Add --tpslimit and --tpslimit-burst to limit transactions per second for HTTP

This is useful if you are being rate limited or banned by your cloud
storage provider.

docs/content/docs.md

@@ -566,6 +566,40 @@ If using `--syslog` this sets the syslog facility (eg `KERN`, `USER`).
 See `man syslog` for a list of possible facilities.  The default
 facility is `DAEMON`.
 
+### --tpslimit float ###
+
+Limit HTTP transactions per second to this. Default is 0 which is used
+to mean unlimited transactions per second.
+
+For example to limit rclone to 10 HTTP transactions per second use
+`--tpslimit 10`, or to 1 transaction every 2 seconds use `--tpslimit
+0.5`.
+
+Use this when the number of transactions per second from rclone is
+causing a problem with the cloud storage provider (eg getting you
+banned or rate limited).
+
+This can be very useful for `rclone mount` to control the behaviour of
+applications using it.
+
+See also `--tpslimit-burst`.
+
+### --tpslimit-burst int ###
+
+Max burst of transactions for `--tpslimit`. (default 1)
+
+Normally `--tpslimit` will do exactly the number of transaction per
+second specified.  However if you supply `--tps-burst` then rclone can
+save up some transactions from when it was idle giving a burst of up
+to the parameter supplied.
+
+For example if you provide `--tpslimit-burst 10` then if rclone has
+been idle for more than 10*`--tpslimit` then it can do 10 transactions
+very quickly before they are limited again.
+
+This may be used to increase performance of `--tpslimit` without
+changing the long term average number of transactions per second.
+
 ### --track-renames ###
 
 By default, rclone doesn't keep track of renamed files, so if you

fs/config.go

@@ -96,6 +96,8 @@ var (
 	backupDir       = StringP("backup-dir", "", "", "Make backups into hierarchy based in DIR.")
 	suffix          = StringP("suffix", "", "", "Suffix for use with --backup-dir.")
 	useListR        = BoolP("fast-list", "", false, "Use recursive list if available. Uses more memory but fewer transactions.")
+	tpsLimit        = Float64P("tpslimit", "", 0, "Limit HTTP transactions per second to this.")
+	tpsLimitBurst   = IntP("tpslimit-burst", "", 1, "Max burst of transactions for --tpslimit.")
 	logLevel        = LogLevelNotice
 	statsLogLevel   = LogLevelInfo
 	bwLimit         BwTimetable
@@ -228,6 +230,8 @@ type ConfigInfo struct {
 	Suffix             string
 	UseListR           bool
 	BufferSize         SizeSuffix
+	TPSLimit           float64
+	TPSLimitBurst      int
 }
 
 // Return the path to the configuration file
@@ -364,6 +368,8 @@ func LoadConfig() {
 	Config.BackupDir = *backupDir
 	Config.Suffix = *suffix
 	Config.UseListR = *useListR
+	Config.TPSLimit = *tpsLimit
+	Config.TPSLimitBurst = *tpsLimitBurst
 	Config.BufferSize = bufferSize
 
 	ConfigPath = *configFile
@@ -413,6 +419,9 @@ func LoadConfig() {
 
 	// Start the bandwidth update ticker
 	startTokenTicker()
+
+	// Start the transactions per second limiter
+	startHTTPTokenBucket()
 }
 
 var errorConfigFileNotFound = errors.New("config file not found")

fs/flags.go

@@ -286,6 +286,15 @@ func IntP(name, shorthand string, value int, usage string) (out *int) {
 	return out
 }
 
+// Float64P defines a flag which can be overridden by an environment variable
+//
+// It is a thin wrapper around pflag.Float64P
+func Float64P(name, shorthand string, value float64, usage string) (out *float64) {
+	out = pflag.Float64P(name, shorthand, value, usage)
+	setDefaultFromEnv(name)
+	return out
+}
+
 // DurationP defines a flag which can be overridden by an environment variable
 //
 // It is a thin wrapper around pflag.DurationP

fs/http.go

@@ -11,6 +11,9 @@ import (
 	"reflect"
 	"sync"
 	"time"
+
+	"golang.org/x/net/context" // switch to "context" when we stop supporting go1.6
+	"golang.org/x/time/rate"
 )
 
 const (
@@ -21,8 +24,21 @@ const (
 var (
 	transport   http.RoundTripper
 	noTransport sync.Once
+	tpsBucket   *rate.Limiter // for limiting number of http transactions per second
 )
 
+// Start the token bucket if necessary
+func startHTTPTokenBucket() {
+	if Config.TPSLimit > 0 {
+		tpsBurst := Config.TPSLimitBurst
+		if tpsBurst < 1 {
+			tpsBurst = 1
+		}
+		tpsBucket = rate.NewLimiter(rate.Limit(Config.TPSLimit), tpsBurst)
+		Infof(nil, "Starting HTTP transaction limiter: max %g transactions/s with burst %d", Config.TPSLimit, tpsBurst)
+	}
+}
+
 // A net.Conn that sets a deadline for every Read or Write operation
 type timeoutConn struct {
 	net.Conn
@@ -217,6 +233,13 @@ func cleanAuth(buf []byte) []byte {
 
 // RoundTrip implements the RoundTripper interface.
 func (t *Transport) RoundTrip(req *http.Request) (resp *http.Response, err error) {
+	// Get transactions per second token first if limiting
+	if tpsBucket != nil {
+		tbErr := tpsBucket.Wait(context.Background()) // FIXME switch to req.Context() when we drop go1.6 support
+		if tbErr != nil {
+			Errorf(nil, "HTTP token bucket error: %v", err)
+		}
+	}
 	// Force user agent
 	req.Header.Set("User-Agent", UserAgent)
 	// Logf request