improve getservbyname_r using new resolver backend

now that host and service lookup have been separated in the backend,
there's no need for service lookup functions to pull in the host
lookup code. moreover, dynamic allocation is no longer needed, so this
function should now be async-signal-safe. it's also significantly
smaller.

one change in getservbyname is also made: knowing that getservbyname_r
needs only two character pointers in the caller-provided buffer, some
wasted bss can be avoided.

src/network/getservbyname.c

@@ -4,7 +4,7 @@
 struct servent *getservbyname(const char *name, const char *prots)
 {
 	static struct servent se;
-	static long buf[32/sizeof(long)];
+	static char *buf[2];
 	struct servent *res;
 	if (getservbyname_r(name, prots, &se, (void *)buf, sizeof buf, &res))
 		return 0;

src/network/getservbyname_r.c

@@ -5,49 +5,43 @@
 #include <inttypes.h>
 #include <errno.h>
 #include <string.h>
+#include "lookup.h"
+
+#define ALIGN (sizeof(struct { char a; char *b; }) - sizeof(char *))
 
 int getservbyname_r(const char *name, const char *prots,
 	struct servent *se, char *buf, size_t buflen, struct servent **res)
 {
-	struct addrinfo *ai, hint = { .ai_family = AF_INET };
-	int i;
-
-	if (!prots) {
-		int r = getservbyname_r(name, "tcp", se, buf, buflen, res);
-		if (r) r = getservbyname_r(name, "udp", se, buf, buflen, res);
-		return r;
-	}
+	struct service servs[MAXSERVS];
+	int cnt, proto, align;
 
 	/* Align buffer */
-	i = (uintptr_t)buf & sizeof(char *)-1;
-	if (!i) i = sizeof(char *);
-	if (buflen < 3*sizeof(char *)-i)
+	align = -(uintptr_t)buf & ALIGN-1;
+	if (buflen < 2*sizeof(char *)+align)
 		return ERANGE;
-	buf += sizeof(char *)-i;
-	buflen -= sizeof(char *)-i;
+	buf += align;
 
-	if (!strcmp(prots, "tcp")) hint.ai_protocol = IPPROTO_TCP;
-	else if (!strcmp(prots, "udp")) hint.ai_protocol = IPPROTO_UDP;
+	if (!prots) proto = 0;
+	else if (!strcmp(prots, "tcp")) proto = IPPROTO_TCP;
+	else if (!strcmp(prots, "udp")) proto = IPPROTO_UDP;
 	else return EINVAL;
 
-	switch (getaddrinfo(0, name, &hint, &ai)) {
+	cnt = __lookup_serv(servs, name, proto, 0);
+	if (cnt<0) switch (cnt) {
 	case EAI_MEMORY:
 	case EAI_SYSTEM:
 		return ENOMEM;
 	default:
 		return ENOENT;
-	case 0:
-		break;
 	}
 
 	se->s_name = (char *)name;
 	se->s_aliases = (void *)buf;
 	se->s_aliases[0] = se->s_name;
 	se->s_aliases[1] = 0;
-	se->s_port = ((struct sockaddr_in *)ai->ai_addr)->sin_port;
-	se->s_proto = (char *)prots;
+	se->s_port = htons(servs[0].port);
+	se->s_proto = servs[0].proto == IPPROTO_TCP ? "tcp" : "udp";
 
-	freeaddrinfo(ai);
 	*res = se;
 	return 0;
 }