src/tools/vppapigen/VPPAPI.rst - fdio/vpp - Gitiles

 VPP API Language
 ================

 The VPP binary API is a message passing API. The VPP API language is
 used to define a RPC interface between VPP and its control plane. The
 API messages supports shared memory transport and Unix domain sockets
 (SOCK_STREAM).

 The wire format is essentially that of a network formatted (big-endian)
 packed C struct.

 The VPP API compiler is located in *src/tools/vppapigen* and can
 currently compile to JSON or C (used by the VPP binary itself).

 Language definition
 -------------------

 Defining a messages
 ~~~~~~~~~~~~~~~~~~~

 There are 3 types of message exchanges:

 -  Request/Reply The client sends a request message and the server
    replies with a single reply message. The convention is that the reply
    message is named as method_name + \_reply.

 -  Dump/Detail The client sends a “bulk” request message to the server,
    and the server replies with a set of detail messages. These messages
    may be of different type. A dump/detail call must be enclosed in a
    control ping block (Otherwise the client will not know the end of the
    bulk transmission). The method name must end with method + “\_dump”,
    the reply message should be named method + “\_details”. The exception
    here is for the methods that return multiple message types
    (e.g. sw_interface_dump). The Dump/Detail methods are typically used
    for acquiring bulk information, like the complete FIB table.

 -  Events The client can register for getting asynchronous notifications
    from the server. This is useful for getting interface state changes,
    and so on. The method name for requesting notifications is
    conventionally prefixed with “want\_”. E.g. “want_interface_events”.
    Which notification types results from an event registration is
    defined in the service definition.

 A message from a client must include the ‘client_index’, an opaque
 cookie identifying the sender, and a ‘context’ field to let the client
 match request with reply.

 An example of a message definition. The client sends the show_version
 request, the server replies with the show_version_reply.

 The *client_index* and *context* fields are required in all requests.
 The *context* is returned by the server and is used by the client to
 match up request and reply messages.

 .. code-block:: c

    define show_version
    {
      u32 client_index;
      u32 context;
    };
    define show_version_reply
    {
      u32 context;
      i32 retval;
      string program [32];
      string version [32];
      string build_date [32];
      /* The final field can be a variable length argument */
      string build_directory [];
    };

 The flags are not used by the clients, but have special meaning for some
 of the tracing and debugging of the API. The *autoreply* flag is a
 shorthand for a reply message with just a *retval* field.

 .. code-block:: c

        define : DEFINE ID '{' block_statements_opt '}' ';'
        define : flist DEFINE ID '{' block_statements_opt '}' ';'
        flist : flag
              | flist flag
        flag : MANUAL_PRINT
             | MANUAL_ENDIAN
             | DONT_TRACE
             | AUTOREPLY

        block_statements_opt : block_statements
        block_statements : block_statement
                         | block_statements block_statement
        block_statement : declaration
                        | option
        declaration : type_specifier ID ';'
                    | type_specifier ID '[' ID '=' assignee ']' ';'
        declaration : type_specifier ID '[' NUM ']' ';'
                    | type_specifier ID '[' ID ']' ';'
        type_specifier : U8
                       | U16
                       | U32
                       | U64
                       | I8
                       | I16
                       | I32
                       | I64
                       | F64
                       | BOOL
                       | STRING
        type_specifier : ID

 Options
 ~~~~~~~

 The *option* word is used to specify meta information. The only current
 use is to specify a semantic version of the .api file itself.

 Example:

 .. code-block:: c

    option version = "1.0.0";

 .. code-block:: c


        option : OPTION ID '=' assignee ';'
        assignee : NUM
                 | TRUE
                 | FALSE
                 | STRING_LITERAL

