Add handling for mempool command.

mempool.go

@@ -771,6 +771,23 @@ func (mp *txMemPool) ProcessTransaction(tx *btcwire.MsgTx) error {
 	return nil
 }
 
+// TxShas returns a slice containing the hashes of all transactions in the
+// memory pool.
+func (mp *txMemPool) TxShas() []*btcwire.ShaHash {
+	mp.lock.Lock()
+	defer mp.lock.Unlock()
+
+	hashes := make([]*btcwire.ShaHash, len(mp.pool))
+	i := 0
+	for hash := range mp.pool {
+		hashCopy := hash
+		hashes[i] = &hashCopy
+		i++
+	}
+
+	return hashes
+}
+
 // newTxMemPool returns a new memory pool for validating and storing standalone
 // transactions until they are mined into a block.
 func newTxMemPool(server *server) *txMemPool {

peer.go

@@ -400,6 +400,29 @@ func (p *peer) PushGetBlocksMsg(locator btcchain.BlockLocator, stopHash *btcwire
 	return nil
 }
 
+// handleMemPoolMsg is invoked when a peer receives a mempool bitcoin message.
+// It creates and sends an inventory message with the contents of the memory
+// pool up to the maximum inventory allowed per message.
+func (p *peer) handleMemPoolMsg(msg *btcwire.MsgMemPool) {
+	// Generate inventory message with the available transactions in the
+	// transaction memory pool.  Limit it to the max allowed inventory
+	// per message.
+	invMsg := btcwire.NewMsgInv()
+	hashes := p.server.txMemPool.TxShas()
+	for i, hash := range hashes {
+		iv := btcwire.NewInvVect(btcwire.InvVect_Tx, hash)
+		invMsg.AddInvVect(iv)
+		if i+1 >= btcwire.MaxInvPerMsg {
+			break
+		}
+	}
+
+	// Send the inventory message if there is anything to send.
+	if len(invMsg.InvList) > 0 {
+		p.QueueMessage(invMsg)
+	}
+}
+
 // handleTxMsg is invoked when a peer receives a tx bitcoin message.  It blocks
 // until the bitcoin transaction has been fully processed.  Unlock the block
 // handler this does not serialize all transactions through a single thread
@@ -912,6 +935,9 @@ out:
 		case *btcwire.MsgAlert:
 			p.server.BroadcastMessage(msg, p)
 
+		case *btcwire.MsgMemPool:
+			p.handleMemPoolMsg(msg)
+
 		case *btcwire.MsgTx:
 			p.handleTxMsg(msg)