Parsing types

Spicy parsers are build up from smaller parsers, at the lowest level from basic types present in the input.

Currently Spicy supports parsing for the following basic types:

• network addresses
• bitfields
• raw bytes
• integers
• floating point numbers
• regular expressions
• vectors

Fields not extracting any data can be marked void. They can still have hooks attached.

Since they are pervasive we give a brief overview for vectors here.

Parsing vectors

A common requirement is to parse vector of the same type, possibly of dynamic length.

To parse a vector of three integers we would write:

type X = unit {
    xs: uint16[3];
};

If the number of elements is not known we can parse until the end of the input data. This will trigger a parse error if the input does not contain enough data to parse all elements.

type X = unit {
    xs: uint16[] &eod;
};

If the vector is followed by e.g., a literal we can dynamically detect with lookahead parsing where the vector ends. The literal does not need to be a field, but could also be in another parser following the vector.

type X = unit {
    xs: uint16[];
      : b"\x00"; # Vector is terminated with null byte.
};

If the terminator is in the domain of the vector elements we can also use the &until attribute.

type X = unit {
    # Vector terminate with a null value
    xs: uint8[] &until=$$==0;
};

If the vector elements require attributes themselves, we can pass them by grouping them with the element type.

type X = unit {
    # Parse a vector of 8-byte integers less than 1024 until we find a null.
    xs: (uint64 &requires=$$<1024)[] &until=$$==0;
};