Source code
Revision control
Copy as Markdown
Other Tools
// Copyright 2020 The Abseil Authors.
//
// 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
//
//
// 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.
#ifndef ABSL_STRINGS_INTERNAL_STR_FORMAT_PARSER_H_
#define ABSL_STRINGS_INTERNAL_STR_FORMAT_PARSER_H_
#include <limits.h>
#include <stddef.h>
#include <stdlib.h>
#include <cassert>
#include <cstdint>
#include <initializer_list>
#include <iosfwd>
#include <iterator>
#include <memory>
#include <string>
#include <vector>
#include "absl/strings/internal/str_format/checker.h"
#include "absl/strings/internal/str_format/constexpr_parser.h"
#include "absl/strings/internal/str_format/extension.h"
namespace absl {
ABSL_NAMESPACE_BEGIN
namespace str_format_internal {
std::string LengthModToString(LengthMod v);
const char* ConsumeUnboundConversionNoInline(const char* p, const char* end,
UnboundConversion* conv,
int* next_arg);
// Parse the format string provided in 'src' and pass the identified items into
// 'consumer'.
// Text runs will be passed by calling
// Consumer::Append(string_view);
// ConversionItems will be passed by calling
// Consumer::ConvertOne(UnboundConversion, string_view);
// In the case of ConvertOne, the string_view that is passed is the
// portion of the format string corresponding to the conversion, not including
// the leading %. On success, it returns true. On failure, it stops and returns
// false.
template <typename Consumer>
bool ParseFormatString(string_view src, Consumer consumer) {
int next_arg = 0;
const char* p = src.data();
const char* const end = p + src.size();
while (p != end) {
const char* percent =
static_cast<const char*>(memchr(p, '%', static_cast<size_t>(end - p)));
if (!percent) {
// We found the last substring.
return consumer.Append(string_view(p, static_cast<size_t>(end - p)));
}
// We found a percent, so push the text run then process the percent.
if (ABSL_PREDICT_FALSE(!consumer.Append(
string_view(p, static_cast<size_t>(percent - p))))) {
return false;
}
if (ABSL_PREDICT_FALSE(percent + 1 >= end)) return false;
auto tag = GetTagForChar(percent[1]);
if (tag.is_conv()) {
if (ABSL_PREDICT_FALSE(next_arg < 0)) {
// This indicates an error in the format string.
// The only way to get `next_arg < 0` here is to have a positional
// argument first which sets next_arg to -1 and then a non-positional
// argument.
return false;
}
p = percent + 2;
// Keep this case separate from the one below.
// ConvertOne is more efficient when the compiler can see that the `basic`
// flag is set.
UnboundConversion conv;
conv.conv = tag.as_conv();
conv.arg_position = ++next_arg;
if (ABSL_PREDICT_FALSE(
!consumer.ConvertOne(conv, string_view(percent + 1, 1)))) {
return false;
}
} else if (percent[1] != '%') {
UnboundConversion conv;
p = ConsumeUnboundConversionNoInline(percent + 1, end, &conv, &next_arg);
if (ABSL_PREDICT_FALSE(p == nullptr)) return false;
if (ABSL_PREDICT_FALSE(!consumer.ConvertOne(
conv, string_view(percent + 1,
static_cast<size_t>(p - (percent + 1)))))) {
return false;
}
} else {
if (ABSL_PREDICT_FALSE(!consumer.Append("%"))) return false;
p = percent + 2;
continue;
}
}
return true;
}
// Always returns true, or fails to compile in a constexpr context if s does not
// point to a constexpr char array.
constexpr bool EnsureConstexpr(string_view s) {
return s.empty() || s[0] == s[0];
}
class ParsedFormatBase {
public:
explicit ParsedFormatBase(
string_view format, bool allow_ignored,
std::initializer_list<FormatConversionCharSet> convs);
ParsedFormatBase(const ParsedFormatBase& other) { *this = other; }
ParsedFormatBase(ParsedFormatBase&& other) { *this = std::move(other); }
ParsedFormatBase& operator=(const ParsedFormatBase& other) {
if (this == &other) return *this;
has_error_ = other.has_error_;
items_ = other.items_;
size_t text_size = items_.empty() ? 0 : items_.back().text_end;
data_.reset(new char[text_size]);
memcpy(data_.get(), other.data_.get(), text_size);
return *this;
}
ParsedFormatBase& operator=(ParsedFormatBase&& other) {
if (this == &other) return *this;
has_error_ = other.has_error_;
data_ = std::move(other.data_);
items_ = std::move(other.items_);
// Reset the vector to make sure the invariants hold.
