An simple, efficient parser for multipart MIME messages, based on Formidable's parser.

MIME multipart messages are a total pain to parse because the grammar is so insane. Furthermore, the MIME specification is incredibly large. This has led to an army of equally large and complex MIME libraries. If you just want to parse a MIME multipart message without hassle then using all of those libraries are less than ideal. They all tend to handle the kitchen sink (e.g. they handling email parsing and all kinds of other stuff you don't need) or they depend on other libraries that you may not want (e.g. APR, glib) or they are under-documented or under-tested or just not efficient (e.g. buffering all data in memory; good luck parsing a 2 GB file upload). You can write your own parser but because the multipart grammar is so much of a pain it's very easy to make mistakes.

• Multipart parsing, and only multipart parsing.
• Event-driven API.
• No dependencies on any external libraries, just straight C++ with STL.
• Efficient. Nothing in the input is buffered except what's absolutely necessary for parsing.
• Only one level of multipart parsing. A multipart message part can itself be a multipart message, but this parser doesn't attempt to provide a complex API for handling nested multipart messages. Instead the developer should just use another parser instance to parse nested messages.
• No I/O is handled for you. This parser won't depend on any particular I/O library or even any particular operating system's I/O API. It won't block on I/O by itself, giving you full control over when (not) to block. It won't save data to files by itself, giving you full control over what to do with the parsed data.
• Not thread-safe, but reentrant. No dependencies on any threading libraries.