Makeing some progress...

.idea/markdown.xml

@@ -0,0 +1,9 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project version="4">
+  <component name="MarkdownSettings">
+    <enabledExtensions>
+      <entry key="MermaidLanguageExtension" value="false" />
+      <entry key="PlantUMLLanguageExtension" value="false" />
+    </enabledExtensions>
+  </component>
+</project>

client.go

@@ -2,10 +2,16 @@ package mail
 
 import (
 	"context"
+	"crypto/tls"
+	"errors"
+	"fmt"
+	"net"
+	"net/smtp"
+	"os"
 	"time"
 )
 
-// DefaultPort is the default connection port to the SMTP server
+// DefaultPort is the default connection port cto the SMTP server
 const DefaultPort = 25
 
 // DefaultTimeout is the default connection timeout
@@ -13,19 +19,50 @@ const DefaultTimeout = time.Second * 30
 
 // Client is the SMTP client struct
 type Client struct {
-	h   string          // Hostname of the target SMTP server to connect to
-	p   int             // Port of the SMTP server to connect to
-	s   bool            // Use SSL/TLS or not
-	ctx context.Context // The context for the connection handling
+	// Hostname of the target SMTP server cto connect cto
+	host string
+
+	// Port of the SMTP server cto connect cto
+	port int
+
+	// Use SSL for the connection
+	ssl bool
+
+	// Sets the client cto use STARTTTLS for the connection (is disabled when SSL is set)
+	starttls bool
+
+	// Timeout for the SMTP server connection
+	cto time.Duration
+
+	// HELO/EHLO string for the greeting the target SMTP server
+	helo string
+
+	// The SMTP client that is set up when using the Dial*() methods
+	sc *smtp.Client
 }
 
 // Option returns a function that can be used for grouping Client options
 type Option func(*Client)
 
+var (
+	// ErrNoHostname should be used if a Client has no hostname set
+	ErrNoHostname = errors.New("hostname for client cannot be empty")
+
+	// ErrInvalidHostname should be used if a Client has an invalid hostname set
+	//ErrInvalidHostname = errors.New("hostname for client is invalid")
+)
+
 // NewClient returns a new Session client object
-func NewClient(o ...Option) Client {
-	c := Client{
-		p: DefaultPort,
+func NewClient(h string, o ...Option) (*Client, error) {
+	c := &Client{
+		host: h,
+		port: DefaultPort,
+		cto:  DefaultTimeout,
+	}
+
+	// Set default HELO/EHLO hostname
+	if err := c.setDefaultHelo(); err != nil {
+		return c, err
 	}
 
 	// Override defaults with optionally provided Option functions
@@ -33,26 +70,100 @@ func NewClient(o ...Option) Client {
 		if co == nil {
 			continue
 		}
-		co(&c)
+		co(c)
 	}
 
-	return c
+	// Some settings in a Client cannot be empty/unset
+	if c.host == "" {
+		return c, ErrNoHostname
+
 	}
 
-// WithHost overrides the default connection port
-func WithHost(h string) Option {
-	return func(c *Client) {
-		c.h = h
-	}
+	return c, nil
 }
 
 // WithPort overrides the default connection port
 func WithPort(p int) Option {
 	return func(c *Client) {
-		c.p = p
+		c.port = p
 	}
 }
 
-func (c Client) Dial() {
-
+// WithTimeout overrides the default connection timeout
+func WithTimeout(t time.Duration) Option {
+	return func(c *Client) {
+		c.cto = t
+	}
+}
+
+// WithSSL tells the client to use a SSL/TLS connection
+func WithSSL() Option {
+	return func(c *Client) {
+		c.ssl = true
+	}
+}
+
+// Dial establishes a connection cto the SMTP server with a default context.Background
+func (c *Client) Dial() error {
+	ctx := context.Background()
+	return c.DialWithContext(ctx)
+}
+
+// DialWithContext establishes a connection cto the SMTP server with a given context.Context
+func (c *Client) DialWithContext(uctx context.Context) error {
+	ctx, cfn := context.WithTimeout(uctx, c.cto)
+	defer cfn()
+
+	nd := net.Dialer{}
+	td := tls.Dialer{}
+	var co net.Conn
+	var err error
+	if c.ssl {
+		co, err = td.DialContext(ctx, "tcp", fmt.Sprintf("%s:%d", c.host, c.port))
+	}
+	if !c.ssl {
+		co, err = nd.DialContext(ctx, "tcp", fmt.Sprintf("%s:%d", c.host, c.port))
+	}
+	if err != nil {
+		return err
+	}
+
+	c.sc, err = smtp.NewClient(co, c.host)
+	if err != nil {
+		return err
+	}
+	if err := c.sc.Hello(c.helo); err != nil {
+		return err
+	}
+
+	return nil
+}
+
+// Send sends out the mail message
+func (c *Client) Send() error {
+	return nil
+}
+
+// Close closes the connection cto the SMTP server
+func (c *Client) Close() error {
+	if err := c.sc.Close(); err != nil {
+		fmt.Printf("failed close: %s\n", err)
+		return err
+	}
+	if ok, auth := c.sc.Extension("PIPELINING"); ok {
+		fmt.Printf("PIPELINING Support: %s\n", auth)
+	} else {
+		fmt.Println("No PIPELINING")
+	}
+	return c.sc.Close()
+}
+
+// setDefaultHelo retrieves the current hostname and sets it as HELO/EHLO hostname
+func (c *Client) setDefaultHelo() error {
+	hn, err := os.Hostname()
+	if err != nil {
+		return fmt.Errorf("failed cto read local hostname: %w", err)
+	}
+	c.helo = hn
+	return nil
 }

cmd/main.go

@@ -0,0 +1,31 @@
+package main
+
+import (
+	"context"
+	"fmt"
+	"github.com/wneessen/go-mail"
+	"os"
+	"time"
+)
+
+func main() {
+	c, err := mail.NewClient("192.168.178.60", mail.WithTimeout(time.Millisecond*500), mail.WithSSL())
+	if err != nil {
+		fmt.Printf("failed to create new client: %s\n", err)
+		os.Exit(1)
+	}
+
+	ctx, cfn := context.WithCancel(context.Background())
+	defer cfn()
+
+	if err := c.DialWithContext(ctx); err != nil {
+		fmt.Printf("failed to dial: %s\n", err)
+		os.Exit(1)
+	}
+	fmt.Printf("Client: %+v\n", c)
+	time.Sleep(time.Millisecond * 1500)
+	if err := c.Close(); err != nil {
+		fmt.Printf("failed to close SMTP connection: %s\n", err)
+		os.Exit(1)
+	}
+}

doc.go

@@ -0,0 +1,2 @@
+// Package mail provides a simple and easy way cto sending mails with Go
+package mail

tls.go

@@ -0,0 +1,19 @@
+package mail
+
+// TLSPolicy type describes a int alias for the different TLS policies we allow
+type TLSPolicy int
+
+const (
+	// TLSMandatory requires that the connection cto the server is
+	// encrypting using STARTTLS. If the server does not support STARTTLS
+	// the connection will be terminated with an error
+	TLSMandatory TLSPolicy = iota
+
+	// TLSOpportunistic tries cto establish an encrypted connection via the
+	// STARTTLS protocol. If the server does not support this, it will fall
+	// back cto non-encrypted plaintext transmission
+	TLSOpportunistic
+
+	// NoTLS forces the transaction cto be not encrypted
+	NoTLS
+)