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      1 /* Copyright libuv contributors. All rights reserved.
      2  *
      3  * Permission is hereby granted, free of charge, to any person obtaining a copy
      4  * of this software and associated documentation files (the "Software"), to
      5  * deal in the Software without restriction, including without limitation the
      6  * rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
      7  * sell copies of the Software, and to permit persons to whom the Software is
      8  * furnished to do so, subject to the following conditions:
      9  *
     10  * The above copyright notice and this permission notice shall be included in
     11  * all copies or substantial portions of the Software.
     12  *
     13  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
     14  * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
     15  * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
     16  * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
     17  * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
     18  * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
     19  * IN THE SOFTWARE.
     20  */
     21 
     22 #include "uv.h"
     23 #include "internal.h"
     24 
     25 #include <sys/stat.h>
     26 #include <unistd.h>
     27 
     28 static uv_once_t once = UV_ONCE_INIT;
     29 static int status;
     30 
     31 
     32 int uv__random_readpath(const char* path, void* buf, size_t buflen) {
     33   struct stat s;
     34   size_t pos;
     35   ssize_t n;
     36   int fd;
     37 
     38   fd = uv__open_cloexec(path, O_RDONLY);
     39 
     40   if (fd < 0)
     41     return fd;
     42 
     43   if (uv__fstat(fd, &s)) {
     44     uv__close(fd);
     45     return UV__ERR(errno);
     46   }
     47 
     48   if (!S_ISCHR(s.st_mode)) {
     49     uv__close(fd);
     50     return UV_EIO;
     51   }
     52 
     53   for (pos = 0; pos != buflen; pos += n) {
     54     do
     55       n = read(fd, (char*) buf + pos, buflen - pos);
     56     while (n == -1 && errno == EINTR);
     57 
     58     if (n == -1) {
     59       uv__close(fd);
     60       return UV__ERR(errno);
     61     }
     62 
     63     if (n == 0) {
     64       uv__close(fd);
     65       return UV_EIO;
     66     }
     67   }
     68 
     69   uv__close(fd);
     70   return 0;
     71 }
     72 
     73 
     74 static void uv__random_devurandom_init(void) {
     75   char c;
     76 
     77   /* Linux's random(4) man page suggests applications should read at least
     78    * once from /dev/random before switching to /dev/urandom in order to seed
     79    * the system RNG. Reads from /dev/random can of course block indefinitely
     80    * until entropy is available but that's the point.
     81    */
     82   status = uv__random_readpath("/dev/random", &c, 1);
     83 }
     84 
     85 
     86 int uv__random_devurandom(void* buf, size_t buflen) {
     87   uv_once(&once, uv__random_devurandom_init);
     88 
     89   if (status != 0)
     90     return status;
     91 
     92   return uv__random_readpath("/dev/urandom", buf, buflen);
     93 }
     94