C++ access to Redis mset binary data interface packaging scheme

demand

Hiredis client interface is used to access redis in C++.
You need to use mset to set multiple binary data at once

The following three packaging implementation schemes are given.

Simple splicing scheme

In redis-cli, the syntax of mset looks like this:

/opt/colin$./redis-cli mset a 11 b 22 c 333

OK

After splicing according to this syntax, directly use the hiredis string interface redisCommand to pass:

void msetNotBinary(redisContext *c, const vector<string> &vtKey, const vector<string> & vtVal )
{
  if(vtKey.size() != vtVal.size())
  {
    throw runtime_error( "Redis error" );
  }

  string strCmd = "MSET";
  for(int i = 0; i < vtKey.size(); i++)
  {
    strCmd += " "+vtKey[i]+" "+vtVal[i];
  }
  cout << "strCmd:" << strCmd << endl;

  void * r = redisCommand(c, strCmd.c_str() );
  if ( !r )
    throw runtime_error( "Redis error" );
  freeReplyObject( r );
}

void do_test( redisContext *c )
{  
  vector<string> vtKey;
  vector<string> vtVal;

  vtKey.push_back("A");
  vtVal.push_back("AAAA");
  vtKey.push_back("B");
  vtVal.push_back("BBBB");
  vtKey.push_back("C");
  vtVal.push_back("CCCC");
  //add a binary data
  vtKey.push_back("D");
  vtVal.push_back("");
  char a[] = "ABCDE";
  a[2] = 0;
  vtVal[3].assign(a,5);

  try
  {
    msetNotBinary(c, vtKey, vtVal );
    //mset1( c, vtKey, vtVal );
    //mset2( c, vtKey, vtVal );
  }
  catch ( runtime_error & )
  {
    cout << "Error" << endl;
  }
}

int main(int argc, char *argv[])
{
  redisContext *c;

  c = redisConnect("127.0.0.1",6379);
  if (c->err)
   {
    cout << "Connection error: " << c->errstr << endl;
    return -1;
  }

  do_test(c);

  redisFree(c);

  return 0;
}

This approach can handle mset multiple string data, but the data content is binary data is powerless;

RedisCommandArgv interface delivery scheme

For multiple parameter passing, hiredis provides the following interface, in which the last parameter is the content length of all incoming data,
This means that the interface is binary safe:

Void *redisCommandArgv(redisContext *c, int argc, const char **argv, const size_t *argvlen);
The main job is to construct a dynamic two-dimensional array char ** argv, which involves the conversion from char ** to const char **, which is a bit risky.
This was covered in the previous article;

void mset1( redisContext *c, const vector<string> &vtKey, const vector<string> & vtVal )
{
  if(vtKey.size() != vtVal.size())
  {
    throw runtime_error( "Redis error" );
  }

  char ** argv = new char*[vtKey.size() + vtVal.size() + 1 ];
  size_t * argvlen = new size_t[vtKey.size() + vtVal.size() + 1 ];

  int j = 0;
  argv[j] = new char[5];
  memcpy(argv[j],"MSET",4);
  argvlen[j] = 4;
  ++j;


  for(int i = 0 ; i < vtKey.size();i++)
  {  
    argvlen[j] = vtKey[i].length();
    argv[j] = new char[argvlen[j]];
     memset((void*)argv[j],0,argvlen[j] );
    memcpy((void*)argv[j],vtKey[i].data(),vtKey[i].length());
    j++;

    argvlen[j] = vtVal[i].length();
    argv[j] = new char[argvlen[j]];
    memset((void*)argv[j],0,argvlen[j]);
    memcpy((void*)argv[j],vtVal[i].data(),vtVal[i].length());
    j++;
  }

  //if not use const_cast<const char**> ,compile error
  //for why assign from char** to const char** error, see my blog ...
   void *r = redisCommandArgv(c, vtKey.size() + vtVal.size() + 1, const_cast<const char**>(argv), argvlen );
  if ( !r )
    throw runtime_error( "Redis error" );
  freeReplyObject( r );

  for(int i = 0;i < vtKey.size();i++)
  {
    delete [] argv[i];
    argv[i] = NULL;
  }

  delete []argv;
  delete []argvlen;
  argv = NULL;
}

Vector scheme delivered by the redisCommandArgv interface

Again, use the redisCommandArgv interface to construct the const char ** using a vector, which you learned from resources 1:

void mset2( redisContext *c, const vector<string> &vtKey, const vector<string> & vtVal)
{
  if(vtKey.size() != vtVal.size())
  {
    throw runtime_error( "Redis error" );
  }

  vector<const char *> argv( vtKey.size() + vtVal.size() + 1 );
  vector<size_t> argvlen( vtKey.size() + vtVal.size() + 1 );
  int j = 0;

  static char msetcmd[] = "MSET";
  argv[j] = msetcmd;
  argvlen[j] = sizeof(msetcmd)-1;
  ++j;

  for(int i = 0;i< vtKey.size();++i)
  {
    argvlen[j] = vtKey[i].length();
    argv[j] = new char[argvlen[j]];
     memset((void*)argv[j],0,argvlen[j] );
    memcpy((void*)argv[j],vtKey[i].data(),vtKey[i].length());
    j++;

    argvlen[j] = vtVal[i].length();
    argv[j] = new char[argvlen[j]];
    memset((void*)argv[j],0,argvlen[j]);
    memcpy((void*)argv[j],vtVal[i].data(),vtVal[i].length());
    j++;
  }

  void *r = redisCommandArgv(c, argv.size(), &(argv[0]), &(argvlen[0]) );
  if ( !r )
    throw runtime_error( "Redis error" );
  freeReplyObject( r );
}

In this way, the transfer of binary data is realized;

Binary check

After the program is executed, redis-cli can be used to verify:

For non-binary secure implementations, the binary content is truncated:

/opt/app/colin$./redis-cli get D

"AB"

As for the binary safe implementation interface, the binary data 0 is displayed by escape:

/opt/app/colin$./redis-cli get D

"ABx00DE"

Complete executable code can be found in the lot: (link: https://github.com/me115/cppset/tree/master/2DimArray)

The above is all the content of this article, I hope you can enjoy it.