src/qcbor_decode.c

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/*==============================================================================
 Modifications beyond the version released on CAF are under the MIT license:
 
 Copyright 2018 Laurence Lundblade
 
 Permission is hereby granted, free of charge, to any person obtaining
 a copy of this software and associated documentation files (the
 "Software"), to deal in the Software without restriction, including
 without limitation the rights to use, copy, modify, merge, publish,
 distribute, sublicense, and/or sell copies of the Software, and to
 permit persons to whom the Software is furnished to do so, subject to
 the following conditions:
 
 The above copyright notice and this permission notice shall be included
 in all copies or substantial portions of the Software.
 
 THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
 EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
 MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
 NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
 BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
 ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
 CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 SOFTWARE.
 ==============================================================================*/

/*===================================================================================
 FILE:  qcbor_decode.c
 
 DESCRIPTION:  This file contains the implementation of QCBOR.
 
 EDIT HISTORY FOR FILE:
 
 This section contains comments describing changes made to the module.
 Notice that changes are listed in reverse chronological order.
 
 when               who             what, where, why
 --------           ----            ---------------------------------------------------
 02/04/17           llundbla        Work on CPUs that don's require pointer alignment
                                    by making use of changes in UsefulBuf
 03/01/17           llundbla        More data types; decoding improvements and fixes
 11/13/16           llundbla        Integrate most TZ changes back into github version.
 09/30/16           gkanike         Porting to TZ.
 03/15/16           llundbla        Initial Version.
 
 =====================================================================================*/

#include "qcbor.h"
#include "ieee754.h"



/*
 Collection of functions to track the map/array nesting for decoding
 */

inline static int IsMapOrArray(uint8_t uDataType)
{
   return uDataType == QCBOR_TYPE_MAP || uDataType == QCBOR_TYPE_ARRAY;
}

inline static int DecodeNesting_IsNested(const QCBORDecodeNesting *pNesting)
{
   return pNesting->pCurrent != &(pNesting->pMapsAndArrays[0]);
}

inline static int DecodeNesting_IsIndefiniteLength(const QCBORDecodeNesting *pNesting)
{
   return pNesting->pCurrent->uCount == UINT16_MAX;
}

inline static uint8_t DecodeNesting_GetLevel(QCBORDecodeNesting *pNesting)
{
   return pNesting->pCurrent - &(pNesting->pMapsAndArrays[0]);
}

inline static int DecodeNesting_TypeIsMap(const QCBORDecodeNesting *pNesting)
{
   if(!DecodeNesting_IsNested(pNesting)) {
      return 0;
   }
   
   return CBOR_MAJOR_TYPE_MAP == pNesting->pCurrent->uMajorType;
}

// Process a break. This will either ascend the nesting or error out
inline static int DecodeNesting_BreakAscend(QCBORDecodeNesting *pNesting)
{
   // breaks must always occur when there is nesting
   if(!DecodeNesting_IsNested(pNesting)) {
      return QCBOR_ERR_BAD_BREAK;
   }
   
   // breaks can only occur when the map/array is indefinite length
   if(!DecodeNesting_IsIndefiniteLength(pNesting)) {
      return QCBOR_ERR_BAD_BREAK;
   }
   
   // if all OK, the break reduces the level of nesting
   pNesting->pCurrent--;
   
   return QCBOR_SUCCESS;
}

// Called on every single item except breaks including the opening of a map/array
inline static void DecodeNesting_DecrementCount(QCBORDecodeNesting *pNesting)
{
   if(!DecodeNesting_IsNested(pNesting)) {
      // at top level where there is no tracking
      return;
   }
   
   if(DecodeNesting_IsIndefiniteLength(pNesting)) {
      // There is no count for indefinite length arrays/maps
      return;
   }
   
   // Decrement the count of items in this array/map
   pNesting->pCurrent->uCount--;

   // Pop up nesting levels if the counts at the levels are zero
   while(DecodeNesting_IsNested(pNesting) && 0 == pNesting->pCurrent->uCount) {
      pNesting->pCurrent--;
      if(!DecodeNesting_IsIndefiniteLength(pNesting)) {
         pNesting->pCurrent->uCount--;
      }
   }
}

// Called on every map/array
inline static int DecodeNesting_Descend(QCBORDecodeNesting *pNesting, QCBORItem *pItem)
{
   int nReturn = QCBOR_SUCCESS;
   
   if(pItem->val.uCount == 0) {
      // Nothing to do for empty definite lenth arrays. They are just are
      // effectively the same as an item that is not a map or array
      goto Done;
      // Empty indefinite length maps and arrays are handled elsewhere; TODO: where?
   }
   
   // Error out if arrays is too long to handle
   if(pItem->val.uCount != UINT16_MAX && pItem->val.uCount > QCBOR_MAX_ITEMS_IN_ARRAY) {
      nReturn = QCBOR_ERR_ARRAY_TOO_LONG;
      goto Done;
   }
   
   // Error out if nesting is too deep
   if(pNesting->pCurrent >= &(pNesting->pMapsAndArrays[QCBOR_MAX_ARRAY_NESTING])) {
      nReturn = QCBOR_ERR_ARRAY_NESTING_TOO_DEEP;
      goto Done;
   }
   
