Add support for authentication and auto-ID-detection

README.md

@@ -5,7 +5,7 @@ Ubiquiti UPS units seem to use a somewhat non-standard format for responses from
 
 ## Usage
 1. Enable the NUT server on your Ubiquiti UniFi-connected UPS unit.
-    - Do **NOT** enable the "Login Credential" option!
+    - The "Login Credential" setting is optional; if enabled, be sure to use the .Authenticate() method immediately after dialing!
 2. This module can now be used to get variables from your UPS's NUT server as follows:
 ```go
 package main
@@ -18,12 +18,29 @@ import (
 
 func main() {
 	host := "IP:PORT"
-	upsID := "UPS-ID"
+	username := "username"
+	password := "password"
+	
+	// connect to NUT server
 	client, err := nut.Dial(host)
 	if err != nil {
 		panic(err)
 	}
-	err = client.GetListVar(upsID)
+	
+	// authenticate (if "Login Credential" is enabled on the NUT server)
+	err = client.Authenticate(username, password)
+	if err != nil {
+		panic(err)
+	}
+	
+	// auto-detect UPS ID
+	upsID, err := client.Identify()
+	if err != nil {
+		panic(err)
+	}
+	
+	// list all variables from your UPS
+	err = client.ListVar(upsID)
 	if err != nil {
 		panic(err)
 	}
@@ -32,3 +49,5 @@ func main() {
 	}
 }
 ```
+
+This module also features a .GetVar() method for retrieving the value of only one variable.

nut.go

@@ -36,6 +36,36 @@ func (c *Client) Close() error {
 	return c.conn.Close()
 }
 
+// Authenticate logs into credential-protected sessions.
+// If authentication is enabled on your NUT server, run
+// this immediately after dialing.
+func (c *Client) Authenticate(username, password string) error {
+	var err error
+	if err = c.write("USERNAME " + username + "\nPASSWORD " + password); err != nil {
+		return err
+	}
+	_, err = c.clearBuffer("OK L", "")
+	if err != nil {
+		return err
+	}
+	return nil
+}
+
+// Identify detects the ID of the connected UPS.
+// This only works when there is only one UPS per
+// NUT server, which is the case with UniFi UPS units.
+func (c *Client) Identify() (string, error) {
+	if err := c.write("LIST UPS"); err != nil {
+		return "", err
+	}
+	l, err := c.clearBuffer("END", "UPS")
+	if err != nil {
+		return "", err
+	}
+
+	return strings.Split(l, " ")[1], nil
+}
+
 // ListVar updates NutKeyValMap with the current status of all variables from <upsID>.
 func (c *Client) ListVar(upsID string) error {
 	cmd := "LIST VAR \"" + upsID + "\""
@@ -70,8 +100,7 @@ outer:
 
 // GetVar returns the value of the specified variable for <upsID>.
 func (c *Client) GetVar(upsID, varName string) (string, error) {
-	cmd := "GET VAR \"" + upsID + "\" \"" + varName + "\""
+	if err := c.write("GET VAR \"" + upsID + "\" \"" + varName + "\""); err != nil {
-	if err := c.write(cmd); err != nil {
 		return "", err
 	}
 	l, err := c.read()
@@ -86,7 +115,6 @@ func (c *Client) GetVar(upsID, varName string) (string, error) {
 	return value, nil
 }
 
-// newClient wraps an existing net.Conn.
 func newClient(conn net.Conn) *Client {
 	return &Client{conn, bufio.NewReader(conn)}
 }
@@ -106,3 +134,19 @@ func (c *Client) read() (string, error) {
 	}
 	return l, nil
 }
+
+func (c *Client) clearBuffer(tillPrefix, storePrefix string) (string, error) {
+	var stored string
+	for {
+		l, err := c.read()
+		if err != nil {
+			return "", err
+		}
+		if storePrefix != "" && strings.HasPrefix(l, storePrefix) {
+			stored = l
+		} else if strings.HasPrefix(l, tillPrefix) {
+			break
+		}
+	}
+	return stored, nil
+}