Implement generate-only option for commands that create txs

The new CLI flag builds an unsigned transaction and writes it to STDOUT.
Likewise, REST clients can now append generate_only=true to a request's
query arguments list and expect a JSON response carrying the unsigned
transaction.

Closes: #966

client/utils/rest.go

@@ -3,11 +3,17 @@ package utils
 import (
 	"fmt"
 	"net/http"
+	"net/url"
 	"strconv"
+
+	sdk "github.com/cosmos/cosmos-sdk/types"
+	auth "github.com/cosmos/cosmos-sdk/x/auth"
+	authctx "github.com/cosmos/cosmos-sdk/x/auth/client/context"
 )
 
 const (
-	queryArgDryRun = "simulate"
+	queryArgDryRun       = "simulate"
+	queryArgGenerateOnly = "generate_only"
 )
 
 // WriteErrorResponse prepares and writes a HTTP error
@@ -26,9 +32,10 @@ func WriteSimulationResponse(w http.ResponseWriter, gas int64) {
 
 // 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"
-}
+func HasDryRunArg(r *http.Request) bool { return urlQueryHasArg(r.URL, queryArgDryRun) }
+
+// HasGenerateOnlyArg returns whether a URL's query "generate-only" parameter is set to "true".
+func HasGenerateOnlyArg(r *http.Request) bool { return urlQueryHasArg(r.URL, queryArgGenerateOnly) }
 
 // ParseFloat64OrReturnBadRequest converts s to a float64 value. It returns a default
 // value if the string is empty. Write
@@ -43,3 +50,21 @@ func ParseFloat64OrReturnBadRequest(w http.ResponseWriter, s string, defaultIfEm
 	}
 	return n, true
 }
+
+// WriteGenerateStdTxResponse writes response for the generate_only mode.
+func WriteGenerateStdTxResponse(w http.ResponseWriter, txCtx authctx.TxContext, msgs []sdk.Msg) {
+	stdMsg, err := txCtx.Build(msgs)
+	if err != nil {
+		WriteErrorResponse(w, http.StatusBadRequest, err.Error())
+		return
+	}
+	output, err := txCtx.Codec.MarshalJSON(auth.NewStdTx(stdMsg.Msgs, stdMsg.Fee, nil, stdMsg.Memo))
+	if err != nil {
+		WriteErrorResponse(w, http.StatusInternalServerError, err.Error())
+		return
+	}
+	w.Write(output)
+	return
+}
+
+func urlQueryHasArg(url *url.URL, arg string) bool { return url.Query().Get(arg) == "true" }

client/utils/utils.go

@@ -7,6 +7,7 @@ import (
 	"github.com/cosmos/cosmos-sdk/client/context"
 	"github.com/cosmos/cosmos-sdk/client/keys"
 	sdk "github.com/cosmos/cosmos-sdk/types"
+	auth "github.com/cosmos/cosmos-sdk/x/auth"
 	authctx "github.com/cosmos/cosmos-sdk/x/auth/client/context"
 	amino "github.com/tendermint/go-amino"
 	"github.com/tendermint/tendermint/libs/common"
@@ -28,7 +29,7 @@ func SendTx(txCtx authctx.TxContext, cliCtx context.CLIContext, msgs []sdk.Msg)
 		if err != nil {
 			return err
 		}
-		fmt.Fprintf(os.Stdout, "estimated gas = %v\n", txCtx.Gas)
+		fmt.Fprintf(os.Stderr, "estimated gas = %v\n", txCtx.Gas)
 	}
 	if cliCtx.DryRun {
 		return nil
@@ -85,6 +86,19 @@ func CalculateGas(queryFunc func(string, common.HexBytes) ([]byte, error), cdc *
 	return
 }
 
+// PrintUnsignedStdTx builds an unsigned StdTx and prints it to os.Stdout.
+func PrintUnsignedStdTx(txCtx authctx.TxContext, cliCtx context.CLIContext, msgs []sdk.Msg) (err error) {
+	stdTx, err := buildUnsignedStdTx(txCtx, cliCtx, msgs)
+	if err != nil {
+		return
+	}
+	json, err := txCtx.Codec.MarshalJSON(stdTx)
+	if err == nil {
+		fmt.Printf("%s\n", json)
+	}
+	return
+}
+
 func adjustGasEstimate(estimate int64, adjustment float64) int64 {
 	return int64(adjustment * float64(estimate))
 }
@@ -128,3 +142,24 @@ func prepareTxContext(txCtx authctx.TxContext, cliCtx context.CLIContext) (authc
 	}
 	return txCtx, nil
 }
+
+// buildUnsignedStdTx builds a StdTx as per the parameters passed in the
+// contexts. Gas is automatically estimated if gas wanted is set to 0.
+func buildUnsignedStdTx(txCtx authctx.TxContext, cliCtx context.CLIContext, msgs []sdk.Msg) (stdTx auth.StdTx, err error) {
+	txCtx, err = prepareTxContext(txCtx, cliCtx)
+	if err != nil {
+		return
+	}
+	if txCtx.Gas == 0 {
+		txCtx, err = EnrichCtxWithGas(txCtx, cliCtx, cliCtx.FromAddressName, msgs)
+		if err != nil {
+			return
+		}
+		fmt.Fprintf(os.Stderr, "estimated gas = %v\n", txCtx.Gas)
+	}
+	stdSignMsg, err := txCtx.Build(msgs)
+	if err != nil {
+		return
+	}
+	return auth.NewStdTx(stdSignMsg.Msgs, stdSignMsg.Fee, nil, stdSignMsg.Memo), nil
+}