add benchmarks for CBOR decoding performance (#44)

Author: philandstuff

binary/cbor.go

@@ -511,7 +511,7 @@ func EncodeAsCbor(w io.Writer, e Term) error {
 // DecodeAsCbor decodes CBOR from the io.Reader and returns the resulting Expr
 func DecodeAsCbor(r io.Reader) (Term, error) {
 	var b interface{}
-	dm, err := cbor.DecOptions{}.DecMode()
+	dm, err := cbor.DecOptions{MaxNestedLevels: 64}.DecMode()
 	if err != nil {
 		return nil, err
 	}

binary/performance_test.go

@@ -0,0 +1,71 @@
+package binary_test
+
+import (
+	"fmt"
+	"io"
+	"os"
+	"path"
+	"testing"
+
+	"github.com/philandstuff/dhall-golang/v3/binary"
+	"github.com/philandstuff/dhall-golang/v3/core"
+	"github.com/philandstuff/dhall-golang/v3/imports"
+	"github.com/philandstuff/dhall-golang/v3/internal"
+	"github.com/philandstuff/dhall-golang/v3/term"
+)
+
+func BenchmarkDecodeLargeExpression(b *testing.B) {
+	file, err := os.Open("../dhall-lang/tests/parser/success/largeExpressionB.dhallb")
+	if err != nil {
+		b.Fatal(err)
+	}
+	defer file.Close()
+	fileinfo, err := file.Stat()
+	if err != nil {
+		b.Fatal(err)
+	}
+	b.SetBytes(fileinfo.Size())
+	for n := 0; n < b.N; n++ {
+		file.Seek(0, io.SeekStart)
+		binary.DecodeAsCbor(file)
+	}
+}
+
+func BenchmarkDecodePrelude(b *testing.B) {
+	file := internal.NewLocalImport("../dhall-lang/Prelude/package.dhall", term.Code)
+	t, err := imports.Load(file)
+	if err != nil {
+		b.Fatal(err)
+	}
+	v := core.Eval(t)
+	cache, err := imports.StandardCache()
+	if err != nil {
+		b.Fatal(err)
+	}
+	hash, err := binary.SemanticHash(v)
+	if err != nil {
+		b.Fatal(err)
+	}
+	// ensure Prelude is saved into the cache
+	cache.Save(hash, core.Quote(v))
+
+	cacheDir, err := imports.DhallCacheDir()
+	if err != nil {
+		b.Fatal(err)
+	}
+	hash16 := fmt.Sprintf("%x", hash)
+	cborfile, err := os.Open(path.Join(cacheDir, hash16))
+	if err != nil {
+		b.Fatal(err)
+	}
+	fileinfo, err := cborfile.Stat()
+	if err != nil {
+		b.Fatal(err)
+	}
+	b.SetBytes(fileinfo.Size())
+	b.ResetTimer()
+	for n := 0; n < b.N; n++ {
+		cborfile.Seek(0, io.SeekStart)
+		binary.DecodeAsCbor(cborfile)
+	}
+}

imports/cache.go

@@ -84,14 +84,16 @@ func (l LocalCache) Save(hash []byte, e term.Term) {
 // StandardCache is the standard DhallCache implementation.  It is a
 // LocalCache in the standard Dhall cache directory.
 func StandardCache() (DhallCache, error) {
-	cacheDir, err := dhallCacheDir()
+	cacheDir, err := DhallCacheDir()
 	if err != nil {
 		return nil, err
 	}
 	return NewLocalCache(cacheDir), nil
 }
 
-func dhallCacheDir() (string, error) {
+// DhallCacheDir returns the path to the Dhall cache directory, as
+// specified in the Dhall standard.
+func DhallCacheDir() (string, error) {
 	cacheDir, err := os.UserCacheDir()
 	if err != nil {
 		return "", err