[PATCH v2 2/2] Make link-local addresses resolvable via running avahi-daemon

Nikolaus Voss n.voss at weinmann.de
Mon Nov 28 15:22:42 UTC 2011


nss-mdns is an extension to glibc to support resolution of link-local
(.local) addresses via GNU Name Service Switch (NSS) which redirects
the queries to a running avahi-daemon, which in turn does the resolution
via multicast DNS (mdns).

However, this does not work for uClibc, as it does not support NSS.

This patch integrates the nss-mdns approach into uClibc's resolver,
so getaddrinfo() and getnameinfo() calls get redirected to a running
avahi-daemon before trying to resolve via unicast DNS.

This increases the size of the library by 50 bytes on ARM.

Signed-off-by: Nikolaus Voss <n.voss at weinmann.de>
---
 extra/Configs/Config.in |   19 +++++
 libc/inet/Makefile.in   |    1 +
 libc/inet/avahi.c       |  182 +++++++++++++++++++++++++++++++++++++++++++++++
 libc/inet/avahi.h       |   33 +++++++++
 libc/inet/resolv.c      |   24 +++++-
 5 files changed, 255 insertions(+), 4 deletions(-)
 create mode 100644 libc/inet/avahi.c
 create mode 100644 libc/inet/avahi.h

diff --git a/extra/Configs/Config.in b/extra/Configs/Config.in
index e41adc4..0846ec2 100644
--- a/extra/Configs/Config.in
+++ b/extra/Configs/Config.in
@@ -1268,6 +1268,25 @@ config UCLIBC_HAS_EXTRA_COMPAT_RES_STATE
 	  Answer Y if selecting UCLIBC_HAS_COMPAT_RES_STATE is not enough.
 	  As far as I can say, this should never be needed.
 
