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.go

@@ -0,0 +1,121 @@
+package debugapi
+
+import (
+	"context"
+	"net/http"
+	"time"
+
+	"github.com/gin-contrib/cors"
+	"github.com/gin-gonic/gin"
+	"github.com/hermeznetwork/hermez-node/common"
+	"github.com/hermeznetwork/hermez-node/db/statedb"
+	"github.com/hermeznetwork/hermez-node/log"
+)
+
+func handleNoRoute(c *gin.Context) {
+	c.JSON(http.StatusNotFound, gin.H{
+		"error": "404 page not found",
+	})
+}
+
+type errorMsg struct {
+	Message string
+}
+
+func badReq(err error, c *gin.Context) {
+	log.Errorw("Bad request", "err", err)
+	c.JSON(http.StatusBadRequest, errorMsg{
+		Message: err.Error(),
+	})
+}
+
+// DebugAPI is an http API with debugging endpoints
+type DebugAPI struct {
+	addr    string
+	stateDB *statedb.StateDB // synchronizer statedb
+}
+
+// NewDebugAPI creates a new DebugAPI
+func NewDebugAPI(addr string, stateDB *statedb.StateDB) *DebugAPI {
+	return &DebugAPI{
+		stateDB: stateDB,
+		addr:    addr,
+	}
+}
+
+func (a *DebugAPI) handleAccount(c *gin.Context) {
+	uri := struct {
+		Idx uint32
+	}{}
+	if err := c.ShouldBindUri(&uri); err != nil {
+		badReq(err, c)
+		return
+	}
+	account, err := a.stateDB.GetAccount(common.Idx(uri.Idx))
+	if err != nil {
+		badReq(err, c)
+		return
+	}
+	c.JSON(http.StatusOK, account)
+}
+
+func (a *DebugAPI) handleAccounts(c *gin.Context) {
+	accounts, err := a.stateDB.GetAccounts()
+	if err != nil {
+		badReq(err, c)
+		return
+	}
+	c.JSON(http.StatusOK, accounts)
+}
+
+func (a *DebugAPI) handleCurrentBatch(c *gin.Context) {
+	batchNum, err := a.stateDB.GetCurrentBatch()
+	if err != nil {
+		badReq(err, c)
+		return
+	}
+	c.JSON(http.StatusOK, batchNum)
+}
+
+func (a *DebugAPI) handleMTRoot(c *gin.Context) {
+	root := a.stateDB.MTGetRoot()
+	c.JSON(http.StatusOK, root)
+}
+
+// Run starts the http server of the DebugAPI.  To stop it, pass a context with
+// cancelation (see `debugapi_test.go` for an example).
+func (a *DebugAPI) Run(ctx context.Context) error {
+	api := gin.Default()
+	api.NoRoute(handleNoRoute)
+	api.Use(cors.Default())
+	debugAPI := api.Group("/debug")
+
+	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)
+
+	debugAPIServer := &http.Server{
+		Addr:    a.addr,
+		Handler: api,
+		// Use some hardcoded numberes that are suitable for testing
+		ReadTimeout:    30 * time.Second, //nolint:gomnd
+		WriteTimeout:   30 * time.Second, //nolint:gomnd
+		MaxHeaderBytes: 1 << 20,          //nolint:gomnd
+	}
+	go func() {
+		log.Infof("Debug API is ready at %v", a.addr)
+		if err := debugAPIServer.ListenAndServe(); err != nil &&
+			err != http.ErrServerClosed {
+			log.Fatalf("Listen: %s\n", err)
+		}
+	}()
+
+	<-ctx.Done()
+	log.Info("Stopping Debug API...")
+	if err := debugAPIServer.Shutdown(context.Background()); err != nil {
+		return err
+	}
+	log.Info("Debug API stopped")
+	return nil
+}