX, SOCK_STREAM|SOCK_CLOEXEC, 0);
if (input_server_socket == -1) { perror("socket()"); return 1; }
int output_server_socket = socket(AF_UNIX, SOCK_STREAM|SOCK_CLOEXEC, 0);
if (output_server_socket == -1) { perror("socket()"); return 1; }
if (bind(input_server_socket, (struct sockaddr*) &input_address, sizeof(sa_family_t) + strlen(input_address_string) + 1) == -1) {
perror("bind(input)");
return 1;
}
if (bind(output_server_socket, (struct sockaddr*) &output_address, sizeof(sa_family_t) + strlen(output_address_string) + 1) == -1) {
perror("bind(output)");
return 1;
}
if (listen(input_server_socket, 1) == -1) { perror("listen()"); return 1; }
if (listen(output_server_socket, 1) == -1) { perror("listen()"); return 1; }
pid_t fork_result = fork();
switch (fork_result) {
case -1: perror("fork()"); return 1;
case 0: exec_am_broadcast(argc, argv, input_address_string, output_address_string);
}
struct sockaddr_un remote_addr;
socklen_t addrlen = sizeof(remote_addr);
int input_client_socket = accept(input_server_socket, (struct sockaddr*) &remote_addr, &addrlen);
pthread_t transmit_thread;
pthread_create(&transmit_thread, NULL, transmit_stdin_to_socket, &output_server_socket);
transmit_socket_to_stdout(input_client_socket);
return 0;
}