uget.c

#include <stddef.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#include <arpa/inet.h>
#include <netdb.h>
#include <sys/socket.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <unistd.h>

#define ERR_GENERAL 1
#define ERR_SOCKET 2
#define ERR_GETADDRINFO 3
#define ERR_CONNECT 4
#define ERR_SEND 5
#define ERR_USAGE 6

#define NDEBUG

int get_http_respcode(const char *inpbuf) {
  char proto[4096], descr[4096];
  int code;

  if (sscanf(inpbuf, "%s %d %s", proto, &code, descr) < 2)
    return -1;
  return code;
}

int download(int writefd, char *hostname, char *uri) {
  int ret = ERR_GENERAL;

  struct addrinfo hints, *res, *res0;

  memset(&hints, 0, sizeof(hints));
  hints.ai_family = PF_UNSPEC;
  hints.ai_socktype = SOCK_STREAM;
  int err = getaddrinfo(hostname, "80", &hints, &res0);
  if (err) {
#ifndef NDEBUG
    fprintf(stderr, "getaddrinfo: %s\n", gai_strerror(err));
#endif
    return ERR_GETADDRINFO;
  }

  int s = -1;
  for (res = res0; res; res = res->ai_next) {
    s = socket(res->ai_family, res->ai_socktype, res->ai_protocol);
    if (s < 0) {
      ret = ERR_SOCKET;
      continue;
    }

#ifndef NDEBUG
    char buf[256];
    inet_ntop(res->ai_family, &((struct sockaddr_in *)res->ai_addr)->sin_addr,
              buf, sizeof(buf));
    fprintf(stderr, "Connecting to %s...\n", buf);
#endif

    if (connect(s, res->ai_addr, res->ai_addrlen) < 0) {
      ret = ERR_CONNECT;
      close(s);
      s = -1;
      continue;
    }
    break; /* okay we got one */
  }
  freeaddrinfo(res0);

  if (s < 0) {
    return ret;
  }

  char buf[4096];
  // use the hack to save some space in .rodata
  strcpy(buf, "GET /");
  if (uri) {
    strncat(buf, uri, sizeof(buf) - strlen(buf) - 1);
  }
  strncat(buf, " HTTP/1.0\r\nHost: ", sizeof(buf) - strlen(buf) - 1);
  strncat(buf, hostname, sizeof(buf) - strlen(buf) - 1);
  strncat(buf, "\r\n\r\n", sizeof(buf) - strlen(buf) - 1);
  int tosent = strlen(buf);
  int nsent = send(s, buf, tosent, 0);
  if (nsent != tosent)
    return ERR_SEND;

  int header = 1;
  int nrecvd;
  while ((nrecvd = recv(s, buf, sizeof(buf), 0))) {
    char *ptr = buf;
    if (header) {
      ptr = strstr(buf, "\r\n\r\n");
      if (!ptr)
        continue;

      int rcode = get_http_respcode(buf);
      if (rcode / 100 != 2)
        return rcode / 100 * 10 + rcode % 10;

      header = 0;
      ptr += 4;
      nrecvd -= ptr - buf;
    }
    write(writefd, ptr, nrecvd);
  }

  return 0;
}

int main(int argc, char **argv) {
  if (argc < 2)
    return ERR_USAGE;

  int url_arg = 1;
  int run_program = 0;
  if (argc == 3) {
    if (strcmp("run", argv[1]) != 0)
      return ERR_USAGE;
    run_program = 1;
    url_arg++;
  }

  char *hostname = argv[url_arg];
  char *uri = NULL;

  char *url = hostname;
  while (*url) {
    if (*url == '/') {
      *url++ = 0;
      uri = url;
      break;
    }
    url++;
  }

  int fd = STDOUT_FILENO;
  char temfname[] = "/tmp/ugetXXXXXX";
  if (run_program) {
    fd = mkstemp(temfname);
  }

  int ret = download(fd, hostname, uri);
  if (ret)
    goto cleanup;

  if (run_program) {
    fchmod(fd, S_IRUSR | S_IXUSR);
    close(fd);
    int child = fork();
    if (child) {
      int wstatus;

      wait(&wstatus);
      ret = WEXITSTATUS(wstatus);
    } else {
      execlp(temfname, temfname, (char *)NULL);
      return EXIT_FAILURE;
    }
  }

cleanup:
  if (run_program)
    unlink(temfname);

  return ret;
}