diff options
Diffstat (limited to 'main')
| -rw-r--r-- | main/rtp.c | 61 |
1 files changed, 60 insertions, 1 deletions
diff --git a/main/rtp.c b/main/rtp.c index ab55a0590..01f1b078c 100644 --- a/main/rtp.c +++ b/main/rtp.c @@ -237,10 +237,34 @@ struct ast_rtcp { int sendfur; }; +/*! + * \brief STUN support code + * + * This code provides some support for doing STUN transactions. + * Eventually it should be moved elsewhere as other protocols + * than RTP can benefit from it - e.g. SIP. + * STUN is described in RFC3489 and it is based on the exchange + * of UDP packets between a client and one or more servers to + * determine the externally visible address (and port) of the client + * once it has gone through the NAT boxes that connect it to the + * outside. + * The simplest request packet is just the header defined in + * struct stun_header, and from the response we may just look at + * one attribute, STUN_MAPPED_ADDRESS, that we find in the response. + * By doing more transactions with different server addresses we + * may determine more about the behaviour of the NAT boxes, of + * course - the details are in the RFC. + * + * All STUN packets start with a simple header made of a type, + * length (excluding the header) and a 16-byte random transaction id. + * Following the header we may have zero or more attributes, each + * structured as a type, length and a value (whose format depends + * on the type, but often contains addresses). + * Of course all fields are in network format. + */ typedef struct { unsigned int id[4]; } __attribute__((packed)) stun_trans_id; -/* XXX Maybe stun belongs in another file if it ever has use outside of RTP */ struct stun_header { unsigned short msgtype; unsigned short msglen; @@ -254,6 +278,9 @@ struct stun_attr { unsigned char value[0]; } __attribute__((packed)); +/* + * The format normally used for addresses carried by STUN messages. + */ struct stun_addr { unsigned char unused; unsigned char family; @@ -264,6 +291,13 @@ struct stun_addr { #define STUN_IGNORE (0) #define STUN_ACCEPT (1) +/*! \brief STUN message types + * 'BIND' refers to transactions used to determine the externally + * visible addresses. 'SEC' refers to transactions used to establish + * a session key for subsequent requests. + * 'SEC' functionality is not supported here. + */ + #define STUN_BINDREQ 0x0001 #define STUN_BINDRESP 0x0101 #define STUN_BINDERR 0x0111 @@ -271,6 +305,9 @@ struct stun_addr { #define STUN_SECRESP 0x0102 #define STUN_SECERR 0x0112 +/*! \brief Basic attribute types in stun messages. + * Messages can also contain custom attributes (codes above 0x7fff) + */ #define STUN_MAPPED_ADDRESS 0x0001 #define STUN_RESPONSE_ADDRESS 0x0002 #define STUN_CHANGE_REQUEST 0x0003 @@ -283,6 +320,7 @@ struct stun_addr { #define STUN_UNKNOWN_ATTRIBUTES 0x000a #define STUN_REFLECTED_FROM 0x000b +/*! \brief helper function to print message names */ static const char *stun_msg2str(int msg) { switch (msg) { @@ -302,6 +340,7 @@ static const char *stun_msg2str(int msg) return "Non-RFC3489 Message"; } +/*! \brief helper function to print attribute names */ static const char *stun_attr2str(int msg) { switch (msg) { @@ -331,6 +370,7 @@ static const char *stun_attr2str(int msg) return "Non-RFC3489 Attribute"; } +/*! \brief here we store credentials extracted from a message */ struct stun_state { const char *username; const char *password; @@ -356,6 +396,7 @@ static int stun_process_attr(struct stun_state *state, struct stun_attr *attr) return 0; } +/*! \brief append a string to an STUN message */ static void append_attr_string(struct stun_attr **attr, int attrval, const char *s, int *len, int *left) { int size = sizeof(**attr) + strlen(s); @@ -369,6 +410,7 @@ static void append_attr_string(struct stun_attr **attr, int attrval, const char } } +/*! \brief append an address to an STUN message */ static void append_attr_address(struct stun_attr **attr, int attrval, struct sockaddr_in *sin, int *len, int *left) { int size = sizeof(**attr) + 8; @@ -387,12 +429,14 @@ static void append_attr_address(struct stun_attr **attr, int attrval, struct soc } } +/*! \brief wrapper to send an STUN message */ static int stun_send(int s, struct sockaddr_in *dst, struct stun_header *resp) { return sendto(s, resp, ntohs(resp->msglen) + sizeof(*resp), 0, (struct sockaddr *)dst, sizeof(*dst)); } +/*! \brief helper function to generate a random request id */ static void stun_req_id(struct stun_header *req) { int x; @@ -405,6 +449,9 @@ size_t ast_rtp_alloc_size(void) return sizeof(struct ast_rtp); } +/*! \brief send a STUN BIND request to the given destination. + * Optionally, add a username if specified. + */ void ast_rtp_stun_request(struct ast_rtp *rtp, struct sockaddr_in *suggestion, const char *username) { struct stun_header *req; @@ -426,6 +473,13 @@ void ast_rtp_stun_request(struct ast_rtp *rtp, struct sockaddr_in *suggestion, c stun_send(rtp->s, suggestion, req); } +/*! \brief handle an incoming STUN message. + * + * Do some basic sanity checks on packet size and content, + * try to extract a bit of information, and possibly reply. + * At the moment this only processes BIND requests, and returns + * the externally visible address of the request. + */ static int stun_handle_packet(int s, struct sockaddr_in *src, unsigned char *data, size_t len) { struct stun_header *resp, *hdr = (struct stun_header *)data; @@ -1259,6 +1313,11 @@ struct ast_frame *ast_rtp_read(struct ast_rtp *rtp) /* Check RTP version */ version = (seqno & 0xC0000000) >> 30; if (!version) { + /* If the two high bits are 0, this might be a + * STUN message, so process it. stun_handle_packet() + * answers to requests, and it returns STUN_ACCEPT + * if the request is valid. + */ if ((stun_handle_packet(rtp->s, &sin, rtp->rawdata + AST_FRIENDLY_OFFSET, res) == STUN_ACCEPT) && (!rtp->them.sin_port && !rtp->them.sin_addr.s_addr)) { memcpy(&rtp->them, &sin, sizeof(rtp->them)); |