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https://github.com/matrix-construct/construct
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37 lines
1.9 KiB
Markdown
37 lines
1.9 KiB
Markdown
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## JavaScript Object Notation
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##### formal grammars & tools
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The IRCd JSON subsystem is meant to be a fast, safe, and extremely
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lightweight interface. We have taken a somewhat non-traditional approach
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and it's important for the developer to understand a few things.
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Most JSON interfaces are functions to convert some JSON input to and from
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text into native-machine state like JSON.parse() for JS, boost::ptree, etc.
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For a parsing operation, they make a pass recursing over the entire text,
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allocating native structures, copying data into them, indexing their keys,
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and perhaps performing native-type conversions and checks to present the
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user with a final tree of machine-state usable in their language. The
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original input is then discarded.
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Instead, we are interested in having the ability to *compute directly over
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JSON text* itself, and perform the allocating, indexing, copying and
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converting entirely at the time and place of our discretion -- if ever.
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The core of this system is a robust and efficient abstract formal grammar
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built with boost::spirit. The formal grammar provides a *proof of robust-
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ness*: security vulnerabilities are more easily spotted by vetting this
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grammar rather than laboriously tracing the program flow of an informal
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handwritten parser.
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Next we have taught boost::spirit how to parse into std::string_view rather
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than std::string. Parsing is now a composition of pointers into the original
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string of JSON. No dynamic allocation ever takes place. No copying of data
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ever takes place. IRCd can service an entire request from the original
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network input with absolutely minimal requisite cost.
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The output side is also ambitious but probably a little more friendly to
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the developer. We leverage boost::spirit here also providing *formally
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proven* output safety. In other words, the grammar prevents exploits like
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injecting and terminating JSON as it composes the output.
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