Refactor "lite" to handle delayed validator set changes.

Also, fix consensus liveness issue.

lite/multiprovider.go

@@ -0,0 +1,72 @@
+package lite
+
+import (
+	lerr "github.com/tendermint/tendermint/lite/errors"
+	"github.com/tendermint/tendermint/types"
+)
+
+// multiProvider 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.
+type multiProvider struct {
+	Providers []PersistentProvider
+}
+
+// NewMultiProvider returns a new provider which wraps multiple other providers.
+func NewMultiProvider(providers ...PersistentProvider) multiProvider {
+	return multiProvider{
+		Providers: providers,
+	}
+}
+
+// SaveFullCommit saves on all providers, and aborts on the first error.
+func (mc multiProvider) SaveFullCommit(fc FullCommit) (err error) {
+	for _, p := range mc.Providers {
+		err = p.SaveFullCommit(fc)
+		if err != nil {
+			return
+		}
+	}
+	return
+}
+
+// LatestFullCommit loads the latest from all providers and provides
+// the latest FullCommit that satisfies the conditions.
+// Returns the first error encountered.
+func (mc multiProvider) LatestFullCommit(chainID string, minHeight, maxHeight int64) (fc FullCommit, err error) {
+	for _, p := range mc.Providers {
+		var fc_ FullCommit
+		fc_, err = p.LatestFullCommit(chainID, minHeight, maxHeight)
+		if lerr.IsErrCommitNotFound(err) {
+			err = nil
+			continue
+		} else if err != nil {
+			return
+		}
+		if fc == (FullCommit{}) {
+			fc = fc_
+		} else if fc_.Height() > fc.Height() {
+			fc = fc_
+		}
+		if fc.Height() == maxHeight {
+			return
+		}
+	}
+	if fc == (FullCommit{}) {
+		err = lerr.ErrCommitNotFound()
+		return
+	}
+	return
+}
+
+// ValidatorSet returns validator set at height as provided by the first
+// provider which has it, or an error otherwise.
+func (mc multiProvider) ValidatorSet(chainID string, height int64) (valset *types.ValidatorSet, err error) {
+	for _, p := range mc.Providers {
+		valset, err = p.ValidatorSet(chainID, height)
+		if err == nil {
+			// TODO Log unexpected types of errors.
+			return valset, nil
+		}
+	}
+	return nil, lerr.ErrMissingValidators(chainID, height)
+}