]> git.meshlink.io Git - meshlink/commitdiff
Send and receive multicast mDNS packets.
authorGuus Sliepen <guus@meshlink.io>
Sun, 12 Jul 2020 15:31:40 +0000 (17:31 +0200)
committerGuus Sliepen <guus@meshlink.io>
Tue, 26 Jan 2021 20:40:42 +0000 (21:40 +0100)
We don't actually support the full mDNS spec, we just send something that
passes for a valid mDNS packet, and expect other nodes to send packets back
with exactly the same format. All other mDNS packets will be ignored.

src/Makefile.am
src/discovery.c
src/mdns.c [new file with mode: 0644]
src/mdns.h [new file with mode: 0644]
src/meshlink_internal.h

index 01e6ff2870b5bf4e907827ba1d011e931668f698..e9c335106d061daf2a91f62a7b6d1f0c0b7e608b 100644 (file)
@@ -53,6 +53,7 @@ libmeshlink_la_SOURCES = \
        have.h \
        list.c list.h \
        logger.c logger.h \
+       mdns.c mdns.h \
        meshlink.c meshlink.h meshlink.sym \
        meshlink_internal.h \
        meshlink_queue.h \
index ece4fbe9e6d56dc3e90ad669df9dbb22e86cf7f8..36d202bde9b192852370e0fc58c53fd9d95ae2b3 100644 (file)
@@ -19,6 +19,7 @@
 #include <linux/rtnetlink.h>
 #endif
 
+#include "mdns.h"
 #include "meshlink_internal.h"
 #include "event.h"
 #include "discovery.h"
 #include "netutl.h"
 #include "node.h"
 #include "connection.h"
+#include "utils.h"
 #include "xalloc.h"
 
 #define MESHLINK_MDNS_SERVICE_TYPE "_%s._tcp"
 #define MESHLINK_MDNS_NAME_KEY "name"
 #define MESHLINK_MDNS_FINGERPRINT_KEY "fingerprint"
 
+static const sockaddr_t mdns_address_ipv4 = {
+       .in.sin_family = AF_INET,
+       .in.sin_addr.s_addr = 0xfb0000e0,
+       .in.sin_port = 0xe914,
+};
+
+static const sockaddr_t mdns_address_ipv6 = {
+       .in6.sin6_family = AF_INET6,
+       .in6.sin6_addr.s6_addr[0x0] = 0xfd,
+       .in6.sin6_addr.s6_addr[0x1] = 0x02,
+       .in6.sin6_addr.s6_addr[0xf] = 0xfb,
+       .in6.sin6_port = 0xe914,
+};
+
 static void generate_rand_string(meshlink_handle_t *mesh, char *buffer, size_t size) {
        assert(size);
 
@@ -379,6 +395,13 @@ static void *discovery_loop(void *userdata) {
                abort();
        }
 
+#if 1
+       // bypass Catta
+       pthread_cond_broadcast(&mesh->discovery_cond);
+       pthread_mutex_unlock(&mesh->discovery_mutex);
+       return NULL;
+#endif
+
        // handle catta logs
        catta_set_log_function(discovery_log_cb);
 
@@ -517,12 +540,228 @@ static int address_compare(const void *va, const void *vb) {
        return sockaddrcmp_noport(&a->address, &b->address);
 }
 
