refactor getaddrinfo and add support for most remaining features

this is the first phase of the "resolver overhaul" project.

conceptually, the results of getaddrinfo are a direct product of a
list of address results and a list of service results. the new code
makes this explicit by computing these lists separately and combining
the results. this adds support for services that have both tcp and udp
versions, where the caller has not specified which it wants, and
eliminates a number of duplicate code paths which were all producing
the final output addrinfo structures, but in subtly different ways,
making it difficult to implement any of the features which were
missing.

in addition to the above benefits, the refactoring allows for legacy
functions like gethostbyname to be implemented without using the
getaddrinfo function itself. such changes to the legacy functions have
not yet been made, however.

further improvements include matching of service alias names from
/etc/services (previously only the primary name was supported),
returning multiple results from /etc/hosts (previously only the first
matching line was honored), and support for the AI_V4MAPPED and AI_ALL
flags.

features which remain unimplemented are IDN translations (encoding
non-ASCII hostnames for DNS lookup) and the AI_ADDRCONFIG flag.

at this point, the DNS-based name resolving code is still based on the
old interfaces in __dns.c, albeit somewhat simpler in its use of them.
there may be some dead code which could already be removed, but
changes to this layer will be a later phase of the resolver overhaul.

1 files changed, 168 insertions, 0 deletions

diff --git a/src/network/lookup_name.c b/src/network/lookup_name.c
new file mode 100644
index 00000000..b1f1ffd0
--- /dev/null
+++ b/src/network/lookup_name.c
@@ -0,0 +1,168 @@
+#include <sys/socket.h>
+#include <netinet/in.h>
+#include <netdb.h>
+#include <arpa/inet.h>
+#include <ctype.h>
+#include <stdlib.h>
+#include <string.h>
+#include <fcntl.h>
+#include "lookup.h"
+#include "stdio_impl.h"
+#include "syscall.h"
+#include "__dns.h"
+
+static int is_valid_hostname(const char *host)
+{
+	const unsigned char *s;
+	if (strnlen(host, 255)-1 > 254 || mbstowcs(0, host, 0) > 255) return 0;
+	for (s=(void *)host; *s>=0x80 || *s=='.' || *s=='-' || isalnum(*s); s++);
+	return !*s;
+}
+
+static int name_from_null(struct address buf[static 2], const char *name, int family, int flags)
+{
+	int cnt = 0;
+	if (name) return 0;
+	if (flags & AI_PASSIVE) {
+		if (family != AF_INET6)
+			buf[cnt++] = (struct address){ .family = AF_INET };
+		if (family != AF_INET)
+			buf[cnt++] = (struct address){ .family = AF_INET6 };
+	} else {
+		if (family != AF_INET6)
+			buf[cnt++] = (struct address){ .family = AF_INET, .addr = { 127,0,0,1 } };
+		if (family != AF_INET)
+			buf[cnt++] = (struct address){ .family = AF_INET6, .addr = { [15] = 1 } };
+	}
+	return cnt;
+}
+
+static int name_from_numeric(struct address buf[static 1], const char *name, int family)
+{
+	struct in_addr a4;
+	struct in6_addr a6;
+	if (family != AF_INET6 && inet_aton(name, &a4)>0) {
+		memcpy(&buf[0].addr, &a4, sizeof a4);
+		buf[0].family = AF_INET;
+		return 1;
+	}
+	if (family != AF_INET && inet_pton(AF_INET6, name, &a6)>0) {
+		memcpy(&buf[0].addr, &a6, sizeof a6);
+		buf[0].family = AF_INET6;
+		return 1;
+	}
+	return 0;
+}
+
