Responder generated by httpmock can now be used concurrently

Closes #93

Signed-off-by: Maxime Soulé <btik-git@scoubidou.com>

response.go

@@ -71,13 +71,28 @@ func (r Responder) Trace(fn func(...interface{})) Responder {
 	}
 }
 
-// ResponderFromResponse wraps an *http.Response in a Responder
+// ResponderFromResponse wraps an *http.Response in a Responder.
+//
+// Be careful, except for responses generated by httpmock
+// (NewStringResponse and NewBytesResponse functions) for which there
+// is no problems, it is the caller responsibility to ensure the
+// response body can be read several times and concurrently if needed,
+// as it is shared among all Responder returned responses.
+//
+// For home-made responses, NewRespBodyFromString and
+// NewRespBodyFromBytes functions can be used to produce response
+// bodies that can be read several times and concurrently.
 func ResponderFromResponse(resp *http.Response) Responder {
 	return func(req *http.Request) (*http.Response, error) {
-		res := new(http.Response)
-		*res = *resp
+		res := *resp
+
+		// Our stuff: generate a new io.ReadCloser instance sharing the same buffer
+		if body, ok := resp.Body.(*dummyReadCloser); ok {
+			res.Body = body.copy()
+		}
+
 		res.Request = req
-		return res, nil
+		return &res, nil
 	}
 }
 
@@ -244,20 +259,39 @@ func NewXmlResponderOrPanic(status int, body interface{}) Responder { // nolint:
 // NewRespBodyFromString creates an io.ReadCloser from a string that is suitable for use as an
 // http response body.
 func NewRespBodyFromString(body string) io.ReadCloser {
-	return &dummyReadCloser{strings.NewReader(body)}
+	return &dummyReadCloser{orig: body}
 }
 
 // NewRespBodyFromBytes creates an io.ReadCloser from a byte slice that is suitable for use as an
 // http response body.
 func NewRespBodyFromBytes(body []byte) io.ReadCloser {
-	return &dummyReadCloser{bytes.NewReader(body)}
+	return &dummyReadCloser{orig: body}
 }
 
 type dummyReadCloser struct {
-	body io.ReadSeeker
+	orig interface{}   // string or []byte
+	body io.ReadSeeker // instanciated on demand from orig
+}
+
+// copy returns a new instance resetting d.body to nil.
+func (d *dummyReadCloser) copy() *dummyReadCloser {
+	return &dummyReadCloser{orig: d.orig}
+}
+
+// setup ensures d.body is correctly initialized.
+func (d *dummyReadCloser) setup() {
+	if d.body == nil {
+		switch body := d.orig.(type) {
+		case string:
+			d.body = strings.NewReader(body)
+		case []byte:
+			d.body = bytes.NewReader(body)
+		}
+	}
 }
 
 func (d *dummyReadCloser) Read(p []byte) (n int, err error) {
+	d.setup()
 	n, err = d.body.Read(p)
 	if err == io.EOF {
 		d.body.Seek(0, 0) // nolint: errcheck
@@ -266,6 +300,7 @@ func (d *dummyReadCloser) Read(p []byte) (n int, err error) {
 }
 
 func (d *dummyReadCloser) Close() error {
+	d.setup()
 	d.body.Seek(0, 0) // nolint: errcheck
 	return nil
 }

response_test.go

@@ -6,6 +6,8 @@ import (
 	"errors"
 	"io/ioutil"
 	"net/http"
+	"strings"
+	"sync"
 	"testing"
 )
 
@@ -340,3 +342,36 @@ func TestResponder(t *testing.T) {
 	chk(rt, resp, "")
 	chkCalled()
 }
+
+func TestParallelResponder(t *testing.T) {
+	req, err := http.NewRequest(http.MethodGet, "http://foo.bar", nil)
+	if err != nil {
+		t.Fatal("Error creating request")
+	}
+
+	body := strings.Repeat("ABC-", 1000)
+
+	for _, r := range []Responder{
+		NewStringResponder(200, body),
+		NewBytesResponder(200, []byte(body)),
+	} {
+		var wg sync.WaitGroup
+		for i := 0; i < 100; i++ {
+			wg.Add(1)
+			go func() {
+				defer wg.Done()
+				resp, _ := r(req)
+				b, err := ioutil.ReadAll(resp.Body)
+				switch {
+				case err != nil:
+					t.Errorf("ReadAll error: %s", err)
+				case len(b) != 4000:
+					t.Errorf("ReadAll read only %d bytes", len(b))
+				case !strings.HasPrefix(string(b), "ABC-"):
+					t.Errorf("ReadAll does not read the right prefix: %s", string(b)[0:4])
+				}
+			}()
+		}
+		wg.Wait()
+	}
+}