   // The actual descend
   pNesting->pCurrent++;
   
   // Record a few details for this nesting level
   pNesting->pCurrent->uMajorType = pItem->uDataType;
   pNesting->pCurrent->uCount     = pItem->val.uCount;
   
Done:
   return nReturn;;
}

inline static void DecodeNesting_Init(QCBORDecodeNesting *pNesting)
{
   pNesting->pCurrent = &(pNesting->pMapsAndArrays[0]);
}




/*
 Public function, see header file
 */
void QCBORDecode_Init(QCBORDecodeContext *me, UsefulBufC EncodedCBOR, int8_t nDecodeMode)
{
   memset(me, 0, sizeof(QCBORDecodeContext));
   UsefulInputBuf_Init(&(me->InBuf), EncodedCBOR);
   // Don't bother with error check on decode mode. If a bad value is passed it will just act as
   // if the default normal mode of 0 was set.
   me->uDecodeMode = nDecodeMode;
   DecodeNesting_Init(&(me->nesting));
}


/*
 Public function, see header file
 */
void QCBORDecode_SetUpAllocator(QCBORDecodeContext *pCtx, const QCBORStringAllocator *pAllocator)
{
    pCtx->pStringAllocator = (void *)pAllocator;
}


/*
 This decodes the fundamental part of a CBOR data item, the type and number
 
 This is the Counterpart to InsertEncodedTypeAndNumber().
 
 This does the network->host byte order conversion. The conversion here
 also results in the conversion for floats in addition to that for
 lengths, tags and integer values.
 
 This returns:
   pnMajorType -- the major type for the item
   puNumber -- the "number" which is used a the value for integers, tags and floats and length for strings and arrays
   puAdditionalInfo -- Pass this along to know what kind of float or if length is indefinite
 
 */
inline static int DecodeTypeAndNumber(UsefulInputBuf *pUInBuf, int *pnMajorType, uint64_t *puNumber, uint8_t *puAdditionalInfo)
{
   int nReturn;
   
   // Get the initial byte that every CBOR data item has
   const uint8_t InitialByte = UsefulInputBuf_GetByte(pUInBuf);
   
   // Break down the initial byte
   const uint8_t uTmpMajorType   = InitialByte >> 5;
   const uint8_t uAdditionalInfo = InitialByte & 0x1f;
   
   // Get the integer that follows the major type. Do not know if this is a length, value, float or tag at this point
   // Also convert from network byte order.
   uint64_t uTmpValue;
   switch(uAdditionalInfo) {
         
      case LEN_IS_ONE_BYTE:
         uTmpValue = UsefulInputBuf_GetByte(pUInBuf);
         break;
         
      case LEN_IS_TWO_BYTES:
         uTmpValue = UsefulInputBuf_GetUint16(pUInBuf);
         break;
         
      case LEN_IS_FOUR_BYTES:
         uTmpValue = UsefulInputBuf_GetUint32(pUInBuf);
         break;
         
      case LEN_IS_EIGHT_BYTES:
         uTmpValue = UsefulInputBuf_GetUint64(pUInBuf);
         break;
         
      case ADDINFO_RESERVED1: // reserved by CBOR spec
      case ADDINFO_RESERVED2: // reserved by CBOR spec
      case ADDINFO_RESERVED3: // reserved by CBOR spec
         nReturn = QCBOR_ERR_UNSUPPORTED;
         goto Done;

      case LEN_IS_INDEFINITE:
         // Fall through to see what happens: TODO: check this.
         
      default:
         // This is when the "number" is in the additional info
         uTmpValue = uAdditionalInfo;
         break;
   }
   
   // If any of the UsefulInputBuf_Get calls fail we will get here with uTmpValue as 0.
   // There is no harm in this. This following check takes care of catching all of
   // these errors. 
   
   if(UsefulInputBuf_GetError(pUInBuf)) {
      nReturn = QCBOR_ERR_HIT_END;
      goto Done;
   }
   
   // All successful if we got here.
   nReturn           = QCBOR_SUCCESS;
   *pnMajorType      = uTmpMajorType;
   *puNumber         = uTmpValue;
   *puAdditionalInfo = uAdditionalInfo;
   
Done:
   return nReturn;
}


/*
 CBOR doesn't explicitly specify two's compliment for integers but all CPUs
 use it these days and the test vectors in the RFC are so. All integers in the CBOR
 structure are positive and the major type indicates positive or negative.
 CBOR can express positive integers up to 2^x - 1 where x is the number of bits
 and negative integers down to 2^x.  Note that negative numbers can be one
 more away from zero than positive.
 Stdint, as far as I can tell, uses two's compliment to represent
 negative integers.
 
