lib/, src/: Consistently use NULL with fgets(3)

fgets(3) returns either NULL or the input pointer.  Checking for NULL is
more explicit, and simpler.

<stddef.h> is the header that provides NULL; add it where appropriate.

The meat of this patch can be approximated with the following semantic
patch:

	$ cat ~/tmp/spatch/fgets_null.sp
	@@
	expression a, b, c;
	@@

	- fgets(a, b, c) == a
	+ fgets(a, b, c) != NULL

	@@
	expression a, b, c;
	@@

	- fgetsx(a, b, c) == a
	+ fgetsx(a, b, c) != NULL

	@@
	expression a, b, c, p;
	@@

	- p->fgets(a, b, c) == a
	+ p->fgets(a, b, c) != NULL

	@@
	expression a, b, c;
	@@

	- fgets(a, b, c) != a
	+ fgets(a, b, c) == NULL

	@@
	expression a, b, c;
	@@

	- fgetsx(a, b, c) != a
	+ fgetsx(a, b, c) == NULL

	@@
	expression a, b, c, p;
	@@

	- p->fgets(a, b, c) != a
	+ p->fgets(a, b, c) == NUL

Applied as

	$ find contrib/ lib* src/ -type f \
	| xargs spatch --sp-file ~/tmp/spatch/fgets_null.sp --in-place;

The differences between the actual patch and the approximation via the
semantic patch from above are includes, whitespace, braces, and a case
where there was an implicit pointer-to-bool comparison which I made
explicit.  When reviewing, it'll be useful to use git-diff(1) with '-w'
and '--color-words=.'.

Signed-off-by: Alejandro Colomar <[email protected]>

lib/commonio.c

@@ -16,6 +16,7 @@
 #include <fcntl.h>
 #include <limits.h>
 #include <signal.h>
+#include <stddef.h>
 #include <stdio.h>
 #include <string.h>
 #include <sys/stat.h>
@@ -643,7 +644,7 @@ int commonio_open (struct commonio_db *db, int mode)
 	if (NULL == buf)
 		goto cleanup_errno;
 
-	while (db->ops->fgets (buf, buflen, db->fp) == buf) {
+	while (db->ops->fgets(buf, buflen, db->fp) != NULL) {
 		struct commonio_entry  *p;
 
 		while (   (strrchr (buf, '\n') == NULL)

lib/fields.c

@@ -12,8 +12,9 @@
 #ident "$Id$"
 
 #include <ctype.h>
-#include <string.h>
+#include <stddef.h>
 #include <stdio.h>
+#include <string.h>
 
 #include "prototypes.h"
 #include "string/strchr/stpspn.h"
@@ -80,9 +81,8 @@ change_field(char *buf, size_t maxsize, const char *prompt)
 
 	printf ("\t%s [%s]: ", prompt, buf);
 	(void) fflush (stdout);
-	if (fgets (newf, maxsize, stdin) != newf) {
+	if (fgets(newf, maxsize, stdin) == NULL)
 		return;
-	}
 
 	if (stpsep(newf, "\n") == NULL)
 		return;

lib/fputsx.c

@@ -9,6 +9,7 @@
 
 #include <config.h>
 
+#include <stddef.h>
 #include <stdio.h>
 #include <string.h>
 
@@ -24,7 +25,7 @@ fgetsx(/*@returned@*/char *restrict buf, int cnt, FILE *restrict f)
 	char *ep;
 
 	while (cnt > 0) {
-		if (fgets (cp, cnt, f) != cp) {
+		if (fgets(cp, cnt, f) == NULL) {
 			if (cp == buf) {
 				return NULL;
 			} else {

lib/getdate.y

@@ -25,6 +25,7 @@
 #endif
 
 #include <ctype.h>
+#include <stddef.h>
 #include <stdio.h>
 #include <string.h>
 #include <time.h>
@@ -935,7 +936,7 @@ main(void)
   (void) fflush (stdout);
 
   buff[MAX_BUFF_LEN] = 0;
-  while (fgets (buff, MAX_BUFF_LEN, stdin) && buff[0])
+  while (fgets(buff, MAX_BUFF_LEN, stdin) != NULL && buff[0])
     {
       d = get_date(buff, NULL);
       if (d == -1)

lib/gshadow.c

@@ -160,9 +160,8 @@ sgetsgent(const char *string)
 		buflen *= 2;
 
 		len = strlen (buf);
-		if (fgetsx(&buf[len], buflen - len, fp) != &buf[len]) {
+		if (fgetsx(&buf[len], buflen - len, fp) == NULL)
 			return NULL;
-		}
 	}
 	stpsep(buf, "\n");
 	return (sgetsgent (buf));

lib/hushed.c

@@ -13,6 +13,7 @@
 #ident "$Id$"
 
