1 package mailmux
2 
3 import (
4 	"encoding/json"
5 	"errors"
6 	"io"
7 	"time"
8 )
9 
10 const (
11 	Tregister = 1 + iota
12 	Rregister
13 	Rerror
14 	Tcreate
15 	Rcreate
16 	Tlist
17 	Rlist
18 	Tremove
19 	Rremove
20 	Tauth
21 	Rauth
22 )
23 
24 // Mcall represents a message passed between mailmux clients and servers.
25 // Operations requested by clients are T-messages (such as Tregister).
26 // Servers respond with the corresponding R-message (such as Rregister).
27 // Servers may instead respond with Rerror to inform the client, with a diagnostic message,
28 // that the request was not completed successfully.
29 // This design is loosely based on the Plan 9 network file protocol 9P.
30 type Mcall struct {
31 	Type     uint
32 	Username string    `json:",omitempty"` // Tregister, Rregister
33 	Password string    `json:",omitempty"` // Tregister
34 	Error    string    `json:",omitempty"` // Rerror
35 	Aliases  []Alias   `json:",omitempty"` // Rnew, Rlist, Tremove
36 	Expiry   time.Time `json:",omitempty"` // Tcreate, Rnew
37 }
38 
39 // ParseMcall parses and validates a JSON-encoded Mcall from r.
40 func ParseMcall(r io.Reader) (*Mcall, error) {
41 	var mc Mcall
42 	if err := json.NewDecoder(r).Decode(&mc); err != nil {
43 		return nil, err
44 	}
45 	switch mc.Type {
46 	case Rerror:
47 		if mc.Error == "" {
48 			return nil, errors.New("empty error message")
49 		}
50 	case Tauth:
51 		if mc.Username == "" {
52 			return nil, errors.New("empty username")
53 		}
54 		if mc.Password == "" {
55 			return nil, errors.New("empty password")
56 		}
57 	case Tregister, Tcreate, Tlist, Tremove:
58 		// check required params
59 	}
60 	return &mc, nil
61 }
62 
63 func writeMcall(w io.Writer, mcall *Mcall) error {
64 	return json.NewEncoder(w).Encode(mcall)
65 }
66 
67 // rerror writes a JSON-encoded Rerror message to the underlying writer
68 // with its Error field set to errormsg.
69 func rerror(w io.Writer, errormsg string) error {
70 	rmsg := &Mcall{Type: Rerror, Error: errormsg}
71 	return writeMcall(w, rmsg)
72 }