go-activesync

A pure-Go client library for the Microsoft Exchange ActiveSync (EAS) protocol, version 14.1.

The library is built spec-first (TDD): every requirement of the underlying Microsoft Open Specifications is backed by a concrete test before any implementation lands. See docs/spec-coverage.md for the traceability matrix.

---

Quick examples

Discover the EAS endpoint and provision a device

import (
    "context"
    "net/http"

    "github.com/remdev/go-activesync/autodiscover"
    "github.com/remdev/go-activesync/client"
)

ctx := context.Background()

ad, err := autodiscover.New(http.DefaultClient).Discover(ctx, "user@example.com",
    &autodiscover.Credentials{Username: "user@example.com", Password: "pass"})
if err != nil { /* handle */ }

c, _ := client.New(client.Config{
    BaseURL:    ad.URL,
    Auth:       &client.BasicAuth{Username: "user@example.com", Password: "pass"},
    DeviceID:   "stable-device-id",
    DeviceType: "SmartPhone",
    UserAgent:  "my-app/1.0",
})

if _, err := c.Provision(ctx, "user@example.com"); err != nil { /* handle */ }

Sync new e-mails from the inbox

import (
    "log"

    "github.com/remdev/go-activesync/client"
    "github.com/remdev/go-activesync/eas"
)

initial, _ := c.Sync(ctx, user, &eas.SyncRequest{
    Collections: eas.SyncCollections{
        Collection: []eas.SyncCollection{{SyncKey: "0", CollectionID: inboxID}},
    },
})
syncKey := initial.Collections.Collection[0].SyncKey

resp, _ := client.SyncTyped[eas.Email](ctx, c, user, &eas.SyncRequest{
    Collections: eas.SyncCollections{
        Collection: []eas.SyncCollection{{
            SyncKey:      syncKey,
            CollectionID: inboxID,
            GetChanges:   1,
            WindowSize:   25,
        }},
    },
})

for _, col := range resp.Collections {
    for _, add := range col.Add {
        if add.ApplicationData == nil {
            continue
        }
        log.Printf("new mail %s: %s", add.ServerID, add.ApplicationData.Subject)
    }
}

For mixed-class collections, call c.Sync directly and use the SyncAdd.Email() / Appointment() / Contact() / Task() helpers, or project a single collection with eas.NewTypedSyncResponse[T].

Long-poll for changes with Ping

resp, _ := c.Ping(ctx, user, &eas.PingRequest{
    HeartbeatInterval: 480,
    Folders: eas.PingFolders{
        Folder: []eas.PingFolder{{ID: inboxID, Class: "Email"}},
    },
})
if eas.PingHasChanges(resp.Status) {
    // pull the changed folders with Sync
}

Runnable end-to-end programs live under examples/: login, inbox-sync, calendar-sync, ping.

---

Install

go get github.com/remdev/go-activesync@latest

Requires Go 1.26 or newer.

---

Status (v0.x)

Implemented and covered by the test suite:

Area	Detail
Transport	MS-ASHTTP — base64-encoded query, plain query fallback, mandatory headers
Codec	MS-ASWBXML — WBXML 1.3 encoder/decoder, all 25 EAS 14.1 code pages
Reflection	wbxml.Marshal / wbxml.Unmarshal driven by wbxml:"Page.Tag" tags
Autodiscover	MS-OXDISCO + MS-ASAB POX (mobilesync schema, SRV fallback, redirects)
Auth	HTTP Basic; pluggable Authenticator interface
Provisioning	Two-pass MS-ASPROV with auto re-provision on Status 142/143
Commands	Provision, FolderSync, Sync, Ping
Typed Sync	client.SyncTyped[T], eas.UnmarshalApplicationData[T], four helpers
PIM data models	MS-ASEMAIL, MS-ASCAL, MS-ASCNTC, MS-ASTASK
Stores	In-memory PolicyStore and SyncStateStore; pluggable interfaces
Hardening	Bounded decoder allocations + FuzzDecode over the WBXML reader

---

Roadmap

Out of scope for v0.x; tracked for future releases.

• Commands: SendMail, SmartReply, SmartForward, MeetingResponse, MoveItems, ItemOperations (Fetch/EmptyFolderContents), GetItemEstimate, Search, ResolveRecipients, ValidateCert, Settings, ResolveRecipients, Find.
• Protocol versions: negotiation of EAS 12.1, 14.0, 16.0, 16.1 in addition to the current hard-coded 14.1.
• Code pages: per-version code-page selection (the current set is pinned to 14.1).
• Auth: OAuth 2.0 bearer (Microsoft 365 / EWS-style), client-certificate / mutual-TLS authenticator, NTLM/Negotiate.
• Body: MIME body type round-tripping, BodyPartPreference + Rights Management (MS-ASRM).
• Search & Document Library: GAL Search, MS-ASDOC document fetch.
• Notes class: typed MS-ASNOTE model.
• Persistence: SQLite/Bolt-backed PolicyStore and SyncStateStore alongside the in-memory implementations.
• Server side: there is no server skeleton; this is purely a client library.
• Observability: structured logging hooks, OpenTelemetry spans on command boundaries.

---

Repository layout

wbxml/             WBXML 1.3 codec + EAS code page tables, fuzz harness
eas/               typed request/response/domain models (one file per spec)
autodiscover/      POX Autodiscover client
client/            high-level EAS client (transport, auth, command methods, stores)
examples/          runnable demos (login, inbox-sync, calendar-sync, ping)
internal/spec/     traceability-matrix linter + coverage gate tool
docs/              spec-coverage.md and other design notes

---

Development

make test       # go test -race ./...
make vet        # go vet ./...
make lint       # golangci-lint run ./...   (auto-installs golangci-lint if absent)
make lint-fix   # golangci-lint run --fix
make spec-lint  # verify the traceability matrix is fully covered
make cover      # go test -race -coverprofile=cover.out
make cover-gate # enforce per-package coverage thresholds
make fuzz       # short FuzzDecode smoke run
make all        # vet + lint + test + cover-gate
make ci         # run the exact CI pipeline locally (mod verify, vet, lint,
                # race tests, cover-gate, spec-lint, fuzz smoke)

Always run make ci before pushing or opening a PR — it mirrors .github/workflows/ci.yml step-for-step. See AGENTS.md for the full contributor checklist.

The configured linter set (see .golangci.yml) bundles staticcheck, govet, errcheck, revive, gosec, gocritic, bodyclose, errorlint, unparam, unconvert, usestdlibvars, usetesting, formatters gofmt and goimports, and a handful of others. Test files relax the noisier rules; see the exclusions block for the exact list.

CI enforces per-package coverage thresholds (covergate):

Package	Threshold
wbxml/	90%
eas/	90%
client/	80%
autodiscover/	80%

---

License

MIT. See LICENSE.