P/Invoke

[Charles]

Hops, do you have an example that wouldn't make the Cobra test suite beep every time we run it?

[hopscc]

Sorry no
- I just took that one cos fm the mag article it looked like the simplest call to use for a q-and-d test.
and so it turned out

if anyone can point me to a another (silent) simple call I can gen a full ticket+patch

[torial]

Hopscc, thanks for what you did in this. I will try to have a safe test call provided sometime today.

[torial]

I'm flying a little blind (haven't applied the patch to my local) so my sample may fail in Cobra. I've included the C# variant which I have confirmed works.

use System.Runtime.InteropServices

class PInvokeTst
    
    #PInvoke entry point
    def getUserName(lpBuffer as byte[] has MarshalAs(UnmanagedType.LPArray), nSize as Int32[] has MarshalAs(UnManagedType.LPArray)) as bool is shared, extern
        has DllImport("Advapi32.dll", setLastError = true, entryPoint = "GetUserName", exactSpelling=false)
        pass
        
    def main is shared
        userNameBytes = byte[](256)
        len = int[](1)
        len[0] = 256
        .getUserName(userNameBytes,len)
        userName = System.Text.Encoding.ASCII.getString(userNameBytes).trim(c'${1}')
        #For confirmation: alternative .Net approach:
        userCred = System.Security.Principal.WindowsIdentity.getCurrent().name.toString
        if userCred.contains("\") # this should be two backslashes, but displays as one in forum code.
            userCred = userCred.split("\")[1]      # this should be two backslashes, but displays as one in forum code.
        assert userCred == userName, "WinAPI call doesn't match the .Net Principal"

Here's the C# (minus the assert):

Code: Select all

using System.Runtime.InteropServices;

class PInvokeTst

        [DllImport("Advapi32.dll", EntryPoint = "GetUserName",
        ExactSpelling = false, SetLastError = true)]
        static extern bool GetUserName(
            [MarshalAs(UnmanagedType.LPArray)] byte[] lpBuffer,
            [MarshalAs(UnmanagedType.LPArray)] Int32[] nSize);

        public PInvokeTst()
       {
            byte[] userNameBytes = new byte[256];
            int[] len = new int[1];
            len[0] = 256;
            GetUserName(userNameBytes, len);
            string userName = System.Text.Encoding.ASCII.GetString(userNameBytes).Trim('\0');
            string userCred = System.Security.Principal.WindowsIdentity.GetCurrent().Name.ToString();
            if (userCred.Contains("\\"))
            {
                userCred = userCred.Split('\\')[1];
            }

            Console.WriteLine(userName +" " + userCred);
       }


[Charles]

Hops, the web site http://pinvoke.net has a bunch of these. Poking around, I found http://pinvoke.net/default.aspx/user32.IsCharLower.

[Charles]

Btw C# does not require a body on methods that are marked with DllImport and we already have methods that don't require a body ("def foo is abstract"). I think the correct approach is to do the same thing with DllImport methods in Cobra.

[hopscc]

Heres the cobra variant compile and run

use System.Runtime.InteropServices

class PInvokeTst
    
    #PInvoke entry point
    def getUserName(lpBuffer as uint8[] has MarshalAs(UnmanagedType.LPArray), nSize as int32[] has MarshalAs(UnmanagedType.LPArray)) as bool is shared, extern
        has DllImport("Advapi32.dll", setLastError = true, entryPoint = "GetUserName", exactSpelling=false)
        pass
        
    def main is shared
        userNameBytes = uint8[](256)
        len = int[](1)
        len[0] = 256
        .getUserName(userNameBytes,len)
        userName = System.Text.Encoding.ascii.getString(userNameBytes).trim(c'${1}')   # c ' \ 0'
        print userName
        #For confirmation: alternative .Net approach:
        userCred = System.Security.Principal.WindowsIdentity.getCurrent.name.toString
        print userCred
        if userCred.contains('')  # dbl backslash in quotes
            userCred = userCred.split(c'')[1]   # dbl backslash in quotes
        assert userCred == userName, "WinAPI call doesn't match the .Net Principal call"

Outputs

Code: Select all

$ cobc0 pinvokeT.cobra
hops
KERERU\hops


[hopscc]

Chuck,
Is there any situation where a method declared extern would be allowed to have statements ?

[Charles]

Up until now, it's never been used for methods--only types:

Code: Select all

./Snapshot/Cobra.Lang/Misc.cobra:48:   class CobraDirectString is extern
./Snapshot/Cobra.Lang/NativeExtern.cobra:10:      class CobraImp is extern
./Snapshot/Cobra.Lang/NativeExtern.cobra:36:      interface ICallable is extern


For P/Invoke, I think it should be sufficient to to have "is shared has DllImport(...)".

[hopscc]

Yes, I realise its not been applied to methods up til now but given that
- it can be applied to methods without a diagnostic and that
- such application does make the (local) declaration of such a method a descriptor/placeholder/forward-reference for a method defined elsewhere
I'm still wondering if anyone thinks that there is any situation where such a method (i.e one declared extern) would
make any sense to have statements.

The DllImport attribute is nicely specific to the .Net platform but it doesnt mean much anywhere else and doesnt exactly self describe
that the method being annotated needs to be bereft of statements..