smtpd

package module
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 Go to latest Published: Mar 8, 2023 License: MIT Imports: 27 Imported by: 0

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smtpd

smtpd is a pure Go implementation of an SMTP server. It allows you to do things like:

package main

import (
    "fmt"
    "net/smtp"

    "github.com/mailproto/smtpd"
)

var helloWorld = `To: sender@example.org
From: recipient@example.net
Content-Type: text/plain

This is the email body`

func main() {
    var server *smtpd.Server
    server = smtpd.NewServer(func(msg *smtpd.Message) error {
        fmt.Println("Got message from:", msg.From)
        fmt.Println(string(msg.RawBody))
        return server.Close()
    })

    go server.ListenAndServe(":2525")
    <-server.Ready

    log.Fatal(smtp.SendMail(server.Address(), nil, "sender@example.com", []string{"recipient@example.com"}, []byte(helloWorld)))
}

@todo document

Documentation

Index

Constants

View Source 
const (
	DefaultReadTimeout        = time.Second * 10
	DefaultWriteTimeout       = time.Second * 10
	DefaultMessageSizeMax     = 131072
	DefaultSessionCommandsMax = 100
)

Default values

Variables

View Source 
var (
	ErrAlreadyRunning = errors.New("This server is already listening for requests")
	ErrAuthFailed     = SMTPError{535, errors.New("Authentication credentials invalid")}
	ErrAuthCancelled  = SMTPError{501, errors.New("Cancelled")}
	ErrRequiresTLS    = SMTPError{538, errors.New("Encryption required for requested authentication mechanism")}
	ErrTransaction    = SMTPError{501, errors.New("Transaction unsuccessful")}
)

Well-defined errors

Functions

This section is empty.

Types

type Auth 

type Auth struct {
	Mechanisms map[string]AuthExtension
}

func NewAuth 

func NewAuth() *Auth

func (*Auth) EHLO 

func (a *Auth) EHLO() string

EHLO returns a stringified list of the installed Auth mechanisms

func (*Auth) Extend 

func (a *Auth) Extend(mechanism string, extension AuthExtension) error

Extend the auth handler by adding a new mechanism

func (*Auth) Handle 

func (a *Auth) Handle(c *Conn, args string) error

Handle authentication by handing off to one of the configured auth mechanisms

type AuthCramMd5 

type AuthCramMd5 struct {
	FindUser func(string) (AuthUser, error)
}

func (*AuthCramMd5) CheckResponse 

func (a *AuthCramMd5) CheckResponse(response string, challenge []byte) (AuthUser, bool)

Note: This is currently very weak & requires storing of the user's password in plaintext one good alternative is to do the HMAC manually and expose handlers for pre-processing the password MD5s

func (*AuthCramMd5) Handle 

func (a *AuthCramMd5) Handle(conn *Conn, params string) (AuthUser, error)

Handles the negotiation of an AUTH CRAM-MD5 request https://en.wikipedia.org/wiki/CRAM-MD5 http://www.samlogic.net/articles/smtp-commands-reference-auth.htm

type AuthExtension 

type AuthExtension interface {
	Handle(*Conn, string) (AuthUser, error)
}

http://tools.ietf.org/html/rfc4422#section-3.1 https://en.wikipedia.org/wiki/Simple_Authentication_and_Security_Layer

type AuthPlain 

type AuthPlain struct {
	Auth SimpleAuthFunc
}

func (*AuthPlain) Handle 

func (a *AuthPlain) Handle(conn *Conn, params string) (AuthUser, error)

Handles the negotiation of an AUTH PLAIN request

type AuthUser 

type AuthUser interface {
	IsUser(value string) bool
	Password() string
}

AuthUser should check if a given string identifies that user

type Conn 

type Conn struct {
	// Conn is primarily a wrapper around a net.Conn object
	net.Conn

	// Track some mutable for this connection
	IsTLS    bool
	Errors   []error
	User     AuthUser
	FromAddr *mail.Address
	ToAddr   []*mail.Address

	// Configuration options
	MaxSize      int64
	ReadTimeout  time.Duration
	WriteTimeout time.Duration
	// contains filtered or unexported fields
}

Conn is a wrapper for net.Conn that provides convenience handlers for SMTP requests

func (*Conn) EndTX 

func (c *Conn) EndTX() error

EndTX closes off a MAIL transaction and returns a message object

func (*Conn) ReadData 

func (c *Conn) ReadData() (string, error)

ReadData brokers the special case of SMTP data messages

func (*Conn) ReadLine 

func (c *Conn) ReadLine() (string, error)

ReadLine reads a single line from the client

func (*Conn) ReadSMTP 

func (c *Conn) ReadSMTP() (string, string, error)

ReadSMTP pulls a single SMTP command line (ending in a carriage return + newline)

func (*Conn) Reset 

func (c *Conn) Reset()

func (*Conn) StartTX 

func (c *Conn) StartTX(from *mail.Address) error

StartTX starts a new MAIL transaction

func (*Conn) WriteEHLO 

func (c *Conn) WriteEHLO(message string) error

WriteEHLO writes an EHLO line, see https://tools.ietf.org/html/rfc2821#section-4.1.1.1

func (*Conn) WriteOK 

func (c *Conn) WriteOK() error

WriteOK is a convenience function for sending the default OK response

func (*Conn) WriteSMTP 

func (c *Conn) WriteSMTP(code int, message string) error

WriteSMTP writes a general SMTP line

type Extension 

type Extension interface {
	Handle(*Conn, string) error
	EHLO() string
}

type Message 

type Message struct {
	To      []*mail.Address
	From    *mail.Address
	Header  mail.Header
	Subject string
	RawBody []byte
	Source  []byte

