rpcclient: Add cookie auth

Based on Hugo Landau's cookie auth implementation for Namecoin's ncdns.

Fixes https://github.com/btcsuite/btcd/issues/1054

rpcclient/cookiefile.go

@@ -0,0 +1,64 @@
+// Copyright (c) 2017 The Namecoin developers
+// Copyright (c) 2019 The btcsuite developers
+// Use of this source code is governed by an ISC
+// license that can be found in the LICENSE file.
+
+package rpcclient
+
+import (
+	"fmt"
+	"io/ioutil"
+	"os"
+	"strings"
+	"time"
+)
+
+func readCookieFile(path string) (username, password string, err error) {
+	b, err := ioutil.ReadFile(path)
+	if err != nil {
+		return
+	}
+
+	s := strings.TrimSpace(string(b))
+	parts := strings.SplitN(s, ":", 2)
+	if len(parts) != 2 {
+		err = fmt.Errorf("malformed cookie file")
+		return
+	}
+
+	username, password = parts[0], parts[1]
+	return
+}
+
+func cookieRetriever(path string) func() (username, password string, err error) {
+	lastCheckTime := time.Time{}
+	lastModTime := time.Time{}
+
+	curUsername, curPassword := "", ""
+	var curError error
+
+	doUpdate := func() {
+		if !lastCheckTime.IsZero() && time.Now().Before(lastCheckTime.Add(30*time.Second)) {
+			return
+		}
+
+		lastCheckTime = time.Now()
+
+		st, err := os.Stat(path)
+		if err != nil {
+			curError = err
+			return
+		}
+
+		modTime := st.ModTime()
+		if !modTime.Equal(lastModTime) {
+			lastModTime = modTime
+			curUsername, curPassword, curError = readCookieFile(path)
+		}
+	}
+
+	return func() (username, password string, err error) {
+		doUpdate()
+		return curUsername, curPassword, curError
+	}
+}

rpcclient/infrastructure.go

@@ -851,7 +851,12 @@ func (c *Client) sendPost(jReq *jsonRequest) {
 	httpReq.Header.Set("Content-Type", "application/json")
 
 	// Configure basic access authorization.
-	httpReq.SetBasicAuth(c.config.User, c.config.Pass)
+	user, pass, err := c.config.getAuth()
+	if err != nil {
+		jReq.responseChan <- &response{result: nil, err: err}
+		return
+	}
+	httpReq.SetBasicAuth(user, pass)
 
 	log.Tracef("Sending command [%s] with id %d", jReq.method, jReq.id)
 	c.sendPostRequest(httpReq, jReq)
@@ -1096,6 +1101,15 @@ type ConnConfig struct {
 	// Pass is the passphrase to use to authenticate to the RPC server.
 	Pass string
 
+	// CookiePath is the path to a cookie file containing the username and
+	// passphrase to use to authenticate to the RPC server.  It is used
+	// instead of User and Pass if non-empty.
+	CookiePath string
+
+	// retrieveCookie is a function that returns the cookie username and
+	// passphrase.
+	retrieveCookie func() (username, passphrase string, err error)
+
 	// Params is the string representing the network that the server
 	// is running. If there is no parameter set in the config, then
 	// mainnet will be used by default.
@@ -1149,6 +1163,25 @@ type ConnConfig struct {
 	EnableBCInfoHacks bool
 }
 
+// getAuth returns the username and passphrase that will actually be used for
+// this connection.  This will be the result of checking the cookie if a cookie
+// path is configured; if not, it will be the user-configured username and
+// passphrase.
+func (config *ConnConfig) getAuth() (username, passphrase string, err error) {
+	// If cookie auth isn't in use, just use the supplied
+	// username/passphrase.
+	if config.CookiePath == "" {
+		return config.User, config.Pass, nil
+	}
+
+	// Initialize the cookie retriever on first run.
+	if config.retrieveCookie == nil {
+		config.retrieveCookie = cookieRetriever(config.CookiePath)
+	}
+
+	return config.retrieveCookie()
+}
+
 // newHTTPClient returns a new http client that is configured according to the
 // proxy and TLS settings in the associated connection configuration.
 func newHTTPClient(config *ConnConfig) (*http.Client, error) {
@@ -1218,7 +1251,11 @@ func dial(config *ConnConfig) (*websocket.Conn, error) {
 
 	// The RPC server requires basic authorization, so create a custom
 	// request header with the Authorization header set.
-	login := config.User + ":" + config.Pass
+	user, pass, err := config.getAuth()
+	if err != nil {
+		return nil, err
+	}
+	login := user + ":" + pass
 	auth := "Basic " + base64.StdEncoding.EncodeToString([]byte(login))
 	requestHeader := make(http.Header)
 	requestHeader.Add("Authorization", auth)