Merge pull request #40 from gojek/plugins

Add plugin support

README.md

@@ -11,10 +11,13 @@
 * [Description](#description)
 * [Installation](#installation)
 * [Usage](#usage)
-	+ [Making a simple `GET` request](#making-a-simple-get-request)
-	+ [Creating a hystrix-like circuit breaker](#creating-a-hystrix-like-circuit-breaker)
-	+ [Creating an HTTP client with a retry mechanism](#creating-an-http-client-with-a-retry-mechanism)
-	+ [Custom retry mechanisms](#custom-retry-mechanisms)
+  + [Making a simple `GET` request](#making-a-simple-get-request)
+  + [Creating a hystrix-like circuit breaker](#creating-a-hystrix-like-circuit-breaker)
+  + [Creating a hystrix-like circuit breaker with fallbacks](#creating-a-hystrix-like-circuit-breaker-with-fallbacks)
+  + [Creating an HTTP client with a retry mechanism](#creating-an-http-client-with-a-retry-mechanism)
+  + [Custom retry mechanisms](#custom-retry-mechanisms)
+  + [Custom HTTP clients](#custom-http-clients)
+* [Plugins](#plugins)
 * [Documentation](#documentation)
 * [FAQ](#faq)
 * [License](#license)
@@ -293,6 +296,39 @@ client := httpclient.NewClient(
 // The rest is the same as the first example
 ```
 
+## Plugins
+
+To add a plugin to an existing client, use the `AddPlugin` method of the client. 
+
+An example, with the [request logger plugin](/plugins/request_logger.go):
+
+```go
+// import "github.com/gojektech/heimdall/plugins"
+
+client := heimdall.NewHTTPClient(timeout)
+requestLogger := plugins.NewRequestLogger(nil, nil)
+client.AddPlugin(requestLogger)
+// use the client as before
+
+req, _ := http.NewRequest(http.MethodGet, "http://google.com", nil)
+res, err := client.Do(req)
+if err != nil {
+	panic(err)
+}
+// This will log:
+//23/Jun/2018 12:48:04 GET http://google.com 200 [412ms]
+// to STDOUT
+```
+
+A plugin is an interface whose methods get called during key events in a requests lifecycle:
+
+- `OnRequestStart` is called just before the request is made
+- `OnRequestEnd` is called once the request has successfully executed
+- `OnError` is called is the request failed
+
+Each method is called with the request object as an argument, with `OnRequestEnd`, and `OnError` additionally being called with the response and error instances respectively.
+For a simple example on how to write plugins, look at the [request logger plugin](/plugins/request_logger.go).
+
 ## Documentation
 
 Further documentation can be found on [godoc.org](https://www.godoc.org/github.com/gojektech/heimdall)

client.go

@@ -19,4 +19,5 @@ type Client interface {
 	Patch(url string, body io.Reader, headers http.Header) (*http.Response, error)
 	Delete(url string, headers http.Header) (*http.Response, error)
 	Do(req *http.Request) (*http.Response, error)
+	AddPlugin(p Plugin)
 }

go.mod

@@ -10,5 +10,6 @@ require (
 	github.com/pmezard/go-difflib v1.0.0 // indirect
 	github.com/smartystreets/assertions v0.0.0-20180927180507-b2de0cb4f26d // indirect
 	github.com/smartystreets/goconvey v0.0.0-20181108003508-044398e4856c // indirect
+	github.com/stretchr/objx v0.1.1 // indirect
 	github.com/stretchr/testify v1.2.1
 )

go.sum

