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AK: Replace UTF-8 string validation with a constexpr implementation

Browse source 
This will allow validating UTF-8 strings at compile time, such as from
String::from_utf8_short_string.
This commit is contained in:
Timothy Flynn 2023-03-03 07:56:24 -05:00 • committed by Tim Flynn
parent f6f62d7ff6
commit 796a615bc1
2 changed files with 91 additions and 78 deletions
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73
AK/Utf8View.cpp
View file

@ -6,7 +6,6 @@
*/
#include <AK/Assertions.h>
#include <AK/CharacterTypes.h>
#include <AK/Debug.h>
#include <AK/Format.h>
#include <AK/Utf8View.h>
@ -71,68 +70,6 @@ Utf8View Utf8View::unicode_substring_view(size_t code_point_offset, size_t code_
VERIFY_NOT_REACHED();
}
static inline bool decode_first_byte(
unsigned char byte,
size_t& out_code_point_length_in_bytes,
u32& out_value)
{
if ((byte & 128) == 0) {
out_value = byte;
out_code_point_length_in_bytes = 1;
return true;
}
if ((byte & 64) == 0) {
return false;
}
if ((byte & 32) == 0) {
out_value = byte & 31;
out_code_point_length_in_bytes = 2;
return true;
}
if ((byte & 16) == 0) {
out_value = byte & 15;
out_code_point_length_in_bytes = 3;
return true;
}
if ((byte & 8) == 0) {
out_value = byte & 7;
out_code_point_length_in_bytes = 4;
return true;
}
return false;
}
bool Utf8View::validate(size_t& valid_bytes) const
{
valid_bytes = 0;
for (auto ptr = begin_ptr(); ptr < end_ptr(); ptr++) {
size_t code_point_length_in_bytes = 0;
u32 code_point = 0;
bool first_byte_makes_sense = decode_first_byte(*ptr, code_point_length_in_bytes, code_point);
if (!first_byte_makes_sense)
return false;
for (size_t i = 1; i < code_point_length_in_bytes; i++) {
ptr++;
if (ptr >= end_ptr())
return false;
if (*ptr >> 6 != 2)
return false;
code_point <<= 6;
code_point |= *ptr & 63;
}
if (!is_unicode(code_point))
return false;
valid_bytes += code_point_length_in_bytes;
}
return true;
}
size_t Utf8View::calculate_length() const
{
size_t length = 0;
@ -223,9 +160,7 @@ Utf8CodePointIterator& Utf8CodePointIterator::operator++()
size_t Utf8CodePointIterator::underlying_code_point_length_in_bytes() const
{
VERIFY(m_length > 0);
size_t code_point_length_in_bytes = 0;
u32 value;
bool first_byte_makes_sense = decode_first_byte(*m_ptr, code_point_length_in_bytes, value);
auto [code_point_length_in_bytes, value, first_byte_makes_sense] = Utf8View::decode_leading_byte(*m_ptr);
// If any of these tests fail, we will output a replacement character for this byte and treat it as a code point of size 1.
if (!first_byte_makes_sense)
@ -250,11 +185,7 @@ ReadonlyBytes Utf8CodePointIterator::underlying_code_point_bytes() const
u32 Utf8CodePointIterator::operator*() const
{
VERIFY(m_length > 0);
u32 code_point_value_so_far = 0;
size_t code_point_length_in_bytes = 0;
bool first_byte_makes_sense = decode_first_byte(m_ptr[0], code_point_length_in_bytes, code_point_value_so_far);
auto [code_point_length_in_bytes, code_point_value_so_far, first_byte_makes_sense] = Utf8View::decode_leading_byte(*m_ptr);
if (!first_byte_makes_sense) {
// The first byte of the code point doesn't make sense: output a replacement character

96
AK/Utf8View.h
View file

@ -7,6 +7,7 @@
#pragma once
#include <AK/CharacterTypes.h>
#include <AK/DeprecatedString.h>
#include <AK/Format.h>
#include <AK/StringView.h>
@ -105,13 +106,6 @@ public:
return byte_offset_of(it);
}
bool validate(size_t& valid_bytes) const;
bool validate() const
{
size_t valid_bytes;
return validate(valid_bytes);
}
size_t length() const
{
if (!m_have_length) {
@ -121,11 +115,99 @@ public:
return m_length;
}
constexpr bool validate() const
{
size_t valid_bytes = 0;
return validate(valid_bytes);
}
constexpr bool validate(size_t& valid_bytes) const
{
valid_bytes = 0;
for (auto it = m_string.begin(); it != m_string.end(); ++it) {
auto [byte_length, code_point, is_valid] = decode_leading_byte(static_cast<u8>(*it));
if (!is_valid)
return false;
for (size_t i = 1; i < byte_length; ++i) {
if (++it == m_string.end())
return false;
auto [code_point_bits, is_valid] = decode_continuation_byte(static_cast<u8>(*it));
if (!is_valid)
return false;
code_point <<= 6;
code_point |= code_point_bits;
}
if (!is_unicode(code_point))
return false;
valid_bytes += byte_length;
}
return true;
}
private:
friend class Utf8CodePointIterator;
u8 const* begin_ptr() const { return (u8 const*)m_string.characters_without_null_termination(); }
u8 const* end_ptr() const { return begin_ptr() + m_string.length(); }
size_t calculate_length() const;
struct Utf8EncodedByteData {
size_t byte_length { 0 };
u8 encoding_bits { 0 };
u8 encoding_mask { 0 };
};
static constexpr Array<Utf8EncodedByteData, 4> utf8_encoded_byte_data { {
{ 1, 0b0000'0000, 0b1000'0000 },
{ 2, 0b1100'0000, 0b1110'0000 },
{ 3, 0b1110'0000, 0b1111'0000 },
{ 4, 0b1111'0000, 0b1111'1000 },
} };
struct LeadingByte {
size_t byte_length { 0 };
u32 code_point_bits { 0 };
bool is_valid { false };
};
static constexpr LeadingByte decode_leading_byte(u8 byte)
{
for (auto const& data : utf8_encoded_byte_data) {
if ((byte & data.encoding_mask) != data.encoding_bits)
continue;
byte &= ~data.encoding_mask;
return { data.byte_length, byte, true };
}
return { .is_valid = false };
}
struct ContinuationByte {
u32 code_point_bits { 0 };
bool is_valid { false };
};
static constexpr ContinuationByte decode_continuation_byte(u8 byte)
{
constexpr u8 continuation_byte_encoding_bits = 0b1000'0000;
constexpr u8 continuation_byte_encoding_mask = 0b1100'0000;
if ((byte & continuation_byte_encoding_mask) == continuation_byte_encoding_bits) {
byte &= ~continuation_byte_encoding_mask;
return { byte, true };
}
return { .is_valid = false };
}
StringView m_string;
mutable size_t m_length { 0 };
mutable bool m_have_length { false };