Detect RAS Connection

• Download demo project - 12 Kb

Introduction

There was a time I needed to detect an internet connection using the modem. I've checked the RAS library and found 2 useful functions: RasEnumConnections and RasGetConnectStatus.

The first function (RasEnumConnections) retrieve a specified amount of connections:

DWORD RasEnumConnections (
  LPRASCONN lprasconn, // buffer to receive connections data

  LPDWORD lpcb, // size in bytes of buffer

  LPDWORD lpcConnections // number of connections written to buffer

);

• lprasconn - Points to a buffer that receives an array of RASCONN structures, one for each RAS connection. Before calling the function, an application must set the dwSize member of the first RASCONN structure in the buffer to sizeof(RASCONN) in order to identify the version of the structure being passed.
• lpcb - Points to a variable that contains the size, in bytes, of the buffer specified by lprasconn. On return, the function sets this variable to the number of bytes required to enumerate the RAS connections.
• lpcConnections - Points to a variable that the function sets to the number of RASCONN structures written to the buffer specified by lprasconn.

Return Value: 0 - Succeed; Other - Error code

The RASCONN is a structure which hold the information on a single connection:

typedef struct _RASCONN {
 DWORD dwSize;
 HRASCONN hrasconn;
 TCHAR szEntryName[RAS_MaxEntryName + 1];
#if (WINVER >= 0x400) 
 CHAR szDeviceType[RAS_MaxDeviceType + 1];
 CHAR szDeviceName[RAS_MaxDeviceName + 1];
#endif
} RASCONN ;

• dwSize - Specifies the size, in bytes, of the RASCONN structure.
• hrasconn - Specifies the remote access connection. This handle is used in other remote access API calls.
• szEntryName - A string that specifies the phone-book entry used to establish the remote access connection. If the connection was established using an empty entry name, this string consists of a "." followed by the connection phone number.
• szDeviceType - A null-terminated string that contains the device type through which the connection is made.
• szDeviceName - A null-terminated string that contains the device name through which the connection is made.

The second function (RasGetConnectStatus) retrieves information on the current status of the specified connection

DWORD RasGetConnectStatus (
  HRASCONN hrasconn, // handle to RAS connection of interest

  LPRASCONNSTATUS lprasconnstatus // buffer to receive status data

);

• hrasconn - Identifies the remote access connection for which to retrieve the status. This handle must have been obtained from RasDial or RasEnumConnections.
• lprasconnstatus - Points to a RASCONNSTATUS structure that the function fills with status information. Before calling the function, an application must set the dwSize member of the structure to sizeof(RASCONNSTATUS) in order to identify the version of the structure being passed.

Return Value: 0 - Succeed; Other - Error code

The RASCONNSTATUS structure describes the current status of a connection.

typedef struct _RASCONNSTATUS {
 DWORD dwSize;
 RASCONNSTATE rasconnstate;
 DWORD dwError;
 TCHAR szDeviceType[RAS_MaxDeviceType + 1];
 TCHAR szDeviceName[RAS_MaxDeviceName + 1];
} RASCONNSTATUS;

• dwSize - Specifies the structure size, in bytes.
• rasconnstate - Specifies a RASCONNSTATE enumerator value that indicates the current state of the RasDial connection process; that is, the piece of the RasDial process that is currently executing.

  Two state values are especially significant:

  State	Meaning
  RASCS_Connected	Indicates that the connection has been successfully established.
  RASCS_Disconnected	Indicates that the connection has failed.

  
  

• dwError - If nonzero, indicates the reason for failure. The value is one of the error values from the RAS header file or one of ERROR_NOT_ENOUGH_MEMORY or ERROR_INVALID_HANDLE.
• szDeviceType  - A string that specifies the type of the current device, if available. For example, common device types supported by RAS are "modem", "pad", "switch", "isdn", or "null".
• szDeviceName - A string that specifies the name of the current device, if available. This would be the name of the modem � for example, "Hayes Smartmodem 2400"; the name of the PAD, for example "US Sprint"; or the name of a switch device, for example "Racal-Guardata".

To use the RAS library, you need to include <ras.h> in your source files and add rasapi32.lib to link with your application.

I've distributed my application and then I had a problem. One day, I got a mail which describes an error. It turns out that my client's computer missing rasapi32.dll. Only when you install the "Dial-out networking" you get rasapi32.dll. So instead linking rasapi32.lib to my application, I've decided to load it at runtime so I can detect if it is installed instead of getting an error message. What I had to remember is that rasapi32.dll contains 2 kinds of functions: ANSI and UNICODE, so the code need to know which one to use. I check the _UNICODE constant definition. Then, I load the library, look for the functions address and call them to get my connection status.

All you need to do to use the code, is to include "rasstatus.h" in your project. I also made a demo project but it is very simple and it only used to check that the code really works.

The code is not so hard to understand and I added some comments so you can understand easily.

////   RAS Connect status function

////

////   Written by Gilad Novik

////   For any questions or comments, gilad@bmidas.com



#ifndef _RASSTATUS
#define _RASSTATUS
#include <ras.h>



// We need to declare the functions type

typedef DWORD (WINAPI *RasEnumConnectionsType)(LPRASCONN lprasconn,
    LPDWORD lpcb,LPDWORD lpcConnections);
typedef DWORD (WINAPI *RasGetConnectStatusType)(HRASCONN hrasconn,
    LPRASCONNSTATUS lprasconnstatus);

#ifdef _UNICODE
#define RasFileName L"RASAPI32.DLL"
#define RasEnumConnectionsName L"RasEnumConnectionsW"
#define RasGetConnectStatusName L"RasGetConnectStatusW"
#else
#define RasFileName "RASAPI32.DLL"
#define RasEnumConnectionsName "RasEnumConnectionsA"
#define RasGetConnectStatusName "RasGetConnectStatusA"
#endif

BOOL IsRasConnected()
{
  HINSTANCE hLib = LoadLibrary(RasFileName);  // Try to load the library

  if (hLib == NULL)
    return FALSE;  // Return FALSE if we can't find it


  // Get functions address

  RasEnumConnectionsType _RasEnumConnections = 
    (RasEnumConnectionsType)GetProcAddress(hLib,RasEnumConnectionsName);
  RasGetConnectStatusType _RasGetConnectStatus = 
    (RasGetConnectStatusType)GetProcAddress(hLib,RasGetConnectStatusName);
  BOOL bResult = FALSE;
  if (_RasEnumConnections && _RasGetConnectStatus)  
          // Check if it is valid pointer

  {
    RASCONN RasConn;
    RASCONNSTATUS RasConnStatus;
    RasConnStatus.dwSize = sizeof(RASCONNSTATUS);    
           // We need to set the size of the structure

    DWORD dwConnSize = sizeof(RASCONN);
    DWORD dwRasCount = 1;  // We only retrieve one connection

    RasConn.dwSize = dwConnSize;  // We need to set the size 

                          // of the structure

    bResult =    // Let's check it out !!!

      (((*_RasEnumConnections)(&RasConn,&dwConnSize,&dwRasCount)) == 0)
        && (((*_RasGetConnectStatus)(RasConn.hrasconn,&RasConnStatus)) == 0) 
        && (RasConnStatus.rasconnstate == RASCS_Connected);
  }
  FreeLibrary(hLib);    // Don't forget to unload the library from memory

  return bResult;
}
#endif // _RASSTATUS

All you need to do is to call IsRasConnected which returns TRUE is your are connected to the internet or FALSE otherwise. Hope it could help :) If you have any questions or comments, you can contact me: Gilad Novik - gilad@bmidas.com