Introduce simulate mode

Add a simulate only flag '--dry-run' to both CLI tx commands
and RESTful endpoints to trigger the simulation of unsigned
transactions.

* Turning --dry-run on causes the --gas flag to be ignored.
  The simulation will return the estimate of the gas required
  to actually run the transaction.
* Adjustment is no longer required. It now defaults to 1.0.
* In some test cases accounts retrieved from the state do not
  come with a PubKey. In such cases, a fake secp256k1 key is
  generated and gas consumption calculated accordingly.

Closes: #2110

PENDING.md

@@ -40,6 +40,7 @@ FEATURES
 
 * Gaia REST API (`gaiacli advanced rest-server`)
   * [lcd] Endpoints to query staking pool and params
+  * [lcd] \#2110 Add support for `simulate=true` requests query argument to endpoints that send txs to run simulations of transactions
 
 * Gaia CLI  (`gaiacli`)
   * [cli] Cmds to query staking pool and params
@@ -48,6 +49,7 @@ FEATURES
   provide desired Bech32 prefix encoding
   * [cli] \#2047 Setting the --gas flag value to 0 triggers a simulation of the tx before the actual execution. The gas estimate obtained via the simulation will be used as gas limit in the actual execution.
   * [cli] \#2047 The --gas-adjustment flag can be used to adjust the estimate obtained via the simulation triggered by --gas=0.
+  * [cli] \#2110 Add --dry-run flag to perform a simulation of a transaction without broadcasting it. The --gas flag is ignored as gas would be automatically estimated.
 
 * Gaia
   * [cli] #2170 added ability to show the node's address via `gaiad tendermint show-address`

client/context/context.go

@@ -37,6 +37,7 @@ type CLIContext struct {
 	JSON            bool
 	PrintResponse   bool
 	Certifier       tmlite.Certifier
+	DryRun          bool
 }
 
 // NewCLIContext returns a new initialized CLIContext with parameters from the
@@ -63,6 +64,7 @@ func NewCLIContext() CLIContext {
 		JSON:            viper.GetBool(client.FlagJson),
 		PrintResponse:   viper.GetBool(client.FlagPrintResponse),
 		Certifier:       createCertifier(),
+		DryRun:          viper.GetBool(client.FlagDryRun),
 	}
 }
 

client/flags.go

@@ -5,7 +5,7 @@ import "github.com/spf13/cobra"
 // nolint
 const (
 	DefaultGasLimit      = 200000
-	DefaultGasAdjustment = 1.2
+	DefaultGasAdjustment = 1.0
 
 	FlagUseLedger     = "ledger"
 	FlagChainID       = "chain-id"
@@ -23,6 +23,7 @@ const (
 	FlagAsync         = "async"
 	FlagJson          = "json"
 	FlagPrintResponse = "print-response"
+	FlagDryRun        = "dry-run"
 )
 
 // LineBreak can be included in a command list to provide a blank line
@@ -54,11 +55,12 @@ func PostCommands(cmds ...*cobra.Command) []*cobra.Command {
 		c.Flags().String(FlagNode, "tcp://localhost:26657", "<host>:<port> to tendermint rpc interface for this chain")
 		c.Flags().Bool(FlagUseLedger, false, "Use a connected Ledger device")
 		c.Flags().Int64(FlagGas, DefaultGasLimit, "gas limit to set per-transaction; set to 0 to calculate required gas automatically")
-		c.Flags().Float64(FlagGasAdjustment, DefaultGasAdjustment, "adjustment factor to be multiplied against the estimate returned by the tx simulation")
+		c.Flags().Float64(FlagGasAdjustment, DefaultGasAdjustment, "adjustment factor to be multiplied against the estimate returned by the tx simulation; if the gas limit is set manually this flag is ignored ")
 		c.Flags().Bool(FlagAsync, false, "broadcast transactions asynchronously")
 		c.Flags().Bool(FlagJson, false, "return output in json format")
 		c.Flags().Bool(FlagPrintResponse, true, "return tx response (only works with async = false)")
 		c.Flags().Bool(FlagTrustNode, true, "Don't verify proofs for query responses")
+		c.Flags().Bool(FlagDryRun, false, "ignore the --gas flag and perform a simulation of a transaction, but don't broadcast it")
 	}
 	return cmds
 }

client/lcd/lcd_test.go

@@ -2,6 +2,7 @@ package lcd
 
 import (
 	"encoding/hex"
+	"encoding/json"
 	"fmt"
 	"net/http"
 	"regexp"
@@ -265,11 +266,17 @@ func TestCoinSend(t *testing.T) {
 	require.Equal(t, int64(1), mycoins.Amount.Int64())
 