+config UCLIBC_HAS_AVAHI_RES
+	bool "Try to resolve link-local IP addresses via avahi-daemon"
+	default y
+	depends on UCLIBC_HAS_SOCKET
+	help
+	  Answer Y if you want to resolve .local addresses via multicast-dns.
+	  The queries are forwarded to a running avahi-daemon via a domain
+	  socket interface.
+	  Note that this might interfere with a .local domain on your DNS.
+	  Answering N saves around 50 bytes.
+
+config UCLIBC_AVAHI_SOCKET_PATH
+	string "Path to avahi unix domain socket"
+	default "/var/run/avahi-daemon/socket"
+	depends on UCLIBC_HAS_AVAHI_RES
+	help
+	  A running avahi-daemon creates a socket to listen for queries.
+	  Enter the path you configured your avahi-daemon to.
+
 config UCLIBC_HAS_LIBRESOLV_STUB
 	bool "Provide libresolv stub"
 	default n
diff --git a/libc/inet/Makefile.in b/libc/inet/Makefile.in
index d588220..7f436c9 100644
--- a/libc/inet/Makefile.in
+++ b/libc/inet/Makefile.in
@@ -33,6 +33,7 @@ CSRC-$(findstring y,$(UCLIBC_HAS_IPV4)$(UCLIBC_HAS_IPV6)) += \
 	dnslookup.c opennameservers.c closenameservers.c \
 	getnameinfo.c \
 	gethostent.c gethostent_r.c
+CSRC-$(UCLIBC_HAS_AVAHI_RES) += avahi.c
 CSRC-$(findstring y,$(UCLIBC_HAS_IPV4)$(UCLIBC_HAS_IPV6)) += \
 	get_hosts_byaddr_r.c get_hosts_byname_r.c \
 	gethostbyaddr_r.c gethostbyname_r.c gethostbyname2_r.c \
diff --git a/libc/inet/avahi.c b/libc/inet/avahi.c
new file mode 100644
index 0000000..7779476
--- /dev/null
+++ b/libc/inet/avahi.c
@@ -0,0 +1,182 @@
+/*
+ *
+ * (C) 2011 Weinmann GmbH, Hamburg, Germany
+ *
+ * Author: Nikolaus Voss <n.voss at weinmann.de>
+ *
+ * Derived from avahi.c / nss-mdns by Lennart Poettering.
+ * Copyright 2004-2007 Lennart Poettering <mzaffzqaf (at) 0pointer (dot) de>
+ *
+ * Licensed under the LGPL v2.1, see the file COPYING.LIB in this tarball.
+ *
+ */
+
+#include <arpa/inet.h>
+#include <assert.h>
+#include <fcntl.h>
+#include <not-cancel.h>
+#include <stdio.h>
+#include <string.h>
+#include <sys/socket.h>
+#include <sys/types.h>
+#include <sys/un.h>
+#include <unistd.h>
+
+#include "avahi.h"
+
+#define WHITESPACE " \t"
+
+static FILE* avahi_open_socket(void)
+{
+	int fd = -1;
+	struct sockaddr_un sa;
+	FILE *f = NULL;
+
+	if ((fd = socket(AF_UNIX, SOCK_STREAM | SOCK_CLOEXEC, 0)) < 0)
+		goto fail;
+
+#ifndef __ASSUME_SOCK_CLOEXEC
+	fcntl_not_cancel(fd, F_SETFD, FD_CLOEXEC);
+#endif
+
+	memset(&sa, 0, sizeof(sa));
+	sa.sun_family = AF_UNIX;
+	strncpy(sa.sun_path, __UCLIBC_AVAHI_SOCKET_PATH__,
+		sizeof(sa.sun_path)-1);
+	sa.sun_path[sizeof(sa.sun_path)-1] = 0;
+
+	if (connect(fd, (struct sockaddr*) &sa, sizeof(sa)) < 0)
+		goto fail;
+
+	if (!(f = fdopen(fd, "r+")))
+		goto fail;
+
+	return f;
+
+fail:
+	if (fd >= 0)
+		close(fd);
+
+	return NULL;
+}
+
+static int avahi_ends_with(const char *name, const char* suffix) {
+	size_t ln, ls;
+	assert(name);
+	assert(suffix);
+
+	if ((ls = strlen(suffix)) > (ln = strlen(name)))
+		return 0;
+
+	return strcasecmp(name + ln - ls, suffix) == 0;
+}
+
+int attribute_hidden __avahi_resolve_name(int af, const char* name, void* data)
+{
+	FILE *f = NULL;
+	char *p;
+	int ret = -1;
+	char ln[256];
+
+	if (af != AF_INET && af != AF_INET6)
+		goto finish;
+
+	if (!avahi_ends_with(name, ".local") &&
+	    !avahi_ends_with(name, ".local."))
+		goto finish;
+
+	if (!(f = avahi_open_socket()))
+		goto finish;
+
+	fprintf(f, "RESOLVE-HOSTNAME-IPV%d %s\n", af == AF_INET ? 4 : 6, name);
+	fflush(f);
+
+	if (!fgets(ln, sizeof(ln), f))
+		goto finish;
+
+	if (ln[0] != '+') {
+		ret = 1;
+		goto finish;
+	}
+
+	p = ln+1;
+	p += strspn(p, WHITESPACE);
+
+	/* Skip interface */
+	p += strcspn(p, WHITESPACE);
+	p += strspn(p, WHITESPACE);
+
+	/* Skip protocol */
+	p += strcspn(p, WHITESPACE);
+	p += strspn(p, WHITESPACE);
+
+	/* Skip host name */
+	p += strcspn(p, WHITESPACE);
+	p += strspn(p, WHITESPACE);
+
+	/* Cut off end of line */
+	p[strcspn(p, "\n\r\t ")] = 0;
+
+	if (inet_pton(af, p, data) <= 0)
+		goto finish;
+
+	ret = 0;
+
+finish:
+
+	if (f)
+		fclose(f);
+
+	return ret;
+}
+
+int attribute_hidden __avahi_resolve_address(int af, const void *data,
+					     char* name, size_t name_len)
+{
+	FILE *f = NULL;
+	char *p;
+	int ret = -1;
+	char a[256], ln[256];
+
+	if (af != AF_INET && af != AF_INET6)
+		goto finish;
+
+	if (!(f = avahi_open_socket()))
+		goto finish;
+
+	fprintf(f, "RESOLVE-ADDRESS %s\n", inet_ntop(af, data, a, sizeof(a)));
+
+	if (!fgets(ln, sizeof(ln), f))
+		goto finish;
+
+	if (ln[0] != '+') {
+		ret = 1;
+		goto finish;
+	}
+
+	p = ln+1;
+	p += strspn(p, WHITESPACE);
+
+	/* Skip interface */
+	p += strcspn(p, WHITESPACE);
+	p += strspn(p, WHITESPACE);
+
+	/* Skip protocol */
+	p += strcspn(p, WHITESPACE);
+	p += strspn(p, WHITESPACE);
+
+	/* Cut off end of line */
+	p[strcspn(p, "\n\r\t ")] = 0;
+
+	strncpy(name, p, name_len-1);
+	name[name_len-1] = 0;
+
+	ret = 0;
+
+finish:
+
+	if (f)
+		fclose(f);
+
+	return ret;
+}
diff --git a/libc/inet/avahi.h b/libc/inet/avahi.h
new file mode 100644
index 0000000..2cd6721
--- /dev/null
+++ b/libc/inet/avahi.h
@@ -0,0 +1,33 @@
+/*
+ *
+ * (C) 2011 Weinmann GmbH, Hamburg, Germany
+ *
+ * Author: Nikolaus Voss <n.voss at weinmann.de>
+ *
+ * Licensed under the LGPL v2.1, see the file COPYING.LIB in this tarball.
+ *
+ */
+
+#ifndef _AVAHI_H_
+#define _AVAHI_H_
+
+#ifdef __UCLIBC_HAS_AVAHI_RES__
+int __avahi_resolve_name(int af, const char* name, void* data) attribute_hidden;
+
+int __avahi_resolve_address(int af, const void *data, char* name,
+			    size_t name_len) attribute_hidden;
+#else
+static inline int __avahi_resolve_name(int af, const char* name, void* data)
+	attribute_hidden
+{
+	return 1;
+}
+
+static inline int __avahi_resolve_address(int af, const void *data, char* name,
+					  size_t name_len) attribute_hidden
+{
+	return 1;
+}
+#endif
+
+#endif
diff --git a/libc/inet/resolv.c b/libc/inet/resolv.c
index 4d96c5c..be3b1db 100644
--- a/libc/inet/resolv.c
+++ b/libc/inet/resolv.c
@@ -318,6 +318,7 @@ Domain name in a message can be represented as either:
 #include <sys/stat.h>
 #include <bits/uClibc_mutex.h>
 #include "internal/parse_config.h"
+#include "avahi.h"
 
