new socket client with connection pool and added http client

client/client.go

@@ -1,12 +1,7 @@
 package client
 
 import (
-	"encoding/json"
-	"errors"
-	"fmt"
-	"io"
-	"net"
-	"strconv"
+	"time"
 
 	"github.com/foomo/contentserver/content"
 	"github.com/foomo/contentserver/requests"
@@ -14,34 +9,47 @@ import (
 	"github.com/foomo/contentserver/server"
 )
 
-type serverResponse struct {
-	Reply interface{}
-}
-
 // Client a content server client
 type Client struct {
-	Server string
-	conn   net.Conn
+	t transport
+}
+
+func NewClient(
+	server string,
+	connectionPoolSize int,
+	waitTimeout time.Duration,
+) (c *Client, err error) {
+	c = &Client{
+		t: newSocketTransport(server, connectionPoolSize, waitTimeout),
+	}
+	return
+}
+
+func NewHTTPClient(server string) (c *Client, err error) {
+	c = &Client{
+		t: newHTTPTransport(server),
+	}
+	return
 }
 
 // Update tell the server to update itself
 func (c *Client) Update() (response *responses.Update, err error) {
 	response = &responses.Update{}
-	err = c.call(server.HandlerUpdate, &requests.Update{}, response)
+	err = c.t.call(server.HandlerUpdate, &requests.Update{}, response)
 	return
 }
 
 // GetContent request site content
 func (c *Client) GetContent(request *requests.Content) (response *content.SiteContent, err error) {
 	response = &content.SiteContent{}
-	err = c.call(server.HandlerGetContent, request, response)
+	err = c.t.call(server.HandlerGetContent, request, response)
 	return
 }
 
 // GetURIs resolve uris for ids in a dimension
 func (c *Client) GetURIs(dimension string, IDs []string) (uriMap map[string]string, err error) {
 	uriMap = map[string]string{}
-	err = c.call(
+	err = c.t.call(
 		server.HandlerGetURIs,
 		&requests.URIs{
 			Dimension: dimension,
@@ -59,97 +67,17 @@ func (c *Client) GetNodes(env *requests.Env, nodes map[string]*requests.Node) (n
 		Nodes: nodes,
 	}
 	nodesResponse = map[string]*content.Node{}
-	err = c.call(server.HandlerGetNodes, r, &nodesResponse)
+	err = c.t.call(server.HandlerGetNodes, r, &nodesResponse)
 	return
 }
 
 // GetRepo get the whole repo
 func (c *Client) GetRepo() (response map[string]*content.RepoNode, err error) {
 	response = map[string]*content.RepoNode{}
-	err = c.call(server.HandlerGetRepo, &requests.Repo{}, &response)
+	err = c.t.call(server.HandlerGetRepo, &requests.Repo{}, &response)
 	return
 }
 
-// func (c *Client) closeConnection() error {
-// 	if c.conn != nil {
-// 		err := c.conn.Close()
-// 		if err != nil {
-// 			return err
-// 		}
-// 		c.conn = nil
-// 	}
-// 	return nil
-// }
-
-// func (c *Client) getConnection() (conn net.Conn, err error) {
-// 	// we need some pooling here
-// 	return
-// }
-
-func (c *Client) call(handler server.Handler, request interface{}, response interface{}) error {
-	jsonBytes, err := json.Marshal(request)
-	if err != nil {
-		return fmt.Errorf("could not marshal request : %q", err)
-	}
-	conn, err := net.Dial("tcp", c.Server)
-	if err != nil {
-		return fmt.Errorf("can not call server - connection error: %q", err)
-	}
-	defer conn.Close()
-	// write header result will be like handler:2{}
-	jsonBytes = append([]byte(fmt.Sprintf("%s:%d", handler, len(jsonBytes))), jsonBytes...)
-
-	// send request
-	written := 0
-	l := len(jsonBytes)
-	for written < l {
-		n, err := conn.Write(jsonBytes[written:])
-		if err != nil {
-			return fmt.Errorf("failed to send request: %q", err)
-		}
-		written += n
-	}
-
-	// read response
-	responseBytes := []byte{}
-	buf := make([]byte, 4096)
-	responseLength := 0
-	for {
-		n, err := conn.Read(buf)
-		if err != nil && err != io.EOF {
-			return fmt.Errorf("an error occured while reading the response: %q", err)
-		}
-		if n == 0 {
-			break
-		}
-		responseBytes = append(responseBytes, buf[0:n]...)
-		if responseLength == 0 {
-			for index, byte := range responseBytes {
-				if byte == 123 {
-					// opening bracket
-					responseLength, err = strconv.Atoi(string(responseBytes[0:index]))
-					if err != nil {
-						return errors.New("could not read response length: " + err.Error())
-					}
-					responseBytes = responseBytes[index:]
-					break
-				}
-			}
-		}
-		if responseLength > 0 && len(responseBytes) == responseLength {
-			break
-		}
-	}
-	// unmarshal response
-	responseJSONErr := json.Unmarshal(responseBytes, &serverResponse{Reply: response})
-	if responseJSONErr != nil {
-		// is it an error ?
-		remoteErr := responses.Error{}
-		remoteErrJSONErr := json.Unmarshal(responseBytes, remoteErr)
-		if remoteErrJSONErr == nil {
-			return remoteErr
-		}
-		return fmt.Errorf("could not unmarshal response : %q %q", remoteErrJSONErr, string(responseBytes))
-	}
-	return nil
+func (c *Client) ShutDown() {
+	c.t.shutdown()
 }

