present: check if too few arguments to image, iframe, or video Previously, using incorrect syntax for one of image, iframe, or video functions caused an index out of range panic. Add a check to prevent the panic and return an error instead. Fixes golang/go#35142 Change-Id: Ifffb4cc5daded5331d617a3db7cad84e37abadc8 Reviewed-on: https://go-review.googlesource.com/c/tools/+/203477 Reviewed-by: Ian Lance Taylor <iant@golang.org> Reviewed-by: Andrew Gerrand <adg@golang.org>

diff --git a/present/iframe.go b/present/iframe.go
index 46649f0..057d229 100644
--- a/present/iframe.go
+++ b/present/iframe.go

@@ -23,6 +23,9 @@
 
 func parseIframe(ctx *Context, fileName string, lineno int, text string) (Elem, error) {
 	args := strings.Fields(text)
+	if len(args) < 2 {
+		return nil, fmt.Errorf("incorrect iframe invocation: %q", text)
+	}
 	i := Iframe{URL: args[1]}
 	a, err := parseArgs(fileName, lineno, args[2:])
 	if err != nil {

diff --git a/present/image.go b/present/image.go
index cfa2af9..84965ca 100644
--- a/present/image.go
+++ b/present/image.go

@@ -23,6 +23,9 @@
 
 func parseImage(ctx *Context, fileName string, lineno int, text string) (Elem, error) {
 	args := strings.Fields(text)
+	if len(args) < 2 {
+		return nil, fmt.Errorf("incorrect image invocation: %q", text)
+	}
 	img := Image{URL: args[1]}
 	a, err := parseArgs(fileName, lineno, args[2:])
 	if err != nil {

diff --git a/present/video.go b/present/video.go
index 913822e..93d9350 100644
--- a/present/video.go
+++ b/present/video.go

@@ -24,6 +24,9 @@
 
 func parseVideo(ctx *Context, fileName string, lineno int, text string) (Elem, error) {
 	args := strings.Fields(text)
+	if len(args) < 3 {
+		return nil, fmt.Errorf("incorrect video invocation: %q", text)
+	}
 	vid := Video{URL: args[1], SourceType: args[2]}
 	a, err := parseArgs(fileName, lineno, args[3:])
 	if err != nil {