version/updates: start of version updates policy package

Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

version/updates/rules.json

@@ -0,0 +1,38 @@
+{
+    "tests": [
+        {
+            "os": "linux",
+            "distro": "synology",
+            "ver": "1.14.5",
+            "want": "",
+        },
+        {
+            "os": "windows",
+            "ver": "1.2.1",
+            "want": "update/security",
+        },
+    ],
+    "rules": [
+        {
+            "ver": "1.12.3",
+            "os": "linux",
+            "distro": "synology",
+            "then": "stop",
+        },
+        {
+            "os": "windows",
+            "thenRules": [],
+            "elseRules": [],
+        },
+        {
+            "ver": "<1.2.3",
+            "os": "windows",
+            "then": "update/security: some notes",
+        },
+        {
+            "ver": "<1.14",
+            "now": ">=2020-09-29",
+            "then": "update",
+        },
+    ],
+}

version/updates/updates.go

@@ -0,0 +1,50 @@
+// Copyright (c) 2021 Tailscale Inc & AUTHORS All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Packate updates is an evalator for a update policy file that controls
+// when users get update available notifications (and which types).
+//
+// It's used and hot reloaded by several servers. It permits us to
+// centralize and test the update policy.
+package updates
+
+type Policy struct {
+	Tests []*Test
+	Rules []*Rule
+}
+
+type Test struct {
+	OS     string
+	Distro string // "synology" on Linux
+	Ver    string // "1.2.3-tXXXX-gXXX"
+	Want   string // "", "update", "update/security"
+}
+
+type Rule struct {
+	// Ver, if non-empty, matches the version number.
+	// If it begins with an operator ("<", "<=", then the comparison
+	// is done semantically based on semver, not lexically.
+	Ver string
+
+	// OS, if non-empty, matches the node operating system.
+	// Possible values: "linux", "windows", "macOS", "iOS", or
+	// else a runtime.GOOS value (except not "darwin" or "ios").
+	OS string
+
+	// Package, if non-empty, matches the packaging variant.
+	// Possible values: "choco", "appstore", "macsys", "tailscaled".
+	Package string
+
+	// Distro, if non-empty, matches the node's distro.
+	// Possible values: "synology".
+	Distro string
+
+	// Now, if non-empty, matches based on the current date in UTC.
+	// e.g. ">=2021-10-07".
+	Now string
+
+	Then      string // "stop", "update", "update/security", "update: note"
+	ThenRules []*Rule
+	ElseRules []*Rule
+}

version/updates/updates_test.go

@@ -0,0 +1,28 @@
+// Copyright (c) 2021 Tailscale Inc & AUTHORS All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package updates
+
+import (
+	"bytes"
+	"os"
+	"testing"
+
+	"github.com/tailscale/hujson"
+)
+
+func TestParse(t *testing.T) {
+	rulesJSON, err := os.ReadFile("rules.json")
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	d := hujson.NewDecoder(bytes.NewReader(rulesJSON))
+	d.DisallowUnknownFields()
+
+	var p Policy
+	if err := d.Decode(&p); err != nil {
+		t.Fatal(err)
+	}
+}