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# Structure sip_msg

This is the most important structure in the whole server. This structure represents a SIP message. When a message is received, it is immediately converted into this structure and all operations are performed over the structure. After the server finished processing, this structure is converted back to character array buffer and the buffer is sent out.

Structure Declaration:

    struct sip_msg {
        unsigned int id;               /* message id, unique/process*/
        struct msg_start first_line;   /* Message first line */
        struct via_body* via1;         /* The first via */
        struct via_body* via2;         /* The second via */
        struct hdr_field* headers;     /* All the parsed headers*/
        struct hdr_field* last_header; /* Pointer to the last parsed header*/
        int parsed_flag;               /* Already parsed header field types */

        /* Via, To, CSeq, Call-Id, From, end of header*/
        /* first occurrence of it; subsequent occurrences
         * saved in 'headers'
         */

        struct hdr_field* h_via1;
        struct hdr_field* h_via2;
        struct hdr_field* callid;
        struct hdr_field* to;
        struct hdr_field* cseq;
        struct hdr_field* from;
        struct hdr_field* contact;
        struct hdr_field* maxforwards;
        struct hdr_field* route;
        struct hdr_field* record_route;
        struct hdr_field* content_type;
        struct hdr_field* content_length;
        struct hdr_field* authorization;
        struct hdr_field* expires;
        struct hdr_field* proxy_auth;
        struct hdr_field* www_auth;
        struct hdr_field* supported;
        struct hdr_field* require;
        struct hdr_field* proxy_require;
        struct hdr_field* unsupported;
        struct hdr_field* allow;
        struct hdr_field* event;

        char* eoh;        /* pointer to the end of header (if found) or null */
        char* unparsed;   /* here we stopped parsing*/

       struct ip_addr src_ip;
       struct ip_addr dst_ip;

       char* orig;       /* original message copy */
       char* buf;        /* scratch pad, holds a modified message,
    	              *  via, etc. point into it
    	              */
       unsigned int len; /* message len (orig) */
                         /* modifications */

       str new_uri;       /* changed first line uri*/
       int parsed_uri_ok; /* 1 if parsed_uri is valid, 0 if not */
       struct sip_uri parsed_uri; /* speed-up > keep here the parsed uri*/

       struct lump* add_rm; /* used for all the forwarded
                             * requests */
       struct lump* repl_add_rm;    /* used for all the forwarded replies */
       struct lump_rpl *reply_lump; /* only for locally generated replies !!!*/
       char add_to_branch_s[MAX_BRANCH_PARAM_LEN];
       int add_to_branch_len;

           /* index to TM hash table; stored in core to avoid unnecessary calcs */
       unsigned int  hash_index;

           /* allows to set various flags on the message; may be used for
    	* simple inter-module communication or remembering processing state
    	* reached
    	*/
       flag_t flags;
    };

Field Description:

- id - Unique ID of the message within a process context.

- first_line - Parsed first line of the message.

- via1 - The first Via - parsed.

- via2 - The second Via - parsed.

- headers - Linked list of all parsed headers.

- last_header - Pointer to the last parsed header (parsing is incremental, that means that the parser will stop if all requested headers were found and next time it will continue at the place where it stopped previously. Therefore this field will not point to the last header of the message if the whole message hasn't been parsed yet).

- parsed_flag - Already parsed header field types (bitwise OR).

The following fields are set to zero if the corresponding header field was not found in the message or hasn't been parsed yet. (These fields are called hooks - they always point to the first occurrence if there is more than one header field of the same type).

- h_via1 - Pointer to the first Via header field.

- h_via2 - Pointer to the second Via header field.

- callid - Pointer to the first Call-ID header field.

- to - Pointer to the first To header field.

- cseq - Pointer to the first CSeq header field.

- from - Pointer to the first From header field.

- contact - Pointer to the first Contact header field.

- maxforwards - Pointer to the first Max-Forwards header field.

- route - Pointer to the first Route header field.

- record_route - Pointer to the first Record-Route header field.

- content_type - Pointer to the first Content-Type header field.

- content_length - Pointer to the first Content-Length header field.

- authorization - Pointer to the first Authorization header field.

- expires - Pointer to the first Expires header field.

- proxy_auth - Pointer to the first Proxy-Authorize header field.

- www_auth - Pointer to the first WWW-Authorize header field.

- supported - Pointer to the first Supported header field.

- require - Pointer to the first Require header field.

- proxy_require - Pointer to the first Proxy-Require header field.

- unsupported - Pointer to the first Unsupported header field.

- allow - Pointer to the first Allow header field.

- event - Pointer to the first Event header field.

The following fields are mostly used internally by the server and should be modified through dedicated functions only.

- eoh - Pointer to the End of Header or null if not found yet (the field will be set if and only if the whole message was parsed already).

- unparsed - Pointer to the first unparsed character in the message.

- src_ip - Sender's IP address.

- dst_ip - Destination's IP address.

- orig - Original (unmodified) message copy, this field will hold unmodified copy of the message during the whole message lifetime.

- buf - Message scratch-pad (modified copy of the message) - All modifications made to the message will be done here.

- len - Length of the message (unmodified).

- new_uri - New Request-URI to be used when forwarding the message.

- parsed_uri_ok - 1 if parsed_uri is valid, 0 if not.

- parsed_uri - The original parsed Request URI, sometimes it might be necessary to revert changes made to the Request URI and therefore we store the original URI here.

- add_rm - Linked list describing all modifications that will be made to REQUEST before it will be forwarded. The list will be processed when the request is being converted to character array (i.e. immediately before the request will be sent out).

- repl_add_rm - Linked list describing all modifications that will be made to REPLY before it will be forwarded. the list will be processed when the reply is being converted to character array (i.e. immediately before the request will be sent out).

- reply_lump - This is list of data chunks that should be appended to locally generated reply, i.e. when the server is generating local reply out of the request. A local reply is reply generated by the server. For example, when processing of a request fails for some reason, the server might generate an error reply and send it back to sender.

- add_to_branch_s - String to be appended to branch parameter.

- add_to_branch_len - Length of the string.

- hash_index - Index to a hash table in TM module.

- flags - Allows to set various flags on the message. May be used for simple inter-module communication or remembering processing state reached.