Repository: go-kratos/kratos (go)
Issue: ResponseEncode should not write any data when it encode nil
<!--
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For questions please use one of our forums: https://go-kratos.dev/docs/getting-started/faq
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#### What happened:
When I don't need to return data to client
1. When using the following code, the DefaultResponseEncode will report an error(http: request method or response status code does not allow body)
```go
func Handle(ctx http.Context) error {
    return ctx.Result(204, nil)
}
```
2. but, when using the following code, will return `null` string to client
```go
func Handle(ctx http.Context) error {
    return ctx.Result(200, nil)
}
```

#### What you expected to happen:

when call ctx.Result(xxx, nil), server don't return any data to client 

#### How to reproduce it (as minimally and precisely as possible):

#### Anything else we need to know?:

#### Environment:
- Kratos version (use `kratos -v`): `kratos version v2.2.1`
- Go version (use `go version`): 
- OS (e.g: `cat /etc/os-release`):
- Others:

Pull request description: fix(transport/http): responseEncoder should not write any data when it need to write nil

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#### Description (what this PR does / why we need it):
<!--
* The description should include the motivation for this PR or contrast this with previous behavior
-->
It should not write any data when we don't need to return data to the client


#### Which issue(s) this PR fixes (resolves / be part of):
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fixes #1946

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Patch:
diff --git a/.golangci.yml b/.golangci.yml
index 78765498..0cd7ecb0 100644
--- a/.golangci.yml
+++ b/.golangci.yml
@@ -28,7 +28,6 @@ linters:
     - structcheck
     - typecheck
     - unused
-    - unconvert
     - varcheck
     - whitespace
     - wastedassign
diff --git a/cmd/kratos/internal/base/repo.go b/cmd/kratos/internal/base/repo.go
index 86d4a154..cd7b650f 100644
--- a/cmd/kratos/internal/base/repo.go
+++ b/cmd/kratos/internal/base/repo.go
@@ -114,3 +114,16 @@ func (r *Repo) CopyTo(ctx context.Context, to string, modPath string, ignores []
 	}
 	return copyDir(r.Path(), to, []string{mod, modPath}, ignores)
 }
+
+// CopyToV2 copies the repository to project path
+func (r *Repo) CopyToV2(ctx context.Context, to string, modPath string, ignores, replaces []string) error {
+	if err := r.Clone(ctx); err != nil {
+		return err
+	}
+	mod, err := ModulePath(path.Join(r.Path(), "go.mod"))
+	if err != nil {
+		return err
+	}
+	replaces = append([]string{mod, modPath}, replaces...)
+	return copyDir(r.Path(), to, replaces, ignores)
+}
diff --git a/cmd/kratos/internal/project/add.go b/cmd/kratos/internal/project/add.go
new file mode 100644
index 00000000..98661cd1
--- /dev/null
+++ b/cmd/kratos/internal/project/add.go
@@ -0,0 +1,66 @@
+package project
+
+import (
+	"context"
+	"fmt"
+	"os"
+	"path"
+
+	"github.com/AlecAivazis/survey/v2"
+	"github.com/fatih/color"
+	"github.com/go-kratos/kratos/cmd/kratos/v2/internal/base"
+)
+
+var repoAddIgnores = []string{
+	".git", ".github", "api", "README.md", "LICENSE", "go.mod", "go.sum", "third_party",
+}
+
+func (p *Project) Add(ctx context.Context, dir string, layout string, branch string, mod string) error {
+	to := path.Join(dir, p.Path)
+
+	if _, err := os.Stat(to); !os.IsNotExist(err) {
+		fmt.Printf("🚫 %s already exists\n", p.Name)
+		override := false
+		prompt := &survey.Confirm{
+			Message: "📂 Do you want to override the folder ?",
+			Help:    "Delete the existing folder and create the project.",
+		}
+		e := survey.AskOne(prompt, &override)
+		if e != nil {
+			return e
+		}
+		if !override {
+			return err
+		}
+		os.RemoveAll(to)
+	}
+
+	fmt.Printf("🚀 Add service %s, layout repo is %s, please wait a moment.\n\n", p.Name, layout)
+
+	repo := base.NewRepo(layout, branch)
+
+	if err := repo.CopyToV2(ctx, to, path.Join(mod, p.Path), repoAddIgnores, []string{path.Join(p.Path, "api"), "api"}); err != nil {
+		return err
+	}
+
+	e := os.Rename(
+		path.Join(to, "cmd", "server"),
+		path.Join(to, "cmd", p.Name),
+	)
+	if e != nil {
+		return e
+	}
+
+	base.Tree(to, dir)
+
+	fmt.Printf("\n🍺 Repository creation succeeded %s\n", color.GreenString(p.Name))
+	fmt.Print("💻 Use the following command to add a project 👇:\n\n")
+
+	fmt.Println(color.WhiteString("$ cd %s", p.Name))
+	fmt.Println(color.WhiteString("$ go generate ./..."))
+	fmt.Println(color.WhiteString("$ go build -o ./bin/ ./... "))
+	fmt.Println(color.WhiteString("$ ./bin/%s -conf ./configs\n", p.Name))
+	fmt.Println("			🤝 Thanks for using Kratos")
+	fmt.Println("	📚 Tutorial: https://go-kratos.dev/docs/getting-started/start")
+	return nil
+}
diff --git a/cmd/kratos/internal/project/project.go b/cmd/kratos/internal/project/project.go
index 0abc4577..bfad066b 100644
--- a/cmd/kratos/internal/project/project.go
+++ b/cmd/kratos/internal/project/project.go
@@ -9,6 +9,7 @@ import (
 	"time"
 
