linkerd inject from remote URL (#2988)

Signed-off-by: Tarun Pothulapati <tarunpothulapati@outlook.com>

cli/cmd/inject.go

@@ -56,8 +56,8 @@ sub-folders, or coming from stdin.`,
 		Example: `  # Inject all the deployments in the default namespace.
   kubectl get deploy -o yaml | linkerd inject - | kubectl apply -f -
 
-  # Download a resource and inject it through stdin.
-  curl http://url.to/yml | linkerd inject - | kubectl apply -f -
+  # Injecting a file from a remote URL
+  linkerd inject http://url.to/yml | kubectl apply -f -
 
   # Inject all the resources inside a folder and its sub-folders.
   linkerd inject <folder> | kubectl apply -f -`,

cli/cmd/inject_util.go

@@ -5,6 +5,8 @@ import (
 	"bytes"
 	"fmt"
 	"io"
+	"net/http"
+	"net/url"
 	"os"
 	"path/filepath"
 
@@ -139,6 +141,24 @@ func read(path string) ([]io.Reader, error) {
 	)
 	if path == "-" {
 		in = append(in, os.Stdin)
+	} else if isValidURL(path) {
+		resp, err := http.Get(path)
+		if err != nil {
+			return nil, err
+		}
+
+		if resp.StatusCode != http.StatusOK {
+			return nil, fmt.Errorf("unable to read URL %q, server reported %s, status code=%d", path, resp.Status, resp.StatusCode)
+		}
+
+		// Save to a buffer, so that response can be closed here
+		buf := new(bytes.Buffer)
+		_, err = buf.ReadFrom(resp.Body)
+		if err != nil {
+			return nil, err
+		}
+		resp.Body.Close()
+		in = append(in, buf)
 	} else {
 		in, err = walk(path)
 		if err != nil {
@@ -149,6 +169,12 @@ func read(path string) ([]io.Reader, error) {
 	return in, nil
 }
 
+// checks if the given string is a valid URL
+func isValidURL(path string) bool {
+	_, err := url.ParseRequestURI(path)
+	return err == nil
+}
+
 // walk walks the file tree rooted at path. path may be a file or a directory.
 // Creates a reader for each file found.
 func walk(path string) ([]io.Reader, error) {