Nail: A Practical Tool for Parsing and Generating Data Formats

Nail is a tool that greatly reduces the programmer effort for safely parsing and generating data formats defined by a grammar. Nail introduces several key ideas to achieve its goal. First, Nail uses a protocol grammar to define not just the data format, but also the internal object model of the data. Second, Nail eliminates the notion of semantic actions, used by existing parser generators, which reduces the expressive power but allows Nail to both parse data formats and generate them from the internal object model, by establishing a semantic bijection between the data format and the object model. Third, Nail introduces dependent fields and stream transforms to capture protocol features such as size and offset fields, checksums, and compressed data, which are impractical to express in existing protocol languages. Using Nail, we implement an authoritative DNS server in C in under 300 lines of code and grammar, and an unzip program in C in 220 lines of code and grammar, demonstrating that Nail makes it easy to parse complex real-world data formats. Performance experiments show that a Nail-based DNS server can outperform the widely used BIND DNS server on an authoritative workload, demonstrating that systems built with Nail can achieve good performance.