 See http://www.unix.org/whitepapers/64bit.html for reasons int isn't
 used here in any way including in the interface
 */
inline static int DecodeInteger(int nMajorType, uint64_t uNumber, QCBORItem *pDecodedItem)
{
   int nReturn = QCBOR_SUCCESS;
   
   if(nMajorType == CBOR_MAJOR_TYPE_POSITIVE_INT) {
      if (uNumber <= INT64_MAX) {
         pDecodedItem->val.int64 = (int64_t)uNumber;
         pDecodedItem->uDataType = QCBOR_TYPE_INT64;
         
      } else {
         pDecodedItem->val.uint64 = uNumber;
         pDecodedItem->uDataType  = QCBOR_TYPE_UINT64;
         
      }
   } else {
      if(uNumber <= INT64_MAX) {
         pDecodedItem->val.int64 = -uNumber-1;
         pDecodedItem->uDataType = QCBOR_TYPE_INT64;
         
      } else {
         // C can't represent a negative integer in this range
         // so it is an error.  todo -- test this condition
         nReturn = QCBOR_ERR_INT_OVERFLOW;
      }
   }
   
   return nReturn;
}

// Make sure #define value line up as DecodeSimple counts on this.
#if QCBOR_TYPE_FALSE != CBOR_SIMPLEV_FALSE
#error QCBOR_TYPE_FALSE macro value wrong
#endif

#if QCBOR_TYPE_TRUE != CBOR_SIMPLEV_TRUE
#error QCBOR_TYPE_TRUE macro value wrong
#endif

#if QCBOR_TYPE_NULL != CBOR_SIMPLEV_NULL
#error QCBOR_TYPE_NULL macro value wrong
#endif

#if QCBOR_TYPE_UNDEF != CBOR_SIMPLEV_UNDEF
#error QCBOR_TYPE_UNDEF macro value wrong
#endif

#if QCBOR_TYPE_BREAK != CBOR_SIMPLE_BREAK
#error QCBOR_TYPE_BREAK macro value wrong
#endif

#if QCBOR_TYPE_DOUBLE != DOUBLE_PREC_FLOAT
#error QCBOR_TYPE_DOUBLE macro value wrong
#endif

#if QCBOR_TYPE_FLOAT != SINGLE_PREC_FLOAT
#error QCBOR_TYPE_FLOAT macro value wrong
#endif

/*
 Decode true, false, floats, break...
 */

inline static int DecodeSimple(uint8_t uAdditionalInfo, uint64_t uNumber, QCBORItem *pDecodedItem)
{
   int nReturn = QCBOR_SUCCESS;
   
   // uAdditionalInfo is 5 bits from the initial byte
   // compile time checks above make sure uAdditionalInfo values line up with uDataType values
   pDecodedItem->uDataType = uAdditionalInfo;
   
   switch(uAdditionalInfo) {
      case ADDINFO_RESERVED1:  // 28
      case ADDINFO_RESERVED2:  // 29
      case ADDINFO_RESERVED3:  // 30
         nReturn = QCBOR_ERR_UNSUPPORTED;
         break;
           
      case HALF_PREC_FLOAT:
         pDecodedItem->val.fnum  = IEEE754_HalfToFloat((uint16_t)uNumber);
         pDecodedItem->uDataType = QCBOR_TYPE_FLOAT;
         break;
      case SINGLE_PREC_FLOAT:
         pDecodedItem->val.fnum = UsefulBufUtil_CopyUint32ToFloat((uint32_t)uNumber);
         break;
      case DOUBLE_PREC_FLOAT:
         pDecodedItem->val.dfnum = UsefulBufUtil_CopyUint64ToDouble(uNumber);
         break;
         
      case CBOR_SIMPLEV_FALSE: // 20
      case CBOR_SIMPLEV_TRUE:  // 21
      case CBOR_SIMPLEV_NULL:  // 22
      case CBOR_SIMPLEV_UNDEF: // 23
      case CBOR_SIMPLE_BREAK:  // 31
         break; // nothing to do
         
      case CBOR_SIMPLEV_ONEBYTE: // 24
         if(uNumber <= CBOR_SIMPLE_BREAK) {
            // This takes out f8 00 ... f8 1f which should be encoded as e0 … f7
            nReturn = QCBOR_ERR_INVALID_CBOR;
            goto Done;
         }
         // fall through intentionally
         
      default: // 0-19
         pDecodedItem->uDataType   = QCBOR_TYPE_UKNOWN_SIMPLE;
         // DecodeTypeAndNumber will make uNumber equal to uAdditionalInfo when uAdditionalInfo is < 24
         // This cast is safe because the 2, 4 and 8 byte lengths of uNumber are in the double/float cases above
         pDecodedItem->val.uSimple = (uint8_t)uNumber;
         break;
   }
   
Done:
   return nReturn;
}



/*
 Decode text and byte strings
 */
inline static int DecodeBytes(QCBORStringAllocator *pAlloc, int nMajorType, uint64_t uNumber, UsefulInputBuf *pUInBuf, QCBORItem *pDecodedItem)
{
    UsefulBufC Bytes = UsefulInputBuf_GetUsefulBuf(pUInBuf, uNumber);
   
   int nReturn = QCBOR_ERR_HIT_END;
   
