CONFORMANT ARRAYS¶

A conformant array is one with that ends in [*] or []. The strange things about conformant arrays are that they can only appear as the last element of a structure (unless there is a pointer to the conformant array, of course) and the array size appears before the structure itself on the wire.

So, in this example:

        typedef struct {
                long abc;
                long count;
                long foo;
                [size_is(count)] long s[*];
        } Struct1;

it appears like this:

        [size_is] [abc] [count] [foo] [s...]

the first [size_is] field is the allocation size of the array, and occurs before the array elements and even before the structure alignment.

Note that size_is() can refer to a constant, but that doesn't change the wire representation. It does not make the array a fixed array.

midl.exe would write the above array as the following C header:

   typedef struct {
                long abc;
                long count;
                long foo;
                long s[1];
        } Struct1;

pidl takes a different approach, and writes it like this:

        typedef struct {
                long abc;
                long count;
                long foo;
                long *s;
        } Struct1;

VARYING ARRAYS¶

A varying array looks like this:

        typedef struct {
                long abc;
                long count;
                long foo;
                [size_is(count)] long *s;
        } Struct1;

This will look like this on the wire:

        [abc] [count] [foo] [PTR_s]    [count] [s...]

FIXED ARRAYS¶

A fixed array looks like this:

        typedef struct {
                long s[10];
        } Struct1;

The NDR representation looks just like 10 separate long declarations. The array size is not encoded on the wire.

pidl also supports "inline" arrays, which are not part of the IDL/NDR standard. These are declared like this:

        typedef struct {
                uint32 foo;
                uint32 count;
                uint32 bar;
                long s[count];
        } Struct1;

This appears like this:

        [foo] [count] [bar] [s...]

Fixed arrays are an extension added to support some of the strange embedded structures in security descriptors and spoolss.

This section is by no means complete. See the OpenGroup and MSDN documentation for additional information.

Missing features in pidl¶

The following MIDL features are not (yet) implemented in pidl or are implemented with an incompatible interface:

• Asynchronous communication
• Typelibs (.tlb files)
• Datagram support (ncadg_*)

Supported attributes and statements¶

in, out, ref, length_is, switch_is, size_is, uuid, case, default, string, unique, ptr, pointer_default, v1_enum, object, helpstring, range, local, call_as, endpoint, switch_type, progid, coclass, iid_is, represent_as, transmit_as, import, include, cpp_quote.

PIDL Specific properties¶

public

The [public] property on a structure or union is a pidl extension that forces the generated pull/push functions to be non-static. This allows you to declare types that can be used between modules. If you don't specify [public] then pull/push functions for other than top-level functions are declared static.

noprint

The [noprint] property is a pidl extension that allows you to specify that pidl should not generate a ndr_print_*() function for that structure or union. This is used when you wish to define your own print function that prints a structure in a nicer manner. A good example is the use of [noprint] on dom_sid, which allows the pretty-printing of SIDs.

value

The [value(expression)] property is a pidl extension that allows you to specify the value of a field when it is put on the wire. This allows fields that always have a well-known value to be automatically filled in, thus making the API more programmer friendly. The expression can be any C expression.

relative

The [relative] property can be supplied on a pointer. When it is used it declares the pointer as a spoolss style "relative" pointer, which means it appears on the wire as an offset within the current encapsulating structure. This is not part of normal IDL/NDR, but it is a very useful extension as it avoids the manual encoding of many complex structures.

subcontext(length)

Specifies that a size of length bytes should be read, followed by a blob of that size, which will be parsed as NDR.

subcontext() is deprecated now, and should not be used in new code. Instead, use represent_as() or transmit_as().

flag

Specify boolean options, mostly used for low-level NDR options. Several options can be specified using the | character. Note that flags are inherited by substructures!

nodiscriminant

The [nodiscriminant] property on a union means that the usual uint16 discriminent field at the start of the union on the wire is omitted. This is not normally allowed in IDL/NDR, but is used for some spoolss structures.

charset(name)

Specify that the array or string uses the specified charset. If this attribute is specified, pidl will take care of converting the character data from this format to the host format. Commonly used values are UCS2, DOS and UTF8.

Unsupported MIDL properties or statements¶

aggregatable, appobject, async_uuid, bindable, control, defaultbind, defaultcollelem, defaultvalue, defaultvtable, dispinterface, displaybind, dual, entry, first_is, helpcontext, helpfile, helpstringcontext, helpstringdll, hidden, idl_module, idl_quote, id, immediatebind, importlib, includelib, last_is, lcid, licensed, max_is, module, ms_union, no_injected_text, nonbrowsable, noncreatable, nonextensible, odl, oleautomation, optional, pragma, propget, propputref, propput, readonly, requestedit, restricted, retval, source, uidefault, usesgetlasterror, vararg, vi_progid, wire_marshal.