Chapter 17: Network Programming

This chapter covers a narrow range of a wide programming area called network programming. The main topic that will be covered here is access to the resources of a local area network (LAN). Another aspect of network programming socket programming is too vast. Therefore, here, I cover only the basics of this topic.

Network Devices

In application programming, it is often necessary to detect network devices. Principally, this problem can be formulated more generally : How do you determine the type of a specific device? If you have some experience with programming for MS-DOS, you might remember that determining the device type in MS-DOS wasn't a trivial task. Windows simplifies this problem. In this operating system, there is a useful function GetDriveType. The only argument of this function is the string containing the name of the root directory of the device under consideration, for example, A:\ or D:\. The device type is determined by the value returned by this function (see the DRIV.INC file in Listing 17.1). The result of executing this program is shown in Fig. 17.1.

Listing 17.1: A simple example demonstrating how to determine the device type

 // The DRIV.RC file // Constant definitions #define WS_SYSMENU            0x00080000L #define WS_MINIMIZEBOX        0x00020000L #define WS_MAXIMIZEBOX        0x00010000L #define WS_VISIBLE            0x10000000L #define WS_TABSTOP            0x00010000L #define WS_VSCROLL            0x00200000L #define DS_3DLOOK             0x0004L #define LBS_NOTIFY            0x0001L #define LBS_SORT              0x0002L #define LBS_WANTKEYBOARDINPUT 0x0400L // Identifiers #define LIST1       101 //Dialog box definition DIAL1 DIALOG 0, 0, 180, 110 STYLE WS_SYSMENU  WS_MINIMIZEBOX  WS_MAXIMIZEBOX  DS_3DLOOK CAPTION "Determining device types" FONT 8, "Arial" { CONTROL "ListBox1", LIST1, "listbox", WS_VISIBLE  WS_TABSTOP  WS_VSCROLL  LBS_NOTIFY  LBS_WANTKEYBOARDINPUT, 16, 16, 100, 75 } ; The DRIV.INC file ; Constants ; Values returned by the GetDriveType function ; Values 0 and 1 can be considered indications ; that the device is missing DRIVE_REMOVABLE       equ 2 ; Floppy drive DRIVE_FIXED           equ 3 ; Hard disk drive DRIVE_REMOTE          equ 4 ; Network disk DRIVE_CDROM           equ 5 ; CD-ROM drive DRIVE_RAMDISK         equ 6 ; RAM disk ; This message arrives when the window is closed WM_CLOSE              equ 10h WM_INITDIALOG         equ 110h WM_COMMAND            equ 111h LB_ADDSTRING          equ 180h LB_RESETCONTENT       equ 184h WM_LBUTTONDOWN        equ 201h ; Prototypes of external procedures IFDEF MASM        EXTERN lstrcpyA@8:NEAR        EXTERN lstrcatA@8:NEAR        EXTERN GetDriveTypeA@4:NEAR        EXTERN ExitProcess@4:NEAR        EXTERN GetModuleHandleA@4:NEAR        EXTERN DialogBoxParamA@20:NEAR        EXTERN EndDialog@8:NEAR        EXTERN SendDlgItemMessageA@20:NEAR ELSE        EXTERN lstrcpyA:NEAR        EXTERN lstrcatA:NEAR        EXTERN GetDriveTypeA:NEAR        EXTERN ExitProcess:NEAR        EXTERN GetModuleHandleA:NEAR        EXTERN DialogBoxParamA:NEAR        EXTERN EndDialog:NEAR        EXTERN SendDlgItemMessageA:NEAR        lstrcpyA@8 = lstrcpyA        lstrcatA@8 = lstrcatA        GetDriveTypeA@4 = GetDriveTypeA        ExitProcess@4 = ExitProcess        GetModuleHandleA@4 = GetModuleHandleA        DialogBoxParamA@20 = DialogBoxParamA        EndDialog@8 = EndDialog        SendDlgItemMessageA@20 = SendDlgItemMessageA ENDIF ; Structures ; Message structure MSGSTRUCT STRUC        MSHWND         DD ?        MSMESSAGE      DD ?        MSWPARAM       DD ?        MSLPARAM       DD ?        MSTIME         DD ?        MSPT           DD ? MSGSTRUCT ENDS ; The DRIV.ASM file .586P ; Flat memory model .MODEL FLAT, stdcall include driv.inc ; INCLUDELIB directives for the linker IFDEF MASM        includelib c:\masm32\lib\user32.lib        includelib c:\masm32\lib\kernel32.lib ELSE        includelib c:\tasm32\lib\import32.lib ENDIF ;--------------------------------------------- ; Data segment _DATA SEGMENT        PRIZ  DB 0        MSG   MSGSTRUCT  <?