Add BodyMultipart (#119)

* Add BodyMultipart

* Test: Make CR visible

config.go

@@ -2,7 +2,9 @@ package requests
 
 import (
 	"compress/gzip"
+	"fmt"
 	"io"
+	"mime/multipart"
 	"net/http/httptest"
 )
 
@@ -43,3 +45,33 @@ func TestServerConfig(s *httptest.Server) Config {
 			Client(s.Client())
 	}
 }
+
+// BodyMultipart returns a Config
+// that uses a multipart.Writer for the request body.
+// If boundary is "", a multipart boundary is chosen at random.
+// The content type of the request is set to multipart/form-data
+// with the correct boundary.
+// The multipart.Writer is automatically closed if the callback succeeds.
+func BodyMultipart(boundary string, h func(multi *multipart.Writer) error) Config {
+	return func(rb *Builder) {
+		if boundary == "" {
+			multi := multipart.NewWriter(nil)
+			boundary = multi.Boundary()
+		}
+		rb.
+			ContentType("multipart/form-data; boundary=" + boundary).
+			BodyWriter(func(w io.Writer) error {
+				multi := multipart.NewWriter(w)
+				if err := multi.SetBoundary(boundary); err != nil {
+					return fmt.Errorf("setting boundary: %w", err)
+				}
+				if err := h(multi); err != nil {
+					return err
+				}
+				if err := multi.Close(); err != nil {
+					return fmt.Errorf("closing multipart writer: %w", err)
+				}
+				return nil
+			})
+	}
+}

config_example_test.go

@@ -4,8 +4,12 @@ import (
 	"compress/gzip"
 	"context"
 	"fmt"
+	"io"
+	"mime/multipart"
 	"net/http"
 	"net/http/httptest"
+	"net/http/httputil"
+	"net/textproto"
 	"strings"
 
 	"github.com/carlmjohnson/requests"
@@ -100,3 +104,59 @@ func ExampleTestServerConfig() {
 	// Hello, world!
 	// Howdy, planet!
 }
+
+func ExampleBodyMultipart() {
+	req, err := requests.
+		URL("http://example.com").
+		Config(requests.BodyMultipart("abc", func(multi *multipart.Writer) error {
+			// CreateFormFile hardcodes the Content-Type as application/octet-stream
+			w, err := multi.CreateFormFile("file", "en.txt")
+			if err != nil {
+				return err
+			}
+			_, err = io.WriteString(w, "Hello, World!")
+			if err != nil {
+				return err
+			}
+			// CreatePart is more flexible and lets you add headers
+			h := make(textproto.MIMEHeader)
+			h.Set("Content-Disposition", `form-data; name="file"; filename="jp.txt"`)
+			h.Set("Content-Type", "text/plain; charset=utf-8")
+			w, err = multi.CreatePart(h)
+			if err != nil {
+				panic(err)
+			}
+			_, err = io.WriteString(w, "こんにちは世界!")
+			if err != nil {
+				return err
+			}
+			return nil
+		})).
+		Request(context.Background())
+	if err != nil {
+		panic(err)
+	}
+	b, err := httputil.DumpRequest(req, true)
+	if err != nil {
+		panic(err)
+	}
+
+	// Make carriage return visible
+	fmt.Println(strings.ReplaceAll(string(b), "\r", "↵"))
+	// Output:
+	// POST / HTTP/1.1↵
+	// Host: example.com↵
+	// Content-Type: multipart/form-data; boundary=abc↵
+	// ↵
+	// --abc↵
+	// Content-Disposition: form-data; name="file"; filename="en.txt"↵
+	// Content-Type: application/octet-stream↵
+	// ↵
+	// Hello, World!↵
+	// --abc↵
+	// Content-Disposition: form-data; name="file"; filename="jp.txt"↵
+	// Content-Type: text/plain; charset=utf-8↵
+	// ↵
+	// こんにちは世界!↵
+	// --abc--↵
+}