+static void send_mdns_packet_ipv4(meshlink_handle_t *mesh, int fd, int index, const sockaddr_t *src, const sockaddr_t *dest, void *data, size_t len) {
+#ifdef IP_PKTINFO
+       struct iovec iov  = {
+               .iov_base = data,
+               .iov_len = len,
+       };
+
+       struct in_pktinfo pkti = {
+               .ipi_ifindex = index,
+               .ipi_addr = src->in.sin_addr,
+       };
+
+       union {
+               char buf[CMSG_SPACE(sizeof(pkti))];
+               struct cmsghdr align;
+       } u;
+
+       struct msghdr msg = {
+               .msg_name = (struct sockaddr *) &dest->sa,
+               .msg_namelen = SALEN(dest->sa),
+               .msg_iov = &iov,
+               .msg_iovlen = 1,
+               .msg_control = u.buf,
+               .msg_controllen = sizeof(u.buf),
+       };
+
+
+       struct cmsghdr *cmsg = CMSG_FIRSTHDR(&msg);
+       cmsg->cmsg_level = IPPROTO_IP;
+       cmsg->cmsg_type = IP_PKTINFO;
+       cmsg->cmsg_len = CMSG_LEN(sizeof(pkti));
+       memcpy(CMSG_DATA(cmsg), &pkti, sizeof(pkti));
+
+       // Send the packet
+       ssize_t result = sendmsg(fd, &msg, MSG_DONTWAIT | MSG_NOSIGNAL);
+#else
+       // Send the packet
+       ssize_t result = sendto(fd, data, len, MSG_DONTWAIT | MSG_NOSIGNAL, &dest->sa, SALEN(dest->sa));
+#endif
+
+       if(result <= 0) {
+               logger(mesh, MESHLINK_ERROR, "Error sending multicast packet: %s", strerror(errno));
+       }
+}
+
+static void send_mdns_packet_ipv6(meshlink_handle_t *mesh, int fd, int index, const sockaddr_t *src, const sockaddr_t *dest, void *data, size_t len) {
+#ifdef IPV6_PKTINFO
+       struct iovec iov  = {
+               .iov_base = data,
+               .iov_len = len,
+       };
+
+       struct in6_pktinfo pkti = {
+               .ipi6_ifindex = index,
+               .ipi6_addr = src->in6.sin6_addr,
+       };
+
+       union {
+               char buf[CMSG_SPACE(sizeof(pkti))];
+               struct cmsghdr align;
+       } u;
+
+       memset(&u, 0, sizeof u);
+
+       struct msghdr msg = {
+               .msg_name = (struct sockaddr *) &dest->sa,
+               .msg_namelen = SALEN(dest->sa),
+               .msg_iov = &iov,
+               .msg_iovlen = 1,
+               .msg_control = u.buf,
+               .msg_controllen = CMSG_LEN(sizeof(pkti)),
+       };
+
+       struct cmsghdr *cmsg = CMSG_FIRSTHDR(&msg);
+       cmsg->cmsg_level = IPPROTO_IPV6;
+       cmsg->cmsg_type = IPV6_PKTINFO;
+       cmsg->cmsg_len = CMSG_LEN(sizeof(pkti));
+       memcpy(CMSG_DATA(cmsg), &pkti, sizeof(pkti));
+
+       // Send the packet
+       ssize_t result = sendmsg(fd, &msg, MSG_DONTWAIT | MSG_NOSIGNAL);
+#else
+       // Send the packet
+       ssize_t result = sendto(fd, data, len, MSG_DONTWAIT | MSG_NOSIGNAL, &dest->sa, SALEN(dest->sa));
+#endif
+
+       if(result <= 0) {
+               logger(mesh, MESHLINK_ERROR, "Error sending multicast packet: %s", strerror(errno));
+       }
+}
+
 static void send_mdns_packet(meshlink_handle_t *mesh, const discovery_address_t *addr) {
        char *host = NULL, *port = NULL;
        sockaddr2str(&addr->address, &host, &port);
        fprintf(stderr, "Sending on iface %d %s port %s\n", addr->index, host, port);
        free(host);
        free(port);
+
+       // Configure the socket to send the packet to the right interface
+       int fd;
+       uint8_t data[1024];
+       char *fingerprint = meshlink_get_fingerprint(mesh, (meshlink_node_t *)mesh->self);
+       const char *keys[] = {MESHLINK_MDNS_NAME_KEY, MESHLINK_MDNS_FINGERPRINT_KEY};
+       const char *values[] = {mesh->name, fingerprint};
+       size_t size = prepare_packet(data, sizeof data, fingerprint, mesh->appname, "tcp", atoi(mesh->myport), 2, keys, values);
+
+       switch(addr->address.sa.sa_family) {
+       case AF_INET:
+               fd = mesh->discovery_sockets[0].fd;
+#ifdef IP_MULTICAST_IF
+               {
+                       struct ip_mreqn mreq = {
+                               .imr_address = addr->address.in.sin_addr,
+                               .imr_ifindex = addr->index,
+                       };
