}
    }
  }else{
    nByte = 1;
    if( aBuf ) aBuf[0] = '\0';
  }

  *pnWrite += nByte;
  return SQLITE_OK;
}


/*
** This macro is used to calculate hash key values for data structures. In
** order to use this macro, the entire data structure must be represented
** as a series of unsigned integers. In order to calculate a hash-key value
** for a data structure represented as three such integers, the macro may
** then be used as follows:
................................................................................
    }else{
      p->aBuf = aNew;
      p->nAlloc = nNew;
    }
  }
  return (*pRc!=SQLITE_OK);
}
























/*
** This function is a no-op if *pRc is other than SQLITE_OK when it is 
** called. Otherwise, append a single byte to the buffer. 
**
** If an OOM condition is encountered, set *pRc to SQLITE_NOMEM before
** returning.
................................................................................
    }
    if( pIn->aData[pIn->iNext + nRead]==0 ) break;
    rc = sessionInputBuffer(pIn, nRead + 100);
  }
  if( pnByte ) *pnByte = nRead+1;
  return rc;
}

































/*
** The input pointer currently points to the second byte of a table-header.
** Specifically, to the following:
**
**   + number of columns in table (varint)
**   + array of PK flags (1 byte per column),
................................................................................
  }
  sqlite3_free(p->tblhdr.aBuf);
  sqlite3_free(p->in.buf.aBuf);
  sqlite3_free(p);
  return rc;
}

/*
** Invert a changeset object.
*/
int sqlite3changeset_invert(
  int nChangeset,                 /* Number of bytes in input */
  const void *pChangeset,         /* Input changeset */
  int *pnInverted,                /* OUT: Number of bytes in output changeset */
  void **ppInverted               /* OUT: Inverse of pChangeset */
){
  int rc = SQLITE_OK;             /* Return value */
  u8 *aOut;
  u8 *aIn;
  int i;
  SessionInput sInput;
  int nCol = 0;                   /* Number of cols in current table */
  u8 *abPK = 0;                   /* PK array for current table */
  sqlite3_value **apVal = 0;      /* Space for values for UPDATE inversion */
  SessionBuffer sPK = {0, 0, 0};  /* PK array for current table */




  /* Zero the output variables in case an error occurs. */

  *ppInverted = 0;
  *pnInverted = 0;
  if( nChangeset==0 ) return SQLITE_OK;

  /* Set up the input stream */
  memset(&sInput, 0, sizeof(SessionInput));
  sInput.nData = nChangeset;
  sInput.aData = (u8*)pChangeset;

  aOut = (u8 *)sqlite3_malloc(nChangeset);
  if( !aOut ) return SQLITE_NOMEM;
  aIn = (u8 *)pChangeset;

  i = 0;
  while( i<nChangeset ){
    u8 eType;


    if( (rc = sessionInputBuffer(&sInput, 2)) ) goto finished_invert;
    eType = sInput.aData[sInput.iNext];



    switch( eType ){
      case 'T': {
        /* A 'table' record consists of:
        **
        **   * A constant 'T' character,
        **   * Number of columns in said table (a varint),
        **   * An array of nCol bytes (sPK),
        **   * A nul-terminated table name.
        */
        int nByte;
        int nVarint;
        int iNext = sInput.iNext;
        sInput.iNext++;
        if( (rc = sessionChangesetBufferTblhdr(&sInput, &nByte)) ){
          goto finished_invert;
        }
        nVarint = sessionVarintGet(&sInput.aData[iNext+1], &nCol);
        sPK.nBuf = 0;
        sessionAppendBlob(&sPK, &sInput.aData[iNext+1+nVarint], nCol, &rc);
        if( rc ) goto finished_invert;
        sInput.iNext += nByte;
        memcpy(&aOut[i], &sInput.aData[iNext], nByte+1);
        i += nByte+1;
        sqlite3_free(apVal);
        apVal = 0;
        abPK = sPK.aBuf;
        break;
      }

      case SQLITE_INSERT:
      case SQLITE_DELETE: {
        int iStart;
        int nByte;
        sInput.iNext += 2;
        iStart = sInput.iNext;
        sessionReadRecord(&sInput, nCol, 0, 0);
        aOut[i] = (eType==SQLITE_DELETE ? SQLITE_INSERT : SQLITE_DELETE);
        aOut[i+1] = aIn[i+1];               /* indirect-flag */
        nByte = sInput.iNext - iStart;
        memcpy(&aOut[i+2], &sInput.aData[iStart], nByte);
        i += 2 + nByte;

        break;
      }

      case SQLITE_UPDATE: {
        int iCol;
        int nWrite = 0;

        if( 0==apVal ){
          apVal = (sqlite3_value **)sqlite3_malloc(sizeof(apVal[0])*nCol*2);
          if( 0==apVal ){
            rc = SQLITE_NOMEM;
            goto finished_invert;
          }
          memset(apVal, 0, sizeof(apVal[0])*nCol*2);
        }