client/client_test.go

@@ -2,6 +2,8 @@ package client
 
 import (
 	"encoding/json"
+	"net"
+	"strconv"
 	"sync"
 	"testing"
 	"time"
@@ -9,6 +11,7 @@ import (
 	"github.com/foomo/contentserver/content"
 	"github.com/foomo/contentserver/log"
 	"github.com/foomo/contentserver/repo/mock"
+	"github.com/foomo/contentserver/requests"
 	"github.com/foomo/contentserver/server"
 )
 
@@ -23,123 +26,208 @@ func dump(t *testing.T, v interface{}) {
 	t.Log(string(jsonBytes))
 }
 
-func getTestClient(t testing.TB) *Client {
+func getFreePort() int {
+	addr, err := net.ResolveTCPAddr("tcp", "localhost:0")
+	if err != nil {
+		panic(err)
+	}
+	l, err := net.ListenTCP("tcp", addr)
+	if err != nil {
+		panic(err)
+	}
+	defer l.Close()
+	return l.Addr().(*net.TCPAddr).Port
+}
+
+func getAvailableAddr() string {
+	return "127.0.0.1:" + strconv.Itoa(getFreePort())
+}
+
+var testServerSocketAddr string
+var testServerWebserverAddr string
+
+func initTestServer(t testing.TB) (socketAddr, webserverAddr string) {
+	socketAddr = getAvailableAddr()
+	webserverAddr = getAvailableAddr()
+	testServer, varDir := mock.GetMockData(t)
 	log.SelectedLevel = log.LevelError
-	addr := "127.0.0.1:9999"
-	if !testServerIsRunning {
-		testServerIsRunning = true
-		testServer, varDir := mock.GetMockData(t)
-		go server.Run(testServer.URL+"/repo-two-dimensions.json", addr, varDir)
+	go server.RunServerSocketAndWebServer(testServer.URL+"/repo-two-dimensions.json", socketAddr, webserverAddr, varDir)
+	socketClient, errClient := NewClient(socketAddr, 1, time.Duration(time.Millisecond*100))
+	if errClient != nil {
+		panic(errClient)
+	}
+	i := 0
+	for {
 		time.Sleep(time.Millisecond * 100)
+		r, err := socketClient.GetRepo()
+		if err != nil {
+			continue
+		}
+		if r["dimension_foo"].Nodes["id-a"].Data["baz"].(float64) == float64(1) {
+			break
+		}
+		if i > 100 {
+			panic("this is taking too long")
+		}
+		i++
 	}
-	return &Client{
-		Server: addr,
+	return
+}
+
+func getTestClients(t testing.TB) (socketClient *Client, httpClient *Client) {
+	if testServerSocketAddr == "" {
+		socketAddr, webserverAddr := initTestServer(t)
+		testServerSocketAddr = socketAddr
+		testServerWebserverAddr = webserverAddr
 	}
+	socketClient, errClient := NewClient(testServerSocketAddr, 30, time.Duration(time.Millisecond*100))
+	if errClient != nil {
+		t.Log(errClient)
+		t.Fail()
+	}
+	httpClient, errHTTPClient := NewHTTPClient("http://" + testServerWebserverAddr + server.PathContentserver)
+	if errHTTPClient != nil {
+		t.Log(errHTTPClient)
+		t.Fail()
+	}
+	return
+}
+
+func testWithClients(t *testing.T, testFunc func(c *Client)) {
+	socketClient, httpClient := getTestClients(t)
+	defer socketClient.ShutDown()
+	defer httpClient.ShutDown()
+	testFunc(socketClient)
+	testFunc(httpClient)
 }
 