 	"github.com/AlecAivazis/survey/v2"
+	"github.com/go-kratos/kratos/cmd/kratos/v2/internal/base"
 	"github.com/spf13/cobra"
 )
 
@@ -24,6 +25,7 @@ var (
 	repoURL string
 	branch  string
 	timeout string
+	nomod   bool
 )
 
 func init() {
@@ -34,6 +36,7 @@ func init() {
 	CmdNew.Flags().StringVarP(&repoURL, "repo-url", "r", repoURL, "layout repo")
 	CmdNew.Flags().StringVarP(&branch, "branch", "b", branch, "repo branch")
 	CmdNew.Flags().StringVarP(&timeout, "timeout", "t", timeout, "time out")
+	CmdNew.Flags().BoolVarP(&nomod, "nomod", "", nomod, "retain go mod")
 }
 
 func run(cmd *cobra.Command, args []string) {
@@ -63,7 +66,20 @@ func run(cmd *cobra.Command, args []string) {
 	p := &Project{Name: path.Base(name), Path: name}
 	done := make(chan error, 1)
 	go func() {
-		done <- p.New(ctx, wd, repoURL, branch)
+		if !nomod {
+			done <- p.New(ctx, wd, repoURL, branch)
+		} else {
+			if _, e := os.Stat(path.Join(wd, "go.mod")); os.IsNotExist(e) {
+				done <- fmt.Errorf("🚫 go.mod don't exists in %s", wd)
+				return
+			}
+
+			mod, e := base.ModulePath(path.Join(wd, "go.mod"))
+			if e != nil {
+				panic(e)
+			}
+			done <- p.Add(ctx, wd, repoURL, branch, mod)
+		}
 	}()
 	select {
 	case <-ctx.Done():
diff --git a/cmd/kratos/internal/run/run.go b/cmd/kratos/internal/run/run.go
index 53ef7abc..556af54b 100644
--- a/cmd/kratos/internal/run/run.go
+++ b/cmd/kratos/internal/run/run.go
@@ -42,8 +42,8 @@ func Run(cmd *cobra.Command, args []string) {
 			fmt.Fprintf(os.Stderr, "\033[31mERROR: %s\033[m\n", "The cmd directory cannot be found in the current directory")
 			return
 		} else if len(cmdPath) == 1 {
-			for k, v := range cmdPath {
-				dir = path.Join(v, k)
+			for _, v := range cmdPath {
+				dir = v
 			}
 		} else {
 			var cmdPaths []string
@@ -51,14 +51,15 @@ func Run(cmd *cobra.Command, args []string) {
 				cmdPaths = append(cmdPaths, k)
 			}
 			prompt := &survey.Select{
-				Message: "Which directory do you want to run?",
-				Options: cmdPaths,
+				Message:  "Which directory do you want to run?",
+				Options:  cmdPaths,
+				PageSize: 10,
 			}
 			e := survey.AskOne(prompt, &dir)
 			if e != nil || dir == "" {
 				return
 			}
-			dir = path.Join(cmdPath[dir], dir)
+			dir = cmdPath[dir]
 		}
 	}
 	fd := exec.Command("go", "run", ".")
@@ -72,6 +73,13 @@ func Run(cmd *cobra.Command, args []string) {
 }
 
