Extend context.File to allow for the content-dispositon attachments v…

…ia a new method context.Attachment (gin-gonic#1260)

* Add FileAttachment method to context to allow instant downloads with filenames

* Add relevant tests for FileAttachment method

context.go

@@ -6,6 +6,7 @@ package gin
 
 import (
 	"errors"
+	"fmt"
 	"io"
 	"io/ioutil"
 	"math"
@@ -880,6 +881,13 @@ func (c *Context) File(filepath string) {
 	http.ServeFile(c.Writer, c.Request, filepath)
 }
 
+// FileAttachment writes the specified file into the body stream in an efficient way
+// On the client side, the file will typically be downloaded with the given filename
+func (c *Context) FileAttachment(filepath, filename string) {
+	c.Writer.Header().Set("content-disposition", fmt.Sprintf("attachment; filename=\"%s\"", filename))
+	http.ServeFile(c.Writer, c.Request, filepath)
+}
+
 // SSEvent writes a Server-Sent Event into the body stream.
 func (c *Context) SSEvent(name string, message interface{}) {
 	c.Render(-1, sse.Event{

context_test.go

@@ -979,6 +979,19 @@ func TestContextRenderFile(t *testing.T) {
 	assert.Equal(t, "text/plain; charset=utf-8", w.Header().Get("Content-Type"))
 }
 
+func TestContextRenderAttachment(t *testing.T) {
+	w := httptest.NewRecorder()
+	c, _ := CreateTestContext(w)
+	newFilename := "new_filename.go"
+
+	c.Request, _ = http.NewRequest("GET", "/", nil)
+	c.FileAttachment("./gin.go", newFilename)
+
+	assert.Equal(t, 200, w.Code)
+	assert.Contains(t, w.Body.String(), "func New() *Engine {")
+	assert.Equal(t, fmt.Sprintf("attachment; filename=\"%s\"", newFilename), w.HeaderMap.Get("Content-Disposition"))
+}
+
 // TestContextRenderYAML tests that the response is serialized as YAML
 // and Content-Type is set to application/x-yaml
 func TestContextRenderYAML(t *testing.T) {