simplify nscd lookup code for alt passwd/group backends

previously, a sentinel value of (FILE *)-1 was used to inform the
caller of __nscd_query that nscd is not in use. aside from being an
ugly hack, this resulted in duplicate code paths for two logically
equivalent cases: no nscd, and "not found" result from nscd.

now, __nscd_query simply skips closing the socket and returns a valid
FILE pointer when nscd is not in use, and produces a fake "not found"
response header. the caller is then responsible for closing the socket
just like it would do if it had gotten a real "not found" response.

src/passwd/getgr_a.c

@@ -63,7 +63,6 @@ int __getgr_a(const char *name, gid_t gid, struct group *gr, char **buf, size_t
 
 		f = __nscd_query(req, key, groupbuf, sizeof groupbuf, &swap);
 		if (!f) { rv = errno; goto done; }
-		if (f == (FILE*)-1) { rv = 0; goto done; }
 
 		if (!groupbuf[GRFOUND]) { rv = 0; goto cleanup_f; }
 

src/passwd/getgrouplist.c

@@ -28,7 +28,7 @@ int getgrouplist(const char *user, gid_t gid, gid_t *groups, int *ngroups)
 
 	f = __nscd_query(GETINITGR, user, resp, sizeof resp, &swap);
 	if (!f) goto cleanup;
-	if (f != (FILE*)-1 && resp[INITGRFOUND]) {
+	if (resp[INITGRFOUND]) {
 		nscdbuf = calloc(resp[INITGRNGRPS], sizeof(uint32_t));
 		if (!nscdbuf) goto cleanup;
 		if (!fread(nscdbuf, sizeof(*nscdbuf)*resp[INITGRNGRPS], 1, f)) {
@@ -40,7 +40,7 @@ int getgrouplist(const char *user, gid_t gid, gid_t *groups, int *ngroups)
 				nscdbuf[i] = bswap_32(nscdbuf[i]);
 		}
 	}
-	if (f != (FILE*)-1) fclose(f);
+	fclose(f);
 
 	f = fopen("/etc/group", "rbe");
 	if (!f && errno != ENOENT && errno != ENOTDIR)

src/passwd/getpw_a.c

@@ -64,7 +64,6 @@ int __getpw_a(const char *name, uid_t uid, struct passwd *pw, char **buf, size_t
 
 		f = __nscd_query(req, key, passwdbuf, sizeof passwdbuf, (int[]){0});
 		if (!f) { rv = errno; goto done; }
-		if (f == (FILE*)-1) { rv = 0; goto done; }
 
 		if(!passwdbuf[PWFOUND]) { rv = 0; goto cleanup_f; }
 

src/passwd/nscd_query.c

@@ -32,32 +32,34 @@ FILE *__nscd_query(int32_t req, const char *key, int32_t *buf, size_t len, int *
 		.msg_iovlen = 2
 	};
 
-	if (strlen(key) > INT32_MAX - 1) {
-		return (FILE*)-1;
-	}
-
 	*swap = 0;
 retry:
+	memset(buf, 0, len);
+	buf[0] = NSCDVERSION;
 
 	fd = socket(PF_UNIX, SOCK_STREAM | SOCK_CLOEXEC, 0);
 	if (fd < 0) return NULL;
 
+	if(!(f = fdopen(fd, "r"))) {
+		close(fd);
+		return 0;
+	}
+
+	if (strlen(key) > INT32_MAX - 1)
+		return f;
+
 	if (connect(fd, (struct sockaddr*)&addr, sizeof(addr)) < 0) {
 		/* If there isn't a running nscd we return -1 to indicate that
 		 * that is precisely what happened
 		 */
-		if (errno == EACCES || errno == ECONNREFUSED || errno == ENOENT) {
-			close(fd);
-			return (FILE *)-1;
-		}
+		if (errno == EACCES || errno == ECONNREFUSED || errno == ENOENT)
+			return f;
 		goto error;
 	}
 
 	if (sendmsg(fd, &msg, MSG_NOSIGNAL) < 0)
 		goto error;
 
-	if(!(f = fdopen(fd, "r"))) goto error;
-
 	if (!fread(buf, len, 1, f)) {
 		/* If the VERSION entry mismatches nscd will disconnect. The
 		 * most likely cause is that the endianness mismatched. So, we
@@ -95,6 +97,6 @@ retry:
 
 	return f;
 error:
-	if (f) fclose(f); else close(fd);
+	fclose(f);
 	return 0;
 }