 Defining new types
 ~~~~~~~~~~~~~~~~~~

 New user defined types are defined just like messages. A typedef has two
 forms. It can either define an alias for a different type (or array).

 Example:

 .. code-block:: c

    typedef u8 ip4_address[4];
    typedef u8 ip6_address[16];

 Where the above defines two new types *vl_api_ip4_address_t* and
 *vl_api_ip6_address_t*. These are aliases for the underlying u8 array.

 In the other form, it is used to specify an abstract data type.

 .. code-block:: c

    enum address_family {
      ADDRESS_IP4 = 0,
      ADDRESS_IP6,
    };

    union address_union {
      vl_api_ip4_address_t ip4;
      vl_api_ip6_address_t ip6;
    };

    typedef address {
      vl_api_address_family_t af;
      vl_api_address_union_t un;
    };

 Where the new type *vl_api_address_t*

 .. code-block:: c

        typedef : TYPEDEF ID '{' block_statements_opt '}' ';'
        typedef : TYPEDEF declaration

 Importing Definitions
 ~~~~~~~~~~~~~~~~~~~~~

 You can use definitions from other .api files by importing them. To
 import another .api’s definitions, you add an import statement to the
 top of your file:

 import “vnet/ip/ip_types.api”;

 By default you can only use definitions from directly imported .api
 files.

 The API compiler searches for imported files in a set of directories
 specified on the API compiler command line using the –includedir flag.

 .. code-block:: c

    import : IMPORT STRING_LITERAL ';'

 Comments
 ~~~~~~~~

 The API language uses C style comments.

 .. code-block:: c

    /* */
    //

 Enumerations
 ~~~~~~~~~~~~

 Enums are similar to enums in C.

 Every enum definition must contain a constant that maps to zero as its
 first element. This is because:

 There must be a zero value, so that we can use 0 as a numeric default
 value. The zero value needs to be the first element.

 As in C, enums can be used as flags or just as numbers. The on-wire, and
 in memory representation size of an enum can be specified. Not all
 language bindings will support that. The default size is 4 (u32).

 Example

 .. code-block:: c

    enum ip_neighbor_flags
    {
      IP_API_NEIGHBOR_FLAG_NONE = 0,
      IP_API_NEIGHBOR_FLAG_STATIC = 0x1,
      IP_API_NEIGHBOR_FLAG_NO_FIB_ENTRY = 0x2,
    };

 Which generates the vl_api_ip_neighbor_flags_t in the C binding. In
 Python that is represented as an IntFlag object
 VppEnum.vl_api_ip_neighbor_flags_t.

 .. code-block:: c

        enum : ENUM ID '{' enum_statements '}' ';'
        enum : ENUM ID ':' enum_size '{' enum_statements '}' ';'
        enum_size : U8
                  | U16
                  | U32
        enum_statements : enum_statement
                        | enum_statements enum_statement
        enum_statement : ID '=' NUM ','
                       | ID ','

 Services
 ~~~~~~~~

 The service statement defines the relationship between messages. For
 request/response and dump/details messages it ties the request with the
 reply. For events, it specifies which events that can be received for a
 given ``want_*`` call.

 Example:

 .. code-block:: c

    service {
      rpc want_interface_events returns want_interface_events_reply
        events sw_interface_event;
    };

 Which states that the request want_interface_events returns a
 want_interface_events_reply and if enabled the client will receive
 sw_interface_event messages whenever interface states changes.

 .. code-block:: c

        service : SERVICE '{' service_statements '}' ';'
        service_statements : service_statement
                        | service_statements service_statement
        service_statement : RPC ID RETURNS NULL ';'
                             | RPC ID RETURNS ID ';'
                             | RPC ID RETURNS STREAM ID ';'
                             | RPC ID RETURNS ID EVENTS event_list ';'
        event_list : events
                   | event_list events
        events : ID
               | ID ','

 Types
 -----

 Scalar Value Types
 ~~~~~~~~~~~~~~~~~~

 ========= ======== =============== ===========
 .api type size     C type          Python type
 ========= ======== =============== ===========
 i8        1        i8              int
 u8        1        u8              int
 i16       2        i16             int
 u16       2        u16             int
 i32       4        i32             int
 u32       4        u32             int
 i64       8        i64             int
 u64       8        u64             int
 f64       8        f64             float
 bool      1        bool            boolean
 string    variable vl_api_string_t str
 ========= ======== =============== ===========

