BRIDGESUPPORT(5) File Formats Manual BRIDGESUPPORT(5)

BridgeSupportScripting bridges support file

BridgeSupport files are XML files that describe the API symbols of frameworks or libraries that cannot be introspected at runtime. These are generally ANSI C symbols that are non-object-oriented items such as constants, enumerations, structures, and functions but can also include some additional information about classes, methods, and informal protocols.

BridgeSupport files are a major component of the Objective-C bridges (PyObjC) supported in Mac OS X for scripting languages such as Python.

gen_bridge_metadata(1) is the tool used to generate BridgeSupport files for particular frameworks or libraries.

To understand the following discussion you should know what “element” and “attribute” mean in XML markup. You should also be familiar with Objective-C and with concepts related to the Objective-C runtime, such as the type-encoding constants.

As of Mac OS 10.7, BridgeSupport uses an improved parser, based on clang. This means the BridgeSupport files should be more correct and complete, and the true parsing allows the automatic extraction of metadata from existing () information supported by the compiler (see below).

As of Mac OS 11.0, 32-bit support is deprecated. BridgeSupport files should only contain 64-bit attributes.

The structure of BridgeSupport XML consists of a hierarchy of elements under the root element, signatures.

signatures is the top-level, or root, element of a BridgeSupport XML file.

Mandatory attributes:

version
The version number of the BridgeSupport format. The only possible value is “1.0” which means the format delivered with Mac OS X 10.5.

Possible children elements: depends_on, struct, cftype, opaque, constant, string_constant, enum, function, function_alias, informal_protocol, class.

This element describes a dependency on other frameworks. This element is deprecated and no longer provided.

Mandatory attributes:

path
The path of the dependency.

This element describes a C structure.

Mandatory attributes:

name
The name of the C structure.
type, type64
The complete type of the C structure, including the field names, as a string of Objective-C runtime encoding types. If the element has a different type on a 64-bit environment, the type64 attribute will contain it. If the element does not exist on a 32-bit environment, only the type64 attribute will be used.

Optional attributes:

opaque
Indicates whether the fields of the structure should be exposed. The default value is “false”.

This element describes a Core Foundation-based type.

Mandatory attributes:

name
The name of the Core Foundation type.
type, type64
The type of the Core Foundation type as a string of Objective-C runtime encoding types. If the element has a different type on a 64-bit environment, the type64 attribute will contain it. If the element does not exist on a 32-bit environment, only the type64 attribute will be used.

Optional attributes:

tollfree
The name of the tollfree-bridged Objective-C class, if any.
gettypeid_func
The name of the function that retrieves the TypeID value of the given Core Foundation type, if any. This name usually ends with “GetTypeID”.

This element describes an opaque type, most generally a C pointer to a C opaque structure.

Mandatory attributes:

name
The name of the opaque type.
type, type64
The type of the opaque type, as a string of Objective-C runtime encoding types. If the element has a different type on a 64-bit environment, the type64 attribute will contain it. If the element does not exist on a 32-bit environment, only the type64 attribute will be used.

This element describes a C constant.

Mandatory attributes:

name
The name of the C constant.
type, type64
The type of the C constant, as a string of Objective-C runtime encoding types. If the element has a different type on a 64-bit environment, the type64 attribute will contain it. If the element does not exist on a 32-bit environment, only the type64 attribute will be used.

Optional attributes:

magic_cookie
Indicates whether the C constant has a “magic” or fixed value and should not be converted at runtime to the given type. The default value is “false”.

This element describes a string constant. The string can either be a C string or an Objective-C string (an NSString object). string_constant elements are usually created from C preprocessor macros.

Mandatory attributes:

name
The name of the string constant.
value
The value of the string constant.

Optional attributes:

nsstring
Indicates whether the string constant has an Objective-C value, and should be converted to an NSString object. The default value is “false”.

This element describes a C enumeration.

Mandatory attributes:

name
The name of the C enumeration.
value, value64
The value of the C enumeration, as an integer. The value can be negative. If the enumeration has a different value on a 64-bit environment, the value64 attribute will contain it. If the enumeration does not exist on a 32-bit environment, only the value64 attribute will be used. (The le_value and be_value values for little and big endian platforms are no longer supported; only native, little endian order is now used.)

Optional attributes:

ignore
Indicates whether the C enumeration should be ignored by the bridges. The default value is “false”.
suggestion
If the ignore attribute is “true” , this attribute may contain a textual message that the bridges can deliver as an exception or error message to be delivered to the user. By default there is no suggestion.

This element describes a C function.

Mandatory attributes:

name
The name of the C function.

Optional attributes:

variadic
Indicates whether the C function accepts a variable number of arguments. The default value is “false”.
sentinel
An integer value that specifies which argument (counting backwards from the end of the argument list) must be a NULL value to indicate the end of a variable length argument list (thus, this is only legal for variadic functions). (The ((sentinel)) compiler attribute will be automatically recognized by the new parser, and the given sentinel value (defaulting to zero), will be assigned to the sentinel attribute.)
inline
Indicates whether the C function is inline. In that case, the symbol can be found in the respective .dylib file that comes with the BridgeSupport file. Consult gen_bridge_metadata(1) to know how the dylib files are generated. The default value is “false”.

Possible children: arg (zero or more), retval (zero or one).

This element defines an alias or shortcut to a C function.

