Refactor "lite" to handle delayed validator set changes.

Also, fix consensus liveness issue.

lite/provider.go

@@ -1,103 +1,28 @@
 package lite
 
-// Provider is used to get more validators by other means.
-//
-// Examples: MemProvider, files.Provider, client.Provider, CacheProvider....
+import (
+	"github.com/tendermint/tendermint/types"
+)
+
+// Provider provides information for the lite client to sync validators.
+// Examples: MemProvider, files.Provider, client.Provider, CacheProvider.
 type Provider interface {
-	// StoreCommit saves a FullCommit after we have verified it,
-	// so we can query for it later. Important for updating our
-	// store of trusted commits.
-	StoreCommit(fc FullCommit) error
-	// GetByHeight returns the closest commit with height <= h.
-	GetByHeight(h int64) (FullCommit, error)
-	// GetByHash returns a commit exactly matching this validator hash.
-	GetByHash(hash []byte) (FullCommit, error)
-	// LatestCommit returns the newest commit stored.
-	LatestCommit() (FullCommit, error)
+
+	// LatestFullCommit returns the latest commit with minHeight <= height <=
+	// maxHeight.
+	// If maxHeight is zero, returns the latest where minHeight <= height.
+	LatestFullCommit(chainID string, minHeight, maxHeight int64) (FullCommit, error)
+
+	// Get the valset that corresponds to chainID and height and return.
+	// Height must be >= 1.
+	ValidatorSet(chainID string, height int64) (*types.ValidatorSet, error)
 }
 
-// cacheProvider allows you to place one or more caches in front of a source
-// Provider.  It runs through them in order until a match is found.
-// So you can keep a local cache, and check with the network if
-// no data is there.
-type cacheProvider struct {
-	Providers []Provider
-}
+// A provider that can also persist new information.
+// Examples: MemProvider, files.Provider, CacheProvider.
+type PersistentProvider interface {
+	Provider
 
-// NewCacheProvider returns a new provider which wraps multiple other providers.
-func NewCacheProvider(providers ...Provider) Provider {
-	return cacheProvider{
-		Providers: providers,
-	}
-}
-
-// StoreCommit tries to add the seed to all providers.
-//
-// Aborts on first error it encounters (closest provider)
-func (c cacheProvider) StoreCommit(fc FullCommit) (err error) {
-	for _, p := range c.Providers {
-		err = p.StoreCommit(fc)
-		if err != nil {
-			break
-		}
-	}
-	return err
-}
-
-// GetByHeight should return the closest possible match from all providers.
-//
-// The Cache is usually organized in order from cheapest call (memory)
-// to most expensive calls (disk/network). However, since GetByHeight returns
-// a FullCommit at h' <= h, if the memory has a seed at h-10, but the network would
-// give us the exact match, a naive "stop at first non-error" would hide
-// the actual desired results.
-//
-// Thus, we query each provider in order until we find an exact match
-// or we finished querying them all.  If at least one returned a non-error,
-// then this returns the best match (minimum h-h').
-func (c cacheProvider) GetByHeight(h int64) (fc FullCommit, err error) {
-	for _, p := range c.Providers {
-		var tfc FullCommit
-		tfc, err = p.GetByHeight(h)
-		if err == nil {
-			if tfc.Height() > fc.Height() {
-				fc = tfc
-			}
-			if tfc.Height() == h {
-				break
-			}
-		}
-	}
-	// even if the last one had an error, if any was a match, this is good
-	if fc.Height() > 0 {
-		err = nil
-	}
-	return fc, err
-}
-
-// GetByHash returns the FullCommit for the hash or an error if the commit is not found.
-func (c cacheProvider) GetByHash(hash []byte) (fc FullCommit, err error) {
-	for _, p := range c.Providers {
-		fc, err = p.GetByHash(hash)
-		if err == nil {
-			break
-		}
-	}
-	return fc, err
-}
-
-// LatestCommit returns the latest FullCommit or an error if no commit exists.
-func (c cacheProvider) LatestCommit() (fc FullCommit, err error) {
-	for _, p := range c.Providers {
-		var tfc FullCommit
-		tfc, err = p.LatestCommit()
-		if err == nil && tfc.Height() > fc.Height() {
-			fc = tfc
-		}
-	}
-	// even if the last one had an error, if any was a match, this is good
-	if fc.Height() > 0 {
-		err = nil
-	}
-	return fc, err
+	// SaveFullCommit saves a FullCommit (without verification).
+	SaveFullCommit(fc FullCommit) error
 }