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Detect truncated utf-8 characters at the end of content as still representing utf-8 (#19773)

Our character detection algorithm can potentially incorrectly detect utf-8 as iso-8859-x
if there is a truncated character at the end of the partially read file.

This PR changes the detection algorithm to truncated utf8 characters at the end of the
buffer.

Fix #19743

Signed-off-by: Andrew Thornton <art27@cantab.net>
This commit is contained in:
zeripath 2022-05-21 14:06:24 +01:00 committed by GitHub
parent f6c992974e
commit bc4764ffc6
No known key found for this signature in database
GPG Key ID: 4AEE18F83AFDEB23
2 changed files with 164 additions and 1 deletions

View File

@ -131,7 +131,26 @@ func RemoveBOMIfPresent(content []byte) []byte {
// DetectEncoding detect the encoding of content // DetectEncoding detect the encoding of content
func DetectEncoding(content []byte) (string, error) { func DetectEncoding(content []byte) (string, error) {
if utf8.Valid(content) { // First we check if the content represents valid utf8 content excepting a truncated character at the end.
// Now we could decode all the runes in turn but this is not necessarily the cheapest thing to do
// instead we walk backwards from the end to trim off a the incomplete character
toValidate := content
end := len(toValidate) - 1
if end < 0 {
// no-op
} else if toValidate[end]>>5 == 0b110 {
// Incomplete 1 byte extension e.g. © <c2><a9> which has been truncated to <c2>
toValidate = toValidate[:end]
} else if end > 0 && toValidate[end]>>6 == 0b10 && toValidate[end-1]>>4 == 0b1110 {
// Incomplete 2 byte extension e.g. ⛔ <e2><9b><94> which has been truncated to <e2><9b>
toValidate = toValidate[:end-1]
} else if end > 1 && toValidate[end]>>6 == 0b10 && toValidate[end-1]>>6 == 0b10 && toValidate[end-2]>>3 == 0b11110 {
// Incomplete 3 byte extension e.g. 💩 <f0><9f><92><a9> which has been truncated to <f0><9f><92>
toValidate = toValidate[:end-2]
}
if utf8.Valid(toValidate) {
log.Debug("Detected encoding: utf-8 (fast)") log.Debug("Detected encoding: utf-8 (fast)")
return "UTF-8", nil return "UTF-8", nil
} }

View File

@ -5,6 +5,8 @@
package charset package charset
import ( import (
"bytes"
"io"
"strings" "strings"
"testing" "testing"
@ -304,3 +306,145 @@ func stringMustEndWith(t *testing.T, expected, value string) {
func bytesMustStartWith(t *testing.T, expected, value []byte) { func bytesMustStartWith(t *testing.T, expected, value []byte) {
assert.Equal(t, expected, value[:len(expected)]) assert.Equal(t, expected, value[:len(expected)])
} }
func TestToUTF8WithFallbackReader(t *testing.T) {
resetDefaultCharsetsOrder()
for testLen := 0; testLen < 2048; testLen++ {
pattern := " test { () }\n"
input := ""
for len(input) < testLen {
input += pattern
}
input = input[:testLen]
input += "// Выключаем"
rd := ToUTF8WithFallbackReader(bytes.NewReader([]byte(input)))
r, _ := io.ReadAll(rd)
assert.EqualValuesf(t, input, string(r), "testing string len=%d", testLen)
}
truncatedOneByteExtension := failFastBytes
encoding, _ := DetectEncoding(truncatedOneByteExtension)
assert.Equal(t, "UTF-8", encoding)
truncatedTwoByteExtension := failFastBytes
truncatedTwoByteExtension[len(failFastBytes)-1] = 0x9b
truncatedTwoByteExtension[len(failFastBytes)-2] = 0xe2
encoding, _ = DetectEncoding(truncatedTwoByteExtension)
assert.Equal(t, "UTF-8", encoding)
truncatedThreeByteExtension := failFastBytes
truncatedThreeByteExtension[len(failFastBytes)-1] = 0x92
truncatedThreeByteExtension[len(failFastBytes)-2] = 0x9f
truncatedThreeByteExtension[len(failFastBytes)-3] = 0xf0
encoding, _ = DetectEncoding(truncatedThreeByteExtension)
assert.Equal(t, "UTF-8", encoding)
}
var failFastBytes = []byte{
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