light/rpc: fix ABCIQuery (#5375)

Closes #5106

cmd/tendermint/commands/light.go

@@ -8,6 +8,7 @@ import (
 	"net/http"
 	"os"
 	"path/filepath"
+	"regexp"
 	"strings"
 	"time"
 
@@ -15,6 +16,7 @@ import (
 
 	dbm "github.com/tendermint/tm-db"
 
+	"github.com/tendermint/tendermint/crypto/merkle"
 	"github.com/tendermint/tendermint/libs/log"
 	tmmath "github.com/tendermint/tendermint/libs/math"
 	tmos "github.com/tendermint/tendermint/libs/os"
@@ -41,6 +43,12 @@ need a primary RPC address, a trusted hash and height and witness RPC addresses
 (if not using sequential verification). To restart the node, thereafter
 only the chainID is required.
 
+When /abci_query is called, the Merkle key path format is:
+
+	/{store name}/{key}
+
+Please verify with your application that this Merkle key format is used (true
+for applications built w/ Cosmos SDK).
 `,
 	RunE: runProxy,
 	Args: cobra.ExactArgs(1),
@@ -215,7 +223,7 @@ func runProxy(cmd *cobra.Command, args []string) error {
 	p := lproxy.Proxy{
 		Addr:   listenAddr,
 		Config: cfg,
-		Client: lrpc.NewClient(rpcClient, c),
+		Client: lrpc.NewClient(rpcClient, c, lrpc.KeyPathFn(defaultMerkleKeyPathFn())),
 		Logger: logger,
 	}
 	// Stop upon receiving SIGTERM or CTRL-C.
@@ -256,3 +264,21 @@ func saveProviders(db dbm.DB, primaryAddr, witnessesAddrs string) error {
 	}
 	return nil
 }
+
+func defaultMerkleKeyPathFn() lrpc.KeyPathFunc {
+	// regexp for extracting store name from /abci_query path
+	storeNameRegexp := regexp.MustCompile(`\/store\/(.+)\/key`)
+
+	return func(path string, key []byte) (merkle.KeyPath, error) {
+		matches := storeNameRegexp.FindStringSubmatch(path)
+		if len(matches) != 2 {
+			return nil, fmt.Errorf("can't find store name in %s using %s", path, storeNameRegexp)
+		}
+		storeName := matches[1]
+
+		kp := merkle.KeyPath{}
+		kp = kp.AppendKey([]byte(storeName), merkle.KeyEncodingURL)
+		kp = kp.AppendKey(key, merkle.KeyEncodingURL)
+		return kp, nil
+	}
+}