util/syspolicy/policyclient: add Client interface to the syspolicy universebradfitz/syspolicy_key

This removes the dependency on syspolicy/... from LocalBackend and tailscaled
when ts_omit_syspolicy is true.

Updates #12614

Change-Id: I309deb0f50f8e7d6bc11454e4210bb3b358abc77
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

1 files changed, 67 insertions, 0 deletions

diff --git a/ipn/localapi/syspolicy_api.go b/ipn/localapi/syspolicy_api.go
new file mode 100644
index 000000000..366045de3
--- /dev/null
+++ b/ipn/localapi/syspolicy_api.go
@@ -0,0 +1,67 @@
+// Copyright (c) Tailscale Inc & AUTHORS
+// SPDX-License-Identifier: BSD-3-Clause
+
+//go:build !ts_omit_syspolicy
+
+package localapi
+
+import (
+	"encoding/json"
+	"fmt"
+	"net/http"
+	"strings"
+
+	"tailscale.com/util/syspolicy/rsop"
+	"tailscale.com/util/syspolicy/setting"
+)
+
+func init() {
+	handler["policy/"] = (*Handler).servePolicy
+}
+
+func (h *Handler) servePolicy(w http.ResponseWriter, r *http.Request) {
+	if !h.PermitRead {
+		http.Error(w, "policy access denied", http.StatusForbidden)
+		return
+	}
+
+	suffix, ok := strings.CutPrefix(r.URL.EscapedPath(), "/localapi/v0/policy/")
+	if !ok {
+		http.Error(w, "misconfigured", http.StatusInternalServerError)
+		return
+	}
+
+	var scope setting.PolicyScope
+	if suffix == "" {
+		scope = setting.DefaultScope()
+	} else if err := scope.UnmarshalText([]byte(suffix)); err != nil {
+		http.Error(w, fmt.Sprintf("%q is not a valid scope", suffix), http.StatusBadRequest)
+		return
+	}
+
+	policy, err := rsop.PolicyFor(scope)
+	if err != nil {
+		http.Error(w, err.Error(), http.StatusInternalServerError)
+		return
+	}
+
+	var effectivePolicy *setting.Snapshot
+	switch r.Method {
+	case "GET":
+		effectivePolicy = policy.Get()
+	case "POST":
+		effectivePolicy, err = policy.Reload()
+		if err != nil {
+			http.Error(w, err.Error(), http.StatusInternalServerError)
+			return
+		}
+	default:
+		http.Error(w, "unsupported method", http.StatusMethodNotAllowed)
+		return
+	}
+
+	w.Header().Set("Content-Type", "application/json")
+	e := json.NewEncoder(w)
+	e.SetIndent("", "\t")
+	e.Encode(effectivePolicy)
+}