+
+                       if(setsockopt(fd, IPPROTO_IP, IP_MULTICAST_IF, &mreq, sizeof(mreq)) != 0) {
+                               logger(mesh, MESHLINK_ERROR, "Could not set outgoing multicast interface on IPv4 socket");
+                               return;
+                       }
+               }
+
+#endif
+
+               send_mdns_packet_ipv4(mesh, fd, addr->index, &addr->address, &mdns_address_ipv4, data, size);
+               break;
+
+       case AF_INET6:
+               fd = mesh->discovery_sockets[1].fd;
+#ifdef IPV6_MULTICAST_IF
+
+               if(setsockopt(fd, IPPROTO_IPV6, IPV6_MULTICAST_IF, &addr->index, sizeof(addr->index)) != 0) {
+                       logger(mesh, MESHLINK_ERROR, "Could not set outgoing multicast interface on IPv6 socket");
+                       return;
+               }
+
+#endif
+
+               send_mdns_packet_ipv6(mesh, fd, addr->index, &addr->address, &mdns_address_ipv6, data, size);
+               break;
+
+       default:
+               break;
+       }
+}
+
+static void mdns_io_handler(event_loop_t *loop, void *data, int flags) {
+       (void)flags;
+       meshlink_handle_t *mesh = loop->data;
+       io_t *io = data;
+       uint8_t buf[1024];
+       sockaddr_t sa;
+       socklen_t sl = sizeof(sa);
+
+       ssize_t len = recvfrom(io->fd, buf, sizeof(buf), MSG_DONTWAIT, &sa.sa, &sl);
+
+       if(len == -1) {
+               if(!sockwouldblock(errno)) {
+                       fprintf(stderr, "Error reading from discovery socket: %s\n", strerror(errno));
+                       logger(mesh, MESHLINK_ERROR, "Error reading from mDNS discovery socket: %s", strerror(errno));
+                       io_set(loop, io, 0);
+               }
+
+               return;
+       }
+
+       char *name = NULL;
+       uint16_t port = 0;
+       const char *keys[2] = {MESHLINK_MDNS_NAME_KEY, MESHLINK_MDNS_FINGERPRINT_KEY};
+       char *values[2] = {NULL, NULL};
+
+       if(parse_packet(buf, len, &name, mesh->appname, "tcp", &port, 2, keys, values)) {
+               node_t *n = (node_t *)meshlink_get_node(mesh, values[0]);
+
+               if(n) {
+                       logger(mesh, MESHLINK_INFO, "Node %s is part of the mesh network.\n", n->name);
+
+                       switch(sa.sa.sa_family) {
+                       case AF_INET:
+                               sa.in.sin_port = port;
+                               break;
+
+                       case AF_INET6:
+                               sa.in6.sin6_port = port;
+                               break;
+
+                       default:
+                               logger(mesh, MESHLINK_WARNING, "Could not resolve node %s to a known address family type.\n", n->name);
+                               sa.sa.sa_family = AF_UNKNOWN;
+                               break;
+                       }
+
+                       if(sa.sa.sa_family != AF_UNKNOWN) {
+                               n->catta_address = sa;
+                               node_add_recent_address(mesh, n, &sa);
+
+                               connection_t *c = n->connection;
+
+                               if(c && c->outgoing && !c->status.active) {
+                                       c->outgoing->timeout = 0;
+
+                                       if(c->outgoing->ev.cb) {
+                                               timeout_set(&mesh->loop, &c->outgoing->ev, &(struct timespec) {
+                                                       0, 0
+                                               });
+                                       }
+
+                                       c->last_ping_time = -3600;
+                               }
+                       }
+               } else {
+                       logger(mesh, MESHLINK_WARNING, "Node %s is not part of the mesh network.\n", values[0]);
+               }
+
+               fprintf(stderr, "Got packet from %s port %u\n%s=%s\n%s=%s\n", name, port, keys[0], values[0], keys[1], values[1]);
+       }
+
+       free(name);
+
+       for(int i = 0; i < 2; i++) {
+               free(values[i]);
+       }
 }
 
