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GoVPP User Guide

This section contains reference documentation for working with GoVPP, generating VPP binary API bindings, calling VPP API, retrieving VPP Stats data and other GoVPP features.

Table of Contents

Binary API Generator

The binary API generator's purpose is to generate Go code bindings for the VPP API. It uses VPP API definitions from *.api.json files as source and generates a Go package for each VPP API file, where each package contains Go types for objects from the VPP API file (messages, types, enums..).

Installation

Prerequisites

Install binapi-generator into $GOPATH/bin (defaults to: $HOME/go/bin) using the Go toolchain:

# Latest release
go install go.fd.io/govpp/cmd/binapi-generator@latest

# Specific version
go install go.fd.io/govpp/cmd/[email protected]

# Development branch
go install go.fd.io/govpp/cmd/binapi-generator@master

Note Development branch might not have stable behavior.

Print the version for the installed binapi-generator:

$ binapi-generator -version
govpp v0.8.0-dev

Using Generator

Source of VPP API files

To generate Go code bindings, you need to provide source of VPP API files in JSON format (*.api.json). There are several ways to get it:

  1. Download and install VPP from packagecloud.io (learn more).
  2. Clone the VPP repository (git clone https://github.com/FDio/vpp.git) and run make json-api-files. The VPP API files will be in: ./vpp/build-root/install-vpp-native/vpp/share/vpp/api/.
  3. If the VPP is already installed in your system, the default location for the VPP API files is: /usr/share/vpp/api/

Generating Go Bindings

If the VPP JSON API definitions are in the default directory /usr/share/vpp/api, call:

binapi-generator --input "/usr/share/vpp/api"

Generated Go code bindings will be under ./binapi directory.

Note The Go package path of generated files will be resolved automatically from the module path in go.mod file. To set the Go package path manually, use option --import-prefix=PREFIX.

If you have a Go project (called myproject in $HOME/myproject/vppbinapi) with GoVPP as a dependency with both, the binary API generator and the VPP connection client, generated bindings are required to be inside the project (for example in $HOME/myproject/vppbinapi)

To modify the VPP API input directory, use -input-dir option. To modify the output directory, use the -output option.

binapi-generator --input-dir="/path/to/vpp/api" --output-dir="/path/to/generated/bindings"

This option might require setting the correct--import-prefix as well.

Options

The list of binapi-generator optional arguments in form binapi-generator [OPTIONS] ARGS

  • binapi-generator -version prints the generator version, for example, govpp v0.8.0-dev
  • binapi-generator -gen=http injects the http plugin to generate additional files. More plugins are separated with comma, i.e. -gen-http,rpc. Note that rpc plugin is used by default
  • binapi-generator -import-prefix=/desired/prefix/path sets the go package name to be used in the generated bindings ( the string used in imports)
  • binapi-generator -input-dir=/vpp/api/input/dir sets the custom input directory instead of the default
  • binapi-generator -output-dir=/bin/api/output/dir sets the custom output directory. It may or may not match the -import-prefx, based on go.mod.
  • binapi-generator -debug prints some additional logs

Generator Plugins

The binary API generator supports extending its functionality with plugins that can generate additional files.

Available built-in plugins:

VPP Startup

Define the minimal startup.conf:

unix {interactive}
socksvr { socket-name /var/run/vpp/api.sock }

Start with startup.conf if the VPP was installed from sources:

<vpp_repo_dir>/build-root/install-vpp_debug-native/vpp/bin/vpp -c /tmp/startup.conf

If it was installed from the package:

vpp -c /tmp/startup.conf

VPP API calls

GoVPP client uses its own (pure Go) implementation to handle the low-level parts of the VPP API communication.

Connection

Two connection types to the binary API socket are exist - synchronous and asynchronous. GoVPP can connect to more VPPs by creating multiple connections (see the multi-vpp example)

Synchronous Connect

The synchronous connecting creates a new adapter instance. The call blocks until the connection is established.

conn, err := govpp.Connect(socketPath)
if err != nil {
  // handle the error
}
defer conn.Disconnect()

Asynchronous Connect

The main difference between the synchronous and asynchronous connection is that the asynchronous connection does not block until the connection is ready. Instead, the caller receives a channel to watch connection events. Asynchronous connection defines additional parameters attemptNum and interval defining the number of reconnecting attempts, and an interval (in seconds) between those attempts.

conn, connEv, err := govpp.AsyncConnect(socketPath, attemptNum, interval)
if err != nil {
  // handle error
}
defer conn.Disconnect()

// wait for the connection event
e := <-connEv
if e.State != core.Connected {
  // handle error in e.Error
}

Sending API messages

Each binary API message in the Go-generated API is a data structure. The caller can send API messages either using a Channel (legacy method) or a Stream. In-depth discussion about differences between Channel and Stream can be found FDio#43.

Messages can be requests, replies or events. The request might expect just one response (request), or more than one response (multirequest). It is possible to determine the message type out of its name.