        /* Write the header for the new UPDATE change. Same as the original. */
        aOut[i] = SQLITE_UPDATE;
        aOut[i+1] = sInput.aData[sInput.iNext+1];
        nWrite = 2;

        /* Read the old.* and new.* records for the update change. */
        sInput.iNext += 2;
        rc = sessionReadRecord(&sInput, nCol, 0, &apVal[0]);
        if( rc==SQLITE_OK ){
          rc = sessionReadRecord(&sInput, nCol, 0, &apVal[nCol]);
        }

        /* Write the new old.* record. Consists of the PK columns from the
        ** original old.* record, and the other values from the original
        ** new.* record. */
        for(iCol=0; rc==SQLITE_OK && iCol<nCol; iCol++){
          sqlite3_value *pVal = apVal[iCol + (abPK[iCol] ? 0 : nCol)];
          rc = sessionSerializeValue(&aOut[i+nWrite], pVal, &nWrite);
        }

        /* Write the new new.* record. Consists of a copy of all values
        ** from the original old.* record, except for the PK columns, which
        ** are set to "undefined". */
        for(iCol=0; rc==SQLITE_OK && iCol<nCol; iCol++){
          sqlite3_value *pVal = (abPK[iCol] ? 0 : apVal[iCol]);
          rc = sessionSerializeValue(&aOut[i+nWrite], pVal, &nWrite);
        }

        for(iCol=0; iCol<nCol*2; iCol++){
          sqlite3ValueFree(apVal[iCol]);
        }
        memset(apVal, 0, sizeof(apVal[0])*nCol*2);
        if( rc!=SQLITE_OK ){
          goto finished_invert;
        }

        i += nWrite;
        assert( i==sInput.iNext );
        break;
      }

      default:
        rc = SQLITE_CORRUPT_BKPT;
        goto finished_invert;
    }







  }

  assert( rc==SQLITE_OK );

  *pnInverted = nChangeset;
  *ppInverted = (void *)aOut;





 finished_invert:
  if( rc!=SQLITE_OK ){
    sqlite3_free(aOut);
  }
  sqlite3_free(apVal);
  sqlite3_free(sPK.aBuf);
  return rc;
}











































typedef struct SessionApplyCtx SessionApplyCtx;
struct SessionApplyCtx {
  sqlite3 *db;
  sqlite3_stmt *pDelete;          /* DELETE statement */
  sqlite3_stmt *pUpdate;          /* UPDATE statement */
  sqlite3_stmt *pInsert;          /* INSERT statement */
  sqlite3_stmt *pSelect;          /* SELECT statement */

      }
    }
  }else{
    nByte = 1;
    if( aBuf ) aBuf[0] = '\0';
  }

  if( pnWrite ) *pnWrite += nByte;
  return SQLITE_OK;
}


/*
** This macro is used to calculate hash key values for data structures. In
** order to use this macro, the entire data structure must be represented
** as a series of unsigned integers. In order to calculate a hash-key value
** for a data structure represented as three such integers, the macro may
** then be used as follows:
................................................................................
    }else{
      p->aBuf = aNew;
      p->nAlloc = nNew;
    }
  }
  return (*pRc!=SQLITE_OK);
}

/*
** Append the value passed as the second argument to the buffer passed
** as the first.
**
** This function is a no-op if *pRc is non-zero when it is called.
** Otherwise, if an error occurs, *pRc is set to an SQLite error code
** before returning.
*/
static void sessionAppendValue(SessionBuffer *p, sqlite3_value *pVal, int *pRc){
  int rc = *pRc;
  if( rc==SQLITE_OK ){
    int nByte = 0;
    sessionSerializeValue(0, pVal, &nByte);
    sessionBufferGrow(p, nByte, &rc);
    if( rc==SQLITE_OK ){
      rc = sessionSerializeValue(&p->aBuf[p->nBuf], pVal, 0);
      p->nBuf += nByte;
    }else{
      *pRc = rc;
    }
  }
}