>        HINST DD 0 ;Application descriptor        PA    DB "DIAL1", 0        ROO   DB "?:\", 0        BUFER DB 40 DUP(0)        TYP0  DB " Device missing", 0        TYP1  DB " Device missing", 0        TYP2  DB " Floppy disk", 0        TYP3  DB " Hard disk", 0        TYP4  DB " Network disk", 0        TYP5  DB " CD", 0        TYP6  DB " RAM drive", 0        INDEX DD OFFSET TYP0              DD OFFSET TYP1              DD OFFSET TYP2              DD OFFSET TYP3              DD OFFSET TYP4              DD OFFSET TYP5              DD OFFSET TYP6 _DATA ENDS ; Code segment _TEXT SEGMENT START: ; Get the application descriptor        PUSH   0        CALL   GetModuleHandleA@4        MOV    [HINST], EAX ;-------------------------------        PUSH   0        PUSH   OFFSET WNDPROC        PUSH   0        PUSH   OFFSET PA        PUSH   [HINST]        CALL   DialogBoxParamA@20        CMP    EAX, -1        JNE    KOL ; Error message KOL: ;-------------------------------        PUSH   0        CALL   ExitProcess@4 ;------------------------------- ; Window procedure ; Position of parameters in the stack ; [BP+014H]  ; LPARAM ; [BP+10H]   ; WAPARAM ; [BP+0CH]   ; MES ; [BP+8]     ; HWND WNDPROC    PROC        PUSH  EBP        MOV   EBP, ESP        PUSH  EBX        PUSH  ESI        PUSH  EDI ;-------------------------------        CMP   DWORD PTR [EBP+0CH], WM_CLOSE        JNE   L1        PUSH  0        PUSH  DWORD PTR [EBP+08H]        CALL  EndDialog@8        JMP   FINISH L1:        CMP   DWORD PTR [EBP+0CH], WM_INITDIALOG        JNE   L2 L4: ; Analyzing the devices and filling the list        MOV   ECX, 65 LOO:        PUSH  ECX        MOV   ROO, CL ; Determining the device type        PUSH   OFFSET ROO        CALL   GetDriveTypeA@4 ; Full list        CMP   PRIZ, 0        JZ    _ALL        CMP   EAX, 2        JB    L3 _ALL: ; Get the index        SHL   EAX, 2        PUSH  EAX ; Create a string for the list        PUSH  OFFSET ROO        PUSH  OFFSET BUFER        CALL  lstrcpyA@8        POP   EBX        PUSH  INDEX[EBX]        PUSH  OFFSET BUFER        CALL  lstrcatA@8 ; Send the string into the list        PUSH  OFFSET BUFER        PUSH  0        PUSH  LB_ADDSTRING        PUSH  101        PUSH  DWORD PTR [EBP+08H]        CALL  SendDlgItemMessageA@20 L3: ; Check whether the loop boundary has been reached        POP   ECX        INC   ECX        CMP   ECX, 91        JNE   LOO        JMP   FINISH L2:        CMP   DWORD PTR [EBP+0CH],, WM_LBUTTONDOWN        JNE   FINISH        PUSH  0        PUSH  0        PUSH  LB_RESETCONTENT        PUSH  101        PUSH  DWORD PTR [EBP+08H]        CALL  SendDlgItemMessageA@20        CMP   PRIZ, 0        JE    YES_0        MOV   PRIZ, 0        JMP   L4 YES_0:        MOV   PRIZ, 1        JMP   L4 FINISH:        MOV   EAX, 0        POP   EDI        POP   ESI        POP   EBX        POP   EBP        RET   16 WNDPROC   ENDP _TEXT ENDS END START 

 

Figure 17.1: Result of executing the program presented in Listing 17.1

To translate the program presented in Listing 17.1, issue the following commands for MASM32:

 ml /c /coff /DMASM driv.asm      rc driv.rc      link /subsystem:windows driv.obj driv.res 

Issue the following commands for TASM32:

 tasm32 /ml driv.asm      brcc32 driv.rc      tlink32 -aa driv.obj,,,,,driv.res 

Having determined that a specific device is a network device, you might ask the following: How do I determine the device status? In this case, I interpret the device status as one of the following possible situations: the device is available for reading and writing, the device is read-only, or the device is unavailable. To achieve this, I prefer the following approach: To check the device status, I use the functions CreateFile and GetDiskFreeSpace. You are already acquainted with the first function. The second function can be used to determine the amount of free disk space. If this device allows you to create a file (the best approach is creating a file with the "delete after closing" attribute, in which case the operating system will automatically delete the file after it is closed) and read information about the device, this means that the device is available for reading and writing. If the device allows you to read information about it but doesn't allow you to create a file, the device is read-only. Finally, if neither of the operations is allowed, the device is unavailable. This approach is simple and straightforward yet efficient.