 	// test failure with too little gas
-	res, body, _ = doSendWithGas(t, port, seed, name, password, addr, 100)
+	res, body, _ = doSendWithGas(t, port, seed, name, password, addr, 100, "")
 	require.Equal(t, http.StatusInternalServerError, res.StatusCode, body)
 
-	// test success with just enough gas
-	res, body, _ = doSendWithGas(t, port, seed, name, password, addr, 3000)
+	// run simulation and test success with estimated gas
+	res, body, _ = doSendWithGas(t, port, seed, name, password, addr, 0, "?simulate=true")
+	require.Equal(t, http.StatusOK, res.StatusCode, body)
+	var responseBody struct {
+		GasEstimate int64 `json:"gas_estimate"`
+	}
+	require.Nil(t, json.Unmarshal([]byte(body), &responseBody))
+	res, body, _ = doSendWithGas(t, port, seed, name, password, addr, responseBody.GasEstimate, "")
 	require.Equal(t, http.StatusOK, res.StatusCode, body)
 }
 
@@ -720,7 +727,7 @@ func getAccount(t *testing.T, port string, addr sdk.AccAddress) auth.Account {
 	return acc
 }
 
-func doSendWithGas(t *testing.T, port, seed, name, password string, addr sdk.AccAddress, gas int64) (res *http.Response, body string, receiveAddr sdk.AccAddress) {
+func doSendWithGas(t *testing.T, port, seed, name, password string, addr sdk.AccAddress, gas int64, queryStr string) (res *http.Response, body string, receiveAddr sdk.AccAddress) {
 
 	// create receive address
 	kb := client.MockKeyBase()
@@ -754,12 +761,12 @@ func doSendWithGas(t *testing.T, port, seed, name, password string, addr sdk.Acc
 		"chain_id":"%s"
 	}`, gasStr, name, password, accnum, sequence, coinbz, chainID))
 
-	res, body = Request(t, port, "POST", fmt.Sprintf("/accounts/%s/send", receiveAddr), jsonStr)
+	res, body = Request(t, port, "POST", fmt.Sprintf("/accounts/%s/send%v", receiveAddr, queryStr), jsonStr)
 	return
 }
 
 func doSend(t *testing.T, port, seed, name, password string, addr sdk.AccAddress) (receiveAddr sdk.AccAddress, resultTx ctypes.ResultBroadcastTxCommit) {
-	res, body, receiveAddr := doSendWithGas(t, port, seed, name, password, addr, 0)
+	res, body, receiveAddr := doSendWithGas(t, port, seed, name, password, addr, 0, "")
 	require.Equal(t, http.StatusOK, res.StatusCode, body)
 
 	err := cdc.UnmarshalJSON([]byte(body), &resultTx)

client/utils/rest.go

@@ -1,12 +1,30 @@
 package utils
 
 import (
+	"fmt"
 	"net/http"
 )
 
