SipServletMessage

The shared functions between SIP requests and responses are represented by the SipServletMessage interface. It offers the fundamental techniques for working with SIP communications, such as obtaining and altering headers and content. This interface extends the java.lang.Cloneable interface and enables the duplication of SIP messages as needed.
The unique needs of SIP communication, which are very different from those of the HTTP model, are met by the SipServletMessage interface. SIP services frequently have to start requests themselves, as contrast to HTTP servlets, which function only as origin servers handling client requests. Because SIP communication is bidirectional, the request and response classes must be more symmetrically designed to be both readable and writable. As a result, the SipServletMessage interface defines a common set of actions, like handling headers and content, that are applicable to both SipServletRequest and SipServletResponse.
Notes:

• Certain SIP headers, such as From, To, Call-ID, and CSeq, are managed by the servlet container and cannot be modified directly.
• Adding or modifying the Contact header is restricted and subject to specific rules based on the type of message (e.g., allowed in REGISTER requests but restricted in others).
• Reliable provisional response headers (RAck and RSeq) are also system headers in implementations supporting this extension.
• SIP headers can appear in both long (e.g., Via, From, To) and compact forms (e.g., v, f, t). For more details, see the official IANA SIP Parameters registry.

Nested class:

SipServletMessage.HeaderForm
The class specifies the types of header formats (COMPACT and NORMAL) used in SIP messages. It allows control over how SIP headers are represented and processed. For more details, refer to the Description.