/*
** This function is a no-op if *pRc is other than SQLITE_OK when it is 
** called. Otherwise, append a single byte to the buffer. 
**
** If an OOM condition is encountered, set *pRc to SQLITE_NOMEM before
** returning.
................................................................................
    }
    if( pIn->aData[pIn->iNext + nRead]==0 ) break;
    rc = sessionInputBuffer(pIn, nRead + 100);
  }
  if( pnByte ) *pnByte = nRead+1;
  return rc;
}

/*
** The input pointer currently points to the first byte of the first field
** of a record consisting of nCol columns. This function ensures the entire
** record is buffered.
*/
static int sessionChangesetBufferRecord(
  SessionInput *pIn, 
  int nCol, 
  int *pnByte
){
  int rc = SQLITE_OK;
  int nByte = 0;
  int i;
  for(i=0; rc==SQLITE_OK && i<nCol; i++){
    int eType;
    rc = sessionInputBuffer(pIn, nByte + 10);
    if( rc==SQLITE_OK ){
      eType = pIn->aData[pIn->iNext + nByte++];
      if( eType==SQLITE_TEXT || eType==SQLITE_BLOB ){
        int n;
        nByte += sessionVarintGet(&pIn->aData[pIn->iNext+nByte], &n);
        nByte += n;
        rc = sessionInputBuffer(pIn, nByte);
      }else if( eType==SQLITE_INTEGER || eType==SQLITE_FLOAT ){
        nByte += 8;
      }
    }
  }
  *pnByte = nByte;
  return rc;
}

/*
** The input pointer currently points to the second byte of a table-header.
** Specifically, to the following:
**
**   + number of columns in table (varint)
**   + array of PK flags (1 byte per column),
................................................................................
  }
  sqlite3_free(p->tblhdr.aBuf);
  sqlite3_free(p->in.buf.aBuf);
  sqlite3_free(p);
  return rc;
}

static int sessionChangesetInvert(
  SessionInput *pInput,           /* Input changeset */
  int (*xOutput)(void *pOut, const void *pData, int nData),
  void *pOut,


  int *pnInverted,                /* OUT: Number of bytes in output changeset */
  void **ppInverted               /* OUT: Inverse of pChangeset */
){
  int rc = SQLITE_OK;             /* Return value */
  SessionBuffer sOut;             /* Output buffer */



  int nCol = 0;                   /* Number of cols in current table */
  u8 *abPK = 0;                   /* PK array for current table */
  sqlite3_value **apVal = 0;      /* Space for values for UPDATE inversion */
  SessionBuffer sPK = {0, 0, 0};  /* PK array for current table */

  /* Initialize the output buffer */
  memset(&sOut, 0, sizeof(SessionBuffer));

  /* Zero the output variables in case an error occurs. */
  if( ppInverted ){
    *ppInverted = 0;
    *pnInverted = 0;

  }










  while( 1 ){
    u8 eType;

    /* Test for EOF. */
    if( (rc = sessionInputBuffer(pInput, 2)) ) goto finished_invert;

    if( pInput->iNext>=pInput->nData ) break;
    eType = pInput->aData[pInput->iNext];

    switch( eType ){
      case 'T': {
        /* A 'table' record consists of:
        **
        **   * A constant 'T' character,
        **   * Number of columns in said table (a varint),
        **   * An array of nCol bytes (sPK),
        **   * A nul-terminated table name.
        */
        int nByte;
        int nVar;
        pInput->iNext++;
        if( (rc = sessionChangesetBufferTblhdr(pInput, &nByte)) ){
          goto finished_invert;
        }
        nVar = sessionVarintGet(&pInput->aData[pInput->iNext], &nCol);
        sPK.nBuf = 0;
        sessionAppendBlob(&sPK, &pInput->aData[pInput->iNext+nVar], nCol, &rc);
        sessionAppendByte(&sOut, eType, &rc);
        sessionAppendBlob(&sOut, &pInput->aData[pInput->iNext], nByte, &rc);
        if( rc ) goto finished_invert;

        pInput->iNext += nByte;
        sqlite3_free(apVal);
        apVal = 0;
        abPK = sPK.aBuf;
        break;
      }

      case SQLITE_INSERT:
      case SQLITE_DELETE: {
        int nByte;
        int bIndirect = pInput->aData[pInput->iNext+1];
        int eType2 = (eType==SQLITE_DELETE ? SQLITE_INSERT : SQLITE_DELETE);
        pInput->iNext += 2;
        assert( rc==SQLITE_OK );
        rc = sessionChangesetBufferRecord(pInput, nCol, &nByte);
        sessionAppendByte(&sOut, eType2, &rc);
        sessionAppendByte(&sOut, bIndirect, &rc);
        sessionAppendBlob(&sOut, &pInput->aData[pInput->iNext], nByte, &rc);
        pInput->iNext += nByte;
        if( rc ) goto finished_invert;
        break;
      }

