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/**
* @file Decoder.cpp
* @copyright (c) 2014 by Petr Zemek (s3rvac@gmail.com) and contributors
* @license BSD, see the @c LICENSE file for more details
* @brief Implementation of the Decoder class.
*/
#include "Decoder.h"
#include <cassert>
#include <regex>
#include <sstream>
#include "BDictionary.h"
#include "BInteger.h"
#include "BList.h"
#include "BString.h"
#include "Utils.h"
namespace bencoding {
/**
* @brief Constructs a new exception with the given message.
*/
DecodingError::DecodingError(const std::string &what):
std::runtime_error(what) {}
/**
* @brief Constructs a decoder.
*/
Decoder::Decoder() {}
/**
* @brief Creates a new decoder.
*/
std::shared_ptr<Decoder> Decoder::create() {
return std::shared_ptr<Decoder>(new Decoder());
}
/**
* @brief Decodes the given bencoded @a data and returns them.
*
* If there are some characters left after the decoded data, this function
* throws DecodingError.
*/
std::shared_ptr<BItem> Decoder::decode(const std::string &data) {
std::istringstream input(data);
auto decodedData = decode(input);
validateInputDoesNotContainUndecodedCharacters(input);
return decodedData;
}
/**
* @brief Reads the data from the given @a input, decodes them and returns them.
*
* If there are some characters left after the decoding, they are left in @a
* input, i.e. they are not read. This behavior differs for the overload of
* decode() that takes @c std::string as the input.
*/
std::shared_ptr<BItem> Decoder::decode(std::istream &input) {
switch (input.peek()) {
case 'd':
return decodeDictionary(input);
case 'i':
return decodeInteger(input);
case 'l':
return decodeList(input);
case '0':
case '1':
case '2':
case '3':
case '4':
case '5':
case '6':
case '7':
case '8':
case '9':
return decodeString(input);
default:
throw DecodingError(std::string("unexpected character: '") +
static_cast<char>(input.peek()) + "'");
}
assert(false && "should never happen");
return std::shared_ptr<BItem>();
}
/**
* @brief Reads @a expected_char from @a input and discards it.
*/
void Decoder::readExpectedChar(std::istream &input, char expected_char) const {
int c = input.get();
if (c != expected_char) {
throw DecodingError(std::string("expected '") + expected_char +
"', got '" + static_cast<char>(c) + "'");
}
}
/**
* @brief Decodes a dictionary from @a input.
*
* @par Format
* @code
* d<bencoded string><bencoded element>e
* @endcode
*
* @par Example
* @code
* d3:cow3:moo4:spam4:eggse represents the dictionary {"cow": "moo", "spam": "eggs"}
* d4:spaml1:a1:bee represents the dictionary {"spam": ["a", "b"]}
* @endcode
*
* The keys must be bencoded strings. The values may be any bencoded type,
* including integers, strings, lists, and other dictionaries. This function
* supports decoding of dictionaries whose keys are not lexicographically sorted
* (according to the <a
* href="https://wiki.theory.org/BitTorrentSpecification#Bencoding">specification</a>,
* they must be sorted).
*/
std::shared_ptr<BDictionary> Decoder::decodeDictionary(std::istream &input) {
readExpectedChar(input, 'd');
auto bDictionary = decodeDictionaryItemsIntoDictionary(input);
readExpectedChar(input, 'e');
return bDictionary;
}
/**
* @brief Decodes items from @a input, adds them to a dictionary, and returns
* that dictionary.
*/
std::shared_ptr<BDictionary> Decoder::decodeDictionaryItemsIntoDictionary(
std::istream &input) {
auto bDictionary = BDictionary::create();
while (input && input.peek() != 'e') {
std::shared_ptr<BString> key(decodeDictionaryKey(input));
std::shared_ptr<BItem> value(decodeDictionaryValue(input));
(*bDictionary)[key] = value;
}
return bDictionary;
}
/**
* @brief Decodes a dictionary key from @a input.
*/
std::shared_ptr<BString> Decoder::decodeDictionaryKey(std::istream &input) {
std::shared_ptr<BItem> key(decode(input));
// A dictionary key has to be a string.
std::shared_ptr<BString> keyAsBString(key->as<BString>());
if (!keyAsBString) {
throw DecodingError(
"found a dictionary key that is not a bencoded string"
);
}
return keyAsBString;
}
/**
* @brief Decodes a dictionary value from @a input.
*/
std::shared_ptr<BItem> Decoder::decodeDictionaryValue(std::istream &input) {
return decode(input);
}
/**
* @brief Decodes an integer from @a input.
*
* @par Format
* @code
* i<integer encoded in base ten ASCII>e
* @endcode
*
* @par Example
* @code
* i3e represents the integer 3
* @endcode
*
* Moreover, only the significant digits should be used, one cannot pad the
* integer with zeroes, such as @c i04e (see the <a
* href="https://wiki.theory.org/BitTorrentSpecification#Bencoding">
* specification</a>).
