Split command into process and adb

The process API provides the system-specific implementation, the adb API
uses it to expose adb commands.

app/src/sys/unix/process.c

@@ -0,0 +1,182 @@
+// for portability (kill, readlink, strdup, strtok_r)
+#define _POSIX_C_SOURCE 200809L
+#define _BSD_SOURCE
+
+// modern glibc will complain without this
+#define _DEFAULT_SOURCE
+
+#ifdef __APPLE__
+# define _DARWIN_C_SOURCE // for strdup(), strtok_r(), memset_pattern4()
+#endif
+
+#include "util/process.h"
+
+#include "config.h"
+
+#include <errno.h>
+#include <fcntl.h>
+#include <limits.h>
+#include <signal.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <sys/wait.h>
+#include <unistd.h>
+
+#include "util/log.h"
+
+bool
+search_executable(const char *file) {
+    char *path = getenv("PATH");
+    if (!path)
+        return false;
+    path = strdup(path);
+    if (!path)
+        return false;
+
+    bool ret = false;
+    size_t file_len = strlen(file);
+    char *saveptr;
+    for (char *dir = strtok_r(path, ":", &saveptr); dir;
+            dir = strtok_r(NULL, ":", &saveptr)) {
+        size_t dir_len = strlen(dir);
+        char *fullpath = malloc(dir_len + file_len + 2);
+        if (!fullpath)
+            continue;
+        memcpy(fullpath, dir, dir_len);
+        fullpath[dir_len] = '/';
+        memcpy(fullpath + dir_len + 1, file, file_len + 1);
+
+        struct stat sb;
+        bool fullpath_executable = stat(fullpath, &sb) == 0 &&
+            sb.st_mode & S_IXUSR;
+        free(fullpath);
+        if (fullpath_executable) {
+            ret = true;
+            break;
+        }
+    }
+
+    free(path);
+    return ret;
+}
+
+enum process_result
+process_execute(const char *const argv[], pid_t *pid) {
+    int fd[2];
+
+    if (pipe(fd) == -1) {
+        perror("pipe");
+        return PROCESS_ERROR_GENERIC;
+    }
+
+    enum process_result ret = PROCESS_SUCCESS;
+
+    *pid = fork();
+    if (*pid == -1) {
+        perror("fork");
+        ret = PROCESS_ERROR_GENERIC;
+        goto end;
+    }
+
+    if (*pid > 0) {
+        // parent close write side
+        close(fd[1]);
+        fd[1] = -1;
+        // wait for EOF or receive errno from child
+        if (read(fd[0], &ret, sizeof(ret)) == -1) {
+            perror("read");
+            ret = PROCESS_ERROR_GENERIC;
+            goto end;
+        }
+    } else if (*pid == 0) {
+        // child close read side
+        close(fd[0]);
+        if (fcntl(fd[1], F_SETFD, FD_CLOEXEC) == 0) {
+            execvp(argv[0], (char *const *)argv);
+            if (errno == ENOENT) {
+                ret = PROCESS_ERROR_MISSING_BINARY;
+            } else {
+                ret = PROCESS_ERROR_GENERIC;
+            }
+            perror("exec");
+        } else {
+            perror("fcntl");
+            ret = PROCESS_ERROR_GENERIC;
+        }
+        // send ret to the parent
+        if (write(fd[1], &ret, sizeof(ret)) == -1) {
+            perror("write");
+        }
+        // close write side before exiting
+        close(fd[1]);
+        _exit(1);
+    }
+
+end:
+    if (fd[0] != -1) {
+        close(fd[0]);
+    }
+    if (fd[1] != -1) {
+        close(fd[1]);
+    }
+    return ret;
+}
+
+bool
+process_terminate(pid_t pid) {
+    if (pid <= 0) {
+        LOGC("Requested to kill %d, this is an error. Please report the bug.\n",
+             (int) pid);
+        abort();
+    }
+    return kill(pid, SIGTERM) != -1;
+}
+
+bool
+process_simple_wait(pid_t pid, int *exit_code) {
+    int status;
+    int code;
+    if (waitpid(pid, &status, 0) == -1 || !WIFEXITED(status)) {
+        // could not wait, or exited unexpectedly, probably by a signal
+        code = -1;
+    } else {
+        code = WEXITSTATUS(status);
+    }
+    if (exit_code) {
+        *exit_code = code;
+    }
+    return !code;
+}
+
+char *
+get_executable_path(void) {
+// <https://stackoverflow.com/a/1024937/1987178>
+#ifdef __linux__
+    char buf[PATH_MAX + 1]; // +1 for the null byte
+    ssize_t len = readlink("/proc/self/exe", buf, PATH_MAX);
+    if (len == -1) {
+        perror("readlink");
+        return NULL;
+    }
+    buf[len] = '\0';
+    return SDL_strdup(buf);
+#else
+    // in practice, we only need this feature for portable builds, only used on
+    // Windows, so we don't care implementing it for every platform
+    // (it's useful to have a working version on Linux for debugging though)
+    return NULL;
+#endif
+}
+
+bool
+is_regular_file(const char *path) {
+    struct stat path_stat;
+
+    if (stat(path, &path_stat)) {
+        perror("stat");
+        return false;
+    }
+    return S_ISREG(path_stat.st_mode);
+}