 func findCMD(base string) (map[string]string, error) {
+	wd, err := os.Getwd()
+	if err != nil {
+		return nil, err
+	}
+	if !strings.HasSuffix(wd, "/") {
+		wd += "/"
+	}
 	var root bool
 	next := func(dir string) (map[string]string, error) {
 		cmdPath := make(map[string]string)
@@ -84,7 +92,8 @@ func findCMD(base string) (map[string]string, error) {
 				}
 				for _, fileInfo := range paths {
 					if fileInfo.IsDir() {
-						cmdPath[path.Join("cmd", fileInfo.Name())] = filepath.Join(walkPath, "..")
+						abs := path.Join(walkPath, fileInfo.Name())
+						cmdPath[strings.TrimPrefix(abs, wd)] = abs
 					}
 				}
 				return nil
diff --git a/contrib/opensergo/go.mod b/contrib/opensergo/go.mod
new file mode 100644
index 00000000..7353fdb5
--- /dev/null
+++ b/contrib/opensergo/go.mod
@@ -0,0 +1,22 @@
+module github.com/go-kratos/kratos/contrib/opensergo/v2
+
+go 1.17
+
+require (
+	github.com/go-kratos/kratos/v2 v2.2.1
+	github.com/opensergo/opensergo-go v0.0.0-20220331070310-e5b01fee4d1c
+	golang.org/x/net v0.0.0-20210405180319-a5a99cb37ef4
+	google.golang.org/grpc v1.44.0
+	google.golang.org/protobuf v1.27.1
+)
+
+require (
+	github.com/go-playground/form/v4 v4.2.0 // indirect
+	github.com/golang/protobuf v1.5.2 // indirect
+	github.com/google/uuid v1.3.0 // indirect
+	golang.org/x/sync v0.0.0-20210220032951-036812b2e83c // indirect
+	golang.org/x/sys v0.0.0-20210816074244-15123e1e1f71 // indirect
+	golang.org/x/text v0.3.5 // indirect
+	google.golang.org/genproto v0.0.0-20220126215142-9970aeb2e350 // indirect
+	gopkg.in/yaml.v3 v3.0.0-20210107192922-496545a6307b // indirect
+)
diff --git a/contrib/opensergo/go.sum b/contrib/opensergo/go.sum
new file mode 100644
index 00000000..8aa00119
--- /dev/null
+++ b/contrib/opensergo/go.sum
@@ -0,0 +1,175 @@
+cloud.google.com/go v0.26.0/go.mod h1:aQUYkXzVsufM+DwF1aE+0xfcU+56JwCaLick0ClmMTw=
+cloud.google.com/go v0.34.0/go.mod h1:aQUYkXzVsufM+DwF1aE+0xfcU+56JwCaLick0ClmMTw=
+github.com/BurntSushi/toml v0.3.1/go.mod h1:xHWCNGjB5oqiDr8zfno3MHue2Ht5sIBksp03qcyfWMU=
+github.com/OneOfOne/xxhash v1.2.2/go.mod h1:HSdplMjZKSmBqAxg5vPj2TmRDmfkzw+cTzAElWljhcU=
+github.com/StackExchange/wmi v1.2.1/go.mod h1:rcmrprowKIVzvc+NUiLncP2uuArMWLCbu9SBzvHz7e8=
+github.com/antihax/optional v1.0.0/go.mod h1:uupD/76wgC+ih3iEmQUL+0Ugr19nfwCT1kdvxnR2qWY=
+github.com/census-instrumentation/opencensus-proto v0.2.1/go.mod h1:f6KPmirojxKA12rnyqOA5BBL4O983OfeGPqjHWSTneU=