	// meta info
	Logger *log.Logger
	// contains filtered or unexported fields
}

Message is a nicely packaged representation of the recieved message

func NewMessage 

func NewMessage(data []byte, rcpt []*mail.Address, logger *log.Logger) (*Message, error)

NewMessage creates a Message from a data blob and a recipients list

func (*Message) Attachments 

func (m *Message) Attachments() ([]*Part, error)

Attachments returns the list of attachments on this message XXX: this assumes that the only mimetype supporting attachments is multipart/mixed need to review https://en.wikipedia.org/wiki/MIME#Multipart_messages to ensure that is the case

func (*Message) BCC 

func (m *Message) BCC() []*mail.Address

BCC returns a list of addresses this message should be

func (*Message) FindBody 

func (m *Message) FindBody(contentType string) ([]byte, error)

FindBody finds the first part of the message with the specified Content-Type

func (*Message) HTML 

func (m *Message) HTML() ([]byte, error)

HTML returns the text/html content of the message, if any

func (*Message) ID 

func (m *Message) ID() string

ID returns an identifier for this message, or generates one if none available using the masked string algorithm from https://stackoverflow.com/questions/22892120/how-to-generate-a-random-string-of-a-fixed-length-in-golang

func (*Message) Parts 

func (m *Message) Parts() ([]*Part, error)

Parts breaks a message body into its mime parts

func (*Message) Plain 

func (m *Message) Plain() ([]byte, error)

Plain returns the text/plain content of the message, if any

type MessageHandler 

type MessageHandler func(m *Message) error

MessageHandler functions handle application of business logic to the inbound message

type Part 

type Part struct {
	Header textproto.MIMEHeader

	Body     []byte
	Children []*Part
	// contains filtered or unexported fields
}

Part represents a single part of the message

type SMTPError 

type SMTPError struct {
	Code int
	Err  error
}

SMTPError is an error + SMTP response code

func NewError 

func NewError(code int, message string) SMTPError

NewError creates an SMTPError with the supplied code

func (SMTPError) Error 

func (a SMTPError) Error() string

Error pulls the base error value

type Server 

type Server struct {
	Name string

	TLSConfig  *tls.Config
	ServerName string

	// MaxSize of incoming message objects, zero for no cap otherwise
	// larger messages are thrown away
	MaxSize int64

	// MaxConn limits the number of concurrent connections being handled
	MaxConn int

	// MaxCommands is the maximum number of commands a server will accept
	// from a single client before terminating the session
	MaxCommands int

	// RateLimiter gets called before proceeding through to message handling
	// TODO: Implement
	RateLimiter func(*Conn) bool

	// Handler is the handoff function for messages
	Handler MessageHandler

	// Auth is an authentication-handling extension
	Auth Extension

	// Extensions is a map of server-specific extensions & overrides, by verb
	Extensions map[string]Extension

	// Disabled features
	Disabled map[string]bool

	// help message to display in response to a HELP request
	Help string

	// Logger to print out status info
	// TODO: implement better logging with configurable verbosity
	Logger *log.Logger

	Verbose bool

	// Timeout handlers
	ReadTimeout  time.Duration
	WriteTimeout time.Duration

	// Ready is a channel that will receive a single `true` when the server has started
	Ready chan bool
	// contains filtered or unexported fields
}

Server is an RFC2821/5321 compatible SMTP server

func NewServer 

func NewServer(handler func(*Message) error) *Server

NewServer creates a server with the default settings

func NewServerWithLogger 

func NewServerWithLogger(handler func(*Message) error, logger *log.Logger) *Server

NewServerWithLogger creates a server with a customer logger

func (*Server) Address 

func (s *Server) Address() string

Address retrieves the address of the server

func (*Server) Close 

func (s *Server) Close() error

Close the server connection

func (*Server) Disable 

func (s *Server) Disable(verbs ...string)

Disable server capabilities

func (*Server) Enable 

func (s *Server) Enable(verbs ...string)

Enable server capabilities that have previously been disabled

func (*Server) Extend 

func (s *Server) Extend(verb string, extension Extension) error

Extend the server to handle the supplied verb

func (*Server) GetAddressArg 

func (s *Server) GetAddressArg(argName string, args string) (*mail.Address, error)

GetAddressArg extracts the address value from a supplied SMTP argument for handling MAIL FROM:address@example.com and RCPT TO:address@example.com XXX: don't like this, feels like a hack

func (*Server) Greeting 

func (s *Server) Greeting(conn *Conn) string

Greeting is a humanized response to EHLO to precede the list of available commands

func (*Server) HandleSMTP 

func (s *Server) HandleSMTP(conn *Conn) error

HandleSMTP handles a single SMTP request

func (*Server) ListenAndServe 

func (s *Server) ListenAndServe(addr string) error

ListenAndServe starts listening for SMTP commands at the supplied TCP address

func (*Server) SetHelp 

func (s *Server) SetHelp(message string) error

SetHelp sets a help message

func (*Server) UseAuth 

func (s *Server) UseAuth(auth Extension)

UseAuth assigns the server authentication extension

func (*Server) UseTLS 

func (s *Server) UseTLS(cert, key string) error

UseTLS tries to enable TLS on the server (can also just explicitly set the TLSConfig)

type SimpleAuthFunc 

type SimpleAuthFunc func(string, string) (AuthUser, bool)

type SimpleExtension 

type SimpleExtension struct {
	Handler func(*Conn, string) error
	Ehlo    string
}

func (*SimpleExtension) EHLO 

func (s *SimpleExtension) EHLO() string

func (*SimpleExtension) Handle 

func (s *SimpleExtension) Handle(c *Conn, args string) error

Source Files

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