Note The naming might not be consistent across the VPP API.

  • Requests have no special suffix for the request, or Dump or Get for the multirequest.
  • Responses have a Reply suffix for the request or Details for multirequest.

Stream client

The Stream is the new and preferred way to call VPP API. It provides a "low-level" API to allow complete control of the communication process. This means that it requires the caller to handle all aspects of VPP API semantics, e.g. send control ping after dump request, check the message type and value of Retval field in responses.

Note: handling of the VPP API semantics mentioned above is only required when using Stream directly. Users should use generated RPC clients which handle all of this automatically.

New Stream can be created by calling Connection's method NewStream:

stream, err := conn.NewStream(context.Background(), options...)
if err != nil {
  // handle error
}

The NewStream method also accepts following options:

  • WithRequestSize(size int) sets the size of the request channel buffer
  • WithReplySize(size int) sets the size of the reply channel buffer
  • WithReplyTimeout(timeout time.Duration) sets the reply timeout

The single request procedure requires the user to convert the generic reply (the Message interface type) to the proper reply type.

req := &interfaces.CreateLoopback{
   // fill with data
}
if err := stream.SendMsg(req); err != nil {
  // handle error
}
replyMsg, err := stream.RecvMsg()
if err != nil {
  // handle error
}
reply := replyMsg.(*interfaces.CreateLoopbackReply)

The simpler way is to use the Invoke() method, which does the same procedure as above.

req := &interfaces.CreateLoopback{
   // fill with data
}
var reply interfaces.CreateLoopbackReply
err := c.conn.Invoke(context.Background(), req, &reply)
if err != nil {
  // handle error
}

The multirequest message must be followed up by the control ping request. The loop collecting replies must watch for the control ping reply signalizing the end.

   if err := stream.SendMsg(&interfaces.SwInterfaceDump{}); err != nil {
     // handle error
   }
   if err := stream.SendMsg(&memclnt.ControlPing{}); err != nil {
     // handle error
   }

Loop:
   for {
      reply, err := stream.RecvMsg()
      if err != nil {
         // handle error
      }
      switch reply.(type) {
         case *interfaces.SwInterfaceDetails:
            // handle the message
         case *memclnt.ControlPingReply:
            break Loop
         default:
            // unexpected message type
      }
   }

There is another type of the multirequest, and this one needs to be handled differently. It can be easily identified with the Get suffix and the cursor parameter. This type of multirequest is read in batches. Each batch has a number of data replies, and if the reader should continue with another batch, the cursor points to the next index.

The user has to expect two reply types, the Details containing the data, and the Reply marking the end of the batch, and the new cursor value.

The initial batch always starts with zero.

cursor uint32 = 0
for {
   if cursor == ^uint32(0) { // cursor pointing to this value marks the end of the multirequest
      return
   }
   if err := stream.SendMsg(&pnat.PnatBindingsGet{
      Cursor: cursor,
   }); err != nil {
      // handle error
   }
   // new batch loop
   for {
      msg, err := stream.RecvMsg()
      if err != nil {
         // handle error
      }
      switch reply := msg.(type) {
         case *pnat.PnatBindingsDetails:
            // handle the data
         case *pnat.PnatBindingsGetReply:
            cursor = reply.Cursor // the new cursor value
            // handle error
            break
         default:
            // unexpected reply type
      }
   }
}

Channel

Warning The Channel are planned to be deprecated in the future.

The Channel is the main communication unit between the caller and the VPP. After the successful connection, the channel is simply created from the connection object.

ch, err := conn.NewAPIChannel()
if err != nil {
   // handle error
}

The new channel starts watching caller requests immediately.

The channel can do a compatibility check for all the messages from any generated VPP API file.

if err := ch.CheckCompatiblity(vpe.AllMessages()...); err != nil {
   // handle error
}

A single request is done by calling the asynchronous request/reply on a channel. The request returns the request context allowing to receive the reply.

req := &interfaces.CreateLoopback{} // fill with data
reply := &interfaces.CreateLoopbackReply{}
if err := ch.SendRequest(req).ReceiveReply(reply); err != nil {
   // handler error
}

The multirequest expects more than one response. Its context contains information about the last item in the request list.

req := &interfaces.SwInterfaceDump{} // fill with data
reqCtx := ch.SendMultiRequest(req)
for {
   reply := &interfaces.SwInterfaceDetails{}
   stop, err := reqCtx.ReceiveReply(reply)
   if err != nil {
      // handle error
   }
   if stop {
      break
   }
   // handle the reply before the next iteration
}

Note The multirequest message suffixed with Get needs a different type of handling using the stream client.

HTTP Service

Before using the HTTP service, the VPP binary API binding must be generated with the http plugin to create HTTP files, and the rpc plugin to create RPC files. RPC is used inside HTTP handler functions.