other.items_.clear();
return *this;
}
template <typename Consumer>
bool ProcessFormat(Consumer consumer) const {
const char* const base = data_.get();
string_view text(base, 0);
for (const auto& item : items_) {
const char* const end = text.data() + text.size();
text =
string_view(end, static_cast<size_t>((base + item.text_end) - end));
if (item.is_conversion) {
if (!consumer.ConvertOne(item.conv, text)) return false;
} else {
if (!consumer.Append(text)) return false;
}
}
return !has_error_;
}
bool has_error() const { return has_error_; }
private:
// Returns whether the conversions match and if !allow_ignored it verifies
// that all conversions are used by the format.
bool MatchesConversions(
bool allow_ignored,
std::initializer_list<FormatConversionCharSet> convs) const;
struct ParsedFormatConsumer;
struct ConversionItem {
bool is_conversion;
// Points to the past-the-end location of this element in the data_ array.
size_t text_end;
UnboundConversion conv;
};
bool has_error_;
std::unique_ptr<char[]> data_;
std::vector<ConversionItem> items_;
};
// A value type representing a preparsed format. These can be created, copied
// around, and reused to speed up formatting loops.
// The user must specify through the template arguments the conversion
// characters used in the format. This will be checked at compile time.
//
// This class uses Conv enum values to specify each argument.
// This allows for more flexibility as you can specify multiple possible
// conversion characters for each argument.
// ParsedFormat<char...> is a simplified alias for when the user only
// needs to specify a single conversion character for each argument.
//
// Example:
// // Extended format supports multiple characters per argument:
// using MyFormat = ExtendedParsedFormat<Conv::d | Conv::x>;
// MyFormat GetFormat(bool use_hex) {
// if (use_hex) return MyFormat("foo %x bar");
// return MyFormat("foo %d bar");
// }
// // 'format' can be used with any value that supports 'd' and 'x',
// // like `int`.
// auto format = GetFormat(use_hex);
// value = StringF(format, i);
//
// This class also supports runtime format checking with the ::New() and
// ::NewAllowIgnored() factory functions.
// This is the only API that allows the user to pass a runtime specified format
// string. These factory functions will return NULL if the format does not match
// the conversions requested by the user.
template <FormatConversionCharSet... C>
class ExtendedParsedFormat : public str_format_internal::ParsedFormatBase {
public:
explicit ExtendedParsedFormat(string_view format)
#ifdef ABSL_INTERNAL_ENABLE_FORMAT_CHECKER
__attribute__((
enable_if(str_format_internal::EnsureConstexpr(format),
"Format string is not constexpr."),
enable_if(str_format_internal::ValidFormatImpl<C...>(format),
"Format specified does not match the template arguments.")))
#endif // ABSL_INTERNAL_ENABLE_FORMAT_CHECKER
: ExtendedParsedFormat(format, false) {
}
// ExtendedParsedFormat factory function.
// The user still has to specify the conversion characters, but they will not
// be checked at compile time. Instead, it will be checked at runtime.
// This delays the checking to runtime, but allows the user to pass
// dynamically sourced formats.
// It returns NULL if the format does not match the conversion characters.
// The user is responsible for checking the return value before using it.
//
// The 'New' variant will check that all the specified arguments are being
// consumed by the format and return NULL if any argument is being ignored.
// The 'NewAllowIgnored' variant will not verify this and will allow formats
// that ignore arguments.
static std::unique_ptr<ExtendedParsedFormat> New(string_view format) {
return New(format, false);
}
static std::unique_ptr<ExtendedParsedFormat> NewAllowIgnored(
string_view format) {
return New(format, true);
}
private:
static std::unique_ptr<ExtendedParsedFormat> New(string_view format,
bool allow_ignored) {
std::unique_ptr<ExtendedParsedFormat> conv(
new ExtendedParsedFormat(format, allow_ignored));
if (conv->has_error()) return nullptr;
return conv;
}
ExtendedParsedFormat(string_view s, bool allow_ignored)
: ParsedFormatBase(s, allow_ignored, {C...}) {}
};
} // namespace str_format_internal
ABSL_NAMESPACE_END
} // namespace absl
#endif // ABSL_STRINGS_INTERNAL_STR_FORMAT_PARSER_H_