 static void iface_up(meshlink_handle_t *mesh, int index) {
@@ -537,9 +776,20 @@ static void iface_up(meshlink_handle_t *mesh, int index) {
        mesh->discovery_ifaces[mesh->discovery_iface_count - 1] = index;
        qsort(mesh->discovery_ifaces, mesh->discovery_iface_count, sizeof(*p), iface_compare);
 
-       for(int i = 0; i < mesh->discovery_iface_count; i++) {
-               fprintf(stderr, "%d", mesh->discovery_ifaces[i]);
-       }
+       // Add multicast membership
+       struct ip_mreqn mreq4 = {
+               .imr_multiaddr = mdns_address_ipv4.in.sin_addr,
+               .imr_ifindex = index,
+       };
+       setsockopt(mesh->discovery_sockets[0].fd, IPPROTO_IP, IP_DROP_MEMBERSHIP, &mreq4, sizeof(mreq4));
+       setsockopt(mesh->discovery_sockets[0].fd, IPPROTO_IP, IP_ADD_MEMBERSHIP, &mreq4, sizeof(mreq4));
+
+       struct ipv6_mreq mreq6 = {
+               .ipv6mr_multiaddr = mdns_address_ipv6.in6.sin6_addr,
+               .ipv6mr_interface = index,
+       };
+       setsockopt(mesh->discovery_sockets[1].fd, IPPROTO_IPV6, IPV6_DROP_MEMBERSHIP, &mreq6, sizeof(mreq6));
+       setsockopt(mesh->discovery_sockets[1].fd, IPPROTO_IPV6, IPV6_ADD_MEMBERSHIP, &mreq6, sizeof(mreq6));
 
        // Send an announcement for all addresses associated with this interface
        for(int i = 0; i < mesh->discovery_address_count; i++) {
@@ -547,27 +797,44 @@ static void iface_up(meshlink_handle_t *mesh, int index) {
                        send_mdns_packet(mesh, &mesh->discovery_addresses[i]);
                }
        }
+
+       handle_network_change(mesh, true);
 }
 
 static void iface_down(meshlink_handle_t *const mesh, int index) {
-       int *p = bsearch(&index, mesh->discovery_ifaces, mesh->discovery_iface_count, sizeof(int), iface_compare);
+       int *p = bsearch(&index, mesh->discovery_ifaces, mesh->discovery_iface_count, sizeof(*p), iface_compare);
 
        if(!p) {
                return;
        }
 
+       // Drop multicast membership
+       struct ip_mreqn mreq4 = {
+               .imr_multiaddr = mdns_address_ipv4.in.sin_addr,
+               .imr_ifindex = index,
+       };
+       setsockopt(mesh->discovery_sockets[0].fd, IPPROTO_IP, IP_DROP_MEMBERSHIP, &mreq4, sizeof(mreq4));
+
+       struct ipv6_mreq mreq6 = {
+               .ipv6mr_multiaddr = mdns_address_ipv6.in6.sin6_addr,
+               .ipv6mr_interface = index,
+       };
+       setsockopt(mesh->discovery_sockets[1].fd, IPPROTO_IPV6, IPV6_DROP_MEMBERSHIP, &mreq6, sizeof(mreq6));
+
        fprintf(stderr, "iface %d down\n", index);
-       memmove(p, p + 1, --mesh->discovery_iface_count * sizeof(*p));
+       memmove(p, p + 1, (mesh->discovery_ifaces + --mesh->discovery_iface_count - p) * sizeof(*p));
+
+       handle_network_change(mesh, mesh->discovery_iface_count);
 }
 
 static void addr_add(meshlink_handle_t *mesh, const discovery_address_t *addr) {
-       discovery_address_t *p = bsearch(addr, mesh->discovery_addresses, mesh->discovery_address_count, sizeof(int), address_compare);
+       discovery_address_t *p = bsearch(addr, mesh->discovery_addresses, mesh->discovery_address_count, sizeof(*p), address_compare);
 
        if(p) {
                return;
        }
 
-       bool up = bsearch(&addr->index, mesh->discovery_ifaces, mesh->discovery_iface_count, sizeof(*p), iface_compare);
+       bool up = bsearch(&addr->index, mesh->discovery_ifaces, mesh->discovery_iface_count, sizeof(int), iface_compare);
        char *host = NULL, *port = NULL;
        sockaddr2str(&addr->address, &host, &port);
        fprintf(stderr, "address %d %s port %s up %d\n", addr->index, host, port, up);
@@ -576,13 +843,13 @@ static void addr_add(meshlink_handle_t *mesh, const discovery_address_t *addr) {
 
        mesh->discovery_addresses = xrealloc(mesh->discovery_addresses, ++mesh->discovery_address_count * sizeof(*p));
        mesh->discovery_addresses[mesh->discovery_address_count - 1] = *addr;
-       qsort(mesh->discovery_addresses, mesh->discovery_address_count, sizeof(*p), address_compare);
-
        mesh->discovery_addresses[mesh->discovery_address_count - 1].up = up;
 
        if(up) {
                send_mdns_packet(mesh, &mesh->discovery_addresses[mesh->discovery_address_count - 1]);
        }
+
+       qsort(mesh->discovery_addresses, mesh->discovery_address_count, sizeof(*p), address_compare);
 }
 
 static void addr_del(meshlink_handle_t *mesh, const discovery_address_t *addr) {
@@ -598,7 +865,7 @@ static void addr_del(meshlink_handle_t *mesh, const discovery_address_t *addr) {
        free(host);
        free(port);
 