+github.com/cespare/xxhash v1.1.0/go.mod h1:XrSqR1VqqWfGrhpAt58auRo0WTKS1nRRg3ghfAqPWnc=
+github.com/cespare/xxhash/v2 v2.1.1/go.mod h1:VGX0DQ3Q6kWi7AoAeZDth3/j3BFtOZR5XLFGgcrjCOs=
+github.com/client9/misspell v0.3.4/go.mod h1:qj6jICC3Q7zFZvVWo7KLAzC3yx5G7kyvSDkc90ppPyw=
+github.com/cncf/udpa/go v0.0.0-20191209042840-269d4d468f6f/go.mod h1:M8M6+tZqaGXZJjfX53e64911xZQV5JYwmTeXPW+k8Sc=
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diff --git a/contrib/opensergo/opensergo.go b/contrib/opensergo/opensergo.go
new file mode 100644
index 00000000..536a8d94
--- /dev/null
+++ b/contrib/opensergo/opensergo.go
@@ -0,0 +1,138 @@
+package opensergo
+
+import (
+	"encoding/json"
+	"io/ioutil"
+	"net"
+	"net/url"
+	"os"
+	"strconv"
+	"time"
+
+	"github.com/go-kratos/kratos/v2"
+	v1 "github.com/opensergo/opensergo-go/proto/service_contract/v1"
+	"golang.org/x/net/context"
+	"google.golang.org/grpc"
+	"google.golang.org/grpc/credentials/insecure"
+	"google.golang.org/protobuf/reflect/protoreflect"
+	"google.golang.org/protobuf/reflect/protoregistry"
+)
+
+type Option func(*options)
+
+func WithEndpoint(endpoint string) Option {
+	return func(o *options) {
+		o.Endpoint = endpoint
+	}
+}
+
+type options struct {
+	Endpoint string `json:"endpoint"`
+}
+
+func (o *options) ParseJSON(data []byte) error {
+	return json.Unmarshal(data, o)
+}
+
+type OpenSergo struct {
+	mdClient v1.MetadataServiceClient
+}
+
+func New(opts ...Option) (*OpenSergo, error) {
+	opt := options{
+		Endpoint: os.Getenv("OPENSERGO_ENDPOINT"),
+	}
+	// https://github.com/opensergo/opensergo-specification/blob/main/specification/en/README.md
+	if v := os.Getenv("OPENSERGO_BOOTSTRAP"); v != "" {
+		if err := opt.ParseJSON([]byte(v)); err != nil {
+			return nil, err
+		}
+	}
+	if v := os.Getenv("OPENSERGO_BOOTSTRAP_CONFIG"); v != "" {
+		b, err := ioutil.ReadFile(v)
+		if err != nil {
+			return nil, err
+		}
+		if err := opt.ParseJSON(b); err != nil {
+			return nil, err
+		}
+	}
+	for _, o := range opts {
+		o(&opt)
+	}
+	dialCtx := context.Background()
+	dialCtx, cancel := context.WithTimeout(dialCtx, time.Second)
+	defer cancel()
+	conn, err := grpc.DialContext(dialCtx, opt.Endpoint, grpc.WithTransportCredentials(insecure.NewCredentials()))
+	if err != nil {
+		return nil, err
+	}
+	return &OpenSergo{
+		mdClient: v1.NewMetadataServiceClient(conn),
+	}, nil