      case SQLITE_UPDATE: {
        int iCol;


        if( 0==apVal ){
          apVal = (sqlite3_value **)sqlite3_malloc(sizeof(apVal[0])*nCol*2);
          if( 0==apVal ){
            rc = SQLITE_NOMEM;
            goto finished_invert;
          }
          memset(apVal, 0, sizeof(apVal[0])*nCol*2);
        }

        /* Write the header for the new UPDATE change. Same as the original. */
        sessionAppendByte(&sOut, eType, &rc);
        sessionAppendByte(&sOut, pInput->aData[pInput->iNext+1], &rc);


        /* Read the old.* and new.* records for the update change. */
        pInput->iNext += 2;
        rc = sessionReadRecord(pInput, nCol, 0, &apVal[0]);
        if( rc==SQLITE_OK ){
          rc = sessionReadRecord(pInput, nCol, 0, &apVal[nCol]);
        }

        /* Write the new old.* record. Consists of the PK columns from the
        ** original old.* record, and the other values from the original
        ** new.* record. */
        for(iCol=0; rc==SQLITE_OK && iCol<nCol; iCol++){
          sqlite3_value *pVal = apVal[iCol + (abPK[iCol] ? 0 : nCol)];
          sessionAppendValue(&sOut, pVal, &rc);
        }

        /* Write the new new.* record. Consists of a copy of all values
        ** from the original old.* record, except for the PK columns, which
        ** are set to "undefined". */
        for(iCol=0; rc==SQLITE_OK && iCol<nCol; iCol++){
          sqlite3_value *pVal = (abPK[iCol] ? 0 : apVal[iCol]);
          sessionAppendValue(&sOut, pVal, &rc);
        }

        for(iCol=0; iCol<nCol*2; iCol++){
          sqlite3ValueFree(apVal[iCol]);
        }
        memset(apVal, 0, sizeof(apVal[0])*nCol*2);
        if( rc!=SQLITE_OK ){
          goto finished_invert;
        }



        break;
      }

      default:
        rc = SQLITE_CORRUPT_BKPT;
        goto finished_invert;
    }

    assert( rc==SQLITE_OK );
    if( xOutput && sOut.nBuf>=SESSIONS_STR_CHUNK_SIZE ){
      rc = xOutput(pOut, sOut.aBuf, sOut.nBuf);
      sOut.nBuf = 0;
      if( rc!=SQLITE_OK ) goto finished_invert;
    }
  }

  assert( rc==SQLITE_OK );
  if( pnInverted ){
    *pnInverted = sOut.nBuf;
    *ppInverted = sOut.aBuf;
    sOut.aBuf = 0;
  }else if( sOut.nBuf>0 ){
    rc = xOutput(pOut, sOut.aBuf, sOut.nBuf);
  }

 finished_invert:

  sqlite3_free(sOut.aBuf);

  sqlite3_free(apVal);
  sqlite3_free(sPK.aBuf);
  return rc;
}


/*
** Invert a changeset object.
*/
int sqlite3changeset_invert(
  int nChangeset,                 /* Number of bytes in input */
  const void *pChangeset,         /* Input changeset */
  int *pnInverted,                /* OUT: Number of bytes in output changeset */
  void **ppInverted               /* OUT: Inverse of pChangeset */
){
  SessionInput sInput;

  /* Set up the input stream */
  memset(&sInput, 0, sizeof(SessionInput));
  sInput.nData = nChangeset;
  sInput.aData = (u8*)pChangeset;

  return sessionChangesetInvert(&sInput, 0, 0, pnInverted, ppInverted);
}

/*
** Streaming version of sqlite3changeset_invert().
*/
int sqlite3changeset_invert_str(
  int (*xInput)(void *pIn, void *pData, int *pnData),
  void *pIn,
  int (*xOutput)(void *pOut, const void *pData, int nData),
  void *pOut
){
  SessionInput sInput;
  int rc;

