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Merge pull request #12 from synfinatic/discovery
Add Alpaca Remote Disovery protocol support
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,132 @@ | ||
| package alpaca | ||
|
|
||
| import ( | ||
| "encoding/json" | ||
| "fmt" | ||
| "net" | ||
| "strings" | ||
| "time" | ||
|
|
||
| log "github.com/sirupsen/logrus" | ||
| ) | ||
|
|
||
| const ( | ||
| ALPACA_DISCOVERY_VERSION = 1 | ||
| ) | ||
|
|
||
| type AlpacaDiscoveryMessage struct { | ||
| Fixed []byte // must be 'alpacadiscovery' | ||
| Version byte | ||
| Reserved []byte | ||
| } | ||
|
|
||
| type AlpacaResponseMessage struct { | ||
| AlpacaPort uint16 `json:"AlpacaPort"` | ||
| } | ||
|
|
||
| func (a *AlpacaDiscoveryMessage) Bytes() []byte { | ||
| var buf []byte = []byte{} | ||
|
|
||
| buf = append(buf[:], a.Fixed[:]...) | ||
| buf = append(buf[:], a.Version) | ||
| buf = append(buf[:], a.Reserved[:]...) | ||
| return buf | ||
| } | ||
|
|
||
| func NewAlpacaDiscoveryMessage(version int) *AlpacaDiscoveryMessage { | ||
| a := AlpacaDiscoveryMessage{ | ||
| Fixed: []byte("alpacadiscovery"), | ||
| Version: byte(fmt.Sprintf("%d", version)[0]), | ||
| Reserved: make([]byte, 48), | ||
| } | ||
| return &a | ||
| } | ||
|
|
||
| // checks if server is on localhost. returns IP or empty string | ||
| func IsRunningLocal(port int32) string { | ||
| log.Infof("Looking for Alpaca Remote Server locally on port %d...", port) | ||
| addrs, err := net.InterfaceAddrs() | ||
| if err != nil { | ||
| log.Errorf("Unable to determine local interface addresses: %s", err.Error()) | ||
| return "" | ||
| } | ||
| log.Debugf("local addrs: %v", addrs) | ||
| for _, addr := range addrs { | ||
| ips := strings.Split(addr.String(), "/") | ||
| ip := net.ParseIP(ips[0]) | ||
| if ip.To4() == nil { | ||
| continue // skip non-IPv4 | ||
| } | ||
|
|
||
| if tryAlpaca(ip.String(), port) { | ||
| log.Infof("Found Alpaca on %s:%d", ip.String(), port) | ||
| return ip.String() | ||
| } else { | ||
| log.Debugf("Alpaca is not running on %s:%d", ip.String(), port) | ||
| } | ||
| } | ||
| log.Info("No local Alpaca Remote Servers found") | ||
| return "" | ||
| } | ||
|
|
||
| // Send a discovery packet to the given IP to see if it's Alpaca | ||
| func tryAlpaca(ip string, port int32) bool { | ||
| conn, err := net.DialTimeout("tcp", fmt.Sprintf("%s:%d", ip, port), time.Second*1) | ||
| if err != nil { | ||
| return false | ||
| } | ||
| conn.Close() | ||
| return true | ||
| } | ||
|
|
||
| // Discover any alpaca servers. returns IP as string and port | ||
| func DiscoverServer(tries int) (string, int32, error) { | ||
| pc, err := net.ListenPacket("udp4", ":32227") | ||
| if err != nil { | ||
| return "", 0, fmt.Errorf("Unable to open Alpaca discovery listen socket: %s", err.Error()) | ||
| } | ||
| defer pc.Close() | ||
|
|
||
| send_addr, err := net.ResolveUDPAddr("udp4", "255.255.255.255:32227") | ||
| if err != nil { | ||
| return "", 0, fmt.Errorf("Unable to resolve Alpaca broadcast address: %s", err.Error()) | ||
| } | ||
|
|
||
| msg := NewAlpacaDiscoveryMessage(ALPACA_DISCOVERY_VERSION) | ||
| msg_bytes := msg.Bytes() | ||
| buf := make([]byte, 1024) | ||
|
|
||
| for i := 0; i < tries; i++ { | ||
| _, err = pc.WriteTo(msg_bytes, send_addr) | ||
| if err != nil { | ||
| return "", 0, fmt.Errorf("Unable to send Alpaca discovery message: %s", err.Error()) | ||
| } | ||
|
|
||
| deadline := time.Now().Add(time.Second * 1) | ||
| for true { | ||
| pc.SetReadDeadline(deadline) | ||
| err = nil | ||
| n, addr, err := pc.ReadFrom(buf) | ||
| if err != nil { | ||
| log.Warnf("Failed to discover Alpaca server: %s", err.Error()) | ||
| break // don't try reading again this cycle | ||
| } else if n == 64 || string(buf) == fmt.Sprintf("alpacadiscovery%d", ALPACA_DISCOVERY_VERSION) { | ||
| log.Debug("Skipping packet we sent") | ||
| continue // this is the message we sent | ||
| } | ||
|
|
||
| ip := strings.Split(addr.String(), ":") | ||
| log.Debugf("receved %d bytes via discovery: %v", n, buf[:n]) | ||
| var a AlpacaResponseMessage | ||
| err = json.Unmarshal(buf[:n], &a) | ||
| if err != nil { | ||
| log.Warnf("Unable to decode message: %s", err.Error()) | ||
| break | ||
| } else { | ||
| log.Infof("Discovered Alpaca Server on %s:%d", ip[0], a.AlpacaPort) | ||
| return ip[0], int32(a.AlpacaPort), nil | ||
| } | ||
| } | ||
| } | ||
| return "", 0, fmt.Errorf("No reply from Alpaca Server") | ||
| } |
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