Added FileDescriptor support

Some DBus methods return file descriptors, such as
"org.freedesktop.login1.Manager.Inhibit". This commit adds support for
these.

I followed the same enum type defining pattern I've seen in the code,
such as with InterfaceNames and BusNames, to prevent integers and
fileDescriptors implicitly casting to each other.

Note that it is kinda hard to test with reading and writing
fileDescriptors, as DBus will duplicate the file descriptor
when reading, leading to relatively unpredicatable behaviour.

I also must admit I focussed most of my attention to reading file
descriptors and less to writing file descriptors, as I don't know a good
way to test those.

source/ddbus/conv.d

@@ -172,7 +172,7 @@ void buildIter(TS...)(DBusMessageIter* iter, TS args)
 }
 
 T readIter(T)(DBusMessageIter* iter)
-    if (is(T == enum) && !is(T == InterfaceName) && !is(T == BusName)) {
+    if (is(T == enum) && !is(T == InterfaceName) && !is(T == BusName) && !is(T == FileDescriptor)) {
   import std.algorithm.searching : canFind;
 
   alias OriginalType!T B;
@@ -198,7 +198,8 @@ T readIter(T)(DBusMessageIter* iter)
 }
 
 T readIter(T)(DBusMessageIter* iter)
-    if (!(is(T == enum) && !is(T == InterfaceName) && !is(T == BusName)) && !isInstanceOf!(BitFlags, T) && canDBus!T) {
+    if (!(is(T == enum) && !is(T == InterfaceName) && !is(T == BusName) && !is(T == FileDescriptor))
+    && !isInstanceOf!(BitFlags, T) && canDBus!T) {
   auto argType = dbus_message_iter_get_arg_type(iter);
   T ret;
 

source/ddbus/thin.d

@@ -171,6 +171,17 @@ InterfaceName interfaceName(string path) pure @nogc nothrow @safe {
   return cast(InterfaceName) path;
 }
 
+/// Serving as a typesafe alias for a FileDescriptor.
+enum FileDescriptor : int {
+  none = -1,
+  max = int.max
+}
+
+/// Casts an integer to a FileDescriptor.
+FileDescriptor fileDescriptor(int fileNo) pure @nogc nothrow @safe {
+  return cast(FileDescriptor) fileNo;
+}
+
 unittest {
   import dunit.toolkit;
 
@@ -284,6 +295,9 @@ struct DBusAny {
     } else static if (is(T == int)) {
       this(typeCode!int, null, false);
       int32 = cast(int) value;
+    } else static if (is(T == FileDescriptor)) {
+      this(typeCode!FileDescriptor, null, false);
+      int32 = cast(int) value;
     } else static if (is(T == uint)) {
       this(typeCode!uint, null, false);
       uint32 = cast(uint) value;
@@ -459,6 +473,9 @@ struct DBusAny {
     case 'e':
       valueStr = entry.key.toString ~ ": " ~ entry.value.toString;
       break;
+    case 'h':
+      valueStr = int32.to!string;
+      break;
     default:
       valueStr = "unknown";
       break;
@@ -488,7 +505,9 @@ struct DBusAny {
         "Cannot get a " ~ T.stringof ~ " from a DBusAny with" ~ " a value of DBus type '" ~ typeSig ~ "'.",
         typeCode!T, type));
 
-    static if (isIntegral!T) {
+    static if (is(T == FileDescriptor)) {
+      return fileDescriptor(int32);
+    } else  static if (isIntegral!T) {
       enum memberName = (isUnsigned!T ? "uint" : "int") ~ (T.sizeof * 8).to!string;
       return __traits(getMember, this, memberName);
     } else static if (is(T == double)) {
@@ -730,6 +749,7 @@ unittest {
   test(variant(cast(short) 184), set!"int16"(DBusAny('n', null, true), cast(short) 184));
   test(variant(cast(ushort) 184), set!"uint16"(DBusAny('q', null, true), cast(ushort) 184));
   test(variant(cast(int) 184), set!"int32"(DBusAny('i', null, true), cast(int) 184));
+  test(variant(cast(FileDescriptor) 184), set!"int32"(DBusAny('h', null, true), cast(FileDescriptor) 184));
   test(variant(cast(uint) 184), set!"uint32"(DBusAny('u', null, true), cast(uint) 184));
   test(variant(cast(long) 184), set!"int64"(DBusAny('x', null, true), cast(long) 184));
   test(variant(cast(ulong) 184), set!"uint64"(DBusAny('t', null, true), cast(ulong) 184));

source/ddbus/util.d

@@ -55,7 +55,7 @@ template allCanDBus(TS...) {
  +/
 package  // Don't add to the API yet, 'cause I intend to move it later
 alias BasicTypes = AliasSeq!(bool, byte, short, ushort, int, uint, long, ulong,
-    double, string, ObjectPath, InterfaceName, BusName);
+    double, string, ObjectPath, InterfaceName, BusName, FileDescriptor);
 
 template basicDBus(T) {
   static if (staticIndexOf!(T, BasicTypes) >= 0) {
@@ -104,6 +104,7 @@ unittest {
   (canDBus!(Tuple!(int[], bool, Variant!short))).assertTrue();
   (canDBus!(Tuple!(int[], int[string]))).assertTrue();
   (canDBus!(int[string])).assertTrue();
+  (canDBus!FileDescriptor).assertTrue();
 }
 
 string typeSig(T)()
@@ -116,6 +117,8 @@ string typeSig(T)()
     return "n";
   } else static if (is(T == ushort)) {
     return "q";
+  } else static if (is(T == FileDescriptor)) {
+    return "h";
   } else static if (is(T == int)) {
     return "i";
   } else static if (is(T == uint)) {
@@ -217,6 +220,7 @@ unittest {
   typeSig!bool().assertEqual("b");
   typeSig!string().assertEqual("s");
   typeSig!(Variant!int)().assertEqual("v");
+  typeSig!FileDescriptor().assertEqual("h");
   // enums
   enum E : byte {
     a,
@@ -256,9 +260,10 @@ unittest {
     string d;
     S1 e;
     uint f;
+    FileDescriptor g;
   }
 
-  typeSig!S2.assertEqual("(vs(ids)u)");
+  typeSig!S2.assertEqual("(vs(ids)uh)");
   // arrays
   typeSig!(int[]).assertEqual("ai");
   typeSig!(Variant!int[]).assertEqual("av");