   if(!UsefulBuf_IsNULLC(Bytes)) {
      if(pAlloc) {
         UsefulBuf NewMem = pAlloc->fAllocate(pAlloc->pAllocaterContext, NULL, uNumber);
         if(UsefulBuf_IsNULL(NewMem)) {
            pDecodedItem->val.string = UsefulBuf_Copy(NewMem, Bytes);
         } else {
            // TODO: failure
         }
      } else {
         pDecodedItem->val.string = Bytes;
      }
      pDecodedItem->uDataType  = (nMajorType == CBOR_MAJOR_TYPE_BYTE_STRING) ? QCBOR_TYPE_BYTE_STRING : QCBOR_TYPE_TEXT_STRING;
      nReturn = QCBOR_SUCCESS;
   }
   
   return nReturn;
}


/*
 Mostly just assign the right data type for the date string.
 */
inline static int DecodeDateString(QCBORItem Item, QCBORItem *pDecodedItem)
{
   if(Item.uDataType != QCBOR_TYPE_TEXT_STRING) {
      return QCBOR_ERR_BAD_OPT_TAG;
   }
   pDecodedItem->val.dateString = Item.val.string;
   pDecodedItem->uDataType = QCBOR_TYPE_DATE_STRING;
   pDecodedItem->uTagBits = Item.uTagBits;
   pDecodedItem->uTag = Item.uTag;
   return QCBOR_SUCCESS;
}


/*
 Mostly just assign the right data type for the bignum.
 */
inline static int DecodeBigNum(QCBORItem Item, QCBORItem *pDecodedItem, uint64_t uTagFlags)
{
   if(Item.uDataType != QCBOR_TYPE_BYTE_STRING) {
      return QCBOR_ERR_BAD_OPT_TAG;
   }
   pDecodedItem->val.bigNum     = Item.val.string;
   pDecodedItem->uDataType      = uTagFlags & QCBOR_TAGFLAG_POS_BIGNUM ? QCBOR_TYPE_POSBIGNUM : QCBOR_TYPE_NEGBIGNUM;
   pDecodedItem->uTagBits       = Item.uTagBits;
   pDecodedItem->uTag           = Item.uTag;
   return QCBOR_SUCCESS;
}


/*
 The epoch formatted date. Turns lots of different forms of encoding date into uniform one
 */
static int DecodeDateEpoch(QCBORItem Item, QCBORItem *pDecodedItem)
{
   int nReturn = QCBOR_SUCCESS;
   
   pDecodedItem->uTagBits                       = Item.uTagBits;
   pDecodedItem->uTag                           = Item.uTag;
   pDecodedItem->uDataType                      = QCBOR_TYPE_DATE_EPOCH;
   pDecodedItem->val.epochDate.fSecondsFraction = 0;
   
   switch (Item.uDataType) {
         
      case QCBOR_TYPE_INT64:
         pDecodedItem->val.epochDate.nSeconds = Item.val.int64;
         break;
         
      case QCBOR_TYPE_UINT64:
         if(Item.val.uint64 > INT64_MAX) {
            nReturn = QCBOR_ERR_DATE_OVERFLOW; 
            goto Done;
         }
         pDecodedItem->val.epochDate.nSeconds = Item.val.uint64;
         break;
         
      case QCBOR_TYPE_FLOAT:
         // TODO: can we save code by widening a float to a double here? Then drop into double-handling code
         if(Item.val.fnum > INT64_MAX) {
            nReturn = QCBOR_ERR_DATE_OVERFLOW;
            goto Done;
         }
         pDecodedItem->val.epochDate.nSeconds = Item.val.fnum;
         pDecodedItem->val.epochDate.fSecondsFraction = Item.val.fnum - pDecodedItem->val.epochDate.nSeconds;
         break;

      case QCBOR_TYPE_DOUBLE:
         if(Item.val.dfnum > INT64_MAX) {
            nReturn = QCBOR_ERR_DATE_OVERFLOW;
            goto Done;
         }
         pDecodedItem->val.epochDate.nSeconds = Item.val.dfnum;
         pDecodedItem->val.epochDate.fSecondsFraction = Item.val.dfnum - pDecodedItem->val.epochDate.nSeconds;
         break;
         
      default:
         nReturn = QCBOR_ERR_BAD_OPT_TAG;
   }
   
Done:
   return nReturn;
}




// Make sure the constants align as this is assumed by the GetAnItem() implementation
#if QCBOR_TYPE_ARRAY != CBOR_MAJOR_TYPE_ARRAY
#error QCBOR_TYPE_ARRAY value not lined up with major type
#endif
#if QCBOR_TYPE_MAP != CBOR_MAJOR_TYPE_MAP
#error QCBOR_TYPE_MAP value not lined up with major type
#endif

/*
 This gets a single data item and decodes it including preceding optional tagging. This does not
 deal with arrays and maps and nesting except to decode the data item introducing them. Arrays and
 maps are handled at the next level up in GetNext().
 