  /* Set up the input stream */
  memset(&sInput, 0, sizeof(SessionInput));
  sInput.xInput = xInput;
  sInput.pIn = pIn;

  rc = sessionChangesetInvert(&sInput, xOutput, pOut, 0, 0);
  sqlite3_free(sInput.buf.aBuf);
  return rc;
}

typedef struct SessionApplyCtx SessionApplyCtx;
struct SessionApplyCtx {
  sqlite3 *db;
  sqlite3_stmt *pDelete;          /* DELETE statement */
  sqlite3_stmt *pUpdate;          /* UPDATE statement */
  sqlite3_stmt *pInsert;          /* INSERT statement */
  sqlite3_stmt *pSelect;          /* SELECT statement */

** WARNING/TODO: This function currently assumes that the input is a valid
** changeset. If it is not, the results are undefined.
*/
int sqlite3changeset_invert(
  int nIn, const void *pIn,       /* Input changeset */
  int *pnOut, void **ppOut        /* OUT: Inverse of input */
);











/*
** CAPI3REF: Concatenate Two Changeset Objects
**
** This function is used to concatenate two changesets, A and B, into a 
** single changeset. The result is a changeset equivalent to applying
** changeset A followed by changeset B. 

** WARNING/TODO: This function currently assumes that the input is a valid
** changeset. If it is not, the results are undefined.
*/
int sqlite3changeset_invert(
  int nIn, const void *pIn,       /* Input changeset */
  int *pnOut, void **ppOut        /* OUT: Inverse of input */
);

/*
** Streaming version of sqlite3changeset_invert().
*/
int sqlite3changeset_invert_str(
  int (*xInput)(void *pIn, void *pData, int *pnData),
  void *pIn,
  int (*xOutput)(void *pOut, const void *pData, int nData),
  void *pOut
);

/*
** CAPI3REF: Concatenate Two Changeset Objects
**
** This function is used to concatenate two changesets, A and B, into a 
** single changeset. The result is a changeset equivalent to applying
** changeset A followed by changeset B. 

static int test_sqlite3changeset_invert(
  void * clientData,
  Tcl_Interp *interp,
  int objc,
  Tcl_Obj *CONST objv[]
){
  int rc;                         /* Return code from changeset_invert() */
  void *aChangeset;               /* Input changeset */
  int nChangeset;                 /* Size of buffer aChangeset in bytes */
  void *aOut;                     /* Output changeset */
  int nOut;                       /* Size of buffer aOut in bytes */

  if( objc!=2 ){
    Tcl_WrongNumArgs(interp, 1, objv, "CHANGESET");
    return TCL_ERROR;
  }




  aChangeset = (void *)Tcl_GetByteArrayFromObj(objv[1], &nChangeset);


  rc = sqlite3changeset_invert(nChangeset, aChangeset, &nOut, &aOut);





  if( rc!=SQLITE_OK ){
    return test_session_error(interp, rc);


  }
  Tcl_SetObjResult(interp, Tcl_NewByteArrayObj((unsigned char *)aOut, nOut));
  sqlite3_free(aOut);
  return TCL_OK;
}

/*
** sqlite3changeset_concat LEFT RIGHT
*/
static int test_sqlite3changeset_concat(
  void * clientData,

static int test_sqlite3changeset_invert(
  void * clientData,
  Tcl_Interp *interp,
  int objc,
  Tcl_Obj *CONST objv[]
){
  int rc;                         /* Return code from changeset_invert() */
  TestStreamInput sIn;            /* Input stream */
  TestSessionsBlob sOut;          /* Output blob */



  if( objc!=2 ){
    Tcl_WrongNumArgs(interp, 1, objv, "CHANGESET");
    return TCL_ERROR;
  }

  memset(&sIn, 0, sizeof(sIn));
  memset(&sOut, 0, sizeof(sOut));
  sIn.nStream = test_tcl_integer(interp, SESSION_STREAM_TCL_VAR);
  sIn.aData = Tcl_GetByteArrayFromObj(objv[1], &sIn.nData);

  if( sIn.nStream ){
    rc = sqlite3changeset_invert_str(
        testStreamInput, (void*)&sIn, testSessionsOutput, (void*)&sOut
    );
  }else{
    rc = sqlite3changeset_invert(sIn.nData, sIn.aData, &sOut.n, &sOut.p);
  }
  if( rc!=SQLITE_OK ){
    rc = test_session_error(interp, rc);
  }else{
    Tcl_SetObjResult(interp,Tcl_NewByteArrayObj((unsigned char*)sOut.p,sOut.n));
  }

  sqlite3_free(sOut.p);
  return rc;
}

/*
** sqlite3changeset_concat LEFT RIGHT
*/
static int test_sqlite3changeset_concat(
  void * clientData,