feat: add "gno.land/p/rand" package, hard-to-guess deterministic random library (#153)

* chore: add new 'std.TestSkipHeights' testing vm helper

* chore: add gno.land/p/rand package

Signed-off-by: Manfred Touron <[email protected]>

Author: moul

examples/gno.land/p/rand/rand.gno

@@ -0,0 +1,120 @@
+package rand
+
+// the goal of this package is to implement a random library that
+// is fully deterministic for validators while being hard to
+// determine by the callers.
+
+import (
+	"crypto/md5"
+	"encoding/binary"
+	"math/rand"
+	"std"
+)
+
+type instance struct {
+	seed int64
+}
+
+func New() *instance {
+	r := instance{}
+	r.addEntropy()
+	return &r
+}
+
+// AddEntropy uses various runtime variables to add entropy to the existing seed.
+func (i *instance) addEntropy() {
+	h := md5.New()
+
+	// why not?
+	h.Write([]byte("now, you gno"))
+
+	// inherit previous entropy
+	{
+		buf := make([]byte, 16)
+		_, _ = rand.New(rand.NewSource(i.seed)).Read(buf)
+		h.Write(buf)
+	}
+
+	// callers
+	h.Write([]byte(std.GetCallerAt(1)))
+	h.Write([]byte(std.GetCallerAt(2)))
+
+	// height
+	{
+		height := std.GetHeight()
+		buf := make([]byte, 8)
+		binary.BigEndian.PutUint64(buf, uint64(height))
+		h.Write(buf)
+	}
+
+	// time
+	{
+		now := std.GetTimestamp()
+		buf := make([]byte, 8)
+		binary.BigEndian.PutUint64(buf, uint64(now))
+		h.Write(buf)
+	}
+
+	// set seed
+	i.seed = int64(binary.BigEndian.Uint64(h.Sum(nil)))
+}
+
+func (i *instance) Float32() float32 {
+	i.addEntropy()
+	return rand.New(rand.NewSource(i.seed)).Float32()
+}
+
+func (i *instance) Float64() float64 {
+	i.addEntropy()
+	return rand.New(rand.NewSource(i.seed)).Float64()
+}
+
+func (i *instance) Int() int {
+	i.addEntropy()
+	return rand.New(rand.NewSource(i.seed)).Int()
+}
+
+func (i *instance) Intn(n int) int {
+	i.addEntropy()
+	return rand.New(rand.NewSource(i.seed)).Intn(n)
+}
+
+func (i *instance) Int63() int64 {
+	i.addEntropy()
+	return rand.New(rand.NewSource(i.seed)).Int63()
+}
+
+func (i *instance) Int63n(n int64) int64 {
+	i.addEntropy()
+	return rand.New(rand.NewSource(i.seed)).Int63n(n)
+}
+
+func (i *instance) Int31() int32 {
+	i.addEntropy()
+	return rand.New(rand.NewSource(i.seed)).Int31()
+}
+
+func (i *instance) Int31n(n int32) int32 {
+	i.addEntropy()
+	return rand.New(rand.NewSource(i.seed)).Int31n(n)
+}
+
+func (i *instance) Uint32() uint32 {
+	i.addEntropy()
+	return rand.New(rand.NewSource(i.seed)).Uint32()
+}
+
+func (i *instance) Uint64() uint64 {
+	i.addEntropy()
+	return rand.New(rand.NewSource(i.seed)).Uint64()
+}
+
+func (i *instance) Read(p []byte) (n int, err error) {
+	i.addEntropy()
+	return rand.New(rand.NewSource(i.seed)).Read(p)
+}
+
+func (i *instance) Shuffle(n int, swap func(i, j int)) {
+	i.addEntropy()
+	rand.New(rand.NewSource(i.seed)).Shuffle(n, swap)
+}

precompile.go

@@ -45,6 +45,7 @@ var stdlibWhitelist = []string{
 	"io/util",
 	"math",
 	"math/big",
+	"math/rand",
 	"regexp",
 	"sort",
 	"strconv",

tests/files2/zrealm_rand0.gno

@@ -0,0 +1,56 @@
+package main
+
+import (
+	"std"
+
+	"gno.land/p/rand"
+)
+
+func main() {
+	// initial
+	println("---")
+	r := rand.New()
+	println(r.Intn(1000))
+	println(r.Intn(1000))
+	println(r.Intn(1000))
+	println(r.Intn(1000))
+	println(r.Intn(1000))
+
+	// should be the same
+	println("---")
+	r = rand.New()
+	println(r.Intn(1000))
+	println(r.Intn(1000))
+	println(r.Intn(1000))
+	println(r.Intn(1000))
+	println(r.Intn(1000))
+
+	std.TestSkipHeights(1)
+	println("---")
+	r = rand.New()
+	println(r.Intn(1000))
+	println(r.Intn(1000))
+	println(r.Intn(1000))
+	println(r.Intn(1000))
+	println(r.Intn(1000))
+}
+
+// Output:
+// ---
+// 71
+// 908
+// 897
+// 955
+// 61
+// ---
+// 71
+// 908
+// 897
+// 955
+// 61
+// ---
+// 410
+// 919
+// 51
+// 342
+// 683

tests/imports_test.go

@@ -557,6 +557,21 @@ func testPackageInjector(store gno.Store, pn *gno.PackageNode) {
 				m.PushValue(typedString(rlmpath))
 			},
 		)
+		pn.DefineNative("TestSkipHeights",
+			gno.Flds( // params
+				"count", "int64",
+			),
+			gno.Flds( // results
+			),
+			func(m *gno.Machine) {
+				arg0 := m.LastBlock().GetParams1().TV
+				count := arg0.GetInt64()
+
+				ctx := m.Context.(stdlibs.ExecContext)
+				ctx.Height += count
+				m.Context = ctx
+			},
+		)
 		pn.DefineNative("TestDerivePkgAddr",
 			gno.Flds( // params
 				"pkgPath", "string",