ssh: breakout ups ssh to its own package

This was done for clearer separation of function. A subsequent update will (hopefully) make the SSL command more robust so it works for both NMC2 and NMC3.

The method for sending shell commands was also updated to use an interactive shell instead. This allows capturing responses of the commands which will be needed to deduce if devices are NMC2 or NMC3.

pkg/apcssh/shell.go

@@ -0,0 +1,88 @@
+package apcssh
+
+import (
+	"bufio"
+	"fmt"
+	"strings"
+
+	"golang.org/x/crypto/ssh"
+)
+
+// upsCmdResponse is a structure that holds all of a shell commands results
+type upsCmdResponse struct {
+	command    string
+	code       string
+	codeText   string
+	resultText string
+}
+
+// cmd creates an interactive shell and executes the specified command
+func (cli *Client) cmd(command string) (*upsCmdResponse, error) {
+	// connect
+	sshClient, err := ssh.Dial("tcp", cli.hostname, cli.sshCfg)
+	if err != nil {
+		return nil, fmt.Errorf("apcssh: failed to dial session (%w)", err)
+	}
+	defer sshClient.Close()
+
+	session, err := sshClient.NewSession()
+	if err != nil {
+		return nil, fmt.Errorf("apcssh: failed to create session (%w)", err)
+	}
+	defer session.Close()
+
+	// pipes to send shell command to; and to receive repsonse
+	sshInput, err := session.StdinPipe()
+	if err != nil {
+		return nil, fmt.Errorf("apcssh: failed to make shell input pipe (%w)", err)
+	}
+	sshOutput, err := session.StdoutPipe()
+	if err != nil {
+		return nil, fmt.Errorf("apcssh: failed to make shell output pipe (%w)", err)
+	}
+
+	// make scanner to read shell continuously
+	scanner := bufio.NewScanner(sshOutput)
+	scanner.Split(scanAPCShell)
+
+	// start interactive shell
+	if err := session.Shell(); err != nil {
+		return nil, fmt.Errorf("apcssh: failed to start shell (%w)", err)
+	}
+	// discard the initial shell response (login message(s) / initial shell prompt)
+	for {
+		if token := scanner.Scan(); token {
+			_ = scanner.Bytes()
+			break
+		}
+	}
+
+	// send command
+	_, err = fmt.Fprint(sshInput, command+"\n")
+	if err != nil {
+		return nil, fmt.Errorf("apcssh: failed to send shell command (%w)", err)
+	}
+
+	res := &upsCmdResponse{}
+	for {
+		if tkn := scanner.Scan(); tkn {
+			result := string(scanner.Bytes())
+
+			cmdIndx := strings.Index(result, "\n")
+			res.command = result[:cmdIndx-1]
+			result = result[cmdIndx+1:]
+
+			codeIndx := strings.Index(result, ": ")
+			res.code = result[:codeIndx]
+			result = result[codeIndx+2:]
+
+			codeTxtIndx := strings.Index(result, "\n")
+			res.codeText = result[:codeTxtIndx-1]
+
+			res.resultText = result[codeTxtIndx+1 : len(result)-2]
+			break
+		}
+	}
+
+	return res, nil
+}