Implement inventory plugin API

This change adds an API to retrieve a read-only copy of the current
inventory and listen for and modify inventory actions.

Closes #90.

2 files changed, 56 insertions, 0 deletions

diff --git a/plugin_inv.go b/plugin_inv.go
new file mode 100644
index 0000000..6a8ffa5
--- /dev/null
+++ b/plugin_inv.go
@@ -0,0 +1,45 @@
+package proxy
+
+import (
+	"bytes"
+	"sync"
+
+	"github.com/HimbeerserverDE/mt"
+)
+
+var (
+	onInvAction   []func(*ClientConn, string) string
+	onInvActionMu sync.RWMutex
+)
+
+// Inv returns a copy of the current server-provided inventory of the client
+// or nil if the client is not connected to a server.
+func (cc *ClientConn) Inv() mt.Inv {
+	sc := cc.server()
+	if sc == nil {
+		return nil
+	}
+
+	var ret mt.Inv
+
+	sb := &bytes.Buffer{}
+	sc.inv.Serialize(sb)
+	ret.Deserialize(sb)
+
+	return ret
+}
+
+// RegisterOnInvAction registers a handler that is called
+// when a client attempts to perform an inventory action.
+// The returned string overrides the original action.
+// Later handlers will receive the modified action.
+// Handlers are called in registration order.
+// If the final action string is empty, the action is not forwarded
+// to the upstream server.
+// You may use the mt package to interact with the action strings.
+func RegisterOnInvAction(handler func(*ClientConn, string) string) {
+	onInvActionMu.Lock()
+	defer onInvActionMu.Unlock()
+
+	onInvAction = append(onInvAction, handler)
+}
diff --git a/process.go b/process.go
index 1d8263f..b7623b5 100644
--- a/process.go
+++ b/process.go
@@ -484,6 +484,17 @@ func (cc *ClientConn) process(pkt mt.Pkt) {
 	case *mt.ToSrvCltInfo:
 		// Store for any future hops (need to send it to the new server).
 		cc.cltInfo = cmd
+	case *mt.ToSrvInvAction:
+		onInvActionMu.RLock()
+		defer onInvActionMu.RUnlock()
+
+		for _, handler := range onInvAction {
+			cmd.Action = handler(cc, cmd.Action)
+		}
+
+		if cmd.Action == "" {
+			return
+		}
 	case *mt.ToSrvInvFields:
 		if handleOnPlayerReceiveFields(cc, cmd) {
 			return