jordwest / imap-server

IMAP Server for golang

This project is no longer active

Check out this much more active and mature project instead:

https://github.com/emersion/go-imap

Go IMAP Server

Barebones IMAP4rev1 server for golang. Designed for integration into a backend app to provide email client access.

Features a simple API for implementing your own email storage by implementing golang interfaces. Currently a dummy (in-memory) storage is included, with plans to include MySQL storage. This would make it simple to integrate into a backend application to allow users to drag-drop emails into the application, without messing around with maildir.

Although it would be possible to implement and plug in a maildir storage interface, that would defeat the purpose of this project and there are much better, tried and tested open source and commercial solutions that have been around for a long time (Courier, Dovecot etc). The goal of this project is to provide simple IMAP access to some kind of existing system without the overhead of installing a full-blown IMAP/POP3 mail server.

NOT READY FOR PRODUCTION USE

Currently only plaintext authentication is implemented. This is really bad, don't use it in any kind of environment where actual passwords or sensitive emails exists. Actually don't use it anywhere.

Supported Commands

Command	Planned	Implemented	Tests
CAPABILITY	✓	✓	✓
NOOP	✓	✗	✗
LOGOUT	✓	✓	✓
AUTHENTICATE	✓	✓	✗
LOGIN	✓	✓	✗
STARTTLS	✓	✗	✗
EXAMINE	✓	✓	✗
CREATE	✓	✗	✗
DELETE	✓	✗	✗
RENAME	✓	✗	✗
SUBSCRIBE	✗	-	-
UNSUBSCRIBE	✗	-	-
LIST	✓	✓	✓
LSUB	✓	✓	✓
STATUS	✓	✓	✓
APPEND	✓	✓	✓
CHECK	?	✗	✗
CLOSE	✓	✓	✗
EXPUNGE	✓	✓	✓
SEARCH	✓	✗	✗
FETCH	✓	✓	✓
STORE	✓	✓	✓
COPY	✓	✓	✓
UID	✓	✓	✓

imap-server's Issues

Implement MySQL mailstore

Finish implementing DummyMailstore to provide full in-memory storage functionality

DummyMailstore currently returns fixed responses for some requests. It should be capable of storing emails in-memory. Currently some of this work is done, with a few sample emails stored in a slice. However functions like MessageSetBySequenceNumber still return hardcoded responses. DummyMailstore should be a full demonstration implementation of a mail storage.

Implement APPEND to allow clients to store emails

See RFC 3501 - 6.3.11

Recent flag should be unset after a SELECT command

A message is no longer considered 'Recent' after a mailbox has been selected the message has been fetched

Tidy up code to pass linting

Prevent data race between Listen() and Close()

The Go Race detector complains about a data race between Listen() and Close(). To illustrate, apply the following patch to create an example test case:

diff --git a/server_test.go b/server_test.go
index a242138..c50dd16 100644
--- a/server_test.go
+++ b/server_test.go
@@ -6,6 +6,7 @@ import (
        "os"
        "regexp"
        "testing"
+       "time"

        "github.com/jordwest/imap-server/conn"
        "github.com/jordwest/imap-server/mailstore"
@@ -288,3 +289,13 @@ func TestFetchFullMessageByUID(t *testing.T) {
        r.expect(t, " UID 11)")
        r.expect(t, "abcd.123 OK UID FETCH Completed")
 }
+
+func TestDataRace(t *testing.T) {
+       s := NewServer(mailstore.NewDummyMailstore())
+       s.Addr = "127.0.0.1:10143"
+       go func() {
+               s.ListenAndServe()
+       }()
+       time.Sleep(time.Millisecond)
+       s.Close()
+}

Then run go test -race -run=DataRace. The race detector should dump something like the following: (edited for readability)

==================
WARNING: DATA RACE
Read by goroutine 5:
  github.com/jordwest/imap-server.(*Server).Close()
      …/src/github.com/jordwest/imap-server/server.go:83 +0xcf
  github.com/jordwest/imap-server.TestDataRace()
      …/src/github.com/jordwest/imap-server/server_test.go:300 +0x2cd
…

Previous write by goroutine 6:
  github.com/jordwest/imap-server.(*Server).Listen()
      …/src/github.com/jordwest/imap-server/server.go:55 +0x481
  github.com/jordwest/imap-server.(*Server).ListenAndServe()
      …/src/github.com/jordwest/imap-server/server.go:36 +0x47
…
==================
==================
WARNING: DATA RACE
Read by goroutine 5:
  net.(*TCPListener).Close()
      …/go-1.4.2/src/net/tcpsock_posix.go:254 +0x4f
  github.com/jordwest/imap-server.(*Server).Close()
      …/src/github.com/jordwest/imap-server/server.go:86 +0x229
…

Previous write by goroutine 6:
  net.ListenTCP()
      …/go-1.4.2/src/net/tcpsock_posix.go:298 +0x4aa
  net.Listen()
      …/go-1.4.2/src/net/dial.go:266 +0x559
  github.com/jordwest/imap-server.(*Server).Listen()
      …/src/github.com/jordwest/imap-server/server.go:50 +0x307
  github.com/jordwest/imap-server.(*Server).ListenAndServe()
      …/src/github.com/jordwest/imap-server/server.go:36 +0x47
…
==================

As this project is young and there are many ways to address this (RWMutex, signaling over chans, etc), I am not submitting a pull request.

This is also not a critical race, since it happens on shutdown, but it does clutter the output of go test -race, which makes it harder to sort out application races.