Mandatory attributes:

name
The name of the C function alias.
original
The name of the original C function the alias points to.

This element defines an Objective-C class. Only classes where additional metadata is needed are described.

Mandatory attributes:

name
The name of the Objective-C class.

Possible children: method (zero or more).

This element defines an Objective-C informal protocol.

Mandatory attributes:

name
The name of the Objective-C informal protocol.

Possible children: method (zero or more).

This element defines an Objective-C method. Only methods where additional metadata is needed are described.

Mandatory attributes:

selector
The selector of the Objective-C method.

Mandatory attributes (only when declared under informal_protocol) :

type, type64
The type of the Objective-C method, as a string of Objective-C runtime encoding types. If the element has a different type on a 64-bit environment, the type64 attribute will contain it. If the element does not exist on a 32-bit environment, only the type64 attribute will be used.

Optional attributes:

class_method
Whether this is a class method or not. The default value is “false”.

Optional attributes (only when not declared under informal_protocol) :

variadic
Indicates whether the method accepts a variable number of arguments. The default value is “false”.
sentinel
An integer value that specifies which argument (counting backwards from the end of the argument list) must be a NULL value to indicate the end of a variable length argument list (thus, this is only legal for variadic methods). (The ((sentinel)) compiler attribute will be automatically recognized by the new parser, and the given sentinel value (defaulting to zero), will be assigned to the sentinel attribute.)
ignore
Indicates whether the method should be ignored by the bridges. The default value is “false”.
suggestion
If the ignore attribute is “true” , this attribute may contain a textual message that the bridges can deliver as an exception or error message to be delivered to the user. By default there is no suggestion.

Possible children (only when not declared under informal_protocol) : arg (zero or more), retval (zero or one).

These elements describe respectively an argument and a return value. They should be defined within both function and method elements, and their attributes depend under which element they are defined under.

Optional attributes:

c_array_length_in_arg
Defines the argument or return value as a C array whose length is defined by the value of the given argument. The value of this attribute is the index position of the argument that should contain the array size. The value can also be two integers separated by a comma, which in that case means that the first value is used when converting to C / Objective-C, and the second when converting back to the scripting language. This attribute cannot be used with another “c_array_” attribute.
c_array_of_fixed_length
Defines the argument or return value as a C array of a fixed length. The value of this attribute is the array size. This attribute cannot be used with another “c_array_” attribute.
c_array_delimited_by_null
Defines the argument or return value as a C array that ends with a NULL value, if the value of this attribute is “true”. The default value of this attribute is “false”. This attribute cannot be used with another “c_array_” attribute.
c_array_of_variable_length
Defines the argument or return value as a C array of a variable length, if the value of this attribute is “true”. The default value of this attribute is “false”. This attribute cannot be used with another “c_array_” attribute.
function_pointer
Indicates whether the argument or return value is a function or block pointer. If “true”, the type attribute will be '^?' for functions and '@?' for blocks, and the current element should have a set of complete arg and retval child elements to define both the argument and the return value types of the function or block pointer.
sel_of_type, sel_of_type64
This attribute, used for arguments or return value of the type “SEL” (an Objective-C selector), is used to provide the signature of the method the selector should point to, as a string of Objective-C runtime encoding types. If the selector has a different type on a 64-bit environment, the sel_of_type64 attribute will contain it. There is no default value. This attribute can be used to give a hint to the bridges when their default behavior isn't sufficient.

Optional attributes (arg only):

c_array_length_in_retval
Defines the argument as a C like array whose length is defined by the value of the return value, if “true”. The default value of this attribute is “false”. This attribute cannot be used with another “c_array_” attribute.
type_modifier
The type modifier of the argument. Possible values are “n” (in), “o” (out) and “N” (inout). There is no default value. (For Objective C methods arguments, the in, out and inout type modifiers will be automatically recognized by the new parser, and the appropriate type_modifier attribute will be set.)
null_accepted
Indicates whether a NULL value can be passed to this argument. The default value is “true”. (The ((nonnull)) compiler attribute will be automatically recognized by the new parser, and the corresponding argument's null_accepted attribute will set to “false”.)
printf_format
Indicates whether this argument accepts a printf(3) format string value. The default value is “false”. (The __attribute__((format(printf, m, n))) compiler attribute will be automatically recognized by the new parser, and the m-th argument's printf_format attribute will be set to “true”.)

Optional attributes (retval only):

already_retained
A value of “true” indicates that the return value should not be retained by the bridges. The default value is “false”.

Mandatory attributes (when declared under function):

type, type64
The type of the argument or return value, as a string of Objective-C runtime encoding types. If the element has a different type on a 64-bit environment, the type64 attribute will contain it. If the element does not exist on a 32-bit environment, only the type64 attribute will be used.

Mandatory attributes (when declared under method, arg only):

index
The index position of the argument.

Optional attributes (when declared under method):

type, type64
The type of the argument or return value, as a string of Objective-C runtime encoding types. If the element has a different type on a 64-bit environment, the type64 attribute will contain it. If the element does not exist on a 32-bit environment, only the type64 attribute will be used. This attribute is optional for methods as the bridges can retrieve the type by asking the runtime, but it is possible to override the default type using this attribute. There is no default value.

gen_bridge_metadata(1) /System/Library/DTDs/BridgeSupport.dtd

May 24, 2010 macOS 14.4