@@ -16,5 +16,7 @@ github.com/smartystreets/assertions v0.0.0-20180927180507-b2de0cb4f26d h1:zE9ykE
 github.com/smartystreets/assertions v0.0.0-20180927180507-b2de0cb4f26d/go.mod h1:OnSkiWE9lh6wB0YB77sQom3nweQdgAjqCqsofrRNTgc=
 github.com/smartystreets/goconvey v0.0.0-20181108003508-044398e4856c h1:Ho+uVpkel/udgjbwB5Lktg9BtvJSh2DT0Hi6LPSyI2w=
 github.com/smartystreets/goconvey v0.0.0-20181108003508-044398e4856c/go.mod h1:XDJAKZRPZ1CvBcN2aX5YOUTYGHki24fSF0Iv48Ibg0s=
+github.com/stretchr/objx v0.1.1 h1:2vfRuCMp5sSVIDSqO8oNnWJq7mPa6KVP3iPIwFBuy8A=
+github.com/stretchr/objx v0.1.1/go.mod h1:HFkY916IF+rwdDfMAkV7OtwuqBVzrE8GR6GFx+wExME=
 github.com/stretchr/testify v1.2.1 h1:52QO5WkIUcHGIR7EnGagH88x1bUzqGXTC5/1bDTUQ7U=
 github.com/stretchr/testify v1.2.1/go.mod h1:a8OnRcib4nhh0OaRAV+Yts87kKdq0PP7pXfy6kDkUVs=

httpclient/client.go

@@ -19,6 +19,7 @@ type Client struct {
 	timeout    time.Duration
 	retryCount int
 	retrier    heimdall.Retriable
+	plugins    []heimdall.Plugin
 }
 
 const (
@@ -49,6 +50,11 @@ func NewClient(opts ...Option) *Client {
 	return &client
 }
 
+// AddPlugin Adds plugin to client
+func (c *Client) AddPlugin(p heimdall.Plugin) {
+	c.plugins = append(c.plugins, p)
+}
+
 // Get makes a HTTP GET request to provided URL
 func (c *Client) Get(url string, headers http.Header) (*http.Response, error) {
 	var response *http.Response
@@ -137,6 +143,7 @@ func (c *Client) Do(request *http.Request) (*http.Response, error) {
 			response.Body.Close()
 		}
 
+		c.reportRequestStart(request)
 		var err error
 		response, err = c.client.Do(request)
 		if bodyReader != nil {
@@ -147,11 +154,12 @@ func (c *Client) Do(request *http.Request) (*http.Response, error) {
 
 		if err != nil {
 			multiErr.Push(err.Error())
-
+			c.reportError(request, err)
 			backoffTime := c.retrier.NextInterval(i)
 			time.Sleep(backoffTime)
 			continue
 		}
+		c.reportRequestEnd(request, response)
 
 		if response.StatusCode >= http.StatusInternalServerError {
 			backoffTime := c.retrier.NextInterval(i)
@@ -165,3 +173,21 @@ func (c *Client) Do(request *http.Request) (*http.Response, error) {
 
 	return response, multiErr.HasError()
 }
+
+func (c *Client) reportRequestStart(request *http.Request) {
+	for _, plugin := range c.plugins {
+		plugin.OnRequestStart(request)
+	}
+}
+
+func (c *Client) reportError(request *http.Request, err error) {
+	for _, plugin := range c.plugins {
+		plugin.OnError(request, err)
+	}
+}
+
+func (c *Client) reportRequestEnd(request *http.Request, response *http.Response) {
+	for _, plugin := range c.plugins {
+		plugin.OnRequestEnd(request, response)
+	}
+}

httpclient/client_test.go

@@ -11,6 +11,7 @@ import (
 
 	"github.com/gojektech/heimdall"
 	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/mock"
 	"github.com/stretchr/testify/require"
 )
 
@@ -417,6 +418,60 @@ func TestHTTPClientGetReturnsErrorOnFailure(t *testing.T) {
 
 }
 
+func TestPluginMethodsCalled(t *testing.T) {
+	client := NewClient(WithHTTPTimeout(10 * time.Millisecond))
+	mockPlugin := &MockPlugin{}
+	client.AddPlugin(mockPlugin)
+
+	dummyHandler := func(w http.ResponseWriter, r *http.Request) {