 #include <pwd.h>
+#include <stddef.h>
 #include <stdio.h>
 #include <string.h>
 #include <sys/types.h>
@@ -73,7 +74,7 @@ bool hushed (const char *username)
 	if (NULL == fp) {
 		return false;
 	}
-	for (found = false; !found && (fgets(buf, sizeof(buf), fp) == buf);) {
+	for (found = false; !found && (fgets(buf, sizeof(buf), fp) != NULL);) {
 		stpsep(buf, "\n");
 		found = streq(buf, pw->pw_shell) ||
 		        streq(buf, pw->pw_name);

lib/loginprompt.c

@@ -12,8 +12,9 @@
 #ident "$Id$"
 
 #include <assert.h>
-#include <stdio.h>
 #include <signal.h>
+#include <stddef.h>
+#include <stdio.h>
 
 #include "attr.h"
 #include "defines.h"
@@ -83,9 +84,8 @@ login_prompt(char *name, int namesize)
 	 */
 
 	MEMZERO(buf);
-	if (fgets(buf, sizeof(buf), stdin) != buf) {
+	if (fgets(buf, sizeof(buf), stdin) == NULL)
 		exit (EXIT_FAILURE);
-	}
 
 	if (stpsep(buf, "\n") == NULL)
 		exit(EXIT_FAILURE);

lib/setupenv.c

@@ -16,6 +16,7 @@
 #ident "$Id$"
 
 #include <assert.h>
+#include <stddef.h>
 #include <sys/types.h>
 #include <sys/stat.h>
 #include <stdio.h>
@@ -55,7 +56,7 @@ static void read_env_file (const char *filename)
 	if (NULL == fp) {
 		return;
 	}
-	while (fgets(buf, sizeof(buf), fp) == buf) {
+	while (fgets(buf, sizeof(buf), fp) != NULL) {
 		if (stpsep(buf, "\n") == NULL)
 			break;
 

lib/ttytype.c

@@ -11,6 +11,7 @@
 
 #ident "$Id$"
 
+#include <stddef.h>
 #include <stdio.h>
 #include <string.h>
 
@@ -47,7 +48,7 @@ void ttytype (const char *line)
 			perror (typefile);
 		return;
 	}
-	while (fgets(buf, sizeof(buf), fp) == buf) {
+	while (fgets(buf, sizeof(buf), fp) != NULL) {
 		if (strprefix(buf, "#")) {
 			continue;
 		}

lib/user_busy.c

@@ -12,6 +12,7 @@
 #ident "$Id: $"
 
 #include <assert.h>
+#include <stddef.h>
 #include <stdio.h>
 #include <sys/types.h>
 #include <dirent.h>
@@ -126,7 +127,7 @@ static int check_status (const char *name, const char *sname, uid_t uid)
 	if (NULL == sfile) {
 		return 0;
 	}
-	while (fgets(line, sizeof(line), sfile) == line) {
+	while (fgets(line, sizeof(line), sfile) != NULL) {
 		if (strprefix(line, "Uid:\t")) {
 			unsigned long ruid, euid, suid;
 

src/login_nopam.c

@@ -97,7 +97,7 @@ login_access(const char *user, const char *from)
 	if (NULL != fp) {
 		int lineno = 0;	/* for diagnostics */
 		while (   !match
-		       && (fgets(line, sizeof(line), fp) == line))
+		       && (fgets(line, sizeof(line), fp) != NULL))
 		{
 			char  *p;
 

src/useradd.c

@@ -18,16 +18,17 @@
 #include <getopt.h>
 #include <grp.h>
 #ifdef ENABLE_LASTLOG
-#include <lastlog.h>
+# include <lastlog.h>
 #endif /* ENABLE_LASTLOG */
 #include <libgen.h>
 #include <pwd.h>
 #include <signal.h>
 #ifdef ACCT_TOOLS_SETUID
-#ifdef USE_PAM
-#include "pam_defs.h"
-#endif				/* USE_PAM */
+# ifdef USE_PAM
+#  include "pam_defs.h"
+# endif				/* USE_PAM */
 #endif				/* ACCT_TOOLS_SETUID */
+#include <stddef.h>
 #include <stdio.h>
 #include <string.h>
 #include <sys/stat.h>
@@ -362,7 +363,7 @@ get_defaults(void)
 	 * Read the file a line at a time. Only the lines that have relevant
 	 * values are used, everything else can be ignored.
 	 */
-	while (fgets(buf, sizeof(buf), fp) == buf) {
+	while (fgets(buf, sizeof(buf), fp) != NULL) {
 		stpsep(buf, "\n");
 
 		cp = stpsep(buf, "=");
@@ -602,7 +603,7 @@ set_defaults(void)
 		goto skip;
 	}
 
-	while (fgets(buf, sizeof(buf), ifp) == buf) {
+	while (fgets(buf, sizeof(buf), ifp) != NULL) {
 		char  *val;
 
 		if (stpsep(buf, "\n") == NULL) {