 func TestUpdate(t *testing.T) {
-	c := getTestClient(t)
-	response, err := c.Update()
-	if err != nil {
-		t.Fatal("unexpected err", err)
-	}
-	if !response.Success {
-		t.Fatal("update has to return .Sucesss true", response)
-	}
-	stats := response.Stats
-	if !(stats.RepoRuntime > float64(0.0)) || !(stats.OwnRuntime > float64(0.0)) {
-		t.Fatal("stats invalid")
-	}
+	testWithClients(t, func(c *Client) {
+		response, err := c.Update()
+		if err != nil {
+			t.Fatal("unexpected err", err)
+		}
+		if !response.Success {
+			t.Fatal("update has to return .Sucesss true", response)
+		}
+		stats := response.Stats
+		if !(stats.RepoRuntime > float64(0.0)) || !(stats.OwnRuntime > float64(0.0)) {
+			t.Fatal("stats invalid")
+		}
+	})
 }
 
 func TestGetURIs(t *testing.T) {
-	c := getTestClient(t)
-	request := mock.MakeValidURIsRequest()
-	uriMap, err := c.GetURIs(request.Dimension, request.IDs)
-	if err != nil {
-		t.Fatal(err)
-	}
-	if uriMap[request.IDs[0]] != "/a" {
-		t.Fatal(uriMap)
-	}
+	testWithClients(t, func(c *Client) {
+		defer c.ShutDown()
+		request := mock.MakeValidURIsRequest()
+		uriMap, err := c.GetURIs(request.Dimension, request.IDs)
+		if err != nil {
+			t.Fatal(err)
+		}
+		if uriMap[request.IDs[0]] != "/a" {
+			t.Fatal(uriMap)
+		}
+	})
 }
 
 func TestGetRepo(t *testing.T) {
-	c := getTestClient(t)
-	r, err := c.GetRepo()
-	if err != nil {
-		t.Fatal(err)
-	}
-	if r["dimension_foo"].Nodes["id-a"].Data["baz"].(float64) != float64(1) {
-		t.Fatal("failed to drill deep for data")
-	}
+	testWithClients(t, func(c *Client) {
+		r, err := c.GetRepo()
+		if err != nil {
+			t.Fatal(err)
+		}
+		if r["dimension_foo"].Nodes["id-a"].Data["baz"].(float64) != float64(1) {
+			t.Fatal("failed to drill deep for data")
+		}
+	})
 }
 
 func TestGetNodes(t *testing.T) {
-	c := getTestClient(t)
-	nodesRequest := mock.MakeNodesRequest()
-	nodes, err := c.GetNodes(nodesRequest.Env, nodesRequest.Nodes)
-	if err != nil {
-		t.Fatal(err)
-	}
-	testNode, ok := nodes["test"]
-	if !ok {
-		t.Fatal("that should be a node")
-	}
-	testData, ok := testNode.Item.Data["foo"]
-	if !ok {
-		t.Fatal("where is foo")
-	}
-	if testData != "bar" {
-		t.Fatal("testData should have bennd bar not", testData)
-	}
-
+	testWithClients(t, func(c *Client) {
+		nodesRequest := mock.MakeNodesRequest()
+		nodes, err := c.GetNodes(nodesRequest.Env, nodesRequest.Nodes)
+		if err != nil {
+			t.Fatal(err)
+		}
+		testNode, ok := nodes["test"]
+		if !ok {
+			t.Fatal("that should be a node")
+		}
+		testData, ok := testNode.Item.Data["foo"]
+		if !ok {
+			t.Fatal("where is foo")
+		}
+		if testData != "bar" {
+			t.Fatal("testData should have bennd bar not", testData)
+		}
+	})
 }
 
