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-# VPP API Language {#api_lang_doc}
-
-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.
-
-```
-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.
-
-```
- 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:
-```
-option version = "1.0.0";
-```
-
-```
-
- 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:
-
-```
-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.
-
-```
-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*
-
-```
- 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.
-```
-import : IMPORT STRING_LITERAL ';'
-```
-
-### Comments
-
-The API language uses C style comments.
-```
-/* */
-//
-```
-
-### 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
-```
-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.
-
-```
- 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:
-```
-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.
-
-```
- 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_api_address_t|`<class 'ipaddress.IPv4Address'> or <class 'ipaddress.IPv6Address'>`
-vl_api_ip4_address_t|4|vl_api_ip4_address_t|`<class 'ipaddress.IPv4Address'>`
-vl_api_ip6_address_t|16|vl_api_ip6_address_t|`<class 'ipaddress.IPv6Address'>`
-vl_api_prefix_t|21|vl_api_prefix_t|`<class 'ipaddress.IPv4Network'> or <class 'ipaddress.IPv6Network'>`
-vl_api_ip4_prefix_t|5|vl_api_ip4_prefix_t|`<class 'ipaddress.IPv4Network'>`
-vl_api_ip6_prefix_t|17|vl_api_ip6_prefix_t|`<class 'ipaddress.IPv6Network'>`
-vl_api_ip4_address_with_prefix_t|5|vl_api_ip4_address_with_prefix_t|`<class 'ipaddress.IPv4Interface'>`
-vl_api_ip6_address_with_prefix_t|17|vl_api_ip6_address_with_prefix_t|`<class 'ipaddress.IPv6Interface'>`
-
-#### vnet/ethernet/ethernet_types.api
-.api type|size|C type|Python type
----------|----|------|-----------
-vl_api_mac_address_t|6|vl_api_mac_address_t|`class 'vpp_papi.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:
-```
-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:
-```
-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.