added readline for file descriptors (from kerrisk)

session2/readline.c

@@ -0,0 +1,71 @@
+/*************************************************************************\
+*                  Copyright (C) Michael Kerrisk, 2015.                   *
+*                                                                         *
+* This program is free software. You may use, modify, and redistribute it *
+* under the terms of the GNU Lesser General Public License as published   *
+* by the Free Software Foundation, either version 3 or (at your option)   *
+* any later version. This program is distributed without any warranty.    *
+* See the files COPYING.lgpl-v3 and COPYING.gpl-v3 for details.           *
+\*************************************************************************/
+
+/* read_line.c
+
+   Implementation of readLine().
+*/
+#include <unistd.h>
+#include <errno.h>
+#include "readline.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;
+}

session2/readline.h

@@ -0,0 +1,22 @@
+/*************************************************************************\
+*                  Copyright (C) Michael Kerrisk, 2015.                   *
+*                                                                         *
+* This program is free software. You may use, modify, and redistribute it *
+* under the terms of the GNU Lesser General Public License as published   *
+* by the Free Software Foundation, either version 3 or (at your option)   *
+* any later version. This program is distributed without any warranty.    *
+* See the files COPYING.lgpl-v3 and COPYING.gpl-v3 for details.           *
+\*************************************************************************/
+
+/* read_line.h
+
+   Header file for read_line.c.
+*/
+#ifndef READ_LINE_H
+#define READ_LINE_H
+
+#include <sys/types.h>
+
+ssize_t readline(int fd, void *buffer, size_t n);
+
+#endif