 func TestGetContent(t *testing.T) {
-	c := getTestClient(t)
-	request := mock.MakeValidContentRequest()
-	response, err := c.GetContent(request)
-	if err != nil {
-		t.Fatal("unexpected err", err)
-	}
-	if request.URI != response.URI {
-		dump(t, request)
-		dump(t, response)
-		t.Fatal("uri mismatch")
-	}
-	if response.Status != content.StatusOk {
-		t.Fatal("unexpected status")
+	testWithClients(t, func(c *Client) {
+		request := mock.MakeValidContentRequest()
+		response, err := c.GetContent(request)
+		if err != nil {
+			t.Fatal("unexpected err", err)
+		}
+		if request.URI != response.URI {
+			dump(t, request)
+			dump(t, response)
+			t.Fatal("uri mismatch")
+		}
+		if response.Status != content.StatusOk {
+			t.Fatal("unexpected status")
+		}
+	})
+}
+
+func BenchmarkSocketClientAndServerGetContent(b *testing.B) {
+	socketClient, _ := getTestClients(b)
+	benchmarkServerAndClientGetContent(b, 30, 100, socketClient)
+
+}
+func BenchmarkWebClientAndServerGetContent(b *testing.B) {
+	_, httpClient := getTestClients(b)
+	benchmarkServerAndClientGetContent(b, 30, 100, httpClient)
+}
+
+func benchmarkServerAndClientGetContent(b *testing.B, numGroups, numCalls int, client GetContentClient) {
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		start := time.Now()
+		benchmarkClientAndServerGetContent(b, numGroups, numCalls, client)
+		dur := time.Since(start)
+		totalCalls := numGroups * numCalls
+		b.Log("requests per second", int(float64(totalCalls)/(float64(dur)/float64(1000000000))), dur, totalCalls)
 	}
 }
 
-// not very meaningful yet
-func BenchmarkServerAndClient(b *testing.B) {
+type GetContentClient interface {
+	GetContent(request *requests.Content) (response *content.SiteContent, err error)
+}
+
+func benchmarkClientAndServerGetContent(b testing.TB, numGroups, numCalls int, client GetContentClient) {
 	var wg sync.WaitGroup
-	stats := make([]int, 100)
-	for group := 0; group < 100; group++ {
-		wg.Add(1)
+	wg.Add(numGroups)
+	for group := 0; group < numGroups; group++ {
 		go func(g int) {
 			defer wg.Done()
-			c := getTestClient(b)
 			request := mock.MakeValidContentRequest()
-			for i := 0; i < 1000; i++ {
-				response, err := c.GetContent(request)
-				if err != nil {
-					b.Fatal("unexpected err", err)
+			for i := 0; i < numCalls; i++ {
+				response, err := client.GetContent(request)
+				if err == nil {
+					if request.URI != response.URI {
+						b.Fatal("uri mismatch")
+					}
+					if response.Status != content.StatusOk {
+						b.Fatal("unexpected status")
+					}
 				}
-				if request.URI != response.URI {
-					b.Fatal("uri mismatch")
-				}
-				if response.Status != content.StatusOk {
-					b.Fatal("unexpected status")
-				}
-				stats[g] = i
 			}
 		}(group)
-
 	}
 	// Wait for all HTTP fetches to complete.
 	wg.Wait()
-	b.Log(stats)
+	return
 }

