257 lines
8 KiB
Go
257 lines
8 KiB
Go
/* Copyright 2016-2017 Vector Creations Ltd
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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package canonicaljson
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import (
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"encoding/binary"
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"fmt"
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"sort"
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"unicode/utf8"
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"github.com/tidwall/gjson"
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)
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// CanonicalJSON re-encodes the JSON in a canonical encoding. The encoding is
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// the shortest possible encoding using integer values with sorted object keys.
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// https://matrix.org/docs/spec/appendices#canonical-json
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func CanonicalJSON(input []byte) ([]byte, error) {
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if !gjson.Valid(string(input)) {
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return nil, fmt.Errorf("invalid json")
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}
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return CanonicalJSONAssumeValid(input), nil
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}
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// CanonicalJSONAssumeValid is the same as CanonicalJSON, but assumes the
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// input is valid JSON
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func CanonicalJSONAssumeValid(input []byte) []byte {
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input = CompactJSON(input, make([]byte, 0, len(input)))
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return SortJSON(input, make([]byte, 0, len(input)))
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}
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// SortJSON reencodes the JSON with the object keys sorted by lexicographically
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// by codepoint. The input must be valid JSON.
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func SortJSON(input, output []byte) []byte {
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result := gjson.ParseBytes(input)
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return sortJSONValue(result, input, output)
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}
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// sortJSONValue takes a gjson.Result and sorts it. inputJSON must be the
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// raw JSON bytes that gjson.Result points to.
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func sortJSONValue(input gjson.Result, inputJSON, output []byte) []byte {
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if input.IsArray() {
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return sortJSONArray(input, inputJSON, output)
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}
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if input.IsObject() {
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return sortJSONObject(input, inputJSON, output)
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}
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// If its neither an object nor an array then there is no sub structure
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// to sort, so just append the raw bytes.
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return append(output, input.Raw...)
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}
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// sortJSONArray takes a gjson.Result and sorts it, assuming its an array.
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// inputJSON must be the raw JSON bytes that gjson.Result points to.
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func sortJSONArray(input gjson.Result, inputJSON, output []byte) []byte {
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sep := byte('[')
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// Iterate over each value in the array and sort it.
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input.ForEach(func(_, value gjson.Result) bool {
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output = append(output, sep)
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sep = ','
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output = sortJSONValue(value, inputJSON, output)
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return true // keep iterating
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})
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if sep == '[' {
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// If sep is still '[' then the array was empty and we never wrote the
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// initial '[', so we write it now along with the closing ']'.
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output = append(output, '[', ']')
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} else {
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// Otherwise we end the array by writing a single ']'
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output = append(output, ']')
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}
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return output
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}
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// sortJSONObject takes a gjson.Result and sorts it, assuming its an object.
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// inputJSON must be the raw JSON bytes that gjson.Result points to.
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func sortJSONObject(input gjson.Result, inputJSON, output []byte) []byte {
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type entry struct {
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key string // The parsed key string
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rawKey string // The raw, unparsed key JSON string
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value gjson.Result
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}
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var entries []entry
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// Iterate over each key/value pair and add it to a slice
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// that we can sort
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input.ForEach(func(key, value gjson.Result) bool {
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entries = append(entries, entry{
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key: key.String(),
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rawKey: key.Raw,
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value: value,
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})
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return true // keep iterating
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})
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// Sort the slice based on the *parsed* key
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sort.Slice(entries, func(a, b int) bool {
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return entries[a].key < entries[b].key
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})
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sep := byte('{')
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for _, entry := range entries {
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output = append(output, sep)
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sep = ','
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// Append the raw unparsed JSON key, *not* the parsed key
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output = append(output, entry.rawKey...)
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output = append(output, ':')
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output = sortJSONValue(entry.value, inputJSON, output)
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}
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if sep == '{' {
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// If sep is still '{' then the object was empty and we never wrote the
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// initial '{', so we write it now along with the closing '}'.
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output = append(output, '{', '}')
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} else {
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// Otherwise we end the object by writing a single '}'
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output = append(output, '}')
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}
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return output
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}
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// CompactJSON makes the encoded JSON as small as possible by removing
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// whitespace and unneeded unicode escapes
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func CompactJSON(input, output []byte) []byte {
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var i int
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for i < len(input) {
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c := input[i]
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i++
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// The valid whitespace characters are all less than or equal to SPACE 0x20.
