peers: allow access to underlying connection

This is a first iteration for @awlx. I think this does
require further investigation as I am also not very happy
with the handler interface. As soon as we try to send data
to HAProxy we do need a base implementation that tracks
sticktable ids and allows us to define new one and reference
known sticktables. This is required as we always have to send
HAProxy all sticktables we want to send updates for and can't
reference the ones we already got from that instance.

peers/DESIGN.md

@@ -0,0 +1,12 @@
+# HAProxy Peers Design
+## Connection
+By default, the peers package only opens listeners and waits for HAProxy to connect to it. 
+
+## Sticktables
+A user can create a sticktable definition which can be used to send to a HAProxy peer. Additionally a user can use a
+sent definition to send updates for that specific sticktable. For this, the table has to be registered in a table 
+registry to allow proper referencing.
+
+## Handler
+A handler is the interface to implement when wanting to react to sticktable updates. A user created handler can implement
+specific sub interfaces to also interact with handshakes. 

peers/example/complex/go.mod

@@ -0,0 +1,22 @@
+module github.com/dropmorepackets/haproxy-go/peers/example/complex
+
+go 1.21
+
+replace github.com/dropmorepackets/haproxy-go => ../../../
+
+require (
+	github.com/dropmorepackets/haproxy-go v0.0.2
+	github.com/prometheus/client_golang v1.17.0
+)
+
+require (
+	github.com/beorn7/perks v1.0.1 // indirect
+	github.com/cespare/xxhash/v2 v2.2.0 // indirect
+	github.com/golang/protobuf v1.5.3 // indirect
+	github.com/matttproud/golang_protobuf_extensions v1.0.4 // indirect
+	github.com/prometheus/client_model v0.5.0 // indirect
+	github.com/prometheus/common v0.44.0 // indirect
+	github.com/prometheus/procfs v0.12.0 // indirect
+	golang.org/x/sys v0.13.0 // indirect
+	google.golang.org/protobuf v1.31.0 // indirect
+)

