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Merge pull request #2 from d--j/mailfilter
feat: introduce mail filter abstraction
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@@ -6,81 +6,81 @@ | |
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| A Go library to write mail filters. | ||
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| With this library you can write both the client (MTA/SMTP-Server) and server (milter filter) | ||
| in pure Go without sendmail's libmilter. | ||
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| ## Features | ||
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| * With this library you can write both the client (MTA/SMTP-Server) and server (milter filter) | ||
| in pure Go without sendmail's libmilter. | ||
| * Easy wrapper of the milter protocol that abstracts away many milter protocol quirks | ||
| and lets you write mail filters with little effort. | ||
| * UTF-8 support | ||
| * IDNA support | ||
| * Client & Server support milter protocol version 6 with all features. E.g.: | ||
| * all milter events including DATA, UNKNOWN, ABORT and QUIT NEW CONNECTION | ||
| * milter can skip e.g. body chunks when it does not need all chunks | ||
| * milter can send progress notifications when response can take some time | ||
| * milter can automatically instruct the MTA which macros it needs. | ||
| * UTF-8 support | ||
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| ## Installation | ||
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| ```shell | ||
| go get -u github.com/d--j/go-milter | ||
| ``` | ||
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| ## Usage | ||
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| The following example is a milter filter that adds `[⚠️EXTERNAL] ` to the subject of all messages of unauthenticated users. | ||
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| See [GoDoc](https://godoc.org/github.com/d--j/go-milter/mailfilter) for more documentation and an example for a milter client or a raw milter server. | ||
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| ```go | ||
| package main | ||
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| import ( | ||
| "log" | ||
| "net" | ||
| "sync" | ||
| "context" | ||
| "flag" | ||
| "log" | ||
| "strings" | ||
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| "github.com/d--j/go-milter" | ||
| "github.com/d--j/go-milter/mailfilter" | ||
| ) | ||
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| type ExampleBackend struct { | ||
| milter.NoOpMilter | ||
| } | ||
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| func (b *ExampleBackend) RcptTo(rcptTo string, esmtpArgs string, m *milter.Modifier) (*milter.Response, error) { | ||
| // reject the mail when it goes to [email protected] and is a local delivery | ||
| if rcptTo == "[email protected]" && m.Macros.Get(milter.MacroRcptMailer) == "local" { | ||
| return milter.RejectWithCodeAndReason(550, "We do not like you\r\nvery much, please go away") | ||
| } | ||
| return milter.RespContinue, nil | ||
| } | ||
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| func main() { | ||
| // create socket to listen on | ||
| socket, err := net.Listen("tcp4", "127.0.0.1:6785") | ||
| if err != nil { | ||
| log.Fatal(err) | ||
| } | ||
| defer socket.Close() | ||
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| // define the backend, required actions, protocol options and macros we want | ||
| server := milter.NewServer( | ||
| milter.WithMilter(func() milter.Milter { | ||
| return &ExampleBackend{} | ||
| }), | ||
| milter.WithProtocol(milter.OptNoConnect|milter.OptNoHelo|milter.OptNoMailFrom|milter.OptNoBody|milter.OptNoHeaders|milter.OptNoEOH|milter.OptNoUnknown|milter.OptNoData), | ||
| milter.WithAction(milter.OptChangeFrom|milter.OptAddRcpt|milter.OptRemoveRcpt), | ||
| milter.WithMaroRequest(milter.StageRcpt, []milter.MacroName{milter.MacroRcptMailer}), | ||
| ) | ||
| defer server.Close() | ||
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| // start the milter | ||
| var wgDone sync.WaitGroup | ||
| wgDone.Add(1) | ||
| go func(socket net.Listener) { | ||
| if err := server.Serve(socket); err != nil { | ||
| log.Fatal(err) | ||
| } | ||
| wgDone.Done() | ||
| }(socket) | ||
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| log.Printf("Started milter on %s:%s", socket.Addr().Network(), socket.Addr().String()) | ||
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| // quit when milter quits | ||
| wgDone.Wait() | ||
| // parse commandline arguments | ||
| var protocol, address string | ||
| flag.StringVar(&protocol, "proto", "tcp", "Protocol family (unix or tcp)") | ||
| flag.StringVar(&address, "addr", "127.0.0.1:10003", "Bind to address or unix domain socket") | ||
| flag.Parse() | ||
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| // create and start the mail filter | ||
| mailFilter, err := mailfilter.New(protocol, address, | ||
| func(_ context.Context, trx *mailfilter.Transaction) (mailfilter.Decision, error) { | ||
| // Reject message when it was sent to our SPAM trap | ||
| if trx.HasRcptTo("spam-trap@スパム.example.com") { | ||
| return mailfilter.CustomErrorResponse(550, "5.7.1 No thank you"), nil | ||
| } | ||
| // Prefix subject with [⚠️EXTERNAL] when user is not logged in | ||
