improve gethostbyname2_r using new resolver backend

these changes reduce the size of the function somewhat and remove many
of its dependencies, including free. in principle it should now be
async-signal-safe, but this has not been verified in detail.

minor changes to error handling are also made.

src/network/gethostbyname2_r.c

@@ -6,41 +6,31 @@
 #include <netinet/in.h>
 #include <errno.h>
 #include <stdint.h>
+#include "lookup.h"
 
 int gethostbyname2_r(const char *name, int af,
 	struct hostent *h, char *buf, size_t buflen,
 	struct hostent **res, int *err)
 {
-	struct addrinfo hint = {
-		.ai_family = af==AF_INET6 ? af : AF_INET,
-		.ai_flags = AI_CANONNAME
-	};
-	struct addrinfo *ai, *p;
-	int i;
-	size_t need;
-	const char *canon;
+	struct address addrs[MAXADDRS];
+	char canon[256];
+	int i, cnt;
+	size_t align, need;
 
-	af = hint.ai_family;
-
-	/* Align buffer */
-	i = (uintptr_t)buf & sizeof(char *)-1;
-	if (i) {
-		if (buflen < sizeof(char *)-i) return ERANGE;
-		buf += sizeof(char *)-i;
-		buflen -= sizeof(char *)-i;
-	}
-
-	switch (getaddrinfo(name, 0, &hint, &ai)) {
+	cnt = __lookup_name(addrs, canon, name, af, AI_CANONNAME);
+	if (cnt<0) switch (cnt) {
 	case EAI_NONAME:
 		*err = HOST_NOT_FOUND;
-		return errno;
+		return ENOENT;
 	case EAI_AGAIN:
 		*err = TRY_AGAIN;
-		return errno;
+		return EAGAIN;
 	default:
+	case EAI_FAIL:
+		*err = NO_RECOVERY;
+		return EBADMSG;
 	case EAI_MEMORY:
 	case EAI_SYSTEM:
-	case EAI_FAIL:
 		*err = NO_RECOVERY;
 		return errno;
 	case 0:
@@ -50,22 +40,22 @@ int gethostbyname2_r(const char *name, int af,
 	h->h_addrtype = af;
 	h->h_length = af==AF_INET6 ? 16 : 4;
 
-	canon = ai->ai_canonname ? ai->ai_canonname : name;
+	/* Align buffer */
+	align = -(uintptr_t)buf & sizeof(char *)-1;
+
 	need = 4*sizeof(char *);
-	for (i=0, p=ai; p; i++, p=p->ai_next)
-		need += sizeof(char *) + h->h_length;
+	need += (cnt + 1) * (sizeof(char *) + h->h_length);
 	need += strlen(name)+1;
 	need += strlen(canon)+1;
+	need += align;
 
-	if (need > buflen) {
-		freeaddrinfo(ai);
-		return ERANGE;
-	}
+	if (need > buflen) return ERANGE;
 
+	buf += align;
 	h->h_aliases = (void *)buf;
 	buf += 3*sizeof(char *);
 	h->h_addr_list = (void *)buf;
-	buf += (i+1)*sizeof(char *);
+	buf += (cnt+1)*sizeof(char *);
 
 	h->h_name = h->h_aliases[0] = buf;
 	strcpy(h->h_name, canon);
@@ -79,16 +69,13 @@ int gethostbyname2_r(const char *name, int af,
 
 	h->h_aliases[2] = 0;
 
-	for (i=0, p=ai; p; i++, p=p->ai_next) {
+	for (i=0; i<cnt; i++) {
 		h->h_addr_list[i] = (void *)buf;
 		buf += h->h_length;
-		memcpy(h->h_addr_list[i],
-			&((struct sockaddr_in *)p->ai_addr)->sin_addr,
-			h->h_length);
+		memcpy(h->h_addr_list[i], addrs[i].addr, h->h_length);
 	}
 	h->h_addr_list[i] = 0;
 
 	*res = h;
-	freeaddrinfo(ai);
 	return 0;
 }