Improve btcctl config.

This commit improves the configuration for btcctl in several ways:

- Add the ability to specify a config file
- Add a default entry to the rpc cert to point to the location
  it will likely be in the btcd home directory
- Move the config bits into a separate file for easier maintenance

util/btcctl/btcctl.go

@@ -13,14 +13,6 @@ import (
 	"strconv"
 )
 
-type config struct {
-	RpcUser       string `short:"u" long:"rpcuser" description:"RPC username"`
-	RpcPassword   string `short:"P" long:"rpcpass" description:"RPC password"`
-	RpcServer     string `short:"s" long:"rpcserver" description:"RPC server to connect to"`
-	RpcCert       string `short:"c" long:"rpccert" description:"RPC server certificate chain for validation"`
-	TlsSkipVerify bool   `long:"skipverify" description:"Do not verify tls certificates (not recommended!)"`
-}
-
 // conversionHandler is a handler that is used to convert parameters from the
 // command line to a specific type.  This is needed since the btcjson API
 // expects certain types for various parameters.
@@ -367,12 +359,7 @@ func usage(parser *flags.Parser) {
 }
 
 func main() {
-	// Parse command line and show usage if needed.
+	parser, cfg, args, err := loadConfig()
-	cfg := config{
-		RpcServer: "127.0.0.1:8334",
-	}
-	parser := flags.NewParser(&cfg, flags.PassDoubleDash|flags.HelpFlag)
-	args, err := parser.Parse()
 	if err != nil {
 		usage(parser)
 		os.Exit(1)
@@ -391,7 +378,7 @@ func main() {
 	}
 
 	// Execute the command.
-	err = commandHandler(&cfg, args[0], data, args[1:])
+	err = commandHandler(cfg, args[0], data, args[1:])
 	if err != nil {
 		if err == ErrUsage {
 			usage(parser)

util/btcctl/config.go

@@ -0,0 +1,74 @@
+package main
+
+import (
+	"fmt"
+	"github.com/conformal/btcutil"
+	"github.com/conformal/go-flags"
+	"os"
+	"path/filepath"
+)
+
+var (
+	btcdHomeDir        = btcutil.AppDataDir("btcd", false)
+	btcctlHomeDir      = btcutil.AppDataDir("btcctl", false)
+	defaultConfigFile  = filepath.Join(btcctlHomeDir, "btcctl.conf")
+	defaultRPCCertFile = filepath.Join(btcdHomeDir, "rpc.cert")
+)
+
+// config defines the configuration options for btcctl.
+//
+// See loadConfig for details on the configuration load process.
+type config struct {
+	ConfigFile    string `short:"C" long:"configfile" description:"Path to configuration file"`
+	RpcUser       string `short:"u" long:"rpcuser" description:"RPC username"`
+	RpcPassword   string `short:"P" long:"rpcpass" description:"RPC password"`
+	RpcServer     string `short:"s" long:"rpcserver" description:"RPC server to connect to"`
+	RpcCert       string `short:"c" long:"rpccert" description:"RPC server certificate chain for validation"`
+	TlsSkipVerify bool   `long:"skipverify" description:"Do not verify tls certificates (not recommended!)"`
+}
+
+// loadConfig initializes and parses the config using a config file and command
+// line options.
+//
+// The configuration proceeds as follows:
+// 	1) Start with a default config with sane settings
+// 	2) Pre-parse the command line to check for an alternative config file
+// 	3) Load configuration file overwriting defaults with any specified options
+// 	4) Parse CLI options and overwrite/add any specified options
+//
+// The above results in functioning properly without any config settings
+// while still allowing the user to override settings with config files and
+// command line options.  Command line options always take precedence.
+func loadConfig() (*flags.Parser, *config, []string, error) {
+	// Default config.
+	cfg := config{
+		ConfigFile: defaultConfigFile,
+		RpcServer:  "localhost:8334",
+		RpcCert:    defaultRPCCertFile,
+	}
+
+	// Pre-parse the command line options to see if an alternative config
+	// file was specified.  Any errors can be ignored here since they will
+	// be caught be the final parse below.
+	preCfg := cfg
+	preParser := flags.NewParser(&preCfg, flags.None)
+	preParser.Parse()
+
+	// Load additional config from file.
+	parser := flags.NewParser(&cfg, flags.PassDoubleDash|flags.HelpFlag)
+	err := parser.ParseIniFile(preCfg.ConfigFile)
+	if err != nil {
+		if _, ok := err.(*os.PathError); !ok {
+			fmt.Fprintln(os.Stderr, err)
+			return parser, nil, nil, err
+		}
+	}
+
+	// Parse command line options again to ensure they take precedence.
+	remainingArgs, err := parser.Parse()
+	if err != nil {
+		return parser, nil, nil, err
+	}
+
+	return parser, &cfg, remainingArgs, nil
+}