+const (
+	queryArgDryRun = "simulate"
+)
+
 // WriteErrorResponse prepares and writes a HTTP error
 // given a status code and an error message.
 func WriteErrorResponse(w *http.ResponseWriter, status int, msg string) {
 	(*w).WriteHeader(status)
 	(*w).Write([]byte(msg))
 }
+
+// WriteGasEstimateResponse prepares and writes an HTTP
+// response for transactions simulations.
+func WriteSimulationResponse(w *http.ResponseWriter, gas int64) {
+	(*w).WriteHeader(http.StatusOK)
+	(*w).Write([]byte(fmt.Sprintf(`{"gas_estimate":%v}`, gas)))
+}
+
+// HasDryRunArg returns true if the request's URL query contains
+// the dry run argument and its value is set to "true".
+func HasDryRunArg(r *http.Request) bool {
+	return r.URL.Query().Get(queryArgDryRun) == "true"
+}

client/utils/utils.go

@@ -15,57 +15,35 @@ import (
 // DefaultGasAdjustment is applied to gas estimates to avoid tx
 // execution failures due to state changes that might
 // occur between the tx simulation and the actual run.
-const DefaultGasAdjustment = 1.2
+const DefaultGasAdjustment = 1.0
 
 // SendTx implements a auxiliary handler that facilitates sending a series of
 // messages in a signed transaction given a TxContext and a QueryContext. It
 // ensures that the account exists, has a proper number and sequence set. In
 // addition, it builds and signs a transaction with the supplied messages.
 // Finally, it broadcasts the signed transaction to a node.
 func SendTx(txCtx authctx.TxContext, cliCtx context.CLIContext, msgs []sdk.Msg) error {
-	if err := cliCtx.EnsureAccountExists(); err != nil {
-		return err
-	}
-
-	from, err := cliCtx.GetFromAddress()
+	txCtx, err := prepareTxContext(txCtx, cliCtx)
 	if err != nil {
 		return err
 	}
-
-	// TODO: (ref #1903) Allow for user supplied account number without
-	// automatically doing a manual lookup.
-	if txCtx.AccountNumber == 0 {
-		accNum, err := cliCtx.GetAccountNumber(from)
+	autogas := cliCtx.DryRun || (cliCtx.Gas == 0)
+	if autogas {
+		txCtx, err = EnrichCtxWithGas(txCtx, cliCtx, cliCtx.FromAddressName, msgs)
 		if err != nil {
 			return err
 		}
-
-		txCtx = txCtx.WithAccountNumber(accNum)
+		fmt.Fprintf(os.Stdout, "estimated gas = %v\n", txCtx.Gas)
 	}
-
-	// TODO: (ref #1903) Allow for user supplied account sequence without
-	// automatically doing a manual lookup.
-	if txCtx.Sequence == 0 {
-		accSeq, err := cliCtx.GetAccountSequence(from)
-		if err != nil {
-			return err
-		}
-
-		txCtx = txCtx.WithSequence(accSeq)
+	if cliCtx.DryRun {
+		return nil
 	}
 
 	passphrase, err := keys.GetPassphrase(cliCtx.FromAddressName)
 	if err != nil {
 		return err
 	}
 
-	if cliCtx.Gas == 0 {
-		txCtx, err = EnrichCtxWithGas(txCtx, cliCtx, cliCtx.FromAddressName, passphrase, msgs)
-		if err != nil {
-			return err
-		}
-	}
-
 	// build and sign the transaction
 	txBytes, err := txCtx.BuildAndSign(cliCtx.FromAddressName, passphrase, msgs)
 	if err != nil {
@@ -75,26 +53,26 @@ func SendTx(txCtx authctx.TxContext, cliCtx context.CLIContext, msgs []sdk.Msg)
 	return cliCtx.EnsureBroadcastTx(txBytes)
 }
 