*/
std::shared_ptr<BInteger> Decoder::decodeInteger(std::istream &input) const {
return decodeEncodedInteger(readEncodedInteger(input));
}
/**
* @brief Reads an encoded integer from @a input.
*/
std::string Decoder::readEncodedInteger(std::istream &input) const {
// See the description of decodeInteger() for the format and example.
std::string encodedInteger;
bool encodedIntegerReadCorrectly = readUntil(input, encodedInteger, 'e');
if (!encodedIntegerReadCorrectly) {
throw DecodingError("error during the decoding of an integer near '" +
encodedInteger + "'");
}
return encodedInteger;
}
/**
* @brief Decodes the given encoded integer.
*/
std::shared_ptr<BInteger> Decoder::decodeEncodedInteger(
const std::string &encodedInteger) const {
// See the description of decodeInteger() for the format and example.
std::regex integerRegex("i([-+]?(0|[1-9][0-9]*))e");
std::smatch match;
bool valid = std::regex_match(encodedInteger, match, integerRegex);
if (!valid) {
throw DecodingError("encountered an encoded integer of invalid format: '" +
encodedInteger + "'");
}
BInteger::ValueType integerValue;
strToNum(match[1].str(), integerValue);
return BInteger::create(integerValue);
}
/**
* @brief Decodes a list from @a input.
*
* @par Format
* @code
* l<bencoded values>e
* @endcode
*
* @par Example
* @code
* l4:spam4:eggse represents a list containing two strings "spam" and "eggs"
* @endcode
*/
std::shared_ptr<BList> Decoder::decodeList(std::istream &input) {
readExpectedChar(input, 'l');
auto bList = decodeListItemsIntoList(input);
readExpectedChar(input, 'e');
return bList;
}
/**
* @brief Decodes items from @a input, appends them to a list, and returns that
* list.
*/
std::shared_ptr<BList> Decoder::decodeListItemsIntoList(std::istream &input) {
auto bList = BList::create();
while (input && input.peek() != 'e') {
bList->push_back(decode(input));
}
return bList;
}
/**
* @brief Decodes a string from @a input.
*
* @par Format
* @code
* <string length encoded in base ten ASCII>:<string data>
* @endcode
*
* @par Example
* @code
* 4:test represents the string "test"
* @endcode
*/
std::shared_ptr<BString> Decoder::decodeString(std::istream &input) const {
std::string::size_type stringLength(readStringLength(input));
readExpectedChar(input, ':');
std::string str(readStringOfGivenLength(input, stringLength));
return BString::create(str);
}
/**
* @brief Reads the string length from @a input, validates it, and returns it.
*/
std::string::size_type Decoder::readStringLength(std::istream &input) const {
std::string stringLengthInASCII;
bool stringLengthInASCIIReadCorrectly = readUpTo(input, stringLengthInASCII, ':');
if (!stringLengthInASCIIReadCorrectly) {
throw DecodingError("error during the decoding of a string near '" +
stringLengthInASCII + "'");
}
std::string::size_type stringLength;
bool stringLengthIsValid = strToNum(stringLengthInASCII, stringLength);
if (!stringLengthIsValid) {
throw DecodingError("invalid string length: '" + stringLengthInASCII + "'");
}
return stringLength;
}
/**
* @brief Reads a string of the given @a length from @a input and returns it.
*/
std::string Decoder::readStringOfGivenLength(std::istream &input,
std::string::size_type length) const {
std::string str(length, char());
input.read(&str[0], length);
std::string::size_type numOfReadChars(input.gcount());
if (numOfReadChars != length) {
throw DecodingError("expected a string containing " + std::to_string(length) +
" characters, but read only " + std::to_string(numOfReadChars) +
" characters");
}
return str;
}
/**
* @brief Throws DecodingError if @a input has not been completely read.
*/
void Decoder::validateInputDoesNotContainUndecodedCharacters(std::istream &input) {
if (input.peek() != std::char_traits<char>::eof()) {
throw DecodingError("input contains undecoded characters");
}
}
/**
* @brief Decodes the given bencoded @a data and returns them.
*
* This function can be handy if you just want to decode bencoded data without
* explicitly creating a decoder and calling @c decode() on it.
*
* See Decoder::decode() for more details.
*/
std::shared_ptr<BItem> decode(const std::string &data) {
auto decoder = Decoder::create();
return decoder->decode(data);
}
/**
* @brief Reads all the data from the given @a input, decodes them and returns
* them.
*
* This function can be handy if you just want to decode bencoded data without
* explicitly creating a decoder and calling @c decode() on it.
*
* See Decoder::decode() for more details.
*/
std::shared_ptr<BItem> decode(std::istream &input) {
auto decoder = Decoder::create();
return decoder->decode(input);
}
} // namespace bencoding
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