mirror of
https://github.com/matrix-construct/construct
synced 2024-08-20 00:24:44 +02:00
218 lines
5.3 KiB
C++
218 lines
5.3 KiB
C++
// Matrix Construct
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//
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// Copyright (C) Matrix Construct Developers, Authors & Contributors
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// Copyright (C) 2016-2019 Jason Volk <jason@zemos.net>
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//
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// Permission to use, copy, modify, and/or distribute this software for any
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// purpose with or without fee is hereby granted, provided that the above
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// copyright notice and this permission notice is present in all copies. The
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// full license for this software is available in the LICENSE file.
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/// Given a buffer of CBOR this function parses the head data and maintains
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/// a const_buffer span of the head. The span includes the leading head byte
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/// and one or more integer bytes following the leading byte. If the major
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/// type found in this head has a data payload which is not a following-integer
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/// then that data starts directly after this head buffer ends.
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///
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/// The argument buffer must be at least one byte and must at least cover the
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/// following-integer bytes (and can also be as large as possible).
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///
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ircd::cbor::head::head(const const_buffer &buf)
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:const_buffer{[&buf]
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{
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if(unlikely(size(buf) < sizeof(uint8_t)))
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throw buffer_underrun
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{
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"Item buffer is too small to contain a header"
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};
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const uint8_t &leading
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{
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*reinterpret_cast<const uint8_t *>(data(buf))
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};
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return const_buffer
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{
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data(buf), length(leading)
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};
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}()}
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{
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if(unlikely(size(*this) > size(buf)))
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throw buffer_underrun
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{
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"Item buffer is too small to contain full header"
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};
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}
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/// Pun a reference to the integer contained by the bytes following the head.
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/// If there are no bytes following the head because the integer is contained
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/// as bits packed into the leading head byte, this function will throw.
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///
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template<class T>
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const T &
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ircd::cbor::head::following()
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const
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{
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if(unlikely(size(following()) < sizeof(T)))
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throw buffer_underrun
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{
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"Buffer following header is too small (%zu) for type requiring %zu",
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size(following()),
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sizeof(T)
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};
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return *reinterpret_cast<const T *>(data(following()));
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}
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/// Return buffer spanning the integer bytes following this head. This may be
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/// an empty buffer if the integer byte is packed into bits of the leading
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/// byte (denoted by minor()).
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ircd::const_buffer
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ircd::cbor::head::following()
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const
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{
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return { data(*this) + 1, length() - 1 };
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}
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/// Extract the length of the head from the buffer (requires 1 byte of buffer)
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size_t
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ircd::cbor::head::length()
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const
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{
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return length(leading());
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}
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/// Extract the minor type from the reference to the leading byte in the head.
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enum ircd::cbor::minor
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ircd::cbor::head::minor()
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const
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{
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return static_cast<enum minor>(minor(leading()));
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}
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/// Extract the major type from the reference to the leading byte in the head.
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enum ircd::cbor::major
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ircd::cbor::head::major()
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const
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{
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return static_cast<enum major>(major(leading()));
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}
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/// Reference the leading byte of the head.
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const uint8_t &
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ircd::cbor::head::leading()
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const
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{
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assert(size(*this) >= sizeof(uint8_t));
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return *reinterpret_cast<const uint8_t *>(data(*this));
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}
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/// Extract length of head from leading head byte (arg); this is the length of
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/// the integer following the leading head byte plus the one leading head
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/// byte. This length covers all bytes which come before item payload bytes
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/// (when such a payload exists). If this length is 1 then no integer bytes
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/// are following the leading head byte. The length/returned value is never 0.
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size_t
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ircd::cbor::head::length(const uint8_t &a)
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{
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switch(major(a))
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{
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case POSITIVE:
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case NEGATIVE:
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case BINARY:
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case STRING:
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case ARRAY:
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case OBJECT:
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case TAG:
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{
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if(minor(a) > 23) switch(minor(a))
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{
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case minor::U8: return 2;
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case minor::U16: return 3;
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case minor::U32: return 5;
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case minor::U64: return 9;
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default: throw type_error
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{
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"Unknown minor type (%u); length of header unknown", minor(a)
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};
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}
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else return 1;
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}
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case PRIMITIVE:
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{
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if(minor(a) > 23) switch(minor(a))
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{
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case FALSE:
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case TRUE:
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case NUL:
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case UD: return 1;
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case minor::F16: return 3;
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case minor::F32: return 5;
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case minor::F64: return 9;
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default: throw type_error
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{
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"Unknown primitive minor type (%u); length of header unknown", minor(a)
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};
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}
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else return 1;
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}
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default: throw type_error
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{
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"Unknown major type; length of header unknown"
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};
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}
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}
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/// Extract major type from leading head byte (arg)
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uint8_t
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ircd::cbor::head::major(const uint8_t &a)
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{
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// shift for higher 3 bits only
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static const int &shift(5);
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return a >> shift;
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}
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/// Extract minor type from leading head byte (arg)
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uint8_t
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ircd::cbor::head::minor(const uint8_t &a)
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{
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// mask of lower 5 bits only
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static const uint8_t &mask
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{
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uint8_t(0xFF) >> 3
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};
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return a & mask;
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}
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//
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// cbor.h
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//
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enum ircd::cbor::major
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ircd::cbor::major(const const_buffer &buf)
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{
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const head head(buf);
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return head.major();
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}
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ircd::string_view
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ircd::cbor::reflect(const enum major &major)
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{
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switch(major)
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{
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case major::POSITIVE: return "POSITIVE";
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case major::NEGATIVE: return "NEGATIVE";
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case major::BINARY: return "BINARY";
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case major::STRING: return "STRING";
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case major::ARRAY: return "ARRAY";
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case major::OBJECT: return "OBJECT";
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case major::TAG: return "TAG";
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case major::PRIMITIVE: return "PRIMITIVE";
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}
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return "??????";
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}
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