lnd: add new chainRegistry struct for multi-chain dispatch

This commit adds a new agent to the codebase: the chainRegistry. In a
multi-chain future, the chainRegistry will be the dispatch point
capable of mapping cross-chain parameters, and a particular chain to
the chainControl for that chain. The chainControl struct encompasses
the 3 primary interfaces used within the daemon to register for events,
and drive other workflows.

chainregistry.go

@@ -0,0 +1,164 @@
+package main
+
+import (
+	"sync"
+
+	"github.com/lightningnetwork/lnd/chainntnfs"
+	"github.com/lightningnetwork/lnd/lnwallet"
+	"github.com/roasbeef/btcd/chaincfg/chainhash"
+)
+
+// chainCode is an enum-like structure for keeping track of the chains currently
+// supported within lnd.
+type chainCode uint32
+
+const (
+	// bitcoinChain is Bitcoin's testnet chain.
+	bitcoinChain chainCode = iota
+
+	// litecoinChain is Litecoin's testnet chain.
+	litecoinChain
+)
+
+// String returns a string representation of the target chainCode.
+func (c chainCode) String() string {
+	switch c {
+	case bitcoinChain:
+		return "bitcoin"
+	case litecoinChain:
+		return "litecoin"
+	default:
+		return "kekcoin"
+	}
+}
+
+// chainControl couples the three primary interfaces lnd utilizes for a
+// particular chain together. A single chainControl instance will exist for all
+// the chains lnd is currently active on.
+type chainControl struct {
+	chainIO       lnwallet.BlockChainIO
+	chainNotifier chainntnfs.ChainNotifier
+
+	wallet *lnwallet.LightningWallet
+}
+
+var (
+	// bitcoinGenesis is the genesis hash of Bitcoin's testnet chain.
+	bitcoinGenesis = chainhash.Hash([chainhash.HashSize]byte{
+		0x6f, 0xe2, 0x8c, 0x0a, 0xb6, 0xf1, 0xb3, 0x72,
+		0xc1, 0xa6, 0xa2, 0x46, 0xae, 0x63, 0xf7, 0x4f,
+		0x93, 0x1e, 0x83, 0x65, 0xe1, 0x5a, 0x08, 0x9c,
+		0x68, 0xd6, 0x19, 0x00, 0x00, 0x00, 0x00, 0x00,
+	})
+
+	// litecoinGenesis is the genesis hash of Litecoin's testnet4 chain.
+	litecoinGenesis = chainhash.Hash([chainhash.HashSize]byte{
+		0xa0, 0x29, 0x3e, 0x4e, 0xeb, 0x3d, 0xa6, 0xe6,
+		0xf5, 0x6f, 0x81, 0xed, 0x59, 0x5f, 0x57, 0x88,
+		0x0d, 0x1a, 0x21, 0x56, 0x9e, 0x13, 0xee, 0xfd,
+		0xd9, 0x51, 0x28, 0x4b, 0x5a, 0x62, 0x66, 0x49,
+	})
+
+	// chainMap is a simple index that maps a chain's genesis hash to the
+	// chainCode enum for that chain.
+	chainMap = map[chainhash.Hash]chainCode{
+		bitcoinGenesis:  bitcoinChain,
+		litecoinGenesis: litecoinChain,
+	}
+
+	// reverseChainMap is the inverse of the chainMap above: it maps the
+	// chain enum for a chain to its genesis hash.
+	reverseChainMap = map[chainCode]chainhash.Hash{
+		bitcoinChain:  bitcoinGenesis,
+		litecoinChain: litecoinGenesis,
+	}
+)
+
+// chainRegistry keeps track of the current chains
+type chainRegistry struct {
+	sync.RWMutex
+
+	activeChains map[chainCode]*chainControl
+	netParams    map[chainCode]*bitcoinNetParams
+
+	primaryChain chainCode
+}
+
+// newChainRegistry creates a new chainRegistry.
+func newChainRegistry() *chainRegistry {
+	return &chainRegistry{
+		activeChains: make(map[chainCode]*chainControl),
+		netParams:    make(map[chainCode]*bitcoinNetParams),
+	}
+}
+
+// RegisterChain assigns an active chainControl instance to a target chain
+// identified by its chainCode.
+func (c *chainRegistry) RegisterChain(newChain chainCode, cc *chainControl) {
+	c.Lock()
+	c.activeChains[newChain] = cc
+	c.Unlock()
+}
+
+// LookupChain attempts to lookup an active chainControl instance for the
+// target chain.
+func (c *chainRegistry) LookupChain(targetChain chainCode) (*chainControl, bool) {
+	c.RLock()
+	cc, ok := c.activeChains[targetChain]
+	c.RUnlock()
+	return cc, ok
+}
+
+// LookupChainByHash attempts to look up an active chainControl which
+// corresponds to the passed genesis hash.
+func (c *chainRegistry) LookupChainByHash(chainHash chainhash.Hash) (*chainControl, bool) {
+	c.RLock()
+	defer c.RUnlock()
+
+	targetChain, ok := chainMap[chainHash]
+	if !ok {
+		return nil, ok
+	}
+
+	cc, ok := c.activeChains[targetChain]
+	return cc, ok
+}
+
+// RegisterPrimaryChain sets a target chain as the "home chain" for lnd.
+func (c *chainRegistry) RegisterPrimaryChain(cc chainCode) {
+	c.Lock()
+	defer c.Unlock()
+
+	c.primaryChain = cc
+}
+
+// PrimaryChain returns the primary chain for this running lnd instance. The
+// primary chain is considered the "home base" while the other registered
+// chains are treated as secondary chains.
+func (c *chainRegistry) PrimaryChain() chainCode {
+	c.RLock()
+	defer c.RUnlock()
+
+	return c.primaryChain
+}
+
+// ActiveChains returns the total number of active chains.
+func (c *chainRegistry) ActiveChains() []chainCode {
+	c.RLock()
+	defer c.RUnlock()
+
+	chains := make([]chainCode, 0, len(c.activeChains))
+	for activeChain := range c.activeChains {
+		chains = append(chains, activeChain)
+	}
+
+	return chains
+}
+
+// NumActiveChains returns the total number of active chains.
+func (c *chainRegistry) NumActiveChains() uint32 {
+	c.RLock()
+	defer c.RUnlock()
+
+	return uint32(len(c.activeChains))
+}