diff --git a/globalfunctions/DleEncoder.cpp b/globalfunctions/DleEncoder.cpp index 088c9d80..8520389d 100644 --- a/globalfunctions/DleEncoder.cpp +++ b/globalfunctions/DleEncoder.cpp @@ -1,95 +1,124 @@ -#include "DleEncoder.h" +#include "../globalfunctions/DleEncoder.h" -DleEncoder::DleEncoder() { -} +DleEncoder::DleEncoder() {} -DleEncoder::~DleEncoder() { +DleEncoder::~DleEncoder() {} + +ReturnValue_t DleEncoder::encode(const uint8_t* sourceStream, + size_t sourceLen, uint8_t* destStream, size_t maxDestLen, + size_t* encodedLen, bool addStxEtx) { + if (maxDestLen < 2) { + return STREAM_TOO_SHORT; + } + size_t encodedIndex = 0, sourceIndex = 0; + uint8_t nextByte; + if (addStxEtx) { + destStream[0] = STX_CHAR; + ++encodedIndex; + } + + while (encodedIndex < maxDestLen and sourceIndex < sourceLen) + { + nextByte = sourceStream[sourceIndex]; + // STX, ETX and CR characters in the stream need to be escaped with DLE + if (nextByte == STX_CHAR or nextByte == ETX_CHAR or nextByte == CARRIAGE_RETURN) { + if (encodedIndex + 1 >= maxDestLen) { + return STREAM_TOO_SHORT; + } + else { + destStream[encodedIndex] = DLE_CHAR; + ++encodedIndex; + /* Escaped byte will be actual byte + 0x40. This prevents + * STX, ETX, and carriage return characters from appearing + * in the encoded data stream at all, so when polling an + * encoded stream, the transmission can be stopped at ETX. + * 0x40 was chosen at random with special requirements: + * - Prevent going from one control char to another + * - Prevent overflow for common characters */ + destStream[encodedIndex] = nextByte + 0x40; + } + } + // DLE characters are simply escaped with DLE. + else if (nextByte == DLE_CHAR) { + if (encodedIndex + 1 >= maxDestLen) { + return STREAM_TOO_SHORT; + } + else { + destStream[encodedIndex] = DLE_CHAR; + ++encodedIndex; + destStream[encodedIndex] = DLE_CHAR; + } + } + else { + destStream[encodedIndex] = nextByte; + } + ++encodedIndex; + ++sourceIndex; + } + + if (sourceIndex == sourceLen and encodedIndex < maxDestLen) { + if (addStxEtx) { + destStream[encodedIndex] = ETX_CHAR; + ++encodedIndex; + } + *encodedLen = encodedIndex; + return RETURN_OK; + } + else { + return STREAM_TOO_SHORT; + } } ReturnValue_t DleEncoder::decode(const uint8_t *sourceStream, - uint32_t sourceStreamLen, uint32_t *readLen, uint8_t *destStream, - uint32_t maxDestStreamlen, uint32_t *decodedLen) { - uint32_t encodedIndex = 0, decodedIndex = 0; + size_t sourceStreamLen, size_t *readLen, uint8_t *destStream, + size_t maxDestStreamlen, size_t *decodedLen) { + size_t encodedIndex = 0, decodedIndex = 0; uint8_t nextByte; - if (*sourceStream != STX) { - return RETURN_FAILED; + if (*sourceStream != STX_CHAR) { + return DECODING_ERROR; } ++encodedIndex; + while ((encodedIndex < sourceStreamLen) && (decodedIndex < maxDestStreamlen) - && (sourceStream[encodedIndex] != ETX) - && (sourceStream[encodedIndex] != STX)) { - if (sourceStream[encodedIndex] == DLE) { + && (sourceStream[encodedIndex] != ETX_CHAR) + && (sourceStream[encodedIndex] != STX_CHAR)) { + if (sourceStream[encodedIndex] == DLE_CHAR) { nextByte = sourceStream[encodedIndex + 1]; - if (nextByte == 0x10) { + // The next byte is a DLE character that was escaped by another + // DLE character, so we can write it to the destination stream. + if (nextByte == DLE_CHAR) { destStream[decodedIndex] = nextByte; - } else { - if ((nextByte == 0x42) || (nextByte == 0x43) - || (nextByte == 0x4D)) { + } + else { + /* The next byte is a STX, DTX or 0x0D character which + * was escaped by a DLE character. The actual byte was + * also encoded by adding + 0x40 to prevent having control chars, + * in the stream at all, so we convert it back. */ + if (nextByte == 0x42 or nextByte == 0x43 or nextByte == 0x4D) { destStream[decodedIndex] = nextByte - 0x40; - } else { - return RETURN_FAILED; + } + else { + return DECODING_ERROR; } } ++encodedIndex; - } else { + } + else { destStream[decodedIndex] = sourceStream[encodedIndex]; } + ++encodedIndex; ++decodedIndex; } - if (sourceStream[encodedIndex] != ETX) { - return RETURN_FAILED; - } else { + + if (sourceStream[encodedIndex] != ETX_CHAR) { + *readLen = ++encodedIndex; + return DECODING_ERROR; + } + else { *readLen = ++encodedIndex; *decodedLen = decodedIndex; return RETURN_OK; } } -ReturnValue_t DleEncoder::encode(const uint8_t* sourceStream, - uint32_t sourceLen, uint8_t* destStream, uint32_t maxDestLen, - uint32_t* encodedLen, bool addStxEtx) { - if (maxDestLen < 2) { - return RETURN_FAILED; - } - uint32_t encodedIndex = 0, sourceIndex = 0; - uint8_t nextByte; - if (addStxEtx) { - destStream[0] = STX; - ++encodedIndex; - } - while ((encodedIndex < maxDestLen) && (sourceIndex < sourceLen)) { - nextByte = sourceStream[sourceIndex]; - if ((nextByte == STX) || (nextByte == ETX) || (nextByte == 0x0D)) { - if (encodedIndex + 1 >= maxDestLen) { - return RETURN_FAILED; - } else { - destStream[encodedIndex] = DLE; - ++encodedIndex; - destStream[encodedIndex] = nextByte + 0x40; - } - } else if (nextByte == DLE) { - if (encodedIndex + 1 >= maxDestLen) { - return RETURN_FAILED; - } else { - destStream[encodedIndex] = DLE; - ++encodedIndex; - destStream[encodedIndex] = DLE; - } - } else { - destStream[encodedIndex] = nextByte; - } - ++encodedIndex; - ++sourceIndex; - } - if ((sourceIndex == sourceLen) && (encodedIndex < maxDestLen)) { - if (addStxEtx) { - destStream[encodedIndex] = ETX; - ++encodedIndex; - } - *encodedLen = encodedIndex; - return RETURN_OK; - } else { - return RETURN_FAILED; - } -} diff --git a/globalfunctions/DleEncoder.h b/globalfunctions/DleEncoder.h index ff3a2727..6d073f9a 100644 --- a/globalfunctions/DleEncoder.h +++ b/globalfunctions/DleEncoder.h @@ -1,25 +1,79 @@ -#ifndef DLEENCODER_H_ -#define DLEENCODER_H_ +#ifndef FRAMEWORK_GLOBALFUNCTIONS_DLEENCODER_H_ +#define FRAMEWORK_GLOBALFUNCTIONS_DLEENCODER_H_ #include "../returnvalues/HasReturnvaluesIF.h" +#include +/** + * @brief This DLE Encoder (Data Link Encoder) can be used to encode and + * decode arbitrary data with ASCII control characters + * @details + * List of control codes: + * https://en.wikipedia.org/wiki/C0_and_C1_control_codes + * + * This encoder can be used to achieve a basic transport layer when using + * char based transmission systems. + * The passed source strean is converted into a encoded stream by adding + * a STX marker at the start of the stream and an ETX marker at the end of + * the stream. Any STX, ETX, DLE and CR occurrences in the source stream are + * escaped by a DLE character. The encoder also replaces escaped control chars + * by another char, so STX, ETX and CR should not appear anywhere in the actual + * encoded data stream. + * + * When using a strictly char based reception of packets encoded with DLE, + * STX can be used to notify a reader that actual data will start to arrive + * while ETX can be used to notify the reader that the data has ended. + */ class DleEncoder: public HasReturnvaluesIF { private: DleEncoder(); virtual ~DleEncoder(); public: - static const uint8_t STX = 0x02; - static const uint8_t ETX = 0x03; - static const uint8_t DLE = 0x10; + static constexpr uint8_t INTERFACE_ID = CLASS_ID::DLE_ENCODER; + static constexpr ReturnValue_t STREAM_TOO_SHORT = MAKE_RETURN_CODE(0x01); + static constexpr ReturnValue_t DECODING_ERROR = MAKE_RETURN_CODE(0x02); + //! Start Of Text character. First character is encoded stream + static constexpr uint8_t STX_CHAR = 0x02; + //! End Of Text character. Last character in encoded stream + static constexpr uint8_t ETX_CHAR = 0x03; + //! Data Link Escape character. Used to escape STX, ETX and DLE occurrences + //! in the source stream. + static constexpr uint8_t DLE_CHAR = 0x10; + static constexpr uint8_t CARRIAGE_RETURN = 0x0D; + + /** + * Encodes the give data stream by preceding it with the STX marker + * and ending it with an ETX marker. STX, ETX and DLE characters inside + * the stream are escaped by DLE characters and also replaced by adding + * 0x40 (which is reverted in the decoding process). + * @param sourceStream + * @param sourceLen + * @param destStream + * @param maxDestLen + * @param encodedLen + * @param addStxEtx + * Adding STX and ETX can be omitted, if they are added manually. + * @return + */ + static ReturnValue_t encode(const uint8_t *sourceStream, size_t sourceLen, + uint8_t *destStream, size_t maxDestLen, size_t *encodedLen, + bool addStxEtx = true); + + /** + * Converts an encoded stream back. + * @param sourceStream + * @param sourceStreamLen + * @param readLen + * @param destStream + * @param maxDestStreamlen + * @param decodedLen + * @return + */ static ReturnValue_t decode(const uint8_t *sourceStream, - uint32_t sourceStreamLen, uint32_t *readLen, uint8_t *destStream, - uint32_t maxDestStreamlen, uint32_t *decodedLen); - - static ReturnValue_t encode(const uint8_t *sourceStream, uint32_t sourceLen, - uint8_t *destStream, uint32_t maxDestLen, uint32_t *encodedLen, - bool addStxEtx = true); + size_t sourceStreamLen, size_t *readLen, uint8_t *destStream, + size_t maxDestStreamlen, size_t *decodedLen); }; -#endif /* DLEENCODER_H_ */ +#endif /* FRAMEWORK_GLOBALFUNCTIONS_DLEENCODER_H_ */ diff --git a/returnvalues/FwClassIds.h b/returnvalues/FwClassIds.h index ddee539e..80df5741 100644 --- a/returnvalues/FwClassIds.h +++ b/returnvalues/FwClassIds.h @@ -64,6 +64,7 @@ enum { LOCAL_POOL_OWNER_IF, //LPIF 58 POOL_VARIABLE_IF, //PVA 59 HOUSEKEEPING_MANAGER, //HKM 60 + DLE_ENCODER, //DLEE 61 FW_CLASS_ID_COUNT //is actually count + 1 ! };