Fix issue on Windows with HANDLE being confused with an io opaque

handle. This adds an opaque handle type that can then be used without
knowing what the underlying OS handle type is. Avoiding a direct alias
means the type is distinct for std.io, and can't be confused with other
opaque types (as was the case for Windows). Closes #20.

src/std/io/driver/package.d

@@ -25,6 +25,13 @@ package
         static assert(0, "unimplemented");
 }
 
+/// All handles in std.io are based on this type. The implementation defines how it is used.
+struct OpaqueHandle
+{
+    enum OpaqueHandle INVALID = OpaqueHandle(cast(void*)-1);
+    void *handle;
+}
+
 /**
    The driver interface used by std.io.
 
@@ -39,16 +46,14 @@ interface Driver
 {
     // FILE and SOCKET handles cannot be manipulated in @safe code, so most of
     // the Driver's API is @safe.
-shared @safe @nogc:
+@safe @nogc:
     /**
        Opaque file handle
 
        Interpretation left to driver, typically `int` file descriptor
        on Posix systems and `HANDLE` on Windows.
     */
-    alias FILE = void*;
-    /// value used for invalid/closed files
-    enum INVALID_FILE = cast(void*)-1;
+    alias FILE = OpaqueHandle;
 
     version (Posix)
         alias tchar = char; /// UTF-8 path on Posix, UTF-16 path on Windows
@@ -57,6 +62,7 @@ shared @safe @nogc:
     else
         static assert(0, "unimplemented");
 
+    shared {
     /**
        Create/open file at `path` in `mode`.
 
@@ -83,16 +89,18 @@ shared @safe @nogc:
     size_t write(scope FILE f, /*in*/ const scope ubyte[][] bufs);
     /// seek file to offset
     ulong seek(scope FILE f, long offset, int whence);
+    }
 
     /**
        Opaque socket handle
 
        Interpretation left to driver, typically `int` file descriptor
        on Posix systems and `SOCKET` on Windows.
     */
-    alias SOCKET = void*;
-    /// value used for invalid/closed sockets
-    enum INVALID_SOCKET = cast(void*)-1;
+    alias SOCKET = OpaqueHandle;
+
+
+    shared {
     /// create socket
     SOCKET createSocket(AddrFamily family, SocketType type, Protocol protocol);
     /**
@@ -151,6 +159,7 @@ shared @safe @nogc:
     int resolve( /*in*/ const scope char[] hostname, /*in*/ const scope char[] service, AddrFamily family,
             SocketType socktype, Protocol protocol,
             scope int delegate(const scope ref AddrInfo ai) @safe @nogc cb);
+    }
 
     ///
     @safe @nogc unittest

src/std/io/driver/sync.d

@@ -525,27 +525,27 @@ version (Posix)
     /// handle to file
     Driver.FILE h2f(return scope int fd) pure nothrow @trusted @nogc
     {
-        return cast(void*) fd;
+        return Driver.FILE(cast(void*) fd);
     }
 
     /// file to handle
     int f2h(scope Driver.FILE f) pure nothrow @trusted @nogc
     {
-        return cast(int) f;
+        return cast(int) f.handle;
     }
 
     static assert(int.sizeof <= Driver.SOCKET.sizeof);
 
     /// handle to socket
     Driver.SOCKET h2s(return scope int fd) pure nothrow @trusted @nogc
     {
-        return cast(Driver.SOCKET) fd;
+        return Driver.SOCKET(cast(void *)fd);
     }
 
     /// socket to handle
     inout(int) s2h(scope inout Driver.SOCKET s) pure nothrow @trusted @nogc
     {
-        return cast(int) s;
+        return cast(int) s.handle;
     }
 }
 else version (Windows)
@@ -557,27 +557,27 @@ else version (Windows)
     /// handle to file
     Driver.FILE h2f(return scope HANDLE fd) pure nothrow @trusted @nogc
     {
-        return cast(Driver.FILE) fd;
+        return Driver.FILE(cast(void*)fd);
     }
 
     /// file to handle
     HANDLE f2h(return scope Driver.FILE f) pure nothrow @trusted @nogc
     {
-        return cast(HANDLE) f;
+        return cast(HANDLE) f.handle;
     }
 
     static assert(ws2.SOCKET.sizeof <= Driver.SOCKET.sizeof);
 
     /// handle to socket
     Driver.SOCKET h2s(return scope ws2.SOCKET fd) pure nothrow @trusted @nogc
     {
-        return cast(Driver.SOCKET) fd;
+        return Driver.SOCKET(cast(void *)fd);
     }
 
     /// socket to handle
     inout(ws2.SOCKET) s2h(scope inout Driver.SOCKET s) pure nothrow @trusted @nogc
     {
-        return cast(ws2.SOCKET) s;
+        return cast(ws2.SOCKET) s.handle;
     }
 }
 

src/std/io/file.d

@@ -189,16 +189,16 @@ struct File
     /// close the file
     void close() scope @trusted
     {
-        if (f is Driver.INVALID_FILE)
+        if (f is Driver.FILE.INVALID)
             return;
         driver.closeFile(f);
-        f = Driver.INVALID_FILE;
+        f = Driver.FILE.INVALID;
     }
 
     /// return whether file is open
     bool isOpen() const scope
     {
-        return f != Driver.INVALID_FILE;
+        return f != Driver.FILE.INVALID;
     }
 
     ///
@@ -353,7 +353,7 @@ struct File
     File move() return scope nothrow /*pure Issue 18590*/
     {
         auto f = this.f;
-        this.f = Driver.INVALID_FILE;
+        this.f = Driver.FILE.INVALID;
         return File(f);
     }
 
@@ -367,7 +367,7 @@ private:
         this.f = f;
     }
 
-    Driver.FILE f = Driver.INVALID_FILE;
+    Driver.FILE f = Driver.FILE.INVALID;
 }
 
 ///

src/std/io/net/socket.d

@@ -127,16 +127,16 @@ struct Socket
     /// close the socket
     void close() @trusted
     {
-        if (s == Driver.INVALID_SOCKET)
+        if (s == Driver.SOCKET.INVALID)
             return;
         driver.closeSocket(s);
-        s = Driver.INVALID_SOCKET;
+        s = Driver.SOCKET.INVALID;
     }
 
     /// return whether the socket is open
     bool isOpen() const pure nothrow
     {
-        return s != Driver.INVALID_SOCKET;
+        return s != Driver.SOCKET.INVALID;
     }
 
     ///
@@ -552,7 +552,7 @@ struct Socket
     Socket move() return scope nothrow /*pure Issue 18590*/
     {
         auto s = this.s;
-        this.s = Driver.INVALID_SOCKET;
+        this.s = Driver.SOCKET.INVALID;
         return Socket(s);
     }
 
@@ -611,5 +611,5 @@ private:
         this.s = s;
     }
 
-    Driver.SOCKET s = Driver.INVALID_SOCKET;
+    Driver.SOCKET s = Driver.SOCKET.INVALID;
 }