Create the new HTTP handler and listener (requires the connection instance, and the RPC service client)

vpeRpcClient := vpe.NewServiceClient(conn)
vpeHttpClient := vpe.HTTPHandler(vpeRpcClient)
if err := http.ListenAndServe(":8000", vpeHttpClient); err != nil {
   // handle error
}

With the http server running, you can use curl command to call VPP API via HTTP request:

$ curl http://localhost:8000/show_version
{
  "program": "vpe",
  "version": "23.06-rc0~71-g182d2b466",
  "build_date": "2023-02-20T07:52:13",
  "build_directory": "/home/go/src/git.fd.io/vpp"
}

RPC Client

The RPC client is a generated client implementation by generator plugin rpc in separate file named *.rpc.ba for each generated file (package) of the VPP binary API.

Each generated VPP binary API file (package) contains RPC service interface RPCService and RPC client serviceClient that implements the RPC service interface. For each service RPC method defined in VPP API file, the RPC service interface defines a method and the RPC client implements it according to the service definition of the VPP binary API file.

To create the new RPC service client, use function NewServiceClient(conn api.Connection), which accepts the connection instance.

nat64RpcClient := nat64.NewServiceClient(conn)
vpeRpcClient := vpe.NewServiceClient(conn)

Simple request:

c := memif.NewServiceClient(conn)
req := &memif.MemifCreate{} // fill with data
reply, err := c.MemifCreate(context.Background(), req)
if err != nil {
   // handle error
}

Multirequest (the end of the multirequest is determined by checking the EOF error):

c := interfaces.NewServiceClient(conn)
stream, err := c.SwInterfaceDump(context.Background(), &interfaces.SwInterfaceDump{})
if err != nil {
   // handle error
}
for {
   iface, err := stream.Recv()
   if err == io.EOF {
      break
   }
   if err != nil {
      // handle error
   }
}

VPP Stats

The statsclient adapter connects to the VPP stats.sock.

statsClient = statsclient.NewStatsClient(socket, options...)

Supported options to customize the connection parameters.

  • SetSocketRetryPeriod - specifies a time period between retries
  • SetSocketRetryTimeout - specifies a timeout duration for retry

The stats connection can be done synchronously or asynchronously (as for the binary API socket).

The synchronous connection:

statsConn, err = core.ConnectStats(statsClient)
if err != nil {
   // handle error
}
defer c.Disconnect()

The asynchronous connection:

statsConn, statsChan, err = core.AsyncConnectStats(statsClient, attemptNum, interval)
if err != nil {
   // handle error
}
e := <-statsChan
if e.State != core.Connected {
   // handle error
}
defer statsConn.Disconnect()

The asynchronous connection comes with additional parameters attemptNum and interval defining the number of reconnection attempts, and an interval (in seconds) between those attempts.

The stats connection implements the StatsProvider interface and gives access to various stats getters.

systemStats := new(api.SystemStats)
if err := statsConn.GetSystemStats(systemStats); err != nil {
   // handle error
}
nodeStats := new(api.NodeStats)
if err := statsConn.GetNodeStats(nodeStats); err != nil {
   // handle error
}
...

Low-level stats API connection

The StatsProvider is considered the "high-level" API with easy access to VPP stats, but it might be restricted in certain cases. Using the stats client directly is the solution. The stats client implements the StatsAPI, the kind of low-level API with broader options for managing stats.

In any case, make sure the stats client is connected. The example above created the new stats client and used the GoVPP core method to connect, giving access to both, the statsClient (low-level API) and the statsConn (high-level API).

statsClient = statsclient.NewStatsClient(socket, options...)
statsConn, err = core.ConnectStats(statsClient) // or core.AsyncConnectStats(statsClient, attemptNum, interval)
   // handle error
}
defer statsConn.Disconnect()

If you do not need the statsConn instance and just use the low-level API, you must connect anyway. Either by ignoring the instance, or calling the connect method directly.

statsClient = statsclient.NewStatsClient(socket, options...)
err = statsClient.Connect()
// handle error
}
defer statsClient.Disconnect()

Low-level stats API usage

List all indexed stats directories. Use patterns to filter the output. The StatIdentifier is a simple name to the index value.

list, err = client.ListStats(patterns...)
if err != nil {
   // handle error
}

Return values of stats directories. Use patterns to filter the output. The StatEntry is the combination of stat identifier, type, data, and the symlink flag.

dump, err = client.DumpStats(patterns...)
if err != nil {
   // handle error
}

Prepare the stat directory. Returns the directory instance with accessible stat entries. Use patterns or indexes as a filter.

// pattern filter
dir, err := client.PrepareDir(patterns...)
if err != nil {
   // handle error
}

// index filter
dir, err := client.PrepareDirOnIndex(patterns...)
if err != nil {
   // handle error
}

Update the previously prepared directory. Suitable for polling VPP stats.

if err := client.UpdateDir(dir); err != nil {
   if err == adapter.ErrStatsDirStale { // if the directory is stale, re-load it
      if dir, err = client.PrepareDir(patterns...); err != nil {
         // handle error
      }
      continue
   }
   // handle error
}