 User Defined Types
 ~~~~~~~~~~~~~~~~~~

 vnet/ip/ip_types.api
 ^^^^^^^^^^^^^^^^^^^^

 +--------------------+--------+-------------+-------------------------+
 | .api type          | size   | C type      | Python type             |
 +====================+========+=============+=========================+
 | vl_api_address_t   | 20     | vl_ap       | `                       |
 |                    |        | i_address_t | `<class 'ipaddress.IPv4 |
 |                    |        |             | Address'> or <class 'ip |
 |                    |        |             | address.IPv6Address'>`` |
 +--------------------+--------+-------------+-------------------------+
 | vl                 | 4      | vl_api_ip   | ``<class 'ip            |
 | _api_ip4_address_t |        | 4_address_t | address.IPv4Address'>`` |
 +--------------------+--------+-------------+-------------------------+
 | vl                 | 16     | vl_api_ip   | ``<class 'ip            |
 | _api_ip6_address_t |        | 6_address_t | address.IPv6Address'>`` |
 +--------------------+--------+-------------+-------------------------+
 | vl_api_prefix_t    | 21     | vl_a        | `                       |
 |                    |        | pi_prefix_t | `<class 'ipaddress.IPv4 |
 |                    |        |             | Network'> or <class 'ip |
 |                    |        |             | address.IPv6Network'>`` |
 +--------------------+--------+-------------+-------------------------+
 | v                  | 5      | vl_api_i    | ``<class 'ip            |
 | l_api_ip4_prefix_t |        | p4_prefix_t | address.IPv4Network'>`` |
 +--------------------+--------+-------------+-------------------------+
 | v                  | 17     | vl_api_i    | ``<class 'ip            |
 | l_api_ip6_prefix_t |        | p6_prefix_t | address.IPv6Network'>`` |
 +--------------------+--------+-------------+-------------------------+
 | vl_api_ip4_add     | 5      | vl_api_ip4  | ``<class 'ipad          |
 | ress_with_prefix_t |        | _address_wi | dress.IPv4Interface'>`` |
 |                    |        | th_prefix_t |                         |
 +--------------------+--------+-------------+-------------------------+
 | vl_api_ip6_add     | 17     | vl_api_ip6  | ``<class 'ipad          |
 | ress_with_prefix_t |        | _address_wi | dress.IPv6Interface'>`` |
 |                    |        | th_prefix_t |                         |
 +--------------------+--------+-------------+-------------------------+

 vnet/ethernet/ethernet_types.api
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

 +---------------------+------+---------------------+-------------------+
 | .api type           | size | C type              | Python type       |
 +=====================+======+=====================+===================+
 | ``vl_               | 6    | ``vl_               | ``class 'vpp_pa   |
 | api_mac_address_t`` |      | api_mac_address_t`` | pi.MACAddress'>`` |
 +---------------------+------+---------------------+-------------------+

 vnet/interface_types.api
 ^^^^^^^^^^^^^^^^^^^^^^^^

 ======================== ==== ======================== ===========
 .api type                size C type                   Python type
 ======================== ==== ======================== ===========
 vl_api_interface_index_t 4    vl_api_interface_index_t int
 ======================== ==== ======================== ===========

 New explicit types
 ~~~~~~~~~~~~~~~~~~

 String versus bytes
 ^^^^^^^^^^^^^^^^^^^

 A byte string with a maximum length of 64:

 .. code-block:: c

    u8 name[64];

 Before the “string” type was added, text string were defined like this.
 The implications of that was the user would have to know if the field
 represented a \\0 ended C-string or a fixed length byte string. The wire
 format of the ‘string’ type is a u32 length

 An IPv4 or IPv6 address was previously defined like:

 .. code-block:: c

    u8 is_ip6;
    u8 address[16];

 Which made it hard for language bindings to represent the address as
 anything but a byte string. The new explicit address types are shown
 above.

 Language generators
 -------------------

 The VPP API compiler currently has two output modules. One generating
 JSON and one generating C header files that are directly used by the VPP
 infrastructure and plugins.

 The C/C++, Python, Go Lua, and Java language bindings are generated
 based on the JSON files.

