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diff --git a/src/tools/vppapigen/VPPAPI.md b/src/tools/vppapigen/VPPAPI.md new file mode 100644 index 00000000000..9f6ef6523d0 --- /dev/null +++ b/src/tools/vppapigen/VPPAPI.md @@ -0,0 +1,343 @@ +# 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 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 [limit = 32]; + string version [limit = 32]; + string build_date [limit = 32]; + string build_directory [limit = 256]; +}; + +``` + +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 underlaying +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'>` + +#### 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. |