 Errors detected here include: an array that is too long to decode, hit end of buffer unexpectedly,
    a few forms of invalid encoded CBOR
 */

static int GetNext_Item(UsefulInputBuf *pUInBuf, QCBORItem *pDecodedItem, QCBORStringAllocator *pAlloc)
{
   int nReturn;
   
   // Get the major type and the number. Number could be length of more bytes or the value depending on the major type
   // nAdditionalInfo is an encoding of the length of the uNumber and is needed to decode floats and doubles
   int      uMajorType;
   uint64_t uNumber;
   uint8_t  uAdditionalInfo;
   
   nReturn = DecodeTypeAndNumber(pUInBuf, &uMajorType, &uNumber, &uAdditionalInfo);
   
   // Error out here if we got into trouble on the type and number.
   // The code after this will not work if the type and number is not good.
   if(nReturn)
      goto Done;
   
   pDecodedItem->uTagBits = 0;
   pDecodedItem->uTag     = 0;
   pDecodedItem->uDataAlloc = 0;
   
   // At this point the major type and the value are valid. We've got the type and the number that
   // starts every CBOR data item.
   switch (uMajorType) {
      case CBOR_MAJOR_TYPE_POSITIVE_INT: // Major type 0
      case CBOR_MAJOR_TYPE_NEGATIVE_INT: // Major type 1
         nReturn = DecodeInteger(uMajorType, uNumber, pDecodedItem);
         break;
         
      case CBOR_MAJOR_TYPE_BYTE_STRING: // Major type 2
      case CBOR_MAJOR_TYPE_TEXT_STRING: // Major type 3
         if(uAdditionalInfo == LEN_IS_INDEFINITE) {
            pDecodedItem->uDataType  = (uMajorType == CBOR_MAJOR_TYPE_BYTE_STRING) ? QCBOR_TYPE_BYTE_STRING : QCBOR_TYPE_TEXT_STRING;
            pDecodedItem->val.string = (UsefulBufC){NULL, SIZE_MAX}; // TODO: SIZE_MAX this is OK, right?
         } else {
            nReturn = DecodeBytes(pAlloc, uMajorType, uNumber, pUInBuf, pDecodedItem);
         }
         break;
         
      case CBOR_MAJOR_TYPE_ARRAY: // Major type 4
      case CBOR_MAJOR_TYPE_MAP:   // Major type 5
         // Record the number of items in the array or map
         if(uNumber > QCBOR_MAX_ITEMS_IN_ARRAY) {
            nReturn = QCBOR_ERR_ARRAY_TOO_LONG;
            goto Done;
         }
         if(uAdditionalInfo == LEN_IS_INDEFINITE) {
            pDecodedItem->val.uCount = UINT16_MAX; // Indicate indefinite length; TODO: a better way?
         } else {
            pDecodedItem->val.uCount = (uint16_t)uNumber; // type conversion OK because of check above
         }
         pDecodedItem->uDataType  = uMajorType; // C preproc #if above makes sure constants align
         break;
         
      case CBOR_MAJOR_TYPE_OPTIONAL: // Major type 6, optional prepended tags
         pDecodedItem->uTag      = uNumber;
         pDecodedItem->uDataType = QCBOR_TYPE_OPTTAG;
         break;
         
      case CBOR_MAJOR_TYPE_SIMPLE: // Major type 7, float, double, true, false, null...
         nReturn = DecodeSimple(uAdditionalInfo, uNumber, pDecodedItem);
         break;
         
      default: // Should never happen because DecodeTypeAndNumber() should never return > 7
         nReturn = QCBOR_ERR_UNSUPPORTED;
         break;
   }
   
Done:
   return nReturn;
}



/*
 This layer deals with indefinite length strings. It pulls all the
 individual segment items together into one QCBORItem
 */
static int GetNext_FullItem(QCBORDecodeContext *me, QCBORItem *pDecodedItem)
{
   int nReturn;
   QCBORStringAllocator *pAlloc = (QCBORStringAllocator *)me->pStringAllocator;
   
   nReturn = GetNext_Item(&(me->InBuf), pDecodedItem, me->bStringAllocateAll ? pAlloc: NULL);
   if(nReturn) {
      goto Done;
   }
   
   // To reduce code size by removing support for indefinite length strings, the
   // code in this function from here down can be eliminated. Run tests to be sure
   // all is OK if you remove this.
   
   // Only do indefinite length processing on strings
   if(pDecodedItem->uDataType != QCBOR_TYPE_BYTE_STRING && pDecodedItem->uDataType != QCBOR_TYPE_TEXT_STRING) {
      goto Done; // no need to do any work here on non-string types
   }
   
   // Is this a string with an indefinite length?
   if(pDecodedItem->val.string.len != SIZE_MAX) { // TODO: is this right? Is there a better way to mark this?
      goto Done; // length is not indefinite, so no work to do here
   }
   
   // can't do indefinite length strings without a string allocator
   if(pAlloc == NULL) {
      nReturn = QCBOR_ERR_NO_STRING_ALLOCATOR;
      goto Done;
   }
   
   // There is an indefinite length string to work on...
   // Track which type of string it is
   const uint8_t uStringType = pDecodedItem->uDataType;
   UsefulBufC FullString = NULLUsefulBufC;
   
   // Loop getting segments of indefinite string
   for(;;) {
      // Get item for next segment
      QCBORItem Item;
      nReturn = GetNext_Item(&(me->InBuf), &Item, NULL); // Never alloc segments of indefinite length strings
      if(nReturn) {
         // Error getting the next segment
         break;
      }
      
      // See if it is marker at end of indefinite length string
      if(Item.uDataType == QCBOR_TYPE_BREAK) {
         // String is complete
         pDecodedItem->val.string = FullString;
         pDecodedItem->uDataAlloc = 1;
         break;
      }
      
