go-activesync

A Go implementation of Microsoft Exchange ActiveSync (EAS) — the mobile-mail sync protocol Outlook for iOS / the iPhone Mail app / etc. speak. Built and tested against Z-Push and SOGo, and protocol-compatible with anything that follows MS-ASCMD (including on-prem Exchange and Office 365).

The full protocol surface — every command in MS-ASCMD across protocol versions 12.0 / 12.1 / 14.0 / 14.1 / 16.0 / 16.1 — is implemented: folder hierarchy, mail (read + send + reply + forward + move + flag + delete), calendar (with recurrence + exceptions + the binary TimeZone blob), contacts, tasks, notes, GAL search, OOF, S/MIME, push notifications via Ping, the works. Stdlib + one third-party dependency (smallstep/pkcs7 for S/MIME).

Install

go get github.com/hstern/go-activesync/eas

Quick start

import (
    "context"
    "github.com/hstern/go-activesync/eas"
)

c, err := eas.NewClient(eas.Config{
    ServerURL: "https://mail.example.com/Microsoft-Server-ActiveSync",
    Username:  "henry",
    Password:  pw,                 // already pulled from your secret store
    DeviceID:  "32hexcharsofdeviceidhere00000000",
    State:     eas.NewMemoryState(),
})
if err != nil { return err }

ctx := context.Background()
_, _ = c.NegotiateVersion(ctx)     // pick the highest version both sides speak
if err := c.Provision(ctx); err != nil { return err }

folders, _ := c.FolderSync(ctx)
for _, f := range folders.Added {
    fmt.Println(f.Type, f.DisplayName, f.ServerID)
}

For the full API tour with diagrams (Provision handshake, Sync state machine, auth-scheme decision tree) and worked examples (S/MIME, calendar recurrence, structured search) see eas/README.md.

Packages

Package	Purpose	Deep dive
eas	EAS client: every MS-ASCMD command, all major auth schemes, durable state	eas/README.md
wbxml	WAP Binary XML codec, all 25 EAS code pages	wbxml/README.md
cmd/eas-autoprobe	One-shot read-only protocol probe; smoke-tests a deployment end-to-end	cmd/eas-autoprobe/README.md

The eas package is what you use; wbxml is the wire-format layer it's built on, exported in case you need to debug a frame, register a custom code page, or build a non-EAS WBXML client. eas-autoprobe is a CLI diagnostic — point it at any EAS endpoint and it reports per-command results.

What's implemented

Commands. Sync, SendMail, SmartReply, SmartForward, MoveItems, FolderSync/Create/Update/Delete, GetItemEstimate, MeetingResponse, Search, Find (16.x), ResolveRecipients, ValidateCert, ItemOperations (Fetch, Move, EmptyFolderContents, DocumentLibrary, FetchAttachment), Settings (DeviceInformation, OOF Get/Set, UserInformation, RightsManagementInformation, DevicePassword), Ping, Provision (with RemoteWipe acknowledgement), Autodiscover (HTTPS POST → HTTP redirect fallback → SRV lookup → well-known OPTIONS probe for SOGo-style deployments).

Authentication. HTTP Basic, OAuth Bearer (with RetryOn401 token-refresh hook), NTLM (via Azure/go-ntlmssp), Negotiate / SPNEGO (Kerberos via jcmturner/gokrb5/v8), and mTLS client certificates (consumer-side, via *tls.Config).

Protocol smoothings. Protocol-version negotiation, transparent 449 re-Provision retry (MS-ASPROV §3.1.5.2), Status=3 InvalidSyncKey reset-and-retry, gzip request/response transport, base64 URL encoding (MS-ASHTTP §2.2.1.1.2), Sync long-polling via Wait / HeartbeatInterval.

Higher-level helpers. Calendar recurrence + exceptions, EAS binary TimeZone blob round-trip, structured Search/Find query AST (And/Or/EqualTo/GreaterThan/LessThan), full Provision policy parsing, S/MIME signing + encryption.

Testing

go test ./...

Pure-Go, no fixtures needed, runs in seconds.

For end-to-end testing against a real EAS server, the eas package ships an integration suite gated on the integration build tag:

EAS_INTEGRATION_URL=https://your.server/Microsoft-Server-ActiveSync \
EAS_INTEGRATION_USER=you \
EAS_INTEGRATION_PASS=… \
go test -tags integration -v ./eas

A self-contained Z-Push test target lives in testenv/ (Docker; one container with Z-Push 2.7.6 + Dovecot + Postfix + Radicale, exercising email + calendar + contacts). One command stands it up:

cd testenv && make up && make test && make down

See testenv/README.md for the stack details and how to extend it.

CI

Every push runs lint (gofmt, go vet, go mod tidy cleanliness, govulncheck) and unit tests under the race detector with coverage. Pull requests + main pushes also bring up the Docker testenv and run the integration suite end-to-end. Total: about 3 minutes. See .github/workflows/ci.yml.

Coverage map

Concentric rings show package → file → function coverage; green is covered, red is not. Each segment is sized by line count, so the visual weight of the gaps tracks real risk. Click through for the underlying report.

Used by

If you're building on top of this library and want to be listed, open a PR adding yourself.

Contributing

PRs welcome — see CONTRIBUTING.md for setup, coding standards, and how to add a new EAS command. Bug reports use the issue templates; security disclosures are private — see SECURITY.md. Project participants agree to the Code of Conduct.

License

MIT — see LICENSE.