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