client/connectionpool.go

@@ -0,0 +1,130 @@
+package client
+
+import (
+	"net"
+	"time"
+)
+
+type connectionPool struct {
+	server         string
+	conn           net.Conn
+	chanConnGet    chan chan net.Conn
+	chanConnReturn chan connReturn
+	chanDrainPool  chan int
+}
+
+func newConnectionPool(server string, connectionPoolSize int, waitTimeout time.Duration) *connectionPool {
+	connPool := &connectionPool{
+		server:         server,
+		chanConnGet:    make(chan chan net.Conn),
+		chanConnReturn: make(chan connReturn),
+		chanDrainPool:  make(chan int),
+	}
+	go connPool.run(connectionPoolSize, waitTimeout)
+	return connPool
+}
+
+func (c *connectionPool) run(connectionPoolSize int, waitTimeout time.Duration) {
+	type poolEntry struct {
+		busy bool
+		err  error
+		conn net.Conn
+	}
+	type waitPoolEntry struct {
+		entryTime time.Time
+		chanConn  chan net.Conn
+	}
+	connectionPool := make(map[int]*poolEntry, connectionPoolSize)
+	waitPool := map[int]*waitPoolEntry{}
+	for i := 0; i < connectionPoolSize; i++ {
+		connectionPool[i] = &poolEntry{
+			conn: nil,
+			busy: false,
+		}
+	}
+RunLoop:
+	for {
+		// fmt.Println("----------------------- run loop ------------------------")
+		select {
+		case <-c.chanDrainPool:
+			// fmt.Println("<-c.chanDrainPool")
+			for _, waitPoolEntry := range waitPool {
+				waitPoolEntry.chanConn <- nil
+			}
+			break RunLoop
+		case <-time.After(waitTimeout):
+		//	fmt.Println("tick", len(connectionPool), len(waitPool))
+		// 	for i, poolEntry := range connectionPool {
+		// 		fmt.Println(i, poolEntry)
+		// 	}
+		// 	for i, waitPoolEntry := range waitPool {
+		// 		fmt.Println(i, waitPoolEntry)
+		// 	}
+		case chanReturnNextConn := <-c.chanConnGet:
+			// fmt.Println("chanReturnNextConn := <-c.chanConnGet:")
+			nextI := 0
+			for i := range waitPool {
+				if i >= nextI {
+					nextI = i + 1
+				}
+			}
+			waitPool[nextI] = &waitPoolEntry{
+				chanConn:  chanReturnNextConn,
+				entryTime: time.Now(),
+			}
+			// fmt.Println("sbdy wants a new conn", nextI)
+		case connReturn := <-c.chanConnReturn:
+			// fmt.Println("connReturn := <-c.chanConnReturn:")
+			for _, poolEntry := range connectionPool {
+				if connReturn.conn == poolEntry.conn {
+					poolEntry.busy = false
+					if connReturn.err != nil {
+						poolEntry.err = connReturn.err
+						poolEntry.conn.Close()
+						poolEntry.conn = nil
+					}
+				}
+			}
+		}
+		// refill connection pool
+		for _, poolEntry := range connectionPool {
+			if poolEntry.conn == nil {
+				newConn, errDial := net.Dial("tcp", c.server)
+				poolEntry.err = errDial
+				poolEntry.conn = newConn
+			}
+		}
+		// redistribute available connections
+		for _, poolEntry := range connectionPool {
+			if len(waitPool) == 0 {
+				break
+			}
+			if poolEntry.err == nil && poolEntry.conn != nil && !poolEntry.busy {
+				for i, waitPoolEntry := range waitPool {
+					// fmt.Println("---------------------------> serving wait pool", i, waitPoolEntry)
+					poolEntry.busy = true
+					delete(waitPool, i)
+					waitPoolEntry.chanConn <- poolEntry.conn
+					break
+				}
+			}
+		}
+		// waitpool cleanup
+		waitPoolLoosers := []int{}
+		now := time.Now()
+		for i, waitPoolEntry := range waitPool {
+			if now.Sub(waitPoolEntry.entryTime) > waitTimeout {
+				waitPoolLoosers = append(waitPoolLoosers, i)
+				waitPoolEntry.chanConn <- nil
+			}
+		}
+		for _, i := range waitPoolLoosers {
+			delete(waitPool, i)
+		}
+
+	}
+	c.chanDrainPool = nil
+	c.chanConnReturn = nil
+	c.chanConnGet = nil
+	//fmt.Println("runloop is done", waitPool)
+}

client/httptransport.go

@@ -0,0 +1,62 @@
+package client
+
+import (
+	"bytes"
+	"encoding/json"
+	"errors"
+	"io/ioutil"
+	"net/http"
+
+	"github.com/foomo/contentserver/server"
+)
+
+type httpTransport struct {
+	client   *http.Client
+	endpoint string
+}
+
+func newHTTPTransport(server string) transport {
+	return &httpTransport{
+		endpoint: server,
+		client:   http.DefaultClient,
+	}
+}
+
+func (ht *httpTransport) shutdown() {
+	// nothing to do here
+}
+
+func (ht *httpTransport) call(handler server.Handler, request interface{}, response interface{}) error {
+	requestBytes, errMarshal := json.Marshal(request)
+	if errMarshal != nil {
+		return errMarshal
+	}
+	req, errNewRequest := http.NewRequest(
+		http.MethodPost,
+		ht.endpoint+"/"+string(handler),
+		bytes.NewBuffer(requestBytes),
+	)
+	if errNewRequest != nil {
+		return errNewRequest
+	}
+	httpResponse, errDo := ht.client.Do(req)
+	if errDo != nil {
+		return errDo
+	}
+	if httpResponse.StatusCode != http.StatusOK {
+		return errors.New("non 200 reply")
+	}
+	if httpResponse.Body == nil {
+		return errors.New("empty response body")
+	}
+	responseBytes, errRead := ioutil.ReadAll(httpResponse.Body)
+	httpResponse.Body.Close()
+	if errRead != nil {
+		return errRead
+	}
+	errUnmarshal := json.Unmarshal(responseBytes, &serverResponse{Reply: response})
+	if errUnmarshal != nil {
+		return errUnmarshal
+	}
+	return errUnmarshal
+}

