IDL data types

IDL supports primitive data types as well as composite data types. The set of supported composite types includes unions, structures, arrays, and sequences.

Primitive types

IDL supports the following primitive types:

• SInt8, SInt16, SInt32, SInt64 – signed integer.
• UInt8, UInt16, UInt32, UInt64 – unsigned integer.
• Handle – value whose binary representation consists of multiple fields, including a handle field and a handle permissions mask field.
• bytes<<size in bytes>> – byte buffer consisting of a memory area with a size that does not exceed the defined number of bytes.
• string<<size in bytes>> – string buffer consisting of a byte buffer whose last byte is a terminating zero. The maximum size of a string buffer is a unit larger than the defined size due to the additional byte with the terminating zero.

Integer literals can be specified in decimal format, hexadecimal format (for example, 0x2f, 0X2f, 0x2F, 0X2F) or octal format (for example, 0O123, 0o123).

You can use the reserved word const to define the named integer constants by assigning their values using integer literals or integer expressions.

Example definitions of named integer constants:

const UInt32 DeviceNameMax = 0o100;

const UInt32 HandleTypeUserLast = 0x0001FFFF;

const UInt32 MaxLogMessageSize = (2 << 3) ** 2;

const UInt32 MaxLogMessageCount = 100;

const UInt64 MaxLen = (MaxLogMessageSize + 4) * MaxLogMessageCount;

Named integer constants can be used to avoid problems associated with so-called "magic numbers". For example, if an IDL description defines named integer constants for return codes of an interface method, you can interpret these codes without additional information when describing a policy. Named integer constants and integer expressions can also be applied in definitions of byte buffers, string buffers, and composite types to define the size of data or the number of data elements.

The bytes<<size in bytes>> and string<<size in bytes>> constructs are used in definitions of composite types, signatures of interface methods, and when creating type aliases because they define anonymous types (types without a name).

Unions

A union stores different types of data in one memory area. In an IPC message, a union is provided with an additional tag field that defines which specific member of the union is used.

The following construct is used to define a union:

union <type name> {

<member type> <member name>;

[...]

}

Example of a union definition:

union ExitInfo {

UInt32 code;

ExceptionInfo exc;

}

Structures

The following construct is used to define a structure:

struct <type name> {

<field type> <field name>;

[...]

}

Example of a structure definition:

struct SessionEvqParams {

UInt32 count;

UInt32 align;

UInt32 size;

}

Arrays

The following construct is used to define an array:

array<<type of elements, number of elements>>

This construct is used in definitions of other composite types, signatures of interface methods, and when creating type aliases because it defines an anonymous type.

The Handle type can be used as the type of array elements if this array is not included in another composite data type. However, the total number of handles in an IPC message cannot exceed 255.

Sequences

A sequence is a variable-sized array. When defining a sequence, the maximum number of elements of the sequence is specified.

The following construct is used to define a sequence:

sequence<<type of elements, number of elements>>

This construct is used in definitions of other composite types, signatures of interface methods, and when creating type aliases because it defines an anonymous type.

The Handle type cannot be used as the type of sequence elements.

Variable-size and fixed-size types

The bytes, string and sequence types are variable-size types. In other words, the maximum number of elements is assigned when defining these types, but less elements (or none) may actually be used. Data of the bytes, string and sequence types are stored in the IPC message arena. All other types are fixed-size types. Data of fixed-size types are stored in the constant part of IPC messages.

Types based on composite types

Composite types can be used to define other composite types. The definition of an array or sequence can also be included in the definition of another type.

Example definition of a structure with embedded definitions of an array and sequence:

const UInt32 MessageSize = 64;

struct BazInfo {

array<UInt8, 100> a;

sequence<sequence<UInt32, MessageSize>, ((2 << 2) + 2 ** 2) * MessageSize> b;

string<100> c;

bytes<4096> d;

UInt64 e;

}

The definition of a union or structure cannot be included in the definition of another type. However, a type definition may include already defined unions and structures. This is done by indicating the names of the included types in the type definition.

Example definition of a structure that includes a union and structure:

union foo {

UInt32 value1;

UInt8 value2;

}

struct bar {

UInt32 a;

UInt8 b;

}

struct BazInfo {

foo x;

bar y;

}

Creating aliases of types

Type aliases make it more convenient to work with types. For example, type aliases can be used to assign mnemonic names to types that have abstract names. Assigned aliases for anonymous types also let you receive named types.

The following construct is used to create a type alias:

typedef <type name/anonymous type definition> <type alias>

Example of creating mnemonic aliases:

typedef UInt64 ApplicationId;

typedef Handle PortHandle;

Example of creating an alias for an array definition:

typedef array<UInt8, 4> IP4;

Example of creating an alias for a sequence definition:

const UInt32 MaxDevices = 8;

struct Device {

string<32> DeviceName;

UInt8 DeviceID;

}

typedef sequence<Device, MaxDevices> Devices;

Example of creating an alias for a union definition:

union foo {

UInt32 value1;

UInt8 value2;

}

typedef foo bar;

Defining anonymous types in signatures of interface methods

Anonymous types can be defined in signatures of interface methods.

Example of defining a sequence in an interface method signature:

const UInt8 DeviceCount = 8;

interface {

Poll(in UInt32 timeout,

out sequence<UInt32, DeviceCount / 2> report,

out UInt32 count,

out UInt32 rc);

}