polycubectl: fix reading from standard input

After 074ece5 ("polycubectl: add reading from standard input capability")
polycubectl tries to read the standard input in all the invocations, this
causes commands typed by the user to hang up.

This commit uses a logic to detect if the standard input is being piped, in
that case it is used.

This bug was probably not detected for two reasons:
- We concentrate in test the new feature, i.e, loading configurations from files,
without testing the standard behaviour.
- The bug is not present in our CI (jenkins) probably because it executes
polycubect without stdin.

Fixes: 074ece5 ("polycubectl: add reading from standard input capability")

Reported-by: Gianluca Scopelliti <gianlu.1033@gmail.com>
Signed-off-by: Mauricio Vasquez B <mauriciovasquezbernal@gmail.com>

Author: mauriciovasquezbernal

src/polycubectl/cliargs/cliargs.go

@@ -436,6 +436,11 @@ func (cli *CLIArgs) GetHTTPRequest() (*httprequest.HTTPRequest, error) {
 	var url string
 
 	url = cli.buildURL()
+	var stat os.FileInfo
+	var staterr error
+	if os.Stdin != nil {
+		stat, staterr = os.Stdin.Stat()
+	}
 
 	// TODO: is command == "" required?
 	if !cli.IsHelp && (cli.Command == AddCommand ||
@@ -445,8 +450,10 @@ func (cli *CLIArgs) GetHTTPRequest() (*httprequest.HTTPRequest, error) {
 			url0, body0 := cli.buildSingleParamBody()
 			url += url0
 			body = body0
-		} else {
-			// if there is text on the standard input that'll used as the body
+		} else if os.Stdin != nil && staterr == nil &&
+			stat.Mode() & os.ModeCharDevice == 0 && stat.Size() > 0 {
+			// os.ModeCharDevice flag is set when piping text to the stdin
+			// use text in the standard input as body
 			var buffer bytes.Buffer
 			reader := bufio.NewReader(os.Stdin)
 			text, _ := reader.ReadString('\n')
@@ -465,6 +472,8 @@ func (cli *CLIArgs) GetHTTPRequest() (*httprequest.HTTPRequest, error) {
 			} else {
 				body = cli.buildBody()
 			}
+		} else {
+			body = cli.buildBody()
 		}
 	}