Is there an easy way to tell if a File stream has opened a directory instead of a file?

Question

Hi, I'm making an HTTP server and when I get the path of the file they request I open it with the following:

returned_file = fopen(path, "r");

this (contrary to what I would think) succeeds even if the path is a directory. Is there an easy way to check if the returned_file stream is a directory instead of a file?

Answer 1

Can you check if the path points to a directory before you call fopen?

Answer 2

you can use fstat on the file descriptor returned by fopen.

Edit: Here's and example program:

#include <sys/stat.h>
#include <stdio.h>

void printISDir( FILE* fp, char const * name ) {
  int fdes = fileno(fp) ;
  struct stat fileInfo ;
  fstat(fdes, &fileInfo ) ;
  if ( S_ISDIR(fileInfo.st_mode ) ) {
    printf("%s: I'm a dir!\n", name ) ;
  } else {
    printf("%s: I'm a file!\n", name ) ;
  }

}

int main( int argc, char** argv ) {
  char const * directoryName = "/etc" ;
  char const * fileName = "/etc/hosts" ;

  FILE* dirFp = fopen(directoryName, "r") ;
  FILE* fileFp = fopen(fileName, "r") ;
  printISDir( dirFp, directoryName ) ;
  printISDir( fileFp, fileName ) ;
  fclose(dirFp) ;
  fclose(fileFp) ;

  return 0 ;
}

Answer 3

Use stat() on the file name before you open it, or fstat() the file descriptor fileno(returned_file).

Answer 4

Elaborating on the other answers, you can call fstat on the returned file descriptor and check the st_mode for the S_IFDIR bit. The S_ISDIR helper macro is helpful:

  #include <sys/stat.h>

...

  FILE* f = fopen(path, "r");

  struct stat buf;
  if (fstat(fileno(f), &buf) == -1) {
    perror("fstat");
  } else {
    if (S_ISDIR(buf.st_mode)) {
      printf("is directory\n");
    } else {
      printf("not directory\n");
    }
  }