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// The valid non-white characters are all greater than SPACE 0x20.
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// So we can check for whitespace by comparing against SPACE 0x20.
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if c <= ' ' {
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// Skip over whitespace.
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continue
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}
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// Add the non-whitespace character to the output.
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output = append(output, c)
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if c == '"' {
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// We are inside a string.
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for i < len(input) {
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c = input[i]
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i++
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// Check if this is an escape sequence.
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if c == '\\' {
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escape := input[i]
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i++
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if escape == 'u' {
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// If this is a unicode escape then we need to handle it specially
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output, i = compactUnicodeEscape(input, output, i)
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} else if escape == '/' {
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// JSON does not require escaping '/', but allows encoders to escape it as a special case.
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// Since the escape isn't required we remove it.
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output = append(output, escape)
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} else {
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// All other permitted escapes are single charater escapes that are already in their shortest form.
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output = append(output, '\\', escape)
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}
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} else {
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output = append(output, c)
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}
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if c == '"' {
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break
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}
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}
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}
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}
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return output
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}
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// compactUnicodeEscape unpacks a 4 byte unicode escape starting at index.
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// If the escape is a surrogate pair then decode the 6 byte \uXXXX escape
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// that follows. Returns the output slice and a new input index.
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func compactUnicodeEscape(input, output []byte, index int) ([]byte, int) {
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const (
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ESCAPES = "uuuuuuuubtnufruuuuuuuuuuuuuuuuuu"
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HEX = "0123456789ABCDEF"
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)
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// If there aren't enough bytes to decode the hex escape then return.
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if len(input)-index < 4 {
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return output, len(input)
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}
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// Decode the 4 hex digits.
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c := readHexDigits(input[index:])
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index += 4
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if c < ' ' {
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// If the character is less than SPACE 0x20 then it will need escaping.
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escape := ESCAPES[c]
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output = append(output, '\\', escape)
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if escape == 'u' {
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output = append(output, '0', '0', byte('0'+(c>>4)), HEX[c&0xF])
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}
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} else if c == '\\' || c == '"' {
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// Otherwise the character only needs escaping if it is a QUOTE '"' or BACKSLASH '\\'.
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output = append(output, '\\', byte(c))
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} else if c < 0xD800 || c >= 0xE000 {
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// If the character isn't a surrogate pair then encoded it directly as UTF-8.
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var buffer [4]byte
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n := utf8.EncodeRune(buffer[:], rune(c))
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output = append(output, buffer[:n]...)
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} else {
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// Otherwise the escaped character was the first part of a UTF-16 style surrogate pair.
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// The next 6 bytes MUST be a '\uXXXX'.
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// If there aren't enough bytes to decode the hex escape then return.
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if len(input)-index < 6 {
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return output, len(input)
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}
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// Decode the 4 hex digits from the '\uXXXX'.
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surrogate := readHexDigits(input[index+2:])
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index += 6
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// Reconstruct the UCS4 codepoint from the surrogates.
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codepoint := 0x10000 + (((c & 0x3FF) << 10) | (surrogate & 0x3FF))
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// Encode the charater as UTF-8.
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var buffer [4]byte
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n := utf8.EncodeRune(buffer[:], rune(codepoint))
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output = append(output, buffer[:n]...)
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}
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return output, index
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}
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// Read 4 hex digits from the input slice.
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// Taken from https://github.com/NegativeMjark/indolentjson-rust/blob/8b959791fe2656a88f189c5d60d153be05fe3deb/src/readhex.rs#L21
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func readHexDigits(input []byte) uint32 {
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hex := binary.BigEndian.Uint32(input)
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// subtract '0'
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hex -= 0x30303030
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// strip the higher bits, maps 'a' => 'A'
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hex &= 0x1F1F1F1F
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mask := hex & 0x10101010
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// subtract 'A' - 10 - '9' - 9 = 7 from the letters.
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hex -= mask >> 1
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hex += mask >> 4
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// collect the nibbles
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hex |= hex >> 4
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hex &= 0xFF00FF
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hex |= hex >> 8
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return hex & 0xFFFF
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}
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