 Future considerations
 ~~~~~~~~~~~~~~~~~~~~~

 -  Generate C/C++ (vapi) client code directly from vppapigen
 -  Embed JSON definitions into the API server, so dynamic languages
    can download them directly without going via the filesystem and JSON
    files.
	VPP API Language
	================

	The VPP binary API is a message passing API. The VPP API language is
	used to define a RPC interface between VPP and its control plane. The
	API messages supports shared memory transport and Unix domain sockets
	(SOCK_STREAM).

	The wire format is essentially that of a network formatted (big-endian)
	packed C struct.

	The VPP API compiler is located in src/tools/vppapigen and can
	currently compile to JSON or C (used by the VPP binary itself).

	Language definition
	-------------------

	Defining a messages
	~~~~~~~~~~~~~~~~~~~

	There are 3 types of message exchanges:

	- Request/Reply The client sends a request message and the server
	replies with a single reply message. The convention is that the reply
	message is named as method_name + \_reply.

	- Dump/Detail The client sends a “bulk” request message to the server,
	and the server replies with a set of detail messages. These messages
	may be of different type. A dump/detail call must be enclosed in a
	control ping block (Otherwise the client will not know the end of the
	bulk transmission). The method name must end with method + “\_dump”,
	the reply message should be named method + “\_details”. The exception
	here is for the methods that return multiple message types
	(e.g. sw_interface_dump). The Dump/Detail methods are typically used
	for acquiring bulk information, like the complete FIB table.

	- Events The client can register for getting asynchronous notifications
	from the server. This is useful for getting interface state changes,
	and so on. The method name for requesting notifications is
	conventionally prefixed with “want\_”. E.g. “want_interface_events”.
	Which notification types results from an event registration is
	defined in the service definition.

	A message from a client must include the ‘client_index’, an opaque
	cookie identifying the sender, and a ‘context’ field to let the client
	match request with reply.

	An example of a message definition. The client sends the show_version
	request, the server replies with the show_version_reply.

	The client_index and context fields are required in all requests.
	The context is returned by the server and is used by the client to
	match up request and reply messages.

	.. code-block:: c

	define show_version
	{
	u32 client_index;
	u32 context;
	};
	define show_version_reply
	{
	u32 context;
	i32 retval;
	string program [32];
	string version [32];
	string build_date [32];
	/* The final field can be a variable length argument */
	string build_directory [];
	};

	The flags are not used by the clients, but have special meaning for some
	of the tracing and debugging of the API. The autoreply flag is a
	shorthand for a reply message with just a retval field.

	.. code-block:: c

	define : DEFINE ID '{' block_statements_opt '}' ';'
	define : flist DEFINE ID '{' block_statements_opt '}' ';'
	flist : flag
	\| flist flag
	flag : MANUAL_PRINT
	\| MANUAL_ENDIAN
	\| DONT_TRACE
	\| AUTOREPLY

	block_statements_opt : block_statements
	block_statements : block_statement
	\| block_statements block_statement
	block_statement : declaration
	\| option
	declaration : type_specifier ID ';'
	\| type_specifier ID '[' ID '=' assignee ']' ';'
	declaration : type_specifier ID '[' NUM ']' ';'
	\| type_specifier ID '[' ID ']' ';'
	type_specifier : U8
	\| U16
	\| U32
	\| U64
	\| I8
	\| I16
	\| I32
	\| I64
	\| F64
	\| BOOL
	\| STRING
	type_specifier : ID

	Options
	~~~~~~~

	The option word is used to specify meta information. The only current
	use is to specify a semantic version of the .api file itself.

	Example:

	.. code-block:: c

	option version = "1.0.0";

	.. code-block:: c


	option : OPTION ID '=' assignee ';'
	assignee : NUM
	\| TRUE
	\| FALSE
	\| STRING_LITERAL

	Defining new types
	~~~~~~~~~~~~~~~~~~

	New user defined types are defined just like messages. A typedef has two
	forms. It can either define an alias for a different type (or array).

	Example:

	.. code-block:: c

	typedef u8 ip4_address[4];
	typedef u8 ip6_address[16];

	Where the above defines two new types vl_api_ip4_address_t and
	vl_api_ip6_address_t. These are aliases for the underlying u8 array.

	In the other form, it is used to specify an abstract data type.

