genopawasm: only unpack wasm and callgraph bytes once (open-policy-ag…

…ent#3644)

The result will always be the same, and on multiple calls to
rego.New() with the wasm target, repeating this work can be
avoided.

A quick benchmark shows this in action, first main, then this
branch:

    BenchmarkWasmCompilation-16    	     133	   8345008 ns/op	 7521141 B/op	   28041 allocs/op
    BenchmarkWasmCompilation-16    	     256	   4529514 ns/op	 3666712 B/op	   27670 allocs/op

Once Go 1.17 is out and we can do something incompatible with
1.15, we can switch to using the go:embed directive instead.

Signed-off-by: Stephan Renatus <[email protected]>

internal/cmd/genopawasm/main.go

@@ -70,27 +70,42 @@ import (
 	"bytes"
 	"compress/gzip"
 	"io/ioutil"
+	"sync"
+)
+
+var (
+	bytesOnce        sync.Once
+	bs               []byte
+	callGraphCSVOnce sync.Once
+	callGraphCSV     []byte
 )
 
 // Bytes returns the OPA-WASM bytecode.
 func Bytes() ([]byte, error) {
-	gr, err := gzip.NewReader(bytes.NewBuffer(gzipped))
-	if err != nil {
-		return nil, err
-	}
-	return ioutil.ReadAll(gr)
+	var err error
+	bytesOnce.Do(func() {
+		gr, err := gzip.NewReader(bytes.NewBuffer(gzipped))
+		if err != nil {
+			return
+		}
+		bs, err = ioutil.ReadAll(gr)
+	})
+	return bs, err
 }
 
 // CallGraphCSV returns a CSV representation of the
 // OPA-WASM bytecode's call graph: 'caller,callee'
 func CallGraphCSV() ([]byte, error) {
-	cg, err := gzip.NewReader(bytes.NewBuffer(gzippedCallGraphCSV))
-	if err != nil {
-		return nil, err
-	}
-	return ioutil.ReadAll(cg)
+	var err error
+	callGraphCSVOnce.Do(func() {
+		cg, err := gzip.NewReader(bytes.NewBuffer(gzippedCallGraphCSV))
+		if err != nil {
+			return
+		}
+		callGraphCSV, err = ioutil.ReadAll(cg)
+	})
+	return callGraphCSV, err
 }
-
 `))
 
 	if err != nil {

internal/wasm/sdk/opa/opa_bench_test.go

@@ -56,6 +56,12 @@ a = true`, "data.p.a = x")
 	}
 }
 
+func BenchmarkWasmCompilation(b *testing.B) {
+	for i := 0; i < b.N; i++ {
+		_ = compileRegoToWasm("a = true", "data.p.a = x", false)
+	}
+}
+
 func BenchmarkWASMArrayIteration(b *testing.B) {
 	sizes := []int{10, 100, 1000, 10000}
 	for _, n := range sizes {