policy: Implement recipient domain policy for #51

- INBUCKET_SMTP_DEFAULTACCEPT
- INBUCKET_SMTP_ACCEPTDOMAINS
- INBUCKET_SMTP_REJECTDOMAINS

doc/config.md

@@ -15,6 +15,9 @@ variables it supports:
     INBUCKET_SMTP_MAXRECIPIENTS         200                 Maximum RCPT TO per message
     INBUCKET_SMTP_MAXMESSAGEBYTES       10240000            Maximum message size
     INBUCKET_SMTP_STOREMESSAGES         true                Store incoming mail?
+    INBUCKET_SMTP_DEFAULTACCEPT         true                Accept all mail by default?
+    INBUCKET_SMTP_ACCEPTDOMAINS                             Domains to accept mail for
+    INBUCKET_SMTP_REJECTDOMAINS                             Domains to reject mail for
     INBUCKET_SMTP_TIMEOUT               300s                Idle network timeout
     INBUCKET_POP3_ADDR                  0.0.0.0:1100        POP3 server IP4 host:port
     INBUCKET_POP3_DOMAIN                inbucket            HELLO domain
@@ -116,6 +119,39 @@ solar system.
 - Default: `true`
 - Values: `true` or `false`
 
+### Default Recipient Accept Policy
+
+`INBUCKET_SMTP_DEFAULTACCEPT`
+
+If true, Inbucket will accept mail to any domain unless present in the reject
+domains list.  If false, recipients will be rejected unless their domain is
+present in the accept domains list.
+
+- Default: `true`
+- Values: `true` or `false`
+
+### Accepted Recipient Domain List
+
+`INBUCKET_SMTP_ACCEPTDOMAINS`
+
+List of domains to accept mail for when `INBUCKET_SMTP_DEFAULTACCEPT` is false;
+has no effect when true.
+
+- Default: None
+- Values: Comma separated list of domains
+- Example: `localhost,mysite.org`
+
+### Rejected Recipient Domain List
+
+`INBUCKET_SMTP_REJECTDOMAINS`
+
+List of domains to reject mail for when `INBUCKET_SMTP_DEFAULTACCEPT` is true;
+has no effect when false.
+
+- Default: None
+- Values: Comma separated list of domains
+- Example: `reject.com,gmail.com`
+
 ### Network Idle Timeout
 
 `INBUCKET_SMTP_TIMEOUT`

pkg/config/config.go

@@ -7,6 +7,7 @@ import (
 	"text/tabwriter"
 	"time"
 
+	"github.com/jhillyerd/inbucket/pkg/stringutil"
 	"github.com/kelseyhightower/envconfig"
 )
 
@@ -45,6 +46,9 @@ type SMTP struct {
 	MaxRecipients   int           `required:"true" default:"200" desc:"Maximum RCPT TO per message"`
 	MaxMessageBytes int           `required:"true" default:"10240000" desc:"Maximum message size"`
 	StoreMessages   bool          `required:"true" default:"true" desc:"Store incoming mail?"`
+	DefaultAccept   bool          `required:"true" default:"true" desc:"Accept all mail by default?"`
+	AcceptDomains   []string      `desc:"Domains to accept mail for"`
+	RejectDomains   []string      `desc:"Domains to reject mail for"`
 	Timeout         time.Duration `required:"true" default:"300s" desc:"Idle network timeout"`
 	Debug           bool          `ignored:"true"`
 }
@@ -83,6 +87,8 @@ func Process() (*Root, error) {
 	c := &Root{}
 	err := envconfig.Process(prefix, c)
 	c.SMTP.DomainNoStore = strings.ToLower(c.SMTP.DomainNoStore)
+	stringutil.SliceToLower(c.SMTP.AcceptDomains)
+	stringutil.SliceToLower(c.SMTP.RejectDomains)
 	return c, err
 }
 

pkg/policy/address.go

@@ -7,6 +7,7 @@ import (
 	"strings"
 
 	"github.com/jhillyerd/inbucket/pkg/config"
+	"github.com/jhillyerd/inbucket/pkg/stringutil"
 )
 
 // Addressing handles email address policy.
@@ -29,14 +30,26 @@ func (a *Addressing) NewRecipient(address string) (*Recipient, error) {
 		return nil, err
 	}
 	return &Recipient{
-		Address:   *ar,
-		apolicy:   a,
-		LocalPart: local,
-		Domain:    domain,
-		Mailbox:   mailbox,
+		Address:    *ar,
+		addrPolicy: a,
+		LocalPart:  local,
+		Domain:     domain,
+		Mailbox:    mailbox,
 	}, nil
 }
 
+// ShouldAcceptDomain indicates if Inbucket accepts mail destined for the specified domain.
+func (a *Addressing) ShouldAcceptDomain(domain string) bool {
+	domain = strings.ToLower(domain)
+	if a.Config.DefaultAccept && !stringutil.SliceContains(a.Config.RejectDomains, domain) {
+		return true
+	}
+	if !a.Config.DefaultAccept && stringutil.SliceContains(a.Config.AcceptDomains, domain) {
+		return true
+	}
+	return false
+}
+
 // ShouldStoreDomain indicates if Inbucket stores email destined for the specified domain.
 func (a *Addressing) ShouldStoreDomain(domain string) bool {
 	if a.Config.StoreMessages {

pkg/policy/address_test.go

@@ -8,6 +8,59 @@ import (
 	"github.com/jhillyerd/inbucket/pkg/policy"
 )
 