	.. code-block:: c

	enum address_family {
	ADDRESS_IP4 = 0,
	ADDRESS_IP6,
	};

	union address_union {
	vl_api_ip4_address_t ip4;
	vl_api_ip6_address_t ip6;
	};

	typedef address {
	vl_api_address_family_t af;
	vl_api_address_union_t un;
	};

	Where the new type vl_api_address_t

	.. code-block:: c

	typedef : TYPEDEF ID '{' block_statements_opt '}' ';'
	typedef : TYPEDEF declaration

	Importing Definitions
	~~~~~~~~~~~~~~~~~~~~~

	You can use definitions from other .api files by importing them. To
	import another .api’s definitions, you add an import statement to the
	top of your file:

	import “vnet/ip/ip_types.api”;

	By default you can only use definitions from directly imported .api
	files.

	The API compiler searches for imported files in a set of directories
	specified on the API compiler command line using the –includedir flag.

	.. code-block:: c

	import : IMPORT STRING_LITERAL ';'

	Comments
	~~~~~~~~

	The API language uses C style comments.

	.. code-block:: c

	/* */
	//

	Enumerations
	~~~~~~~~~~~~

	Enums are similar to enums in C.

	Every enum definition must contain a constant that maps to zero as its
	first element. This is because:

	There must be a zero value, so that we can use 0 as a numeric default
	value. The zero value needs to be the first element.

	As in C, enums can be used as flags or just as numbers. The on-wire, and
	in memory representation size of an enum can be specified. Not all
	language bindings will support that. The default size is 4 (u32).

	Example

	.. code-block:: c

	enum ip_neighbor_flags
	{
	IP_API_NEIGHBOR_FLAG_NONE = 0,
	IP_API_NEIGHBOR_FLAG_STATIC = 0x1,
	IP_API_NEIGHBOR_FLAG_NO_FIB_ENTRY = 0x2,
	};

	Which generates the vl_api_ip_neighbor_flags_t in the C binding. In
	Python that is represented as an IntFlag object
	VppEnum.vl_api_ip_neighbor_flags_t.

	.. code-block:: c

	enum : ENUM ID '{' enum_statements '}' ';'
	enum : ENUM ID ':' enum_size '{' enum_statements '}' ';'
	enum_size : U8
	\| U16
	\| U32
	enum_statements : enum_statement
	\| enum_statements enum_statement
	enum_statement : ID '=' NUM ','
	\| ID ','

	Services
	~~~~~~~~

	The service statement defines the relationship between messages. For
	request/response and dump/details messages it ties the request with the
	reply. For events, it specifies which events that can be received for a
	given ``want_*`` call.

	Example:

	.. code-block:: c

	service {
	rpc want_interface_events returns want_interface_events_reply
	events sw_interface_event;
	};

	Which states that the request want_interface_events returns a
	want_interface_events_reply and if enabled the client will receive
	sw_interface_event messages whenever interface states changes.

	.. code-block:: c

	service : SERVICE '{' service_statements '}' ';'
	service_statements : service_statement
	\| service_statements service_statement
	service_statement : RPC ID RETURNS NULL ';'
	\| RPC ID RETURNS ID ';'
	\| RPC ID RETURNS STREAM ID ';'
	\| RPC ID RETURNS ID EVENTS event_list ';'
	event_list : events
	\| event_list events
	events : ID
	\| ID ','

	Types
	-----

	Scalar Value Types
	~~~~~~~~~~~~~~~~~~

	========= ======== =============== ===========
	.api type size C type Python type
	========= ======== =============== ===========
	i8 1 i8 int
	u8 1 u8 int
	i16 2 i16 int
	u16 2 u16 int
	i32 4 i32 int
	u32 4 u32 int
	i64 8 i64 int
	u64 8 u64 int
	f64 8 f64 float
	bool 1 bool boolean
	string variable vl_api_string_t str
	========= ======== =============== ===========

	User Defined Types
	~~~~~~~~~~~~~~~~~~

