URI Escaping

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The general rules about escaping and unescaping reserved characters in SIP message elements in PJSIP are as follows:

1. For incoming message, escaped strings will be unescaped by the parser before they are placed in the corresponding elements. For example, an element containing this URI:

   sip:good%20user@example.com
   

   will result in the following values to be placed in the pjsip_sip_uri structure:

   pjsip_sip_uri.user = pj_str("good user");
   pjsip_sip_uri.host = pj_str("example.com");
   

   Notice the value of the user field in the example above.
2. A pjsip_sip_uri that is passed around within the application MUST contain unescaped values. Keep this in mind especially when constructing a pjsip_sip_uri structure manually. The library will take care about escaping them when needed, i.e. before transmitting the message to the wire. Hence using the example above, when setting the user field, put "good user" instead of "good%20user" as the value.
3. URI string that is passed around within the application MUST be escaped. Keep this in mind when constructing any URI strings. If you can't control the characters that go into an URI (for example, the username character set is not strictly enforced), then you need to construct a pjsip_sip_uri and print it in order to get a properly escaped URI. For example:

   pjsip_sip_uri sip_uri;
   char buf[PJSIP_MAX_URL_SIZE];
   
   pjsip_sip_uri_init(&sip_uri, PJ_FALSE);
   sip_uri.user = pj_str("good user");
   sip_uri.host = pj_str("example.com");
   
   len = pjsip_uri_print(PJSIP_URI_IN_FROMTO_HDR, 
                         &sip_uri, buf, sizeof(buf));
   buf[len] = '\0';
   
   // buf now contains "sip:good%20user@example.com"