A network application communicates with other applications according to a set of rules known as a protocol. This communication is managed by the part of the application known as the protocol-handling layer, which enables the manipulation of protocol messages. The protocol-handling layer is a critical component of a network application since it represents the interface between the application and the outside world. It must thus satisfy two constraints: It must be efficient to be able to treat a large number of messages and it must be robust to face various attacks targeting the application itself or the underlying platform. Despite these constraints, the development process of this layer still remains rudimentary and requires a high level of expertise. It includes translating the protocol specification written in a high-level formalism such as ABNF toward low-level code such as C. The gap between these abstraction levels can entail many errors. This paper proposes a new language-based approach to developing protocol-handling layers, to improve their robustness without compromising their performance. Our approach is based on the use of a domain-specific language, Zebu, to specify the protocol-handling layer of network applications that use textual HTTP-like application protocols. The Zebu syntax is very close to that of ABNF, facilitating the adoption of Zebu by domain experts. By annotating the original ABNF specification of a protocol, the Zebu user can dedicate the protocol-handling layer to the needs of a given application. The Zebu compiler first checks the annotated specification for inconsistencies, and then generates a protocol-handling layer according to the annotations. This protocol-handling layer is made up of a set of data structures that represent a message, a parser that fills in these data structures, and various stub functions to access these data structures or drive the parsing of a message.

The secure and robust functioning of a network relies on the defect-free implementation of network applications. As network protocols have become increasingly complex, however, hand-writing network message processing code has become increasingly error-prone. In this paper, we present a domain-specific language, Zebu, for generating robust and efficient message processing layers. A Zebu specification, based on the notation used in RFCs, describes protocol message formats and related processing constraints. Zebu-based applications are efficient, since message fragments can be specified to be processed on demand. Zebu-based applications are also robust, as the Zebu compiler automatically checks specification consistency and generates parsing stubs that include validation of the message structure. Using a message torture suite in the context of SIP and RTSP, we show that Zebu-generated code is both complete and defect-free.

Telephony is evolving at a frantic pace, critically relying on the development of services to offer a host of new functionalities. However, programming Internet telephony services requires an intimate knowledge of a variety of protocols and technologies, which can be a challenge for many programmers. Furthermore, because telephony is a resource heavily relied on, programmability of telephony platforms should not compromise their robustness. This paper presents an approach to creating telephony services that builds on programming language technology (i.e., language design and implementation, language semantics, and program analysis). We have developed a language, named Session Processing Language (SPL), that offers domain-specific constructs, abstracting over the intricacies of the underlying technologies. By design, SPL guarantees critical properties that cannot be verified in general-purpose languages. SPL relies on a Service Logic Execution Environment for SIP (SIP-SLEE) that introduces a design framework for service development based around the notion of session. SPL and SIP-SLEE have been implemented and they are now being used to develop and deploy real services, demonstrating the practical benefits of our approach.