+}
+
+func (s *OpenSergo) ReportMetadata(ctx context.Context, app kratos.AppInfo) error {
+	services, err := s.listServiceDescriptors()
+	if err != nil {
+		return err
+	}
+	serviceMetadata := &v1.ServiceMetadata{
+		ServiceContract: &v1.ServiceContract{
+			Services: services,
+		},
+	}
+	for _, endpoint := range app.Endpoint() {
+		u, err := url.Parse(endpoint) //nolint
+		if err != nil {
+			return err
+		}
+		host, port, err := net.SplitHostPort(u.Host)
+		if err != nil {
+			return err
+		}
+		portValue, err := strconv.Atoi(port)
+		if err != nil {
+			return err
+		}
+		serviceMetadata.Protocols = append(serviceMetadata.Protocols, u.Scheme)
+		serviceMetadata.ListeningAddresses = append(serviceMetadata.ListeningAddresses, &v1.SocketAddress{
+			Address:   host,
+			PortValue: uint32(portValue),
+		})
+	}
+	_, err = s.mdClient.ReportMetadata(ctx, &v1.ReportMetadataRequest{
+		AppName:         app.Name(),
+		ServiceMetadata: []*v1.ServiceMetadata{serviceMetadata},
+	})
+	return err
+}
+
+func (s *OpenSergo) listServiceDescriptors() (services []*v1.ServiceDescriptor, err error) {
+	protoregistry.GlobalFiles.RangeFiles(func(fd protoreflect.FileDescriptor) bool {
+		for i := 0; i < fd.Services().Len(); i++ {
+			var (
+				methods []*v1.MethodDescriptor
+				sd      = fd.Services().Get(i)
+			)
+			for j := 0; j < sd.Methods().Len(); j++ {
+				md := sd.Methods().Get(j)
+				mName := string(md.Name())
+				inputType := string(md.Input().FullName())
+				outputType := string(md.Output().FullName())
+				methodDesc := v1.MethodDescriptor{
+					Name:        mName,
+					InputTypes:  []string{inputType},
+					OutputTypes: []string{outputType},
+				}
+				methods = append(methods, &methodDesc)
+			}
+			services = append(services, &v1.ServiceDescriptor{
+				Name:    string(sd.Name()),
+				Methods: methods,
+			})
+		}
+		return true
+	})
+	return
+}
diff --git a/transport/http/client.go b/transport/http/client.go
index 55719eb9..2ae29ffb 100644
--- a/transport/http/client.go
+++ b/transport/http/client.go
@@ -289,13 +289,12 @@ func (client *Client) do(req *http.Request) (*http.Response, error) {
 	if err == nil {
 		err = client.opts.errorDecoder(req.Context(), resp)
 	}
-
-	if err != nil {
-		return nil, err
-	}
 	if done != nil {
 		done(req.Context(), selector.DoneInfo{Err: err})
 	}
+	if err != nil {
+		return nil, err
+	}
 	return resp, nil
 }
 