-       memmove(p, p + 1, --mesh->discovery_address_count * sizeof(*p));
+       memmove(p, p + 1, (mesh->discovery_addresses + --mesh->discovery_address_count - p) * sizeof(*p));
 }
 
 #if defined(__linux)
@@ -828,6 +1095,33 @@ bool discovery_start(meshlink_handle_t *mesh) {
 
        mesh->discovery_threadstarted = true;
 
+       // Set up multicast sockets for mDNS
+       static const int one = 1;
+       static const int ttl = 255;
+
+       int fd = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP);
+       sockaddr_t sa4 = {
+               .in.sin_family = AF_INET,
+               .in.sin_port = ntohs(5353),
+       };
+       setsockopt(fd, SOL_SOCKET, SO_REUSEADDR, &one, sizeof(one));
+       bind(fd, &sa4.sa, SALEN(sa4.sa));
+       setsockopt(fd, IPPROTO_IP, IP_MULTICAST_LOOP, &one, sizeof(one));
+       setsockopt(fd, IPPROTO_IP, IP_MULTICAST_TTL, &ttl, sizeof(ttl));
+       io_add(&mesh->loop, &mesh->discovery_sockets[0], mdns_io_handler, &mesh->discovery_sockets[0], fd, IO_READ);
+
+       sockaddr_t sa6 = {
+               .in6.sin6_family = AF_INET6,
+               .in6.sin6_port = ntohs(5353),
+       };
+       fd = socket(AF_INET6, SOCK_DGRAM, IPPROTO_UDP);
+       setsockopt(fd, SOL_SOCKET, SO_REUSEADDR, &one, sizeof(one));
+       setsockopt(fd, IPPROTO_IPV6, IPV6_V6ONLY, &one, sizeof(one));
+       bind(fd, &sa6.sa, SALEN(sa6.sa));
+       setsockopt(fd, IPPROTO_IPV6, IPV6_MULTICAST_LOOP, &one, sizeof(one));
+       setsockopt(fd, IPPROTO_IPV6, IPV6_MULTICAST_HOPS, &ttl, sizeof(ttl));
+       io_add(&mesh->loop, &mesh->discovery_sockets[1], mdns_io_handler, &mesh->discovery_sockets[1], fd, IO_READ);
+
 #if defined(__linux)
        int sock = socket(AF_NETLINK, SOCK_DGRAM, NETLINK_ROUTE);
 
@@ -876,6 +1170,13 @@ void discovery_stop(meshlink_handle_t *mesh) {
                io_del(&mesh->loop, &mesh->pfroute_io);
        }
 
