sockets/read_line.c

+/* read_line.c
+
+   Implementation of readLine().
+*/
 #include <unistd.h>
 #include <errno.h>
 #include "read_line.h"                  /* Declaration of readLine() */
 
+/* Read characters from 'fd' until a newline is encountered. If a newline
+  character is not encountered in the first (n - 1) bytes, then the excess
+  characters are discarded. The returned string placed in 'buf' is
+  null-terminated and includes the newline character if it was read in the
+  first (n - 1) bytes. The function return value is the number of bytes
+  placed in buffer (which includes the newline character if encountered,
+  but excludes the terminating null byte). */
+
 ssize_t
 readLine(int fd, void *buffer, size_t n)
 {
     ssize_t numRead;                    /* # of bytes fetched by last read() */
     size_t totRead;                     /* Total bytes read so far */
     char *buf;
     char ch;
 
     if (n <= 0 || buffer == NULL) {
         errno = EINVAL;
         return -1;
     }
 
     buf = buffer;                       /* No pointer arithmetic on "void *" */
 
     totRead = 0;
     for (;;) {
         numRead = read(fd, &ch, 1);
 
         if (numRead == -1) {
             if (errno == EINTR)         /* Interrupted --> restart read() */
                 continue;
             else
                 return -1;              /* Some other error */
 
         } else if (numRead == 0) {      /* EOF */
             if (totRead == 0)           /* No bytes read; return 0 */
                 return 0;
             else                        /* Some bytes read; add '\0' */
                 break;
 
         } else {                        /* 'numRead' must be 1 if we get here */
             if (totRead < n - 1) {      /* Discard > (n - 1) bytes */
                 totRead++;
                 *buf++ = ch;
             }
 
             if (ch == '\n')
                 break;
         }
     }
 
     *buf = '\0';
     return totRead;
 }