-// EnrichCtxWithGas calculates the gas estimate that would be consumed by the
-// transaction and set the transaction's respective value accordingly.
-func EnrichCtxWithGas(txCtx authctx.TxContext, cliCtx context.CLIContext, name, passphrase string, msgs []sdk.Msg) (authctx.TxContext, error) {
-	txBytes, err := BuildAndSignTxWithZeroGas(txCtx, name, passphrase, msgs)
+// SimulateMsgs simulates the transaction and returns the gas estimate and the adjusted value.
+func SimulateMsgs(txCtx authctx.TxContext, cliCtx context.CLIContext, name string, msgs []sdk.Msg, gas int64) (estimated, adjusted int64, err error) {
+	txBytes, err := txCtx.WithGas(gas).BuildWithPubKey(name, msgs)
 	if err != nil {
-		return txCtx, err
+		return
 	}
-	estimate, adjusted, err := CalculateGas(cliCtx.Query, cliCtx.Codec, txBytes, cliCtx.GasAdjustment)
+	estimated, adjusted, err = CalculateGas(cliCtx.Query, cliCtx.Codec, txBytes, cliCtx.GasAdjustment)
+	return
+}
+
+// EnrichCtxWithGas calculates the gas estimate that would be consumed by the
+// transaction and set the transaction's respective value accordingly.
+func EnrichCtxWithGas(txCtx authctx.TxContext, cliCtx context.CLIContext, name string, msgs []sdk.Msg) (authctx.TxContext, error) {
+	_, adjusted, err := SimulateMsgs(txCtx, cliCtx, name, msgs, 0)
 	if err != nil {
 		return txCtx, err
 	}
-	fmt.Fprintf(os.Stderr, "gas: [estimated = %v] [adjusted = %v]\n", estimate, adjusted)
 	return txCtx.WithGas(adjusted), nil
 }
 
-// BuildAndSignTxWithZeroGas builds transactions with GasWanted set to 0.
-func BuildAndSignTxWithZeroGas(txCtx authctx.TxContext, name, passphrase string, msgs []sdk.Msg) ([]byte, error) {
-	return txCtx.WithGas(0).BuildAndSign(name, passphrase, msgs)
-}
-
 // CalculateGas simulates the execution of a transaction and returns
 // both the estimate obtained by the query and the adjusted amount.
 func CalculateGas(queryFunc func(string, common.HexBytes) ([]byte, error), cdc *amino.Codec, txBytes []byte, adjustment float64) (estimate, adjusted int64, err error) {
@@ -109,13 +87,12 @@ func CalculateGas(queryFunc func(string, common.HexBytes) ([]byte, error), cdc *
 		return
 	}
 	adjusted = adjustGasEstimate(estimate, adjustment)
-	fmt.Fprintf(os.Stderr, "gas: [estimated = %v] [adjusted = %v]\n", estimate, adjusted)
 	return
 }
 
 func adjustGasEstimate(estimate int64, adjustment float64) int64 {
 	if adjustment == 0 {
-		return int64(DefaultGasAdjustment * float64(estimate))
+		adjustment = DefaultGasAdjustment
 	}
 	return int64(adjustment * float64(estimate))
 }
@@ -127,3 +104,35 @@ func parseQueryResponse(cdc *amino.Codec, rawRes []byte) (int64, error) {
 	}
 	return simulationResult.GasUsed, nil
 }
+
+func prepareTxContext(txCtx authctx.TxContext, cliCtx context.CLIContext) (authctx.TxContext, error) {
+	if err := cliCtx.EnsureAccountExists(); err != nil {
+		return txCtx, err
+	}
+
+	from, err := cliCtx.GetFromAddress()
+	if err != nil {
+		return txCtx, err
+	}
+
+	// TODO: (ref #1903) Allow for user supplied account number without
+	// automatically doing a manual lookup.
+	if txCtx.AccountNumber == 0 {
+		accNum, err := cliCtx.GetAccountNumber(from)
+		if err != nil {
+			return txCtx, err
+		}
+		txCtx = txCtx.WithAccountNumber(accNum)
+	}
+
+	// TODO: (ref #1903) Allow for user supplied account sequence without
+	// automatically doing a manual lookup.
+	if txCtx.Sequence == 0 {
+		accSeq, err := cliCtx.GetAccountSequence(from)
+		if err != nil {
+			return txCtx, err
+		}
+		txCtx = txCtx.WithSequence(accSeq)
+	}
+	return txCtx, nil
+}

cmd/gaia/cli_test/cli_test.go

@@ -58,6 +58,13 @@ func TestGaiaCLISend(t *testing.T) {
 	fooAcc = executeGetAccount(t, fmt.Sprintf("gaiacli account %s %v", fooAddr, flags))
 	require.Equal(t, int64(40), fooAcc.GetCoins().AmountOf("steak").Int64())
 