      // Match data type of segment to type at beginning
      if(Item.uDataType != uStringType) {
         nReturn = QCBOR_ERR_INDEFINITE_STRING_SEG;
         break;
      }
      
      // Expand the buffer so it can fit
      UsefulBuf NewMem = (*pAlloc->fAllocate)(pAlloc->pAllocaterContext, (void *)FullString.ptr, FullString.len + Item.val.string.len);
      if(UsefulBuf_IsNULL(NewMem)) {
         nReturn = QCBOR_ERR_STRING_ALLOC;
         break;
      }
      
      // Copy data to the end of it.
      FullString = UsefulBuf_CopyOffset(NewMem, FullString.len, Item.val.string);
   }
   
Done:
   if(pAlloc && nReturn && FullString.ptr) {
      // Getting item failed, clean up the allocated memory
      (pAlloc->fFree)(pAlloc->pAllocaterContext, (void *)FullString.ptr); // TODO unconst construct
   }
   
   return nReturn;
}


/*
 Returns an error if there was something wrong with the optional item or it couldn't
 be handled.
 */
static int GetNext_TaggedItem(QCBORDecodeContext *me, QCBORItem *pDecodedItem)
{
   int nReturn;
   
   // TODO: optimize loop below so there is only one call to GetNext_FullItem
   nReturn = GetNext_FullItem(me, pDecodedItem);
   if(nReturn) {
      goto Done;
   }
   
   if(pDecodedItem->uDataType != QCBOR_TYPE_OPTTAG) {
      goto Done;
   }
   
   uint64_t uTagFlags = 0; // accumulate the tags in the form of flags
   uint64_t uTagToProcess = pDecodedItem->uTag; // First process tag passed in
   
   QCBORItem Item;
   
   do {
      if(uTagToProcess < 63) { // 63 is the number of bits in a uint64 - 1
         uTagFlags |= 0x01LL << uTagToProcess;
      } else if(uTagToProcess == CBOR_TAG_CBOR_MAGIC) {
         uTagFlags |= QCBOR_TAGFLAG_CBOR_MAGIC;
      }
      /* This code ignores the all but the first tag of value
       greater than 63. Ignoring tags that are not understoof
       is allowed by the standard. Multiple tags are
       presumably rare. */
      
      nReturn = GetNext_FullItem(me, &Item);
      if(nReturn) {
         // Bail out of the whole item fetch on any sort of error here
         goto Done;
      }
      
      if(Item.uDataType != QCBOR_TYPE_OPTTAG) {
         break;
      }
      
      uTagToProcess = Item.uTag;
   } while (1);
   
   
   /*
    CBOR allows multiple tags on a data item. It also defines
    a number of standard tag values, most of which are
    less than 64.  This code can deal with multiple tag
    values that are less than 64 and the last tag of multiple
    if the value is more than 64. Or said another way
    if there is one tag with a value >64 this code works.
    
    The assumption is that multiple tag values > 64 are rare.
    
    At this point in this code. uTagFlags has all the flags
    < 64 and uTagToProcess has the last tag.
    
    Does this deal with multiple tags on an item we process?
    */
   
   Item.uTagBits = uTagFlags;
   Item.uTag = uTagToProcess;
   
   switch(uTagFlags & (QCBOR_TAGFLAG_DATE_STRING | QCBOR_TAGFLAG_DATE_EPOCH | QCBOR_TAGFLAG_POS_BIGNUM |QCBOR_TAGFLAG_NEG_BIGNUM)) {
      case 0:
         // No tags we know about. Pass them up
         *pDecodedItem = Item;
         break;
         
      case QCBOR_TAGFLAG_DATE_STRING:
         nReturn = DecodeDateString(Item, pDecodedItem);
         break;
         
      case QCBOR_TAGFLAG_DATE_EPOCH:
         nReturn = DecodeDateEpoch(Item, pDecodedItem);
         break;
         
      case QCBOR_TAGFLAG_POS_BIGNUM:
      case QCBOR_TAGFLAG_NEG_BIGNUM:
         nReturn = DecodeBigNum(Item, pDecodedItem, uTagFlags);
         break;
         
      default:
         // Encountering some mixed up CBOR like something that
         // is tagged as both a string and integer date.
         nReturn = QCBOR_ERR_BAD_OPT_TAG ;
   }
   
Done:
   return nReturn;
}


/*
 This layer takes care of map entries. It combines the label and data items into one QCBORItem.
 */
static inline int GetNext_MapEntry(QCBORDecodeContext *me, QCBORItem *pDecodedItem)
{
   int nReturn = GetNext_TaggedItem(me, pDecodedItem);
   if(nReturn)
      goto Done;
   
   if(pDecodedItem->uDataType == QCBOR_TYPE_BREAK) {
      goto Done;
   }
   
   // If in a map and the right decoding mode, get the label
   if(DecodeNesting_TypeIsMap(&(me->nesting)) && me->uDecodeMode != QCBOR_DECODE_MODE_MAP_AS_ARRAY) {
      // In a map and caller wants maps decoded, not treated as arrays
      