| if trx.MailFrom.AuthenticatedUser() == "" { | ||
| subject, _ := trx.Headers.Subject() | ||
| if !strings.HasPrefix(subject, "[⚠️EXTERNAL] ") { | ||
| subject = "[⚠️EXTERNAL] " + subject | ||
| } | ||
| trx.Headers.SetSubject(subject) | ||
| } | ||
| return mailfilter.Accept, nil | ||
| }, | ||
| // optimization: we do not need the body of the message for our decision | ||
| mailfilter.WithoutBody(), | ||
| ) | ||
| if err != nil { | ||
| log.Fatal(err) | ||
| } | ||
| log.Printf("Started milter on %s:%s", mailFilter.Addr().Network(), mailFilter.Addr().String()) | ||
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| // wait for the mail filter to end | ||
| mailFilter.Wait() | ||
| } | ||
| ``` | ||
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| See [](https://godoc.org/github.com/d--j/go-milter) for more documentation and an example for a milter client. | ||
|
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| ## License | ||
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| BSD 2-Clause | ||
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,131 @@ | ||
| package mailfilter | ||
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| import ( | ||
| "strings" | ||
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| "golang.org/x/net/idna" | ||
| ) | ||
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| // split an user@domain address into user and domain. | ||
| // Includes the input address as third array element to quickly check if splitting must be re-done | ||
| func split(addr string) []string { | ||
| at := strings.LastIndex(addr, "@") | ||
| if at < 0 { | ||
| return []string{addr, "", addr} | ||
| } | ||
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| return []string{addr[:at], addr[at+1:], addr} | ||
| } | ||
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| type addr struct { | ||
| Addr string | ||
| Args string | ||
| parts []string | ||
| asciiDomain string | ||
| unicodeDomain string | ||
| } | ||
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| func (a *addr) initParts() { | ||
| if len(a.parts) != 3 || a.parts[2] != a.Addr { | ||
| a.parts = split(a.Addr) | ||
| a.asciiDomain = "" | ||
| a.unicodeDomain = "" | ||
| } | ||
| } | ||
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| func (a *addr) Local() string { | ||
| a.initParts() | ||
| return a.parts[0] | ||
| } | ||
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| func (a *addr) Domain() string { | ||
| a.initParts() | ||
| return a.parts[1] | ||
| } | ||
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| func (a *addr) AsciiDomain() string { | ||
| domain := a.Domain() | ||
| if domain == "" { | ||
| return "" | ||
| } | ||
| if a.asciiDomain != "" { | ||
| return a.asciiDomain | ||
| } | ||
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| asciiDomain, err := idna.Lookup.ToASCII(domain) | ||
| if err != nil { | ||
| a.asciiDomain = domain | ||
| return domain | ||
| } | ||
| a.asciiDomain = asciiDomain | ||
| return asciiDomain | ||
| } | ||
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| func (a *addr) UnicodeDomain() string { | ||
| domain := a.Domain() | ||
| if domain == "" { | ||
| return "" | ||
| } | ||
| if a.unicodeDomain != "" { | ||
| return a.unicodeDomain | ||
| } | ||
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| unicodeDomain, err := idna.Lookup.ToUnicode(domain) | ||
| if err != nil { | ||
| a.unicodeDomain = domain | ||
| return domain | ||
| } | ||
| a.unicodeDomain = unicodeDomain | ||
| return unicodeDomain | ||
| } | ||
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| type MailFrom struct { | ||
| addr | ||
| transport string | ||
| authenticatedUser string | ||
| authenticationMethod string | ||
| } | ||
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| func (m *MailFrom) Transport() string { | ||
| return m.transport | ||
| } | ||
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| func (m *MailFrom) AuthenticatedUser() string { | ||
| return m.authenticatedUser | ||
| } | ||
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| func (m *MailFrom) AuthenticationMethod() string { | ||
| return m.authenticationMethod | ||
| } | ||
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| type RcptTo struct { | ||
| addr | ||
| transport string | ||
| } | ||
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| func (r *RcptTo) Transport() string { | ||
| return r.transport | ||
| } | ||
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| func calculateRcptToDiff(orig []RcptTo, changed []RcptTo) (deletions []RcptTo, additions []RcptTo) { | ||
| foundOrig := make(map[string]*RcptTo) | ||
| foundChanged := make(map[string]bool) | ||
| for _, r := range orig { | ||
| foundOrig[r.Addr] = &r | ||
| } | ||
| for _, r := range changed { | ||
| if o := foundOrig[r.Addr]; o == nil && !foundChanged[r.Addr] { | ||
| additions = append(additions, r) | ||
| } else if o != nil && o.Args != r.Args && !foundChanged[r.Addr] { | ||
| deletions = append(deletions, *o) | ||
| additions = append(additions, r) | ||
| } | ||
| foundChanged[r.Addr] = true | ||
| } | ||
| for _, r := range orig { | ||
| if !foundChanged[r.Addr] { | ||
| deletions = append(deletions, r) | ||
| } | ||
| } | ||
| return | ||
| } |
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