+static int name_from_hosts(struct address buf[static MAXADDRS], char canon[static 256], const char *name, int family)
+{
+	char line[512];
+	size_t l = strlen(name);
+	int cnt = 0;
+	unsigned char _buf[1032];
+	FILE _f, *f = __fopen_rb_ca("/etc/hosts", &_f, _buf, sizeof _buf);
+	if (!f) return 0;
+	while (fgets(line, sizeof line, f) && cnt < MAXADDRS) {
+		char *p, *z;
+
+		if ((p=strchr(line, '#'))) *p++='\n', *p=0;
+		for(p=line+1; (p=strstr(p, name)) &&
+			(!isspace(p[-1]) || !isspace(p[l])); p++);
+		if (!p) continue;
+
+		/* Isolate IP address to parse */
+		for (p=line; *p && !isspace(*p); p++);
+		*p++ = 0;
+		if (name_from_numeric(buf+cnt, line, family))
+			cnt++;
+
+		/* Extract first name as canonical name */
+		for (; *p && isspace(*p); p++);
+		for (z=p; *z && !isspace(*z); z++);
+		*z = 0;
+		if (is_valid_hostname(p)) memcpy(canon, p, z-p+1);
+	}
+	__fclose_ca(f);
+	return cnt;
+}
+
+static int name_from_dns(struct address buf[static MAXADDRS], char canon[static 256], const char *name, int family)
+{
+	unsigned char reply[1024] = { 0 }, *p = reply;
+	char tmp[256];
+	int i, cnt = 0;
+
+	/* Perform one or more DNS queries for host */
+	int result = __dns_query(reply, name, family, 0);
+	if (result < 0) return result;
+
+	for (i=0; i<result; i++) {
+		if (family != AF_INET6) {
+			int j = __dns_get_rr(&buf[cnt].addr, sizeof *buf, 4, MAXADDRS-cnt, p, RR_A, 0);
+			while (j--) buf[cnt++].family = AF_INET;
+		}
+		if (family != AF_INET) {
+			int j = __dns_get_rr(&buf[cnt].addr, sizeof *buf, 16, MAXADDRS-cnt, p, RR_AAAA, 0);
+			while (j--) buf[cnt++].family = AF_INET6;
+		}
+		p += 512;
+	}
+	__dns_get_rr(tmp, 0, 256, 1, reply, RR_CNAME, 1);
+	if (is_valid_hostname(tmp)) strcpy(canon, tmp);
+	return cnt;
+}
+
+int __lookup_name(struct address buf[static MAXADDRS], char canon[static 256], const char *name, int family, int flags)
+{
+	int cnt = 0, i, j;
+
+	*canon = 0;
+	if (name) {
+		size_t l;
+		if ((l = strnlen(name, 255))-1 > 254)
+			return EAI_NONAME;
+		memcpy(canon, name, l+1);
+	}
+
+	/* Procedurally, a request for v6 addresses with the v4-mapped
+	 * flag set is like a request for unspecified family, followed
+	 * by filtering of the results. */
+	if (flags & AI_V4MAPPED) {
+		if (family == AF_INET6) family = AF_UNSPEC;
+		else flags -= AI_V4MAPPED;
+	}
+
+	/* Try each backend until there's at least one result. */
+	cnt = name_from_null(buf, name, family, flags);
+	if (cnt<=0) cnt = name_from_numeric(buf, name, family);
+	if (cnt<=0 && !(flags & AI_NUMERICHOST)) {
+		cnt = name_from_hosts(buf, canon, name, family);
+		if (cnt<=0) cnt = name_from_dns(buf, canon, name, family);
+	}
+	if (cnt<=0) return cnt ? cnt : EAI_NONAME;
+
+	/* Filter/transform results for v4-mapped lookup, if requested. */
+	if (flags & AI_V4MAPPED) {
+		if (!(flags & AI_ALL)) {
+			/* If any v6 results exist, remove v4 results. */
+			for (i=0; i<cnt && buf[i].family != AF_INET6; i++);
+			if (i<cnt) {
+				for (j=0; i<cnt; i++) {
+					if (buf[i].family == AF_INET6)
+						buf[j++] = buf[i];
+				}
+				cnt = i = j;
+			}
+		}
+		/* Translate any remaining v4 results to v6 */
+		for (i=0; i<cnt; i++) {
+			if (buf[i].family != AF_INET) continue;
+			memcpy(buf[i].addr+12, buf[i].addr, 4);
+			memcpy(buf[i].addr, "\0\0\0\0\0\0\0\0\0\0\xff\xff", 12);
+			buf[i].scopeid = 0;
+			buf[i].family = AF_INET6;
+		}
+	}
+
+	return cnt;
+}