add Client field to HttpGetter

Add Client field to allow an http.Client instance to be provided for
http requests. Continue to default to the `http.DefaultClient` to
maintain previous behavior.

get_http.go

@@ -36,6 +36,10 @@ type HttpGetter struct {
 	// Netrc, if true, will lookup and use auth information found
 	// in the user's netrc file if available.
 	Netrc bool
+
+	// Client is the http.Client to use for Get requests.
+	// This defaults to http.DefaultClient if left unset.
+	Client *http.Client
 }
 
 func (g *HttpGetter) ClientMode(u *url.URL) (ClientMode, error) {
@@ -57,13 +61,17 @@ func (g *HttpGetter) Get(dst string, u *url.URL) error {
 		}
 	}
 
+	if g.Client == nil {
+		g.Client = http.DefaultClient
+	}
+
 	// Add terraform-get to the parameter.
 	q := u.Query()
 	q.Add("terraform-get", "1")
 	u.RawQuery = q.Encode()
 
 	// Get the URL
-	resp, err := http.Get(u.String())
+	resp, err := g.Client.Get(u.String())
 	if err != nil {
 		return err
 	}
@@ -106,7 +114,11 @@ func (g *HttpGetter) GetFile(dst string, u *url.URL) error {
 		}
 	}
 
-	resp, err := http.Get(u.String())
+	if g.Client == nil {
+		g.Client = http.DefaultClient
+	}
+
+	resp, err := g.Client.Get(u.String())
 	if err != nil {
 		return err
 	}