Add support for hidden fields

example/example.go

@@ -30,9 +30,12 @@ var screen1 = go3270.Screen{
 	{Row: 5, Col: 0, Content: "Last Name . . . ."},
 	{Row: 5, Col: 19, Name: "lname", Write: true},
 	{Row: 5, Col: 40}, // field "stop" character,
-	{Row: 7, Col: 0, Content: "Press"},
-	{Row: 7, Col: 6, Intense: true, Content: "enter"},
-	{Row: 7, Col: 12, Content: "to submit your name."},
+	{Row: 6, Col: 0, Content: "Password  . . . ."},
+	{Row: 6, Col: 19, Name: "password", Write: true, Hidden: true},
+	{Row: 6, Col: 40}, // field "stop" character,
+	{Row: 8, Col: 0, Content: "Press"},
+	{Row: 8, Col: 6, Intense: true, Content: "enter"},
+	{Row: 8, Col: 12, Content: "to submit your name."},
 	{Row: 10, Col: 0, Intense: true, Name: "errormsg"}, // a blank field for error messages
 	{Row: 22, Col: 0, Content: "PF3 Exit"},
 }
@@ -44,11 +47,12 @@ var screen2 = go3270.Screen{
 	{Row: 4, Col: 19, Name: "fname"}, // We're giving this field a name to replace its value at runtime
 	{Row: 5, Col: 0, Content: "And your last name is"},
 	{Row: 5, Col: 22, Name: "lname"}, // We're giving this field a name to replace its value at runtime
-	{Row: 7, Col: 0, Content: "Press"},
-	{Row: 7, Col: 6, Intense: true, Content: "enter"},
-	{Row: 7, Col: 12, Content: "to enter your name again, or"},
-	{Row: 7, Col: 41, Intense: true, Content: "PF3"},
-	{Row: 7, Col: 45, Content: "to quit and disconnect."},
+	{Row: 6, Col: 0, Name: "passwordOutput"},
+	{Row: 8, Col: 0, Content: "Press"},
+	{Row: 8, Col: 6, Intense: true, Content: "enter"},
+	{Row: 8, Col: 12, Content: "to enter your name again, or"},
+	{Row: 8, Col: 41, Intense: true, Content: "PF3"},
+	{Row: 8, Col: 45, Content: "to quit and disconnect."},
 	{Row: 22, Col: 0, Content: "PF3 Exit"},
 }
 
@@ -75,14 +79,18 @@ func handle(conn net.Conn) {
 	// Always begin new connection by negotiating the telnet options
 	go3270.NegotiateTelnet(conn)
 
+	fieldValues := make(map[string]string)
+
 	// We will loop forever until the user quits with PF3
-	var fieldValues map[string]string
 mainLoop:
 	for {
 	screen1Loop:
 		for {
 			// loop until the user passes input validation, or quits
 
+			// Always reset password input to blank each time through the loop
+			fieldValues["password"] = ""
+
 			// Show the first screen, and wait to get a client response. Place
 			// the cursor at the beginning of the first input field.
 			// We're passing in the fieldValues map to carry values over from
@@ -129,6 +137,13 @@ mainLoop:
 		}
 
 		// Now we're ready to display screen2
+		passwordLength := len(strings.TrimSpace(fieldValues["password"]))
+		passwordPlural := "s"
+		if passwordLength == 1 {
+			passwordPlural = ""
+		}
+		fieldValues["passwordOutput"] = fmt.Sprintf("Your password was %d character%s long",
+			passwordLength, passwordPlural)
 		response, err := go3270.ShowScreen(screen2, fieldValues, 0, 0, conn)
 		if err != nil {
 			fmt.Println(err)

screen.go

@@ -30,6 +30,10 @@ type Field struct {
 	// Intense indicates this field should be displayed with high intensity.
 	Intense bool
 
+	// Hidden indicates the field content should not be displayed (e.g. a
+	// password input field).
+	Hidden bool
+
 	// Name is the name of this field, which is used to get the user-entered
 	// data. All writeable fields on a screen must have a unique name.
 	Name string
@@ -69,7 +73,7 @@ func ShowScreen(screen Screen, values map[string]string, crow, ccol int,
 		}
 
 		b.Write(sba(fld.Row, fld.Col))
-		b.Write(sf(fld.Write, fld.Intense))
+		b.Write(sf(fld.Write, fld.Intense, fld.Hidden))
 
 		// Use fld.Content, unless the field is named and appears in the
 		// value map.
@@ -122,7 +126,7 @@ func sba(row, col int) []byte {
 }
 
 // sf is the "start field" 3270 command
-func sf(write, intense bool) []byte {
+func sf(write, intense, hidden bool) []byte {
 	result := make([]byte, 2)
 	result[0] = 0x1d // SF
 	if !write {
@@ -136,6 +140,10 @@ func sf(write, intense bool) []byte {
 	if intense {
 		result[1] |= 1 << 3 // set "bit 4"
 	}
+	if hidden {
+		result[1] |= 1 << 3 // set "bit 4"
+		result[1] |= 1 << 2 // set "bit 5"
+	}
 	// Fill in top 2 bits with appropriate values
 	result[1] = codes[result[1]]
 	return result