peers/example/complex/go.sum

@@ -0,0 +1,37 @@
+github.com/beorn7/perks v1.0.1 h1:VlbKKnNfV8bJzeqoa4cOKqO6bYr3WgKZxO8Z16+hsOM=
+github.com/beorn7/perks v1.0.1/go.mod h1:G2ZrVWU2WbWT9wwq4/hrbKbnv/1ERSJQ0ibhJ6rlkpw=
+github.com/cespare/xxhash/v2 v2.2.0 h1:DC2CZ1Ep5Y4k3ZQ899DldepgrayRUGE6BBZ/cd9Cj44=
+github.com/cespare/xxhash/v2 v2.2.0/go.mod h1:VGX0DQ3Q6kWi7AoAeZDth3/j3BFtOZR5XLFGgcrjCOs=
+github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=
+github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
+github.com/golang/protobuf v1.2.0/go.mod h1:6lQm79b+lXiMfvg/cZm0SGofjICqVBUtrP5yJMmIC1U=
+github.com/golang/protobuf v1.5.0/go.mod h1:FsONVRAS9T7sI+LIUmWTfcYkHO4aIWwzhcaSAoJOfIk=
+github.com/golang/protobuf v1.5.3 h1:KhyjKVUg7Usr/dYsdSqoFveMYd5ko72D+zANwlG1mmg=
+github.com/golang/protobuf v1.5.3/go.mod h1:XVQd3VNwM+JqD3oG2Ue2ip4fOMUkwXdXDdiuN0vRsmY=
+github.com/google/go-cmp v0.5.5/go.mod h1:v8dTdLbMG2kIc/vJvl+f65V22dbkXbowE6jgT/gNBxE=
+github.com/google/go-cmp v0.5.9 h1:O2Tfq5qg4qc4AmwVlvv0oLiVAGB7enBSJ2x2DqQFi38=
+github.com/google/go-cmp v0.5.9/go.mod h1:17dUlkBOakJ0+DkrSSNjCkIjxS6bF9zb3elmeNGIjoY=
+github.com/matttproud/golang_protobuf_extensions v1.0.4 h1:mmDVorXM7PCGKw94cs5zkfA9PSy5pEvNWRP0ET0TIVo=
+github.com/matttproud/golang_protobuf_extensions v1.0.4/go.mod h1:BSXmuO+STAnVfrANrmjBb36TMTDstsz7MSK+HVaYKv4=
+github.com/prometheus/client_golang v1.17.0 h1:rl2sfwZMtSthVU752MqfjQozy7blglC+1SOtjMAMh+Q=
+github.com/prometheus/client_golang v1.17.0/go.mod h1:VeL+gMmOAxkS2IqfCq0ZmHSL+LjWfWDUmp1mBz9JgUY=
+github.com/prometheus/client_model v0.4.1-0.20230718164431-9a2bf3000d16 h1:v7DLqVdK4VrYkVD5diGdl4sxJurKJEMnODWRJlxV9oM=
+github.com/prometheus/client_model v0.4.1-0.20230718164431-9a2bf3000d16/go.mod h1:oMQmHW1/JoDwqLtg57MGgP/Fb1CJEYF2imWWhWtMkYU=
+github.com/prometheus/client_model v0.5.0 h1:VQw1hfvPvk3Uv6Qf29VrPF32JB6rtbgI6cYPYQjL0Qw=
+github.com/prometheus/client_model v0.5.0/go.mod h1:dTiFglRmd66nLR9Pv9f0mZi7B7fk5Pm3gvsjB5tr+kI=
+github.com/prometheus/common v0.44.0 h1:+5BrQJwiBB9xsMygAB3TNvpQKOwlkc25LbISbrdOOfY=
+github.com/prometheus/common v0.44.0/go.mod h1:ofAIvZbQ1e/nugmZGz4/qCb9Ap1VoSTIO7x0VV9VvuY=
+github.com/prometheus/procfs v0.11.1 h1:xRC8Iq1yyca5ypa9n1EZnWZkt7dwcoRPQwX/5gwaUuI=
+github.com/prometheus/procfs v0.11.1/go.mod h1:eesXgaPo1q7lBpVMoMy0ZOFTth9hBn4W/y0/p/ScXhY=
+github.com/prometheus/procfs v0.12.0 h1:jluTpSng7V9hY0O2R9DzzJHYb2xULk9VTR1V1R/k6Bo=
+github.com/prometheus/procfs v0.12.0/go.mod h1:pcuDEFsWDnvcgNzo4EEweacyhjeA9Zk3cnaOZAZEfOo=
+golang.org/x/sync v0.0.0-20181221193216-37e7f081c4d4/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
+golang.org/x/sys v0.11.0 h1:eG7RXZHdqOJ1i+0lgLgCpSXAp6M3LYlAo6osgSi0xOM=
+golang.org/x/sys v0.11.0/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
+golang.org/x/sys v0.13.0 h1:Af8nKPmuFypiUBjVoU9V20FiaFXOcuZI21p0ycVYYGE=
+golang.org/x/sys v0.13.0/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
+golang.org/x/xerrors v0.0.0-20191204190536-9bdfabe68543/go.mod h1:I/5z698sn9Ka8TeJc9MKroUUfqBBauWjQqLJ2OPfmY0=
+google.golang.org/protobuf v1.26.0-rc.1/go.mod h1:jlhhOSvTdKEhbULTjvd4ARK9grFBp09yW+WbY/TyQbw=
+google.golang.org/protobuf v1.26.0/go.mod h1:9q0QmTI4eRPtz6boOQmLYwt+qCgq0jsYwAQnmE0givc=
+google.golang.org/protobuf v1.31.0 h1:g0LDEJHgrBl9N9r17Ru3sqWhkIx2NB67okBHPwC7hs8=
+google.golang.org/protobuf v1.31.0/go.mod h1:HV8QOd/L58Z+nl8r43ehVNZIU/HEI6OcFqwMG9pJV4I=

peers/example/complex/main.go

@@ -0,0 +1,31 @@
+package main
+
+import (
+	"log"
+	"net/http"
+
+	"github.com/prometheus/client_golang/prometheus/promhttp"
+
+	"github.com/dropmorepackets/haproxy-go/peers"
+	"github.com/dropmorepackets/haproxy-go/peers/sticktable"
+)
+
+type myHandler struct {
+	peers.PeerHandler
+}
+
+func (e *PeerHandler) HandleUpdate(ctx context.Context, update *sticktable.EntryUpdate) {}
+
+func (e *PeerHandler) HandleHandshake(ctx context.Context, handshake *Handshake) {}
+
+func main() {
+	log.SetFlags(log.LstdFlags | log.Lshortfile)
+
+	go http.ListenAndServe(":8081", promhttp.Handler())
+
+	err := peers.ListenAndServe(":21000", &myHandler{})
+
+	if err != nil {
+		log.Fatal(err)
+	}
+}

peers/peers.go

@@ -56,7 +56,10 @@ func (a *Peer) Serve(l net.Listener) error {
 			return fmt.Errorf("accepting conn: %w", err)
 		}
 
-		p := newProtocolClient(a.BaseContext, nc, a.HandlerSource())
+		// Wrap the context to provide access to the underlying connection.
+		// TODO(tim): Do we really want this?
+		ctx := context.WithValue(a.BaseContext, connectionKey, nc)
+		p := newProtocolClient(ctx, nc, a.HandlerSource())
 		go func() {
 			defer nc.Close()
 			defer p.Close()
@@ -67,3 +70,15 @@ func (a *Peer) Serve(l net.Listener) error {
 		}()
 	}
 }
+
+type contextKey string
+
+const (
+	connectionKey = contextKey("connection")
+)
+
+// Connection returns the underlying connection used in calls
+// to function in a Handler.
+func Connection(ctx context.Context) net.Conn {
+	return ctx.Value(connectionKey).(net.Conn)
+}