Sockets in C: read() returns > 0 bytes read, but buffer is zero -

i'm trying read data socket in c. there 2 messages.

i trying send size of message socket read() command know when message ends , can stop reading @ point. otherwise, read both messages 1 blob. problem read command sets buffer 0 though read > 0 bytes.

here code:

n = read(newsockfd, buffer, sizeof(int));       int bytes_to_read = atoi(buffer);       fprintf(stdout, "here size of data for: %d", bytes_to_read);      /*read message*/      fprintf(stdout, "reading first message.\n");      int bytesread = 0;      int chunk = bytes_to_read > 255 ? 255 : bytes_to_read;        {         bzero(buffer,256);         n = read(newsockfd,buffer,chunk);         bytes_read += n;          fprintf(stdout, "the value of n %d , here new buffer after first read: %s , new buffer length : %d\n", n, buffer, strlen(buffer));         strcat(plaintext, buffer);          size += 256;         plaintext = realloc(plaintext, size);       } while (bytes_read < bytes_to_read); 

the output shows n = 36 (as expected) buffer 0 , length of buffer 1.

why read() command setting buffer 0? there easier way tell read() stop reading?

edit: based on feedback got, drastically re-wrote this. note know client send 1 packet containing number of bytes in data unit32_t, send data.

char * readtext(int newsockfd) { char * text = malloc(256);  char buffer[256]; int n;  int size = 256; /*find out how many bytes in data*/  uint32_t bytes_to_read;   n = read(newsockfd, &bytes_to_read, sizeof(uint32_t));   bytes_to_read = ntohl(bytes_to_read);    /*read data client*/  int bytes_read = 0;  int bytes_left = bytes_to_read;   /*the maximum can read @ 1 time 255 bytes since size of buffer.   * buffer have been larger we'd still have check data size , keep calling  * read() until of data.   * if data read smaller buffer, read in 1 go. if data larger,   * read in 255 byte-sized chunks until have read of it*/   int chunk = (bytes_to_read > 255) ? 255 : bytes_to_read;  {     bzero(buffer,256);     n = read(newsockfd,buffer,chunk);     /*copy on data have read far text buffer     offset amount have read in not overwrite data      in array*/     memcpy(text + bytes_read, buffer, n);     bytes_read += n;      bytes_left -= n;      /*if have less 255 bytes left, read amount. prevents read() pulling in data , messing next read() call*/  chunk = (bytes_left > 255) ? 255 : bytes_left;     size += n;     /*grow text variable as read in. makes room      next chunk of data. next chunk large 255 bytes*/      text = realloc(text, size);   } while (bytes_read < bytes_to_read);   text[bytes_read] = '\0'; //null terminate our string can use string functions on it.   if (n < 0) error("error reading socket"); return text; }` 

1. there's no guarantee received entire length message.

2. you're reading sizeof int bytes, suggests binary data, you're calling atoi(), suggests null-terminated ascii data in form of decimal string. it?

3. if you're getting return value of 36 that's how many bytes received, , if buffer contains {0, 1} that's received too.

4. it isn't valid use strlen() or strcat() on arbitrary array of bytes. these functions null-terminated strings. there nothing tcp says every buffer receive null-terminated string, , nothing says receive printable.

what you're doing not valid.