diff --git a/transport/http/codec.go b/transport/http/codec.go
index bda31839..67a23739 100644
--- a/transport/http/codec.go
+++ b/transport/http/codec.go
@@ -42,6 +42,10 @@ func DefaultRequestDecoder(r *http.Request, v interface{}) error {
 
 // DefaultResponseEncoder encodes the object to the HTTP response.
 func DefaultResponseEncoder(w http.ResponseWriter, r *http.Request, v interface{}) error {
+	if v == nil {
+		_, err := w.Write(nil)
+		return err
+	}
 	codec, _ := CodecForRequest(r, "Accept")
 	data, err := codec.Marshal(v)
 	if err != nil {


Test patch:
diff --git a/transport/http/binding/bind_test.go b/transport/http/binding/bind_test.go
index dae7faa8..5e2552f9 100644
--- a/transport/http/binding/bind_test.go
+++ b/transport/http/binding/bind_test.go
@@ -1,9 +1,11 @@
 package binding
 
 import (
+	"io"
 	"net/http"
 	"net/url"
 	"reflect"
+	"strings"
 	"testing"
 )
 
@@ -30,7 +32,7 @@ func TestBindQuery(t *testing.T) {
 				target: &p1,
 			},
 			wantErr: false,
-			want:    TestBind{"kratos", "https://go-kratos.dev/"},
+			want:    &TestBind{"kratos", "https://go-kratos.dev/"},
 		},
 	}
 	for _, tt := range tests {
@@ -38,7 +40,7 @@ func TestBindQuery(t *testing.T) {
 			if err := BindQuery(tt.args.vars, tt.args.target); (err != nil) != tt.wantErr {
 				t.Errorf("BindQuery() error = %v, wantErr %v", err, tt.wantErr)
 			}
-			if reflect.DeepEqual(tt.args.target, tt.want) {
+			if !tt.wantErr && !reflect.DeepEqual(tt.args.target, tt.want) {
 				t.Errorf("BindQuery() target = %v, want %v", tt.args.target, tt.want)
 			}
 		})
@@ -73,11 +75,15 @@ func TestBindForm(t *testing.T) {
 		{
 			name: "error is nil",
 			args: args{
-				req:    &http.Request{Form: map[string][]string{"name": {"kratos"}, "url": {"https://go-kratos.dev/"}}},
+				req: &http.Request{
+					Method: "POST",
+					Header: http.Header{"Content-Type": {"application/x-www-form-urlencoded; param=value"}},
+					Body:   io.NopCloser(strings.NewReader("name=kratos&url=https://go-kratos.dev/")),
+				},
 				target: &p1,
 			},
 			wantErr: false,
-			want:    TestBind{"kratos", "https://go-kratos.dev/"},
+			want:    &TestBind{"kratos", "https://go-kratos.dev/"},
 		},
 	}
 	for _, tt := range tests {
@@ -86,8 +92,8 @@ func TestBindForm(t *testing.T) {
 			if (err != nil) != tt.wantErr {
 				t.Errorf("BindForm() error = %v, wantErr %v", err, tt.wantErr)
 			}
-			if err != nil && reflect.DeepEqual(tt.args.target, tt.want) {
-				t.Errorf("BindQuery() target = %v, want %v", tt.args.target, tt.want)
+			if !tt.wantErr && !reflect.DeepEqual(tt.args.target, tt.want) {
+				t.Errorf("BindForm() target = %v, want %v", tt.args.target, tt.want)
 			}
 		})
 	}
diff --git a/transport/http/codec_test.go b/transport/http/codec_test.go
index ad77eeb6..562f55de 100644
--- a/transport/http/codec_test.go
+++ b/transport/http/codec_test.go
@@ -100,6 +100,28 @@ func TestDefaultResponseEncoderWithError(t *testing.T) {
 	}
 }
 
+func TestDefaultResponseEncoderEncodeNil(t *testing.T) {
+	w := &mockResponseWriter{StatusCode: 204, header: make(nethttp.Header)}
+	req1 := &nethttp.Request{
+		Header: make(nethttp.Header),
+	}
+	req1.Header.Set("Content-Type", "application/json")
+
+	err := DefaultResponseEncoder(w, req1, nil)
+	if err != nil {
+		t.Errorf("expected no error, got %v", err)
+	}
+	if !reflect.DeepEqual("", w.Header().Get("Content-Type")) {
+		t.Errorf("expected empty string, got %v", w.Header().Get("Content-Type"))
+	}
+	if !reflect.DeepEqual(204, w.StatusCode) {
+		t.Errorf("expected %v, got %v", 204, w.StatusCode)
+	}
+	if w.Data != nil {
+		t.Errorf("expected nil, got %v", w.Data)
+	}
+}
+
 func TestCodecForRequest(t *testing.T) {
 	req1 := &nethttp.Request{
 		Header: make(nethttp.Header),