+       for(int i = 0; i < 2; i++) {
+               if(mesh->discovery_sockets[i].cb) {
+                       close(mesh->discovery_sockets[i].fd);
+                       io_del(&mesh->loop, &mesh->discovery_sockets[i]);
+               }
+       }
+
        // Shut down
        if(mesh->catta_poll) {
                catta_simple_poll_quit(mesh->catta_poll);
diff --git a/src/mdns.c b/src/mdns.c
new file mode 100644 (file)
index 0000000..b243b3a
--- /dev/null
@@ -0,0 +1,393 @@
+// SPDX-FileCopyrightText: 2020 Guus Sliepen <guus@meshlink.io>
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+#include "system.h"
+
+#include <stddef.h>
+
+#include "mdns.h"
+#include "xalloc.h"
+
+// Creating a buffer
+
+typedef struct {
+       uint8_t *ptr;
+       ptrdiff_t len;
+} buf_t;
+
+static void buf_add(buf_t *buf, const void *data, uint32_t len) {
+       if(buf->len >= len) {
+               memcpy(buf->ptr, data, len);
+               buf->ptr += len;
+               buf->len -= len;
+       } else {
+               buf->len = -1;
+       }
+}
+
+static void buf_add_uint8(buf_t *buf, uint8_t val) {
+       if(buf->len >= 1) {
+               buf->ptr[0] = val;
+               buf->ptr++;
+               buf->len--;
+       } else {
+               buf->len = -1;
+       }
+}
+
+static void buf_add_uint16(buf_t *buf, uint16_t val) {
+       uint16_t nval = htons(val);
+       buf_add(buf, &nval, sizeof(nval));
+}
+
+static void buf_add_uint32(buf_t *buf, uint32_t val) {
+       uint32_t nval = htonl(val);
+       buf_add(buf, &nval, sizeof(nval));
+}
+
+static void buf_add_label(buf_t *buf, const char *str) {
+       size_t len = strlen(str);
+
+       if(len < 256) {
+               buf_add_uint8(buf, len);
+               buf_add(buf, str, len);
+       } else {
+               buf->len = -1;
+       }
+}
+
+static void buf_add_ulabel(buf_t *buf, const char *str) {
+       size_t len = strlen(str);
+
+       if(len + 1 < 256) {
+               buf_add_uint8(buf, len + 1);
+               buf_add_uint8(buf, '_');
+               buf_add(buf, str, len);
+       } else {
+               buf->len = -1;
+       }
+}
+
+static void buf_add_kvp(buf_t *buf, const char *key, const char *val) {
+       size_t key_len = strlen(key);
+       size_t val_len = strlen(val);
+
+       if(key_len + val_len + 1 < 256) {
+               buf_add_uint8(buf, key_len + val_len + 1);
+               buf_add(buf, key, key_len);
+               buf_add_uint8(buf, '=');
+               buf_add(buf, val, val_len);
+       } else {
+               buf->len = -1;
+       }
+}
+
+static uint8_t *buf_len_start(buf_t *buf) {
+       if(buf->len < 2) {
+               buf->len = -1;
+               return NULL;
+       } else {
+               uint8_t *ptr = buf->ptr;
+               buf->ptr += 2;
+               buf->len -= 2;
+               return ptr;
+       }
+}
+
+static void buf_len_end(buf_t *buf, uint8_t *ptr) {
+       if(buf->len < 0) {
+               return;
+       }
+
+       uint16_t len = htons(buf->ptr - ptr - 2);
+       memcpy(ptr, &len, sizeof(len));
+}
+
+// Functions reading a buffer
+
+typedef struct {
+       const uint8_t *ptr;
+       ptrdiff_t len;
+} cbuf_t;
+
+static void buf_check(cbuf_t *buf, const void *data, uint32_t len) {
+       if(buf->len >= len && !memcmp(buf->ptr, data, len)) {
+               buf->ptr += len;
+               buf->len -= len;
+       } else {
+               buf->len = -1;
+       }
+}
+
+static void buf_check_uint8(cbuf_t *buf, uint8_t val) {
+       if(buf->len >= 1 && buf->ptr[0] == val) {
+               buf->ptr++;
+               buf->len--;
+       } else {
+               buf->len = -1;
+       }
+}
+
+static void buf_check_uint16(cbuf_t *buf, uint16_t val) {
+       uint16_t nval = htons(val);
+       buf_check(buf, &nval, sizeof(nval));
+}
+
+static uint16_t buf_get_uint16(cbuf_t *buf) {
+       uint16_t nval;
+
+       if(buf->len >= 2) {
+               memcpy(&nval, buf->ptr, 2);
+               buf->ptr += 2;
+               buf->len -= 2;
+               return ntohs(nval);
+       } else {
+               buf->len = -1;
+               return 0;
+       }
+}
+
+static void buf_check_uint32(cbuf_t *buf, uint32_t val) {
+       uint32_t nval = htonl(val);
+       buf_check(buf, &nval, sizeof(nval));
+}
+
