Extend statedb and use prefixes, add debugapi

In statedb:
- Store all values using prefixes for keys to allow iteration
- Add methods MTGetRoot, GetAccounts

Implement debugapi, an http server with debugging endpoints:
- debugAPI.GET("sdb/batchnum", a.handleCurrentBatch)
- debugAPI.GET("sdb/mtroot", a.handleMTRoot)
- debugAPI.GET("sdb/accounts", a.handleAccounts)
- debugAPI.GET("sdb/accounts/:Idx", a.handleAccount)

test/debugapi/debugapi_test.go

@@ -0,0 +1,101 @@
+package debugapi
+
+import (
+	"crypto/ecdsa"
+	"fmt"
+	"io/ioutil"
+	"math/big"
+	"net/http"
+	"strconv"
+	"testing"
+
+	"github.com/dghubble/sling"
+	ethCrypto "github.com/ethereum/go-ethereum/crypto"
+	"github.com/hermeznetwork/hermez-node/common"
+	"github.com/hermeznetwork/hermez-node/db/statedb"
+	"github.com/iden3/go-iden3-crypto/babyjub"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+	"golang.org/x/net/context"
+)
+
+func newAccount(t *testing.T, i int) *common.Account {
+	var sk babyjub.PrivateKey
+	copy(sk[:], []byte(strconv.Itoa(i))) // only for testing
+	pk := sk.Public()
+
+	var key ecdsa.PrivateKey
+	key.D = big.NewInt(int64(i + 1)) // only for testing
+	key.PublicKey.X, key.PublicKey.Y = ethCrypto.S256().ScalarBaseMult(key.D.Bytes())
+	key.Curve = ethCrypto.S256()
+	address := ethCrypto.PubkeyToAddress(key.PublicKey)
+
+	return &common.Account{
+		Idx:       common.Idx(256 + i),
+		TokenID:   common.TokenID(i),
+		Nonce:     common.Nonce(i),
+		Balance:   big.NewInt(1000),
+		PublicKey: pk,
+		EthAddr:   address,
+	}
+}
+
+func TestDebugAPI(t *testing.T) {
+	dir, err := ioutil.TempDir("", "tmpdb")
+	require.Nil(t, err)
+
+	sdb, err := statedb.NewStateDB(dir, statedb.TypeSynchronizer, 32)
+	require.Nil(t, err)
+	err = sdb.MakeCheckpoint() // Make a checkpoint to increment the batchNum
+	require.Nil(t, err)
+
+	addr := "localhost:12345"
+	debugAPI := NewDebugAPI(addr, sdb)
+
+	ctx, cancel := context.WithCancel(context.Background())
+	go func() {
+		err := debugAPI.Run(ctx)
+		require.Nil(t, err)
+	}()
+
+	var accounts []common.Account
+	for i := 0; i < 16; i++ {
+		account := newAccount(t, i)
+		accounts = append(accounts, *account)
+		_, err = sdb.CreateAccount(account.Idx, account)
+		require.Nil(t, err)
+	}
+
+	url := fmt.Sprintf("http://%v/debug/", addr)
+
+	var batchNum common.BatchNum
+	req, err := sling.New().Get(url).Path("sdb/batchnum").ReceiveSuccess(&batchNum)
+	require.Equal(t, http.StatusOK, req.StatusCode)
+	require.Nil(t, err)
+	assert.Equal(t, common.BatchNum(1), batchNum)
+
+	var mtroot *big.Int
+	req, err = sling.New().Get(url).Path("sdb/mtroot").ReceiveSuccess(&mtroot)
+	require.Equal(t, http.StatusOK, req.StatusCode)
+	require.Nil(t, err)
+	// Testing against a hardcoded value obtained by running the test and
+	// printing the value previously.
+	assert.Equal(t, "8902613552504893273500019895709436294962812188236308621387152512232191202510",
+		mtroot.String())
+
+	var accountAPI common.Account
+	req, err = sling.New().Get(url).
+		Path(fmt.Sprintf("sdb/accounts/%v", accounts[0].Idx)).
+		ReceiveSuccess(&accountAPI)
+	require.Equal(t, http.StatusOK, req.StatusCode)
+	require.Nil(t, err)
+	assert.Equal(t, accounts[0], accountAPI)
+
+	var accountsAPI []common.Account
+	req, err = sling.New().Get(url).Path("sdb/accounts").ReceiveSuccess(&accountsAPI)
+	require.Equal(t, http.StatusOK, req.StatusCode)
+	require.Nil(t, err)
+	assert.Equal(t, accounts, accountsAPI)
+
+	cancel()
+}