+func TestShouldAcceptDomain(t *testing.T) {
+	// Test with default accept.
+	ap := &policy.Addressing{
+		Config: config.SMTP{
+			DefaultAccept: true,
+			RejectDomains: []string{"a.deny.com", "deny.com"},
+		},
+	}
+	testCases := []struct {
+		domain string
+		want   bool
+	}{
+		{domain: "bar.com", want: true},
+		{domain: "DENY.com", want: false},
+		{domain: "a.deny.com", want: false},
+		{domain: "b.deny.com", want: true},
+	}
+	for _, tc := range testCases {
+		t.Run(tc.domain, func(t *testing.T) {
+			got := ap.ShouldAcceptDomain(tc.domain)
+			if got != tc.want {
+				t.Errorf("Got %v for %q, want: %v", got, tc.domain, tc.want)
+			}
+
+		})
+	}
+	// Test with default reject.
+	ap = &policy.Addressing{
+		Config: config.SMTP{
+			DefaultAccept: false,
+			AcceptDomains: []string{"a.allow.com", "allow.com"},
+		},
+	}
+	testCases = []struct {
+		domain string
+		want   bool
+	}{
+		{domain: "bar.com", want: false},
+		{domain: "ALLOW.com", want: true},
+		{domain: "a.allow.com", want: true},
+		{domain: "b.allow.com", want: false},
+	}
+	for _, tc := range testCases {
+		t.Run(tc.domain, func(t *testing.T) {
+			got := ap.ShouldAcceptDomain(tc.domain)
+			if got != tc.want {
+				t.Errorf("Got %v for %q, want: %v", got, tc.domain, tc.want)
+			}
+
+		})
+	}
+}
+
 func TestShouldStoreDomain(t *testing.T) {
 	// Test with storage enabled.
 	ap := &policy.Addressing{

pkg/policy/recipient.go

@@ -5,7 +5,7 @@ import "net/mail"
 // Recipient represents a potential email recipient, allows policies for it to be queried.
 type Recipient struct {
 	mail.Address
-	apolicy *Addressing
+	addrPolicy *Addressing
 	// LocalPart is the part of the address before @, including +extension.
 	LocalPart string
 	// Domain is the part of the address after @.
@@ -16,10 +16,10 @@ type Recipient struct {
 
 // ShouldAccept returns true if Inbucket should accept mail for this recipient.
 func (r *Recipient) ShouldAccept() bool {
-	return true
+	return r.addrPolicy.ShouldAcceptDomain(r.Domain)
 }
 
 // ShouldStore returns true if Inbucket should store mail for this recipient.
 func (r *Recipient) ShouldStore() bool {
-	return r.apolicy.ShouldStoreDomain(r.Domain)
+	return r.addrPolicy.ShouldStoreDomain(r.Domain)
 }

pkg/server/smtp/handler.go

@@ -329,6 +329,11 @@ func (s *Session) mailHandler(cmd string, arg string) {
 			s.logger.Warn().Msgf("Bad address as RCPT arg: %q, %s", addr, err)
 			return
 		}
+		if !recip.ShouldAccept() {
+			s.logger.Warn().Str("addr", addr).Msg("Rejecting recipient")
+			s.send("550 Relay not permitted")
+			return
+		}
 		if len(s.recipients) >= s.config.MaxRecipients {
 			s.logger.Warn().Msgf("Maximum limit of %v recipients reached",
 				s.config.MaxRecipients)

pkg/server/smtp/handler_test.go

@@ -169,6 +169,7 @@ func TestMailState(t *testing.T) {
 		{"RCPT TO:<u1@gmail.com>", 250},
 		{"RCPT TO: <u2@gmail.com>", 250},
 		{"RCPT TO:u3@gmail.com", 250},
+		{"RCPT TO:u3@deny.com", 550},
 		{"RCPT TO: u4@gmail.com", 250},
 		{"RSET", 250},
 		{"MAIL FROM:<john@gmail.com>", 250},
@@ -366,9 +367,11 @@ func setupSMTPServer(ds storage.Store) (s *Server, buf *bytes.Buffer, teardown f
 		Domain:          "inbucket.local",
 		DomainNoStore:   "bitbucket.local",
 		MaxRecipients:   5,
-		Timeout:         5,
 		MaxMessageBytes: 5000,
 		StoreMessages:   true,
+		DefaultAccept:   true,
+		RejectDomains:   []string{"deny.com"},
+		Timeout:         5,
 	}
 
 	// Capture log output

pkg/stringutil/utils.go

@@ -5,6 +5,7 @@ import (
 	"fmt"
 	"io"
 	"net/mail"
+	"strings"
 )
 
 // HashMailboxName accepts a mailbox name and hashes it.  filestore uses this as
@@ -28,3 +29,20 @@ func StringAddressList(addrs []*mail.Address) []string {
 	}
 	return s
 }
+
+// SliceContains returns true if s is present in slice.
+func SliceContains(slice []string, s string) bool {
+	for _, v := range slice {
+		if s == v {
+			return true
+		}
+	}
+	return false
+}
+
+// SliceToLower lowercases the contents of slice of strings.
+func SliceToLower(slice []string) {
+	for i, s := range slice {
+		slice[i] = strings.ToLower(s)
+	}
+}