+static void buf_check_label(cbuf_t *buf, const char *str) {
+       size_t len = strlen(str);
+
+       if(len < 256) {
+               buf_check_uint8(buf, len);
+               buf_check(buf, str, len);
+       } else {
+               buf->len = -1;
+       }
+}
+
+static char *buf_get_label(cbuf_t *buf) {
+       if(buf->len < 1) {
+               buf->len = -1;
+               return NULL;
+       }
+
+       uint8_t len = buf->ptr[0];
+       buf->ptr++;
+       buf->len--;
+
+       if(buf->len < len) {
+               buf->len = -1;
+               return NULL;
+       }
+
+       char *label = xmalloc(len + 1);
+       memcpy(label, buf->ptr, len);
+       label[len] = 0;
+       buf->ptr += len;
+       buf->len -= len;
+       return label;
+}
+
+static void buf_check_ulabel(cbuf_t *buf, const char *str) {
+       size_t len = strlen(str);
+
+       if(len + 1 < 256) {
+               buf_check_uint8(buf, len + 1);
+               buf_check_uint8(buf, '_');
+               buf_check(buf, str, len);
+       } else {
+               buf->len = -1;
+       }
+}
+
+static void buf_get_kvp(cbuf_t *buf, const char *key, char **val) {
+       char *kvp = buf_get_label(buf);
+
+       if(buf->len == -1) {
+               return;
+       }
+
+       char *split = strchr(kvp, '=');
+
+       if(!split) {
+               buf->len = -1;
+               return;
+       }
+
+       *split++ = 0;
+
+       if(strcmp(kvp, key)) {
+               buf->len = -1;
+               return;
+       }
+
+       memmove(kvp, split, strlen(split) + 1);
+       *val = kvp;
+}
+
+static const uint8_t *buf_check_len_start(cbuf_t *buf) {
+       if(buf->len < 2) {
+               buf->len = -1;
+               return NULL;
+       } else {
+               const uint8_t *ptr = buf->ptr;
+               buf->ptr += 2;
+               buf->len -= 2;
+               return ptr;
+       }
+}
+
+static void buf_check_len_end(cbuf_t *buf, const uint8_t *ptr) {
+       if(buf->len < 0) {
+               return;
+       }
+
+       uint16_t len = htons(buf->ptr - ptr - 2);
+
+       if(memcmp(ptr, &len, sizeof(len))) {
+               buf->len = -1;
+       }
+}
+
+size_t prepare_packet(void *vdata, size_t size, const char *name, const char *protocol, const char *transport, uint16_t port, int nkeys, const char **keys, const char **values) {
+       // Create the request/response packet right now
+       uint8_t *data = vdata;
+       buf_t buf = {data, size};
+
+       // Header
+       buf_add_uint16(&buf, 0); // TX ID
+       buf_add_uint16(&buf, 0); // flags
+       buf_add_uint16(&buf, 1); // 1 question
+       buf_add_uint16(&buf, 1); // 1 answer RR
+       buf_add_uint16(&buf, 0); // 0 authority RRs
+       buf_add_uint16(&buf, 2); // 1 additional RR
+
+       // Question section: _protocol._transport.local PTR IN
+       buf_add_ulabel(&buf, protocol);
+       buf_add_ulabel(&buf, transport);
+       uint16_t local = buf.ptr - data;
+       buf_add_label(&buf, "local");
+       buf_add_uint8(&buf, 0);
+       buf_add_uint16(&buf, 0xc); // PTR
+       buf_add_uint16(&buf, 0x1); // IN
+
+       // Answer section: _protocol._transport local PTR IN 3600 name._protocol._transport
+       buf_add_uint16(&buf, 0xc00c); // _protocol._transport.local
+       buf_add_uint16(&buf, 0xc); // PTR
+       buf_add_uint16(&buf, 0x1); // IN
+       buf_add_uint32(&buf, 3600); // TTL
+       uint8_t *len_ptr = buf_len_start(&buf);
+       uint16_t full_name = buf.ptr - data; // remember start of full name
+       buf_add_label(&buf, name);
+       buf_add_uint16(&buf, 0xc00c); // _protocol._transport.local
+       buf_len_end(&buf, len_ptr);
+
+       // Add the SRV record: name._protocol._transport.local SRV IN 120 0 0 port name.local
+       buf_add_uint16(&buf, 0xc000 | full_name);
+       buf_add_uint16(&buf, 0x21); // SRV
+       buf_add_uint16(&buf, 0x1); // IN
+       buf_add_uint32(&buf, 120); // TTL
+       len_ptr = buf_len_start(&buf);
+       buf_add_uint16(&buf, 0); // priority
+       buf_add_uint16(&buf, 0); // weight
+       buf_add_uint16(&buf, port); // port
+       buf_add_label(&buf, name);
+       buf_add_uint16(&buf, 0xc000 | local);
+       buf_len_end(&buf, len_ptr);
+
+       // Add the TXT records: name._protocol._transport.local TXT IN 3600 key=value...
+       buf_add_uint16(&buf, 0xc000 | full_name);
