Update GQLgen test client to work with multipart form data

Update the GQLgen to support multipart form data, like those present
within the fileupload examples.

- Add missing space between "unsupported encoding " and failing
  content-type header error

client/client.go

@@ -9,6 +9,7 @@ import (
 	"io/ioutil"
 	"net/http"
 	"net/http/httptest"
+	"regexp"
 
 	"github.com/mitchellh/mapstructure"
 )
@@ -119,15 +120,18 @@ func (p *Client) newRequest(query string, options ...Option) (*http.Request, err
 		option(bd)
 	}
 
-	switch bd.HTTP.Header.Get("Content-Type") {
-	case "application/json":
+	contentType := bd.HTTP.Header.Get("Content-Type")
+	switch {
+	case regexp.MustCompile(`multipart/form-data; ?boundary=.*`).MatchString(contentType):
+		break
+	case "application/json" == contentType:
 		requestBody, err := json.Marshal(bd)
 		if err != nil {
 			return nil, fmt.Errorf("encode: %s", err.Error())
 		}
 		bd.HTTP.Body = ioutil.NopCloser(bytes.NewBuffer(requestBody))
 	default:
-		panic("unsupported encoding" + bd.HTTP.Header.Get("Content-Type"))
+		panic("unsupported encoding " + bd.HTTP.Header.Get("Content-Type"))
 	}
 
 	return bd.HTTP, nil

client/client_test.go

@@ -1,9 +1,12 @@
 package client_test
 
 import (
+	"bytes"
 	"encoding/json"
 	"io/ioutil"
+	"mime/multipart"
 	"net/http"
+	"net/textproto"
 	"testing"
 
 	"github.com/99designs/gqlgen/client"
@@ -39,6 +42,44 @@ func TestClient(t *testing.T) {
 	require.Equal(t, "bob", resp.Name)
 }
 
+func TestClientMultipartFormData(t *testing.T) {
+	h := http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		bodyBytes, err := ioutil.ReadAll(r.Body)
+		require.NoError(t, err)
+		require.Contains(t, string(bodyBytes), `Content-Disposition: form-data; name="operations"`)
+		require.Contains(t, string(bodyBytes), `{"query":"mutation ($input: Input!) {}","variables":{"file":{}}`)
+		require.Contains(t, string(bodyBytes), `Content-Disposition: form-data; name="map"`)
+		require.Contains(t, string(bodyBytes), `{"0":["variables.file"]}`)
+		require.Contains(t, string(bodyBytes), `Content-Disposition: form-data; name="0"; filename="example.txt"`)
+		require.Contains(t, string(bodyBytes), `Content-Type: text/plain`)
+		require.Contains(t, string(bodyBytes), `Hello World`)
+
+		w.Write([]byte(`{}`))
+	})
+
+	c := client.New(h)
+
+	var resp struct{}
+	c.MustPost("{ id }", &resp,
+		func(bd *client.Request) {
+			bodyBuf := &bytes.Buffer{}
+			bodyWriter := multipart.NewWriter(bodyBuf)
+			bodyWriter.WriteField("operations", `{"query":"mutation ($input: Input!) {}","variables":{"file":{}}`)
+			bodyWriter.WriteField("map", `{"0":["variables.file"]}`)
+
+			h := make(textproto.MIMEHeader)
+			h.Set("Content-Disposition", `form-data; name="0"; filename="example.txt"`)
+			h.Set("Content-Type", "text/plain")
+			ff, _ := bodyWriter.CreatePart(h)
+			ff.Write([]byte("Hello World"))
+			bodyWriter.Close()
+
+			bd.HTTP.Body = ioutil.NopCloser(bodyBuf)
+			bd.HTTP.Header.Set("Content-Type", bodyWriter.FormDataContentType())
+		},
+	)
+}
+
 func TestAddHeader(t *testing.T) {
 	h := http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		require.Equal(t, "ASDF", r.Header.Get("Test-Key"))