Reading whole file into a Buffer

Question

I am trying to read a RSA key file into a buffer with the code below

 char* readkeyBuffer(){
    char *buffer;
    long length;
    FILE *f;
    f= fopen ("file.p12", "rb");

    if (f)
    {
      fseek (f, 0, SEEK_END);
      length = ftell (f);
      rewind(f);
      //fseek (f, 0, SEEK_SET);
      buffer = (char *) malloc (sizeof(char) * (length +1 ));
      
      
      lr_message("Length = %d",length);
      lr_message("sizeof Buffer = %d",sizeof(buffer));
      
      if (buffer)
      {
        fread (buffer, 1, length, f);
        //strcat(buffer,'\0');
      }
     
      
      lr_message("sizeof Buffer = %d",sizeof(buffer));
      lr_message("buffer len = %d",strlen(buffer));
      
      //lr_message("%s",buffer);
       fclose (f);
    }
    return buffer;
 }

The file size is 4476 , but somehow the file being read into the buffer has only 59 chars. Can you please suggest what is the issue?

Output ---

Length = 4476
sizeof Buffer = 4
sizeof Buffer = 4
buffer len = 59

check the return value of `fread` which is number of bytes read, your buffer might have null byte inbetween. — kiran Biradar, Nov 10 '20 at 09:21
Side note: `sizeof(buffer) == sizeof(char*) ==` size of an address (usually 4 or 8 bytes) on your platform. — goodvibration, Nov 10 '20 at 09:21
@kiranBiradar where rsa keys is base64 or so coded and can't contain `\0` — Алексей Неудачин, Nov 10 '20 at 09:29
Once you `malloc()` there's no way to know how big an allocation is. You must track this separately if you need to preserve it. — tadman, Nov 10 '20 at 09:31
fread is returning correct length ```readLen= fread (buffer, 1, length, f); read len = 4476 ``` — Shinu S, Nov 10 '20 at 09:33
You just need to keep track of what you allocated. In this case it's `length + 1`, so that's easy. Normally you do it like `size_t buffer_size = length + 1` then `malloc(buffer_size)`. — tadman, Nov 10 '20 at 09:36
there's Binary DER-encoded format , so `\0` could have been there. https://www.cryptosys.net/pki/rsakeyformats.html .didn't know . — Алексей Неудачин, Nov 10 '20 at 10:08
@АлексейНеудачин b[59] , b[58] are ```00 0x01``` — Shinu S, Nov 10 '20 at 10:27
Also since fread is reading the whole file length ```readLen= fread (buffer, 1, length, f); read len = 4476``` so the null termination \0 shouldn't be an issue — Shinu S, Nov 10 '20 at 10:37
@ShinuS `00` is `\0` . so use `mecpy()` instead of `string.h` stuff with it. — Алексей Неудачин, Nov 10 '20 at 12:15

Reading whole file into a Buffer

0 Answers0