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added doc to dle encoder

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This commit is contained in:
Robin Müller 2020-08-26 17:42:13 +02:00
parent 9465c8f2b2
commit 2748a8b93b
2 changed files with 203 additions and 120 deletions
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219
globalfunctions/DleEncoder.cpp
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@ -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,
ReturnValue_t DleEncoder::decode(const uint8_t *sourceStream, size_t* encodedLen, bool addStxEtx) {
uint32_t sourceStreamLen, uint32_t *readLen, uint8_t *destStream, if (maxDestLen < 2) {
uint32_t maxDestStreamlen, uint32_t *decodedLen) { return STREAM_TOO_SHORT;
uint32_t encodedIndex = 0, decodedIndex = 0; }
uint8_t nextByte; size_t encodedIndex = 0, sourceIndex = 0;
if (*sourceStream != STX) { uint8_t nextByte;
return RETURN_FAILED; if (addStxEtx) {
} destStream[0] = STX_CHAR;
++encodedIndex; ++encodedIndex;
while ((encodedIndex < sourceStreamLen) && (decodedIndex < maxDestStreamlen) }
&& (sourceStream[encodedIndex] != ETX)
&& (sourceStream[encodedIndex] != STX)) { while (encodedIndex < maxDestLen and sourceIndex < sourceLen)
if (sourceStream[encodedIndex] == DLE) { {
nextByte = sourceStream[encodedIndex + 1]; nextByte = sourceStream[sourceIndex];
if (nextByte == 0x10) { // STX, ETX and CR characters in the stream need to be escaped with DLE
destStream[decodedIndex] = nextByte; if (nextByte == STX_CHAR or nextByte == ETX_CHAR or nextByte == CARRIAGE_RETURN) {
} else { if (encodedIndex + 1 >= maxDestLen) {
if ((nextByte == 0x42) || (nextByte == 0x43) return STREAM_TOO_SHORT;
|| (nextByte == 0x4D)) { }
destStream[decodedIndex] = nextByte - 0x40; else {
} else { destStream[encodedIndex] = DLE_CHAR;
return RETURN_FAILED; ++encodedIndex;
} /* Escaped byte will be actual byte + 0x40. This prevents
} * STX, ETX, and carriage return characters from appearing
++encodedIndex; * in the encoded data stream at all, so when polling an
} else { * encoded stream, the transmission can be stopped at ETX.
destStream[decodedIndex] = sourceStream[encodedIndex]; * 0x40 was chosen at random with special requirements:
} * - Prevent going from one control char to another
++encodedIndex; * - Prevent overflow for common characters */
++decodedIndex; destStream[encodedIndex] = nextByte + 0x40;
} }
if (sourceStream[encodedIndex] != ETX) { }
return RETURN_FAILED; // DLE characters are simply escaped with DLE.
} else { else if (nextByte == DLE_CHAR) {
*readLen = ++encodedIndex; if (encodedIndex + 1 >= maxDestLen) {
*decodedLen = decodedIndex; return STREAM_TOO_SHORT;
return RETURN_OK; }
} else {
} destStream[encodedIndex] = DLE_CHAR;
++encodedIndex;
ReturnValue_t DleEncoder::encode(const uint8_t* sourceStream, destStream[encodedIndex] = DLE_CHAR;
uint32_t sourceLen, uint8_t* destStream, uint32_t maxDestLen, }
uint32_t* encodedLen, bool addStxEtx) { }
if (maxDestLen < 2) { else {
return RETURN_FAILED; destStream[encodedIndex] = nextByte;
} }
uint32_t encodedIndex = 0, sourceIndex = 0; ++encodedIndex;
uint8_t nextByte; ++sourceIndex;
if (addStxEtx) { }
destStream[0] = STX;
++encodedIndex; if (sourceIndex == sourceLen and encodedIndex < maxDestLen) {
} if (addStxEtx) {
while ((encodedIndex < maxDestLen) && (sourceIndex < sourceLen)) { destStream[encodedIndex] = ETX_CHAR;
nextByte = sourceStream[sourceIndex]; ++encodedIndex;
if ((nextByte == STX) || (nextByte == ETX) || (nextByte == 0x0D)) { }
if (encodedIndex + 1 >= maxDestLen) { *encodedLen = encodedIndex;
return RETURN_FAILED; return RETURN_OK;
} else { }
destStream[encodedIndex] = DLE; else {
++encodedIndex; return STREAM_TOO_SHORT;
destStream[encodedIndex] = nextByte + 0x40; }
} }
} else if (nextByte == DLE) {
if (encodedIndex + 1 >= maxDestLen) { ReturnValue_t DleEncoder::decode(const uint8_t *sourceStream,
