From 46049b423645c0943747ac179d322e1f48bc9a2e Mon Sep 17 00:00:00 2001
From: Alexander Neumann <alexander@bumpern.de>
Date: Tue, 6 Jun 2017 00:25:22 +0200
Subject: [PATCH] rest: Use semaphore

---
 src/restic/backend/rest/config.go      | 18 +++++++++--
 src/restic/backend/rest/config_test.go |  3 +-
 src/restic/backend/rest/rest.go        | 44 +++++++++++++-------------
 src/restic/backend/rest/rest_test.go   |  5 ++-
 4 files changed, 42 insertions(+), 28 deletions(-)

diff --git a/src/restic/backend/rest/config.go b/src/restic/backend/rest/config.go
index 929fda120..e1ad4e726 100644
--- a/src/restic/backend/rest/config.go
+++ b/src/restic/backend/rest/config.go
@@ -5,11 +5,24 @@ import (
 	"strings"
 
 	"restic/errors"
+	"restic/options"
 )
 
 // Config contains all configuration necessary to connect to a REST server.
 type Config struct {
-	URL *url.URL
+	URL         *url.URL
+	Connections uint `option:"connections" help:"set a limit for the number of concurrent connections (default: 20)"`
+}
+
+func init() {
+	options.Register("rest", Config{})
+}
+
+// NewConfig returns a new Config with the default values filled in.
+func NewConfig() Config {
+	return Config{
+		Connections: 20,
+	}
 }
 
 // ParseConfig parses the string s and extracts the REST server URL.
@@ -25,6 +38,7 @@ func ParseConfig(s string) (interface{}, error) {
 		return nil, errors.Wrap(err, "url.Parse")
 	}
 
-	cfg := Config{URL: u}
+	cfg := NewConfig()
+	cfg.URL = u
 	return cfg, nil
 }
diff --git a/src/restic/backend/rest/config_test.go b/src/restic/backend/rest/config_test.go
index 937204a57..0f27d1c09 100644
--- a/src/restic/backend/rest/config_test.go
+++ b/src/restic/backend/rest/config_test.go
@@ -20,7 +20,8 @@ var configTests = []struct {
 	cfg Config
 }{
 	{"rest:http://localhost:1234", Config{
-		URL: parseURL("http://localhost:1234"),
+		URL:         parseURL("http://localhost:1234"),
+		Connections: 20,
 	}},
 }
 
diff --git a/src/restic/backend/rest/rest.go b/src/restic/backend/rest/rest.go
index cb3fdadc8..852b9ce1a 100644
--- a/src/restic/backend/rest/rest.go
+++ b/src/restic/backend/rest/rest.go
@@ -23,21 +23,21 @@ const connLimit = 40
 var _ restic.Backend = &restBackend{}
 
 type restBackend struct {
-	url      *url.URL
-	connChan chan struct{}
-	client   http.Client
+	url    *url.URL
+	sem    *backend.Semaphore
+	client http.Client
 	backend.Layout
 }
 
 // Open opens the REST backend with the given config.
 func Open(cfg Config) (restic.Backend, error) {
-	connChan := make(chan struct{}, connLimit)
-	for i := 0; i < connLimit; i++ {
-		connChan <- struct{}{}
-	}
-
 	client := http.Client{Transport: backend.Transport()}
 
+	sem, err := backend.NewSemaphore(cfg.Connections)
+	if err != nil {
+		return nil, err
+	}
+
 	// use url without trailing slash for layout
 	url := cfg.URL.String()
 	if url[len(url)-1] == '/' {
@@ -45,10 +45,10 @@ func Open(cfg Config) (restic.Backend, error) {
 	}
 
 	be := &restBackend{
-		url:      cfg.URL,
-		connChan: connChan,
-		client:   client,
-		Layout:   &backend.RESTLayout{URL: url, Join: path.Join},
+		url:    cfg.URL,
+		client: client,
+		Layout: &backend.RESTLayout{URL: url, Join: path.Join},
+		sem:    sem,
 	}
 
 	return be, nil
@@ -108,9 +108,9 @@ func (b *restBackend) Save(h restic.Handle, rd io.Reader) (err error) {
 	// backend.Closer, which has a noop method.
 	rd = backend.Closer{Reader: rd}
 
-	<-b.connChan
+	b.sem.GetToken()
 	resp, err := b.client.Post(b.Filename(h), "binary/octet-stream", rd)
-	b.connChan <- struct{}{}
+	b.sem.ReleaseToken()
 
 	if resp != nil {
 		defer func() {
@@ -163,9 +163,9 @@ func (b *restBackend) Load(h restic.Handle, length int, offset int64) (io.ReadCl
 	req.Header.Add("Range", byteRange)
 	debug.Log("Load(%v) send range %v", h, byteRange)
 
-	<-b.connChan
+	b.sem.GetToken()
 	resp, err := b.client.Do(req)
-	b.connChan <- struct{}{}
+	b.sem.ReleaseToken()
 
 	if err != nil {
 		if resp != nil {
@@ -190,9 +190,9 @@ func (b *restBackend) Stat(h restic.Handle) (restic.FileInfo, error) {
 		return restic.FileInfo{}, err
 	}
 
-	<-b.connChan
+	b.sem.GetToken()
 	resp, err := b.client.Head(b.Filename(h))
-	b.connChan <- struct{}{}
+	b.sem.ReleaseToken()
 	if err != nil {
 		return restic.FileInfo{}, errors.Wrap(err, "client.Head")
 	}
@@ -237,9 +237,9 @@ func (b *restBackend) Remove(h restic.Handle) error {
 	if err != nil {
 		return errors.Wrap(err, "http.NewRequest")
 	}
-	<-b.connChan
+	b.sem.GetToken()
 	resp, err := b.client.Do(req)
-	b.connChan <- struct{}{}
+	b.sem.ReleaseToken()
 
 	if err != nil {
 		return errors.Wrap(err, "client.Do")
@@ -264,9 +264,9 @@ func (b *restBackend) List(t restic.FileType, done <-chan struct{}) <-chan strin
 		url += "/"
 	}
 
-	<-b.connChan
+	b.sem.GetToken()
 	resp, err := b.client.Get(url)
-	b.connChan <- struct{}{}
+	b.sem.ReleaseToken()
 
 	if resp != nil {
 		defer func() {
diff --git a/src/restic/backend/rest/rest_test.go b/src/restic/backend/rest/rest_test.go
index d951eea05..d8a7afbe3 100644
--- a/src/restic/backend/rest/rest_test.go
+++ b/src/restic/backend/rest/rest_test.go
@@ -76,9 +76,8 @@ func newTestSuite(ctx context.Context, t testing.TB) *test.Suite {
 				t.Fatal(err)
 			}
 
-			cfg := rest.Config{
-				URL: url,
-			}
+			cfg := rest.NewConfig()
+			cfg.URL = url
 			return cfg, nil
 		},