Add Rego lang extension to work with the cache

regoext/cache.go

+package regoext
+
+import (
+	"fmt"
+	"net/http"
+
+	"github.com/open-policy-agent/opa/ast"
+	"github.com/open-policy-agent/opa/rego"
+	"github.com/open-policy-agent/opa/types"
+)
+
+type CacheExt struct {
+	path string
+}
+
+func NewCacheExt(path string) *CacheExt {
+	return &CacheExt{path: path}
+}
+
+func (ce *CacheExt) GetCacheFunc() (*rego.Function, rego.Builtin3) {
+	return &rego.Function{
+			Name:    "cache.get",
+			Decl:    types.NewFunction(types.Args(types.S, types.S, types.S), types.A),
+			Memoize: true,
+		},
+		func(bctx rego.BuiltinContext, a, b, c *ast.Term) (*ast.Term, error) {
+
+			var key, namespace, scope string
+
+			if err := ast.As(a.Value, &key); err != nil {
+				return nil, err
+			} else if ast.As(b.Value, &namespace); err != nil {
+				return nil, err
+			} else if ast.As(c.Value, &scope); err != nil {
+				return nil, err
+			}
+
+			req, err := http.NewRequest("GET", ce.path+"/v1/cache", nil)
+			req.Header = http.Header{
+				"x-cache-key":       []string{key},
+				"x-cache-namespace": []string{namespace},
+				"x-cache-scope":     []string{scope},
+			}
+			if err != nil {
+				return nil, err
+			}
+
+			resp, err := http.DefaultClient.Do(req.WithContext(bctx.Context))
+			if err != nil {
+				return nil, err
+			}
+
+			defer resp.Body.Close()
+
+			if resp.StatusCode != http.StatusOK {
+				return nil, fmt.Errorf(resp.Status)
+			}
+
+			v, err := ast.ValueFromReader(resp.Body)
+			if err != nil {
+				return nil, err
+			}
+
+			return ast.NewTerm(v), nil
+		}
+}

regoext/cache_test.go

+package regoext_test
+
+import (
+	"context"
+	"encoding/json"
+	"fmt"
+	"net/http"
+	"net/http/httptest"
+	"testing"
+
+	"code.vereign.com/gaiax/tsa/policy/regoext"
+	"github.com/open-policy-agent/opa/rego"
+)
+
+func TestCacheExt_GetCacheFunc(t *testing.T) {
+	expected := "{}"
+
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		fmt.Fprint(w, expected)
+	}))
+	defer srv.Close()
+	fmt.Println(srv.URL)
+
+	cache := regoext.NewCacheExt(srv.URL)
+
+	r := rego.New(
+		rego.Query(`cache.get("open-policy-agent", "opa", "111")`),
+		rego.Function3(cache.GetCacheFunc()),
+	)
+
+	rs, err := r.Eval(context.Background())
+
+	if err != nil {
+		t.Errorf("unexpected error, %v", err)
+		return
+	}
+
+	bs, err := json.MarshalIndent(rs[0].Expressions[0].Value, "", "  ")
+	if err != nil {
+		t.Errorf("unexpected error, %v", err)
+		return
+	}
+	if string(bs) != expected {
+		t.Errorf("expected %s, got %s", expected, string(bs))
+	}
+}