+       buf_add_uint16(&buf, 0x10); // TXT
+       buf_add_uint16(&buf, 0x1); // IN
+       buf_add_uint32(&buf, 3600); // TTL
+       len_ptr = buf_len_start(&buf);
+
+       for(int i = 0; i < nkeys; i++) {
+               buf_add_kvp(&buf, keys[i], values[i]);
+       }
+
+       buf_len_end(&buf, len_ptr);
+
+       // Done.
+       if(buf.len < 0) {
+               return 0;
+       } else {
+               return buf.ptr - data;
+       }
+}
+
+bool parse_packet(const void *vdata, size_t size, char **name, const char *protocol, const char *transport, uint16_t *port, int nkeys, const char **keys, char **values) {
+       const uint8_t *data = vdata;
+       cbuf_t buf = {data, size};
+
+       // Header
+       buf_check_uint16(&buf, 0); // TX ID
+       buf_check_uint16(&buf, 0); // flags
+       buf_check_uint16(&buf, 1); // 1 question
+       buf_check_uint16(&buf, 1); // 1 answer RR
+       buf_check_uint16(&buf, 0); // 0 authority RRs
+       buf_check_uint16(&buf, 2); // 1 checkitional RR
+
+       if(buf.len == -1) {
+               return false;
+       }
+
+       // Question section: _protocol._transport.local PTR IN
+       buf_check_ulabel(&buf, protocol);
+       buf_check_ulabel(&buf, transport);
+       uint16_t local = buf.ptr - data;
+       buf_check_label(&buf, "local");
+       buf_check_uint8(&buf, 0);
+       buf_check_uint16(&buf, 0xc); // PTR
+       buf_check_uint16(&buf, 0x1); // IN
+
+       if(buf.len == -1) {
+               return false;
+       }
+
+       // Answer section: _protocol._transport local PTR IN 3600 name._protocol._transport
+       buf_check_uint16(&buf, 0xc00c); // _protocol._transport.local
+       buf_check_uint16(&buf, 0xc); // PTR
+       buf_check_uint16(&buf, 0x1); // IN
+       buf_check_uint32(&buf, 3600); // TTL
+       const uint8_t *len_ptr = buf_check_len_start(&buf);
+       uint16_t full_name = buf.ptr - data; // remember start of full name
+       *name = buf_get_label(&buf);
+       buf_check_uint16(&buf, 0xc00c); // _protocol._transport.local
+       buf_check_len_end(&buf, len_ptr);
+
+       if(buf.len == -1) {
+               return false;
+       }
+
+       // Check the SRV record: name._protocol._transport.local SRV IN 120 0 0 port name.local
+       buf_check_uint16(&buf, 0xc000 | full_name);
+       buf_check_uint16(&buf, 0x21); // SRV
+       buf_check_uint16(&buf, 0x1); // IN
+       buf_check_uint32(&buf, 120); // TTL
+       len_ptr = buf_check_len_start(&buf);
+       buf_check_uint16(&buf, 0); // priority
+       buf_check_uint16(&buf, 0); // weight
+       *port = buf_get_uint16(&buf); // port
+       buf_check_label(&buf, *name);
+       buf_check_uint16(&buf, 0xc000 | local);
+       buf_check_len_end(&buf, len_ptr);
+
+       if(buf.len == -1) {
+               return false;
+       }
+
+       // Check the TXT records: name._protocol._transport.local TXT IN 3600 key=value...
+       buf_check_uint16(&buf, 0xc000 | full_name);
+       buf_check_uint16(&buf, 0x10); // TXT
+       buf_check_uint16(&buf, 0x1); // IN
+       buf_check_uint32(&buf, 3600); // TTL
+       len_ptr = buf_check_len_start(&buf);
+
+       for(int i = 0; i < nkeys; i++) {
+               buf_get_kvp(&buf, keys[i], &values[i]);
+       }
+
+       buf_check_len_end(&buf, len_ptr);
+
+       // Done.
+       return buf.len == 0;
+}
diff --git a/src/mdns.h b/src/mdns.h
new file mode 100644 (file)
index 0000000..a538459
--- /dev/null
@@ -0,0 +1,11 @@
+#pragma once
+
+// SPDX-FileCopyrightText: 2020 Guus Sliepen <guus@meshlink.io>
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+#include <stdint.h>
+#include <unistd.h>
+
+size_t prepare_packet(void *buf, size_t size, const char *name, const char *protocol, const char *transport, uint16_t port, int nkeys, const char **keys, const char **values);
+bool parse_packet(const void *buf, size_t size, char **name, const char *protocol, const char *transport, uint16_t *port, int nkeys, const char **keys, char **values);
+
index aca65564b4522402bba053d21b939528950324ca..077705fada7690875bc6b300c053ae2678aed7d4 100644 (file)
@@ -194,6 +194,7 @@ struct meshlink_handle {
        struct discovery_address *discovery_addresses;
        int discovery_iface_count;
        int discovery_address_count;
+       io_t discovery_sockets[2];
 
        // ADNS
        pthread_t adns_thread;