Added optional request and response logging

.gitignore

@@ -1,2 +1,3 @@
 .DS_Store
 debug.test
+.idea

docs/README.md

@@ -234,3 +234,36 @@ client.SetUserAgent("your-user-agent-value")
 
 // send API request...
 ```
+
+# Logging
+
+## Adding a custom logger
+
+You can add a custom logger to the client that will be used to print outgoing requests and incoming responses. Debug
+mode must be set to `true` to enable logging.
+
+This is an example of how to enable logging and log to a file:
+
+```go
+// Create a logger, which outputs to file.
+f, err := os.OpenFile("log.txt", os.O_RDWR | os.O_CREATE | os.O_APPEND, 0666)
+if err != nil {
+    log.Fatalf("error opening file: %v", err)
+}
+defer f.Close()
+
+fileLogger := &log.Logger{}
+fileLogger.SetOutput(f)
+
+client, err := helix.NewClient(&helix.Options{
+    logger: fileLogger,	
+    debug: true,	
+})
+if err != nil {
+    log.Fatalf("error opening file: %v", err)
+
+}
+```
+
+Should you want to enable debug mode but not want to use a custom logger, stdout will be used as the default log output.
+

helix.go

@@ -5,7 +5,9 @@ import (
 	"errors"
 	"fmt"
 	"io/ioutil"
+	"log"
 	"net/http"
+	"net/http/httputil"
 	"reflect"
 	"strconv"
 	"strings"
@@ -39,6 +41,10 @@ type Client struct {
 
 	baseURL      string
 	lastResponse *Response
+
+	// Logging
+	debug  bool
+	logger *log.Logger
 }
 
 // Options ...
@@ -52,6 +58,8 @@ type Options struct {
 	Scopes          []string
 	HTTPClient      HTTPClient
 	RateLimitFunc   RateLimitFunc
+	Debug			bool
+	Logger			*log.Logger
 }
 
 // RateLimitFunc ...
@@ -108,9 +116,17 @@ func NewClient(options *Options) (*Client, error) {
 	c := &Client{
 		clientID:   options.ClientID,
 		httpClient: http.DefaultClient,
+		logger: 	options.Logger,
+		debug:		options.Debug,
 	}
 
 	// Set options
+
+	// Use the default logger, if none was set by the user.
+	if options.Logger == nil {
+		c.logger = log.New(os.Stdout, "Helix: ", log.LstdFlags)
+	}
+
 	if options.HTTPClient != nil {
 		c.httpClient = options.HTTPClient
 	}
@@ -151,11 +167,19 @@ func (c *Client) sendRequest(method, path string, respData, reqData interface{})
 		return nil, err
 	}
 
+	if c.debug {
+		c.logger.Printf("%+v\n", req)
+	}
+
 	err = c.doRequest(req, resp)
 	if err != nil {
 		return nil, err
 	}
 
+	if c.debug {
+		c.logger.Printf("%+v\n", resp)
+	}
+
 	return resp, nil
 }
 
@@ -279,12 +303,30 @@ func (c *Client) doRequest(req *http.Request, resp *Response) error {
 			}
 		}
 
+		// Dump request on debug.
+		if c.debug {
+			bodyBytes, err := httputil.DumpRequest(req, true)
+			if err != nil {
+				return fmt.Errorf("Failed to dump API request: %s", err.Error())
+			}
+			c.logger.Println(string(bodyBytes))
+		}
+
 		response, err := c.httpClient.Do(req)
 		if err != nil {
 			return fmt.Errorf("Failed to execute API request: %s", err.Error())
 		}
 		defer response.Body.Close()
 
+		// Dump response on debug.
+		if c.debug {
+			bodyBytes, err := httputil.DumpResponse(response, true)
+			if err != nil {
+				return fmt.Errorf("Failed to dump API response: %s", err.Error())
+			}
+			c.logger.Println(string(bodyBytes))
+		}
+
 		resp.Header = response.Header
 
 		setResponseStatusCode(resp, "StatusCode", response.StatusCode)