client/sockettransport.go

@@ -0,0 +1,122 @@
+package client
+
+import (
+	"encoding/json"
+	"errors"
+	"fmt"
+	"io"
+	"net"
+	"strconv"
+	"time"
+
+	"github.com/foomo/contentserver/responses"
+	"github.com/foomo/contentserver/server"
+)
+
+type serverResponse struct {
+	Reply interface{}
+}
+
+type connReturn struct {
+	conn net.Conn
+	err  error
+}
+
+type socketTransport struct {
+	connPool *connectionPool
+}
+
+func newSocketTransport(server string, connectionPoolSize int, waitTimeout time.Duration) transport {
+	return &socketTransport{
+		connPool: newConnectionPool(server, connectionPoolSize, waitTimeout),
+	}
+}
+
+func (st *socketTransport) shutdown() {
+	if st.connPool.chanDrainPool != nil {
+		st.connPool.chanDrainPool <- 1
+	}
+}
+
+func (c *socketTransport) call(handler server.Handler, request interface{}, response interface{}) error {
+	if c.connPool.chanDrainPool == nil {
+		return errors.New("connection pool has been drained, client is dead")
+	}
+	jsonBytes, err := json.Marshal(request)
+	if err != nil {
+		return fmt.Errorf("could not marshal request : %q", err)
+	}
+	netChan := make(chan net.Conn)
+	c.connPool.chanConnGet <- netChan
+	conn := <-netChan
+	if conn == nil {
+		return errors.New("could not get a connection")
+	}
+	returnConn := func(err error) {
+		c.connPool.chanConnReturn <- connReturn{
+			conn: conn,
+			err:  err,
+		}
+	}
+	// write header result will be like handler:2{}
+	jsonBytes = append([]byte(fmt.Sprintf("%s:%d", handler, len(jsonBytes))), jsonBytes...)
+
+	// send request
+	written := 0
+	l := len(jsonBytes)
+	for written < l {
+		n, err := conn.Write(jsonBytes[written:])
+		if err != nil {
+			returnConn(err)
+			return fmt.Errorf("failed to send request: %q", err)
+		}
+		written += n
+	}
+
+	// read response
+	responseBytes := []byte{}
+	buf := make([]byte, 4096)
+	responseLength := 0
+	for {
+		n, err := conn.Read(buf)
+		if err != nil && err != io.EOF {
+			returnConn(err)
+			return fmt.Errorf("an error occured while reading the response: %q", err)
+		}
+		if n == 0 {
+			break
+		}
+		responseBytes = append(responseBytes, buf[0:n]...)
+		if responseLength == 0 {
+			for index, byte := range responseBytes {
+				if byte == 123 {
+					// opening bracket
+					responseLength, err = strconv.Atoi(string(responseBytes[0:index]))
+					if err != nil {
+						returnConn(err)
+						return errors.New("could not read response length: " + err.Error())
+					}
+					responseBytes = responseBytes[index:]
+					break
+				}
+			}
+		}
+		if responseLength > 0 && len(responseBytes) == responseLength {
+			break
+		}
+	}
+	// unmarshal response
+	responseJSONErr := json.Unmarshal(responseBytes, &serverResponse{Reply: response})
+	if responseJSONErr != nil {
+		// is it an error ?
+		remoteErr := responses.Error{}
+		remoteErrJSONErr := json.Unmarshal(responseBytes, remoteErr)
+		if remoteErrJSONErr == nil {
+			returnConn(remoteErrJSONErr)
+			return remoteErr
+		}
+		return fmt.Errorf("could not unmarshal response : %q %q", remoteErrJSONErr, string(responseBytes))
+	}
+	returnConn(nil)
+	return nil
+}

client/transport.go

@@ -0,0 +1,8 @@
+package client
+
+import "github.com/foomo/contentserver/server"
+
+type transport interface {
+	call(handler server.Handler, request interface{}, response interface{}) error
+	shutdown()
+}