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input_parser.cc
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input_parser.cc
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// Copyright 2015 Google Inc. All Rights Reserved.
//
// 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.
#include "input_parser.h"
#include <algorithm>
#include <sstream>
// Returns whether the given character is a valid word character.
static bool IsWordChar(int c) {
return std::isalnum(c) ||
(std::ispunct(c) && c != ' ' && c != '"' && c != ';' && c != '[' &&
c != ']' && c != '\\' && c != '{' && c != '}');
}
// InputParser
InputParser::InputParser() : pos_(buffer_.begin()), end_(buffer_.end()) {
Reset();
}
InputParser::~InputParser() {}
void InputParser::Feed(const char* input, std::size_t input_length) {
// If pos_ is not at the start of the buffer, move the rest of the text back
// to the beginning of the buffer.
if (pos_ > buffer_.begin()) {
std::copy(pos_, end_, buffer_.begin());
buffer_.resize(end_ - pos_);
}
// Append the new input to the end of the buffer.
buffer_.append(input, input_length);
pos_ = buffer_.begin();
end_ = buffer_.end();
}
std::unique_ptr<StatementInfo> InputParser::Parse() {
// Keeps parsing the input buffer until there is a complete statement ready
// or it reaches the end of the buffer.
while (!statement_done_ && pos_ < end_) {
(this->*rules_.top())();
}
// It there is a statement, return it.
if (statement_done_) {
statement_done_ = false;
return std::move(statement_);
} else {
return nullptr;
}
}
void InputParser::Reset() {
decltype(rules_) empty;
std::swap(rules_, empty);
Push(&InputParser::Statement);
}
void InputParser::Push(InputParser::Rule rule) { rules_.push(rule); }
void InputParser::Pop() { rules_.pop(); }
void InputParser::Continue(InputParser::Rule rule) {
Pop();
Push(rule);
}
void InputParser::Unexpected(const std::string& context) {
auto word_pos = pos_;
if (IsWordChar(*pos_)) {
while (pos_ < end_ && IsWordChar(*pos_)) {
++pos_;
}
} else {
++pos_;
}
std::string near(word_pos, pos_);
while (pos_ < end_ && *pos_ != '\n') {
++pos_;
}
Reset();
throw InputParsingError(context, near);
}
// Statement ::= Command ArgumentList EOL
void InputParser::Statement() {
// Skip any spaces before the first token.
while (pos_ < end_ && std::isspace(*pos_)) ++pos_;
if (pos_ < end_) {
// A statement starts with a command, which starts with a letter.
if (std::isalpha(*pos_)) {
statement_.reset(new StatementInfo());
Continue(&InputParser::Command);
} else {
Unexpected("Statement");
}
}
}
// Command ::= WordChar+
void InputParser::Command() {
// Extract a contiguous set of word chars for the command.
auto word_pos = pos_;
while (pos_ < end_ && IsWordChar(*pos_)) {
++pos_;
}
// Set the statement command.
statement_->command.append(word_pos, pos_);
// If a non-word char was found, start the argument list, but skip any
// spaces first.
if (pos_ < end_) {
Pop();
Push(&InputParser::ArgumentList);
Push(&InputParser::Spaces);
}
}
// ArgumentList ::= Argument Spaces ArgumentList
// | BracedString Spaces ArgumentList
void InputParser::ArgumentList() {
if (IsWordChar(*pos_)) {
statement_->arguments.emplace_back();
Push(&InputParser::Argument);
} else if (*pos_ == '{') {
++pos_;
statement_->arguments.emplace_back();
Push(&InputParser::BracedString);
} else if (*pos_ == '\n') {
++pos_;
statement_done_ = true;
Continue(&InputParser::Statement);
} else {
Unexpected("ArgumentList");
}
}
// Argument ::= WordChar+
void InputParser::Argument() {
// Extract a contiguous set of word chars for the argument.
auto word_pos = pos_;
while (pos_ < end_ && IsWordChar(*pos_)) {
++pos_;
}
// Append to the last argument.
statement_->arguments.back().append(word_pos, pos_);
// If a non-word char was found, start start a new argument, skipping any
// spaces.
if (pos_ < end_) {
Continue(&InputParser::Spaces);
}
}
// BracedString ::= '{' char* '}'
void InputParser::BracedString() {
auto start = pos_;
while (pos_ < end_ && *pos_ != '}') ++pos_;
statement_->arguments.back().append(start, pos_);
if (pos_ < end_) {
++pos_; // Consume the '}'.
Continue(&InputParser::Spaces);
}
}
// Spaces ::= ' '*
void InputParser::Spaces() {
while (pos_ < end_) {
if (*pos_ == '\n' || !std::isspace(*pos_)) {
Pop();
break;
}
++pos_;
}
}
// StatementInfo
bool StatementInfo::operator==(const StatementInfo& o) {
return command == o.command && arguments == o.arguments;
}
bool StatementInfo::operator!=(const StatementInfo& o) {
return !operator==(o);
}
std::ostream& operator<<(std::ostream& o, const StatementInfo& s) {
o << "StatementInfo(\"" << s.command << "\", {";
for (unsigned i = 0; i < s.arguments.size(); ++i) {
o << "," + (i == 0) << " \"" << s.arguments[i] << "\"";
}
return o << " })";
}
// InputParsingError
InputParsingError::InputParsingError(const std::string& context,
const std::string& near)
: runtime_error(GenerateMessage(context, near)) {}
std::string InputParsingError::GenerateMessage(const std::string& context,
const std::string& near) {
std::ostringstream sstr;
sstr << "Failed to parse input: In context '" << context << "', near '"
<< near << "'.";
return sstr.str();
}