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defmodule JSONOLD.Parser.Unicode do
@moduledoc """
Implements a JSONOLD Unicode Parser for Bitstring values
"""
use Bitwise
@doc """
parses a valid chain of escaped unicode and returns the string representation,
plus the remainder of the string
## Examples
iex> JSONOLD.Parser.parse ""
{:error, :unexpected_end_of_buffer}
iex> JSONOLD.Parser.parse "face0ff"
{:error, {:unexpected_token, "face0ff"}}
iex> JSONOLD.Parser.parse "-hello"
{:error, {:unexpected_token, "-hello"}}
"""
def parse(<<?\\, ?u, json::binary>>), do: parse_escaped_unicode_codepoint(json, 0, 0)
def parse(<<>>), do: {:error, :unexpected_end_of_buffer}
def parse(json), do: {:error, {:unexpected_token, json}}
# Parsing sugorrogate pairs
# http://unicodebook.readthedocs.org/unicode_encodings.html
# Inspired by Poison's function
defp parse_escaped_unicode_codepoint(
<<?d, hex::utf8, f1, f2, ?\\, ?u, ?d, hex2::utf8, s1, s2, json::binary>>,
_,
0
)
when hex >= 56 do
first_part = (List.to_integer([?d, hex, f1, f2], 16) &&& 1023) <<< 10
second_part = List.to_integer([?d, hex2, s1, s2], 16) &&& 1023
complete = 0x10000 + first_part + second_part
{:ok, <<complete::utf8>>, json}
end
# parse_escaped_unicode_codepoint tries to parse
# a valid hexadecimal (composed of 4 characters) value that potentially
# represents a unicode codepoint
defp parse_escaped_unicode_codepoint(json, acc, chars_parsed) when 4 === chars_parsed do
{:ok, <<acc::utf8>>, json}
end
defp parse_escaped_unicode_codepoint(<<hex::utf8, json::binary>>, acc, chars_parsed)
when hex in ?0..?9 do
parse_escaped_unicode_codepoint(json, 16 * acc + hex - ?0, chars_parsed + 1)
end
defp parse_escaped_unicode_codepoint(<<hex::utf8, json::binary>>, acc, chars_parsed)
when hex in ?a..?f do
parse_escaped_unicode_codepoint(json, 16 * acc + 10 + hex - ?a, chars_parsed + 1)
end
defp parse_escaped_unicode_codepoint(<<hex::utf8, json::binary>>, acc, chars_parsed)
when hex in ?A..?F do
parse_escaped_unicode_codepoint(json, 16 * acc + 10 + hex - ?A, chars_parsed + 1)
end
defp parse_escaped_unicode_codepoint(<<>>, _, _), do: {:error, :unexpected_end_of_buffer}
defp parse_escaped_unicode_codepoint(json, _, _), do: {:error, {:unexpected_token, json}}
end
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