Thanks again!

Implement `EXPUNGE` command

Expunge should permanently delete all messages marked with the flag \Deleted

Remove remaining hardcoded test responses

Check for any remaining hardcoded responses which should be using Mailstore interface

Command not understood should return the request ID

The current response to an unsupported command is:

C: 10 uid copy 10:11,13 "Trash"
S: * BAD Command not understood

It should be

C: 10 uid copy 10:11,13 "Trash"
S: 10 BAD Command not understood

Switch to using proper testing framework

Test code is starting to get messy, look into switching to Ginkgo or similar

Implement `COPY` command

From the RFC:

Arguments: sequence set, mailbox name
Responses: no specific responses for this command
Result:
OK - copy completed
NO - copy error: can't copy those messages or to that name
BAD - command unknown or arguments invalid

The COPY command copies the specified message(s) to the end of the specified destination mailbox. The flags and internal date of the message(s) SHOULD be preserved, and the Recent flag SHOULD be set,
in the copy.

If the destination mailbox does not exist, a server SHOULD return an error. It SHOULD NOT automatically create the mailbox. Unless it is certain that the destination mailbox can not be created, the server MUST send the response code "[TRYCREATE]" as the prefix of the text of the tagged NO response. This gives a hint to the client that it can attempt a CREATE command and retry the COPY if the CREATE is successful.

If the COPY command is unsuccessful for any reason, server implementations MUST restore the destination mailbox to its state before the COPY attempt.

Example: C: A003 COPY 2:4 MEETING
S: A003 OK COPY completed

Proposal
Flags, headers and body of the message except the UID and sequence numbers MUST be preserved. The UID MUST change to the latest unassigned value for the given mailbox and sequence number will also have the latest value. The server MUST NOT automatically create the target mailbox.

Support `BODYSTRUCTURE` in `FETCH`

Request Example:
UID FETCH 20 (BODY.PEEK[] BODYSTRUCTURE)

Get tests working again after refactor

Refactoring code into packages (#9, #10) has broken the tests

Implement STORE command

Finish implementing STORE for updating a message's flags

Refactor commands into sub-package

all commands_*.go files should go in a sub folder/package

All sequence numbers and UIDs should be uint32

The RFC specifies that UIDs and sequence numbers are unsigned 32 bit integers

Specs of example conversations with particular clients

Some mail clients do unusual things - eg Apple mail uses it's own flags which are currently not recognised by the server.

Create test specs of sample conversations for various mail clients based on observed conversations.

• Apple Mail
• Thunderbird
• MS Outlook
• Gmail

Project Status

Are you planning on adding other features like the mail store? or have you stopped working on the project?

Implement STARTTLS

This would reduce the impact of PLAIN-only authentication a bit.

Possible approach that I took in my toy server:

cert, err := tls.LoadX509KeyPair("/tmp/goimapd.crt", "/tmp/goimapd.key")
if err != nil {
  fmt.Printf("loadkeys: %s\n", err)
  textconn.PrintfLine("%s BAD Sorry, server-side problem loading certs.", tag, cmd)
  return
}
tlsconfig := &tls.Config{
  Certificates: []tls.Certificate{cert},
}

textconn.PrintfLine("%s OK STARTTLS commencing.", tag)
conn = tls.Server(conn, tlsconfig)
textconn = textproto.NewConn(conn)

It looks like a similar approach could be implemented in imap-server, too: the STARTTLS command could replace c.Rwc with an instance of tls.Server.

Refactor mailstore into sub package

Server should notify client of any updates during a `NOOP` command

A NOOP command from the client currently does not do anything. However a NOOP should trigger the server to check the mailbox for new messages and notify the client using EXISTS etc.

Support non system flags

STORE command is not recognised when Apple Mail tries to store it's own user defined flags, partly because of a $ character in the flag name.

Should support storage of user-defined flags if the Mailstore implementor chooses to.

Separate IMAP commands into separate files

commands.go is getting unwieldy, should separate commands or at least command groups out into separate source files

Implement `CHECK` command

A CHECK should be the same as a NOOP, but also call a function on the Mailstore to prompt it to do any cleanup, refreshing, re-caching etc. as required

Automate testing and build process

Restarting server and running tests manually during development is tedious, set up fswatch for re-running tests and restarting server

• Watch for changes, rerun go test
• Watch for changes, build and restart demo server

Interpret IMAP message ID ranges and request the relevant messages

Create a MessageRangeSpecifier type which handles numeric identification of messages and distinguishes between single messages (UID 5, or 2), ranges of messages (UID 3:10, 15:17), or unbounded ranges (UID 6:*)

Create helper function that interprets the message UID/sequence number range and calls the relevant function on the Mailbox interface, returning the list of Messages.

Panic due to empty DummyMessage when non existent sequence set requested

cmdFetch expected literal parens around final argument to FETCH

When mutt attempts to fetch the body of a message, the client sends:

C: a0006 UID FETCH 10 BODY.PEEK[]

Which doesn't match the pattern in conn/commands.go:

    registerCommand("((?i)UID )?(?i:FETCH) ("+sequenceSet+") \\(([A-z0-9\\s\\(\\)\\[\\]\\.-]+)\\)", cmdFetch)

Do you have a client that has explicit parens around the 'BODY.PEEK[]' part? I'm not seeing anything to that effect in http://tools.ietf.org/html/rfc3501#section-6.4.5

PS, you may want to check out string literals specified with backticks instead of double-quotes when writing regexps. It saves on some of the backslash escaping.