      // Get the next item which will be the real data; Item will be the label
      QCBORItem LabelItem = *pDecodedItem;
      nReturn = GetNext_TaggedItem(me, pDecodedItem);
      if(nReturn)
         goto Done;
      
      if(LabelItem.uDataType == QCBOR_TYPE_TEXT_STRING) {
         // strings are always good labels
         pDecodedItem->label.string = LabelItem.val.string;
         pDecodedItem->uLabelType = QCBOR_TYPE_TEXT_STRING;
      } else if (QCBOR_DECODE_MODE_MAP_STRINGS_ONLY == me->uDecodeMode) {
         // It's not a string and we only want strings, probably for easy translation to JSON
         nReturn = QCBOR_ERR_MAP_LABEL_TYPE;
         goto Done;
      } else if(LabelItem.uDataType == QCBOR_TYPE_INT64) {
         pDecodedItem->label.int64 = LabelItem.val.int64;
         pDecodedItem->uLabelType = QCBOR_TYPE_INT64;
      } else if(LabelItem.uDataType == QCBOR_TYPE_UINT64) {
         pDecodedItem->label.uint64 = LabelItem.val.uint64;
         pDecodedItem->uLabelType = QCBOR_TYPE_UINT64;
      } else if(LabelItem.uDataType == QCBOR_TYPE_BYTE_STRING) {
         pDecodedItem->label.string = LabelItem.val.string;
         pDecodedItem->uLabelAlloc = LabelItem.uDataAlloc;
         pDecodedItem->uLabelType = QCBOR_TYPE_BYTE_STRING;
      } else {
         // label is not an int or a string. It is an arrray
         // or a float or such and this implementation doesn't handle that.
         nReturn = QCBOR_ERR_MAP_LABEL_TYPE ;
         goto Done;
      }
   }
   
Done:
   return nReturn;
}


/*
 Public function, see header qcbor.h file
 */
int QCBORDecode_GetNext(QCBORDecodeContext *me, QCBORItem *pDecodedItem)
{
   int nReturn;
   
   nReturn = GetNext_MapEntry(me, pDecodedItem);
   if(nReturn) {
      goto Done;
   }
   
   if(pDecodedItem->uDataType == QCBOR_TYPE_BREAK) {
      // Breaks are always processed at the end of this function
      // They should never show up here.
      nReturn = QCBOR_ERR_BAD_BREAK;
      goto Done;
   }
   
   // Record the nesting level for this data item before processing any of
   // decrementing and descending
   pDecodedItem->uNestingLevel = DecodeNesting_GetLevel(&(me->nesting));
   
   // Process the item just received for descent or decrement, and
   // ascent if decrements are enough to close out a definite length array/map
   if(IsMapOrArray(pDecodedItem->uDataType)) {
      // If the new item is array or map, the nesting level descends
      nReturn = DecodeNesting_Descend(&(me->nesting), pDecodedItem);
      // Maps and arrays do count in as items in the map/array that encloses
      // them so a decrement needs to be done for them too, but that is done
      // only when all the items in them have been processed, not when they
      // are opened.
   } else {
      // Decrement the count of items in the enclosing map/array
      // If the count in the enclosing map/array goes to zero, that
      // triggers a decrement in the map/array above that and
      // an ascend in nesting level.
      DecodeNesting_DecrementCount(&(me->nesting));
   }
   if(nReturn) {
      goto Done;
   }
   
   // For indefinite length maps/arrays, looking at any and
   // all breaks that might terminate them. The equivalent
   // for definite length maps/arrays happens in
   // DecodeNesting_DecrementCount().
   if(DecodeNesting_IsNested(&(me->nesting)) && DecodeNesting_IsIndefiniteLength(&(me->nesting))) {
      while(UsefulInputBuf_BytesUnconsumed(&(me->InBuf))) {
         // Peek forward one item to see if it is a break.
         QCBORItem Peek;
         size_t uPeek = UsefulInputBuf_Tell(&(me->InBuf));
         nReturn = GetNext_Item(&(me->InBuf), &Peek, NULL);
         if(nReturn) {
            goto Done;
         }
         if(Peek.uDataType != QCBOR_TYPE_BREAK) {
            // It is not a break, rewind so it can be processed normally.
            UsefulInputBuf_Seek(&(me->InBuf), uPeek);
            break;
         }
         // It is a break. Ascend one nesting level.
         // The break consumed.
         nReturn = DecodeNesting_BreakAscend(&(me->nesting));
         if(nReturn) {
            // break occured outside of an indefinite length array/map
            goto Done;
         }
      }
   }
   
   // Tell the caller what level is next. This tells them what maps/arrays
   // were closed out and makes it possible for them to reconstruct
   // the tree with just the information returned by GetNext
   pDecodedItem->uNextNestLevel = DecodeNesting_GetLevel(&(me->nesting));
   
Done:
   return nReturn;
}


/*
 Decoding items is done in 5 layered functions, one calling the
 next one down. If a layer has no work to do for a particular item
 it returns quickly.
 
 - QCBORDecode_GetNext -- The top layer manages the beginnings and
 ends of maps and arrays. It tracks descending into and ascending
 out of maps/arrays. It processes all breaks that terminate
 maps and arrays.
 