+	// Test --dry-run
+	success := executeWrite(t, fmt.Sprintf("gaiacli send %v --amount=10steak --to=%s --from=foo --dry-run", flags, barAddr), app.DefaultKeyPass)
+	require.True(t, success)
+	// Check state didn't change
+	fooAcc = executeGetAccount(t, fmt.Sprintf("gaiacli account %s %v", fooAddr, flags))
+	require.Equal(t, int64(40), fooAcc.GetCoins().AmountOf("steak").Int64())
+
 	// test autosequencing
 	executeWrite(t, fmt.Sprintf("gaiacli send %v --amount=10steak --to=%s --from=foo", flags, barAddr), app.DefaultKeyPass)
 	tests.WaitForNextNBlocksTM(2, port)
@@ -148,6 +155,10 @@ func TestGaiaCLICreateValidator(t *testing.T) {
 
 	initialPool.BondedTokens = initialPool.BondedTokens.Add(sdk.NewDec(1))
 
+	// Test --dry-run
+	success := executeWrite(t, cvStr+" --dry-run", app.DefaultKeyPass)
+	require.True(t, success)
+
 	executeWrite(t, cvStr, app.DefaultKeyPass)
 	tests.WaitForNextNBlocksTM(2, port)
 
@@ -164,7 +175,7 @@ func TestGaiaCLICreateValidator(t *testing.T) {
 	unbondStr += fmt.Sprintf(" --validator=%s", sdk.ValAddress(barAddr))
 	unbondStr += fmt.Sprintf(" --shares-amount=%v", "1")
 
-	success := executeWrite(t, unbondStr, app.DefaultKeyPass)
+	success = executeWrite(t, unbondStr, app.DefaultKeyPass)
 	require.True(t, success)
 	tests.WaitForNextNBlocksTM(2, port)
 
@@ -211,6 +222,10 @@ func TestGaiaCLISubmitProposal(t *testing.T) {
 	spStr += fmt.Sprintf(" --title=%s", "Test")
 	spStr += fmt.Sprintf(" --description=%s", "test")
 
+	// Test --dry-run
+	success := executeWrite(t, spStr+" --dry-run", app.DefaultKeyPass)
+	require.True(t, success)
+
 	executeWrite(t, spStr, app.DefaultKeyPass)
 	tests.WaitForNextNBlocksTM(2, port)
 

docs/sdk/clients.md

@@ -95,6 +95,8 @@ When you query an account balance with zero tokens, you will get this error: `No
 
 ### Send Tokens
 
+The following command could be used to send coins from one account to another:
+
 ```bash
 gaiacli send \
   --amount=10faucetToken \
@@ -110,7 +112,7 @@ The `--amount` flag accepts the format `--amount=<value|coin_name>`.
 ::: tip Note
 You may want to cap the maximum gas that can be consumed by the transaction via the `--gas` flag.
 If set to 0, the gas limit will be automatically estimated.
-Gas estimate might be inaccurate as state changes could occur in between the end of the simulation and the actual execution of a transaction, thus an adjustment is applied on top of the original estimate in order to ensure the transaction is broadcasted successfully. The adjustment can be controlled via the `--gas-adjustment` flag, whose default value is 1.2.
+Gas estimate might be inaccurate as state changes could occur in between the end of the simulation and the actual execution of a transaction, thus an adjustment is applied on top of the original estimate in order to ensure the transaction is broadcasted successfully. The adjustment can be controlled via the `--gas-adjustment` flag, whose default value is 1.0.
 :::
 
 Now, view the updated balances of the origin and destination accounts:
@@ -126,6 +128,17 @@ You can also check your balance at a given block by using the `--block` flag:
 gaiacli account <account_cosmos> --block=<block_height>
 ```
 
+You can simulate a transaction without actually broadcasting it by appending the `--dry-run` flag to the command line:
+
+```bash
+gaiacli send \
+  --amount=10faucetToken \
+  --chain-id=<chain_id> \
+  --name=<key_name> \
+  --to=<destination_cosmosaccaddr> \
+  --dry-run
+```
+
 ### Staking
 
 #### Set up a Validator