	vnet/ip/ip_types.api
	^^^^^^^^^^^^^^^^^^^^

	+--------------------+--------+-------------+-------------------------+
	\| .api type \| size \| C type \| Python type \|
	+====================+========+=============+=========================+
	\| vl_api_address_t \| 20 \| vl_ap \| ` \|
	\| \| \| i_address_t \| `<class 'ipaddress.IPv4 \|
	\| \| \| \| Address'> or <class 'ip \|
	\| \| \| \| address.IPv6Address'>`` \|
	+--------------------+--------+-------------+-------------------------+
	\| vl \| 4 \| vl_api_ip \| ``<class 'ip \|
	\| _api_ip4_address_t \| \| 4_address_t \| address.IPv4Address'>`` \|
	+--------------------+--------+-------------+-------------------------+
	\| vl \| 16 \| vl_api_ip \| ``<class 'ip \|
	\| _api_ip6_address_t \| \| 6_address_t \| address.IPv6Address'>`` \|
	+--------------------+--------+-------------+-------------------------+
	\| vl_api_prefix_t \| 21 \| vl_a \| ` \|
	\| \| \| pi_prefix_t \| `<class 'ipaddress.IPv4 \|
	\| \| \| \| Network'> or <class 'ip \|
	\| \| \| \| address.IPv6Network'>`` \|
	+--------------------+--------+-------------+-------------------------+
	\| v \| 5 \| vl_api_i \| ``<class 'ip \|
	\| l_api_ip4_prefix_t \| \| p4_prefix_t \| address.IPv4Network'>`` \|
	+--------------------+--------+-------------+-------------------------+
	\| v \| 17 \| vl_api_i \| ``<class 'ip \|
	\| l_api_ip6_prefix_t \| \| p6_prefix_t \| address.IPv6Network'>`` \|
	+--------------------+--------+-------------+-------------------------+
	\| vl_api_ip4_add \| 5 \| vl_api_ip4 \| ``<class 'ipad \|
	\| ress_with_prefix_t \| \| _address_wi \| dress.IPv4Interface'>`` \|
	\| \| \| th_prefix_t \| \|
	+--------------------+--------+-------------+-------------------------+
	\| vl_api_ip6_add \| 17 \| vl_api_ip6 \| ``<class 'ipad \|
	\| ress_with_prefix_t \| \| _address_wi \| dress.IPv6Interface'>`` \|
	\| \| \| th_prefix_t \| \|
	+--------------------+--------+-------------+-------------------------+

	vnet/ethernet/ethernet_types.api
	^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

	+---------------------+------+---------------------+-------------------+
	\| .api type \| size \| C type \| Python type \|
	+=====================+======+=====================+===================+
	\| ``vl_ \| 6 \| ``vl_ \| ``class 'vpp_pa \|
	\| api_mac_address_t`` \| \| api_mac_address_t`` \| pi.MACAddress'>`` \|
	+---------------------+------+---------------------+-------------------+

	vnet/interface_types.api
	^^^^^^^^^^^^^^^^^^^^^^^^

	======================== ==== ======================== ===========
	.api type size C type Python type
	======================== ==== ======================== ===========
	vl_api_interface_index_t 4 vl_api_interface_index_t int
	======================== ==== ======================== ===========

	New explicit types
	~~~~~~~~~~~~~~~~~~

	String versus bytes
	^^^^^^^^^^^^^^^^^^^

	A byte string with a maximum length of 64:

	.. code-block:: c

	u8 name[64];

	Before the “string” type was added, text string were defined like this.
	The implications of that was the user would have to know if the field
	represented a \\0 ended C-string or a fixed length byte string. The wire
	format of the ‘string’ type is a u32 length

	An IPv4 or IPv6 address was previously defined like:

	.. code-block:: c

	u8 is_ip6;
	u8 address[16];

	Which made it hard for language bindings to represent the address as
	anything but a byte string. The new explicit address types are shown
	above.

	Language generators
	-------------------

	The VPP API compiler currently has two output modules. One generating
	JSON and one generating C header files that are directly used by the VPP
	infrastructure and plugins.

	The C/C++, Python, Go Lua, and Java language bindings are generated
	based on the JSON files.

	Future considerations
	~~~~~~~~~~~~~~~~~~~~~

	- Generate C/C++ (vapi) client code directly from vppapigen
	- Embed JSON definitions into the API server, so dynamic languages
	can download them directly without going via the filesystem and JSON
	files.