+		w.WriteHeader(http.StatusOK)
+		w.Write([]byte(`{ "response": "something went wrong" }`))
+	}
+
+	server := httptest.NewServer(http.HandlerFunc(dummyHandler))
+	defer server.Close()
+
+	mockPlugin.On("OnRequestStart", mock.Anything)
+	mockPlugin.On("OnRequestEnd", mock.Anything, mock.Anything)
+
+	_, err := client.Get(server.URL, http.Header{})
+
+	require.NoError(t, err)
+	mockPlugin.AssertNumberOfCalls(t, "OnRequestStart", 1)
+	pluginRequest, ok := mockPlugin.Calls[0].Arguments[0].(*http.Request)
+	require.True(t, ok)
+	assert.Equal(t, http.MethodGet, pluginRequest.Method)
+	assert.Equal(t, server.URL, pluginRequest.URL.String())
+
+	mockPlugin.AssertNumberOfCalls(t, "OnRequestEnd", 1)
+	pluginResponse, ok := mockPlugin.Calls[1].Arguments[1].(*http.Response)
+	require.True(t, ok)
+	assert.Equal(t, http.StatusOK, pluginResponse.StatusCode)
+}
+
+func TestPluginErrorMethodCalled(t *testing.T) {
+	client := NewClient(WithHTTPTimeout(10 * time.Millisecond))
+	mockPlugin := &MockPlugin{}
+	client.AddPlugin(mockPlugin)
+
+	mockPlugin.On("OnRequestStart", mock.Anything)
+	mockPlugin.On("OnError", mock.Anything, mock.Anything)
+
+	serverURL := "does_not_exist"
+	_, err := client.Get(serverURL, http.Header{})
+
+	mockPlugin.AssertNumberOfCalls(t, "OnRequestStart", 1)
+	pluginRequest, ok := mockPlugin.Calls[0].Arguments[0].(*http.Request)
+	require.True(t, ok)
+	assert.Equal(t, http.MethodGet, pluginRequest.Method)
+	assert.Equal(t, serverURL, pluginRequest.URL.String())
+
+	mockPlugin.AssertNumberOfCalls(t, "OnError", 1)
+	err, ok = mockPlugin.Calls[1].Arguments[1].(error)
+	require.True(t, ok)
+	assert.EqualError(t, err, "Get does_not_exist: unsupported protocol scheme \"\"")
+}
+
 type myHTTPClient struct {
 	client http.Client
 }

httpclient/options_test.go

@@ -1,6 +1,7 @@
 package httpclient
 
 import (
+	"fmt"
 	"net/http"
 	"testing"
 	"time"
@@ -44,3 +45,89 @@ func TestOptionsHaveDefaults(t *testing.T) {
 	assert.Equal(t, retrier, c.retrier)
 	assert.Equal(t, noOfRetries, c.retryCount)
 }
+
+func ExampleWithHTTPTimeout() {
+	c := NewClient(WithHTTPTimeout(5 * time.Second))
+	req, err := http.NewRequest(http.MethodGet, "https://www.gojek.io/", nil)
+	if err != nil {
+		panic(err)
+	}
+	res, err := c.Do(req)
+	if err != nil {
+		panic(err)
+	}
+	fmt.Println("Response status : ", res.StatusCode)
+	// Output: Response status :  200
+}
+
+func ExampleWithHTTPTimeout_expired() {
+	c := NewClient(WithHTTPTimeout(1 * time.Millisecond))
+	req, err := http.NewRequest(http.MethodGet, "https://www.gojek.io/", nil)
+	if err != nil {
+		panic(err)
+	}
+	res, err := c.Do(req)
+	if err != nil {
+		fmt.Println("error:", err)
+		return
+	}
+	fmt.Println("Response status : ", res.StatusCode)
+}
+
+func ExampleWithRetryCount() {
+	c := NewClient(WithHTTPTimeout(1*time.Millisecond), WithRetryCount(3))
+	req, err := http.NewRequest(http.MethodGet, "https://www.gojek.io/", nil)
+	if err != nil {
+		panic(err)
+	}
+	res, err := c.Do(req)
+	if err != nil {
+		fmt.Println("error:", err)
+		return
+	}
+	fmt.Println("Response status : ", res.StatusCode)
+}
+
+type mockClient struct{}
+