 /* poll() is not supported in kernel <= 2.0, therefore if __NR_poll is
  * not available, we assume an old Linux kernel is in use and we will
@@ -2073,10 +2074,11 @@ int gethostbyname_r(const char *name,
 	alias[0] = alias0;
 	alias[1] = NULL;
 
-	/* maybe it is already an address? */
+	/* maybe it is resolvable via avahi or already an address? */
 	{
 		struct in_addr *in = (struct in_addr *)(buf + sizeof(addr_list[0]) * 2);
-		if (inet_aton(name, in)) {
+		if (!__avahi_resolve_name(AF_INET, name, in) ||
+		    inet_aton(name, in)) {
 			addr_list[0] = in;
 			addr_list[1] = NULL;
 			result_buf->h_name = alias0;
@@ -2263,8 +2265,9 @@ int gethostbyname2_r(const char *name,
 	strncpy(buf, name, buflen);
 	buf[buflen] = '\0';
 
-	/* maybe it is already an address? */
-	if (inet_pton(AF_INET6, name, in)) {
+	/* maybe it is resolvable via avahi or already an address? */
+	if (!__avahi_resolve_name(AF_INET6, name, in) ||
+	    inet_pton(AF_INET6, name, in)) {
 		result_buf->h_name = buf;
 		result_buf->h_addrtype = AF_INET6;
 		result_buf->h_length = sizeof(*in);
@@ -2427,6 +2430,19 @@ int gethostbyaddr_r(const void *addr, socklen_t addrlen,
 	addr_list[1] = NULL;
 	memcpy(in, addr, addrlen);
 
+	// is this a .local address?
+	if (!__avahi_resolve_address(type, in, buf, buflen))
+	{
+		result_buf->h_name = buf;
+		result_buf->h_addrtype = type;
+		result_buf->h_length = addrlen;
+		result_buf->h_addr_list = (char **) addr_list;
+		result_buf->h_aliases = alias;
+		*result = result_buf;
+		*h_errnop = NETDB_SUCCESS;
+		return NETDB_SUCCESS;
+	}
+
 	if (0) /* nothing */;
 #ifdef __UCLIBC_HAS_IPV4__
 	else IF_HAS_BOTH(if (type == AF_INET)) {
-- 
1.7.5.4



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