return RETURN_FAILED; size_t sourceStreamLen, size_t *readLen, uint8_t *destStream,
} else { size_t maxDestStreamlen, size_t *decodedLen) {
destStream[encodedIndex] = DLE; size_t encodedIndex = 0, decodedIndex = 0;
++encodedIndex; uint8_t nextByte;
destStream[encodedIndex] = DLE; if (*sourceStream != STX_CHAR) {
} return DECODING_ERROR;
} else { }
destStream[encodedIndex] = nextByte; ++encodedIndex;
}
++encodedIndex; while ((encodedIndex < sourceStreamLen) && (decodedIndex < maxDestStreamlen)
++sourceIndex; && (sourceStream[encodedIndex] != ETX_CHAR)
} && (sourceStream[encodedIndex] != STX_CHAR)) {
if ((sourceIndex == sourceLen) && (encodedIndex < maxDestLen)) { if (sourceStream[encodedIndex] == DLE_CHAR) {
if (addStxEtx) { nextByte = sourceStream[encodedIndex + 1];
destStream[encodedIndex] = ETX; // The next byte is a DLE character that was escaped by another
++encodedIndex; // DLE character, so we can write it to the destination stream.
} if (nextByte == DLE_CHAR) {
*encodedLen = encodedIndex; destStream[decodedIndex] = nextByte;
return RETURN_OK; }
} else { else {
return RETURN_FAILED; /* 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 preven 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 DECODING_ERROR;
}
}
++encodedIndex;
}
else {
destStream[decodedIndex] = sourceStream[encodedIndex];
}
++encodedIndex;
++decodedIndex;
}
if (sourceStream[encodedIndex] != ETX_CHAR) {
*readLen = ++encodedIndex;
return DECODING_ERROR;
}
else {
*readLen = ++encodedIndex;
*decodedLen = decodedIndex;
return RETURN_OK;
}
}

104
globalfunctions/DleEncoder.h
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@ -1,25 +1,79 @@
#ifndef DLEENCODER_H_ #ifndef FRAMEWORK_GLOBALFUNCTIONS_DLEENCODER_H_
#define DLEENCODER_H_ #define FRAMEWORK_GLOBALFUNCTIONS_DLEENCODER_H_
#include "../returnvalues/HasReturnvaluesIF.h" #include "../returnvalues/HasReturnvaluesIF.h"
#include <cstddef>
class DleEncoder: public HasReturnvaluesIF {
private: /**
DleEncoder(); * @brief This DLE Encoder (Data Link Encoder) can be used to encode and
virtual ~DleEncoder(); * decode arbitrary data with ASCII control characters
* @details
public: * List of control codes:
static const uint8_t STX = 0x02; * https://en.wikipedia.org/wiki/C0_and_C1_control_codes
static const uint8_t ETX = 0x03; *
static const uint8_t DLE = 0x10; * This encoder can be used to achieve a basic transport layer when using
* char based transmission systems.
static ReturnValue_t decode(const uint8_t *sourceStream, * The passed source strean is converted into a encoded stream by adding
uint32_t sourceStreamLen, uint32_t *readLen, uint8_t *destStream, * a STX marker at the start of the stream and an ETX marker at the end of
uint32_t maxDestStreamlen, uint32_t *decodedLen); * the stream. Any STX, ETX, DLE and CR occurences in the source stream are
* escaped by a DLE character. The encoder also replaces escaped control chars
static ReturnValue_t encode(const uint8_t *sourceStream, uint32_t sourceLen, * by another char, so STX, ETX and CR should not appear anywhere in the actual
uint8_t *destStream, uint32_t maxDestLen, uint32_t *encodedLen, * encoded data stream.
bool addStxEtx = true); *
}; * When using a strictly char based reception of packets enoded with DLE,
* STX can be used to notify a reader that actual data will start to arrive
#endif /* DLEENCODER_H_ */ * while ETX can be used to notify the reader that the data has ended.
*/
class DleEncoder: public HasReturnvaluesIF {
private:
DleEncoder();
virtual ~DleEncoder();
public:
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 occurences
//! 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 decoing 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,
size_t sourceStreamLen, size_t *readLen, uint8_t *destStream,
size_t maxDestStreamlen, size_t *decodedLen);
};
#endif /* FRAMEWORK_GLOBALFUNCTIONS_DLEENCODER_H_ */