 - GetNext_MapEntry -- This handles the combining of two
 items, the label and the data, that make up a map entry.
 It only does work on maps. It combines the label and data
 items into one labeled item.
 
 - GetNext_TaggedItem -- This handles the type 6 tagged items.
 It accumulates all the tags and combines them with the following
 non-tagged item. If the tagged item is something that is understood
 like a date, the decoding of that item is invoked.
 
 - GetNext_FullItem -- This assembles the sub items that make up
 an indefinte length string into one string item. It uses the
 string allocater to create contiguous space for the item. It
 processes all breaks that are part of indefinite length strings.
 
 - GetNext_Item -- This gets and decodes the most atomic
 item in CBOR, the thing with an initial byte containing
 the major type.
 
 */


/*
 Public function, see header qcbor.h file
 */
int QCBORDecode_Finish(QCBORDecodeContext *me)
{
   int nReturn = QCBOR_SUCCESS;
   
   // Error out if all the maps/arrays are not closed out
   if(DecodeNesting_IsNested(&(me->nesting))) {
      nReturn = QCBOR_ERR_ARRAY_OR_MAP_STILL_OPEN;
      goto Done;
   }

   // Error out if not all the bytes are consumed
   if(UsefulInputBuf_BytesUnconsumed(&(me->InBuf))) {
      nReturn = QCBOR_ERR_EXTRA_BYTES;
   }
   
Done:
   // Call the destructor for the string allocator if there is one.
   // Always called, even if there are errors; always have to clean up
   if(me->pStringAllocator) {
      QCBORStringAllocator *pAllocator = (QCBORStringAllocator *)me->pStringAllocator;
      if(pAllocator->fDestructor) {
         (pAllocator->fDestructor)(pAllocator->pAllocaterContext);
      }
   }
   
   return nReturn;
}



/*
 
 Use the 64-bit map. 48 8-bit tags built in, 1 16 bit tag, 15 64-bit tags can be assigned as of interest
 
 There is a tag map.

 
 */


/* 
 
Decoder errors handled in this file
 
 - Hit end of input before it was expected while decoding type and number QCBOR_ERR_HIT_END
  
 - negative integer that is too large for C QCBOR_ERR_INT_OVERFLOW
 
 - Hit end of input while decoding a text or byte string QCBOR_ERR_HIT_END
 
 - Encountered conflicting tags -- e.g., an item is tagged both a date string and an epoch date QCBOR_ERR_UNSUPPORTED
  
 - Encontered an array or mapp that has too many items QCBOR_ERR_ARRAY_TOO_LONG
 
 - Encountered array/map nesting that is too deep QCBOR_ERR_ARRAY_NESTING_TOO_DEEP
 
 - An epoch date > INT64_MAX or < INT64_MIN was encountered QCBOR_ERR_DATE_OVERFLOW
 
 - The type of a map label is not a string or int QCBOR_ERR_MAP_LABEL_TYPE
 
 - Hit end with arrays or maps still open -- QCBOR_ERR_EXTRA_BYTES
 
 */



typedef struct {
   QCBORStringAllocator  StringAllocator;
   uint8_t              *pStart;
   uint8_t              *pEnd;
   uint8_t              *pFree;
} MemPool;


/*
 Code Reviewers: THIS FUNCTION DOES POINTER MATH
 */
static UsefulBuf MemPool_Alloc(void *ctx, void *pMem, size_t uNewSize)
{
   MemPool *me = (MemPool *)ctx;
   void *pReturn = NULL;
   
   if(pMem) {
      // Realloc case
      // TODO: review this pointer math
      if((uint8_t *)pMem + uNewSize <= me->pEnd) {//} && (uint8_t *)pMem > me->pStart) {
         me->pFree = (uint8_t *)pMem + uNewSize;
         pReturn = pMem;
      }
   } else {
      // New chunk case
      if(me->pFree + uNewSize <= me->pEnd) {
         pReturn = me->pFree;
         me->pFree += uNewSize;
      }
   }
   
   return (UsefulBuf){pReturn, uNewSize};
}


static void MemPool_Free(void *ctx, void *pOldMem)
{
   MemPool *me = (MemPool *)ctx;
   me->pFree = pOldMem;
}


int QCBORDecode_SetMemPool(QCBORDecodeContext *me, UsefulBuf Pool, bool bAllStrings)
{
   if(Pool.len < sizeof(MemPool)+1) {
      return 1;
   }
   
   MemPool *pMP = (MemPool *)Pool.ptr;
   
   pMP->StringAllocator.fAllocate   = MemPool_Alloc;
   pMP->StringAllocator.fFree       = MemPool_Free;
   pMP->StringAllocator.fDestructor = NULL;
   
   pMP->pStart = (uint8_t *)Pool.ptr + sizeof(MemPool);
   pMP->pFree  = pMP->pStart;
   pMP->pEnd   = (uint8_t *)Pool.ptr + Pool.len;
   pMP->StringAllocator.pAllocaterContext = pMP;
   
   me->pStringAllocator = pMP;
   me->bStringAllocateAll = bAllStrings;
   
   return 0;
}