+func (m *mockClient) Do(r *http.Request) (*http.Response, error) {
+	fmt.Println("mock client called")
+	return &http.Response{}, nil
+}
+
+func ExampleWithHTTPClient() {
+	m := &mockClient{}
+	c := NewClient(WithHTTPClient(m))
+	req, err := http.NewRequest(http.MethodGet, "https://www.gojek.io/", nil)
+	if err != nil {
+		panic(err)
+	}
+	_, _ = c.Do(req)
+	// Output: mock client called
+}
+
+type mockRetrier struct{}
+
+func (m *mockRetrier) NextInterval(attempt int) time.Duration {
+	fmt.Println("retry attempt", attempt)
+	return time.Millisecond
+}
+
+func ExampleWithRetrier() {
+	c := NewClient(WithHTTPTimeout(1*time.Millisecond), WithRetryCount(3), WithRetrier(&mockRetrier{}))
+	req, err := http.NewRequest(http.MethodGet, "https://www.gojek.io/", nil)
+	if err != nil {
+		panic(err)
+	}
+	res, err := c.Do(req)
+	if err != nil {
+		fmt.Println("error")
+		return
+	}
+	fmt.Println("Response status : ", res.StatusCode)
+	// Output: retry attempt 0
+	// retry attempt 1
+	// retry attempt 2
+	// retry attempt 3
+	// error
+}

httpclient/plugin_mock.go

@@ -0,0 +1,27 @@
+package httpclient
+
+import (
+	"net/http"
+
+	"github.com/stretchr/testify/mock"
+)
+
+// MockPlugin provides a mock plugin for heimdall
+type MockPlugin struct {
+	mock.Mock
+}
+
+// OnRequestStart is called when the request starts
+func (m *MockPlugin) OnRequestStart(req *http.Request) {
+	m.Called(req)
+}
+
+// OnRequestEnd is called when the request ends
+func (m *MockPlugin) OnRequestEnd(req *http.Request, res *http.Response) {
+	m.Called(req, res)
+}
+
+// OnError is called when the request errors out
+func (m *MockPlugin) OnError(req *http.Request, err error) {
+	m.Called(req, err)
+}

hystrix/hystrix_client.go

@@ -2,6 +2,7 @@ package hystrix
 
 import (
 	"bytes"
+	"github.com/gojektech/heimdall/httpclient"
 	"io"
 	"io/ioutil"
 	"net/http"
@@ -16,7 +17,7 @@ type fallbackFunc func(error) error
 
 // Client is the hystrix client implementation
 type Client struct {
-	client heimdall.Doer
+	client *httpclient.Client
 
 	timeout                time.Duration
 	hystrixTimeout         time.Duration
@@ -49,6 +50,7 @@ var err5xx = errors.New("server returned 5xx status code")
 // NewClient returns a new instance of hystrix Client
 func NewClient(opts ...Option) *Client {
 	client := Client{
+		client:                 httpclient.NewClient(),
 		timeout:                defaultHTTPTimeout,
 		hystrixTimeout:         defaultHystrixTimeout,
 		maxConcurrentRequests:  defaultMaxConcurrentRequests,
@@ -63,12 +65,6 @@ func NewClient(opts ...Option) *Client {
 		opt(&client)
 	}
 
-	if client.client == nil {
-		client.client = &http.Client{
-			Timeout: client.timeout,
-		}
-	}
-
 	hystrix.ConfigureCommand(client.hystrixCommandName, hystrix.CommandConfig{
 		Timeout:                durationToInt(client.hystrixTimeout, time.Millisecond),
 		MaxConcurrentRequests:  client.maxConcurrentRequests,
@@ -211,3 +207,8 @@ func (hhc *Client) Do(request *http.Request) (*http.Response, error) {
 
 	return response, err
 }
+
+// AddPlugin Adds plugin to client
+func (hhc *Client) AddPlugin(p heimdall.Plugin) {
+	hhc.client.AddPlugin(p)
+}