From d965f9f43e581bfddb34113cca5468dcb3ca5506 Mon Sep 17 00:00:00 2001
From: Gregory Petrosyan <gregory.petrosyan@gmail.com>
Date: Mon, 4 Jul 2022 18:56:10 +0300
Subject: [PATCH] Integrated fuzzing support

Fixes #32.
---
 TODO.md             |  1 -
 engine.go           | 47 +++++++++++++++++++++++++++++++++++++++++
 engine_fuzz_test.go | 51 +++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 98 insertions(+), 1 deletion(-)
 create mode 100644 engine_fuzz_test.go

diff --git a/TODO.md b/TODO.md
index de3c5f9..874f532 100644
--- a/TODO.md
+++ b/TODO.md
@@ -4,7 +4,6 @@
 
 - explicit examples support (based on `refDraws` shrink test machinery)
 - explicit settings support (to not depend on global environment)
-- [go-fuzz](https://github.com/golang/proposal/blob/master/design/draft-fuzzing.md) integration
 
 ## Generators
 
diff --git a/engine.go b/engine.go
index dc6d540..5c09e0d 100644
--- a/engine.go
+++ b/engine.go
@@ -8,6 +8,7 @@ package rapid
 
 import (
 	"bytes"
+	"encoding/binary"
 	"flag"
 	"fmt"
 	"log"
@@ -113,6 +114,46 @@ func MakeCheck(prop func(*T)) func(*testing.T) {
 	}
 }
 
+// MakeFuzz creates a fuzz target for [*testing.F.Fuzz]:
+//
+//	func FuzzFoo(f *testing.F) {
+//	    f.Fuzz(rapid.MakeFuzz(func(t *rapid.T) {
+//	        // test code
+//	    }))
+//	}
+func MakeFuzz(prop func(*T)) func(*testing.T, []byte) {
+	return func(t *testing.T, input []byte) {
+		t.Helper()
+		checkFuzz(t, prop, input)
+	}
+}
+
+func checkFuzz(tb tb, prop func(*T), input []byte) {
+	tb.Helper()
+
+	var buf []uint64
+	for len(input) > 0 {
+		var tmp [8]byte
+		n := copy(tmp[:], input)
+		buf = append(buf, binary.LittleEndian.Uint64(tmp[:]))
+		input = input[n:]
+	}
+
+	t := newT(tb, newBufBitStream(buf, false), flags.verbose, nil)
+	err := checkOnce(t, prop)
+
+	switch {
+	case err == nil:
+		// do nothing
+	case err.isInvalidData():
+		tb.SkipNow()
+	case err.isStopTest():
+		tb.Fatalf("[rapid] failed: %v", err)
+	default:
+		tb.Fatalf("[rapid] panic: %v\nTraceback:\n%v", err, traceback(err))
+	}
+}
+
 func checkTB(tb tb, prop func(*T)) {
 	tb.Helper()
 
@@ -373,6 +414,9 @@ type TB interface {
 	Name() string
 	Logf(format string, args ...any)
 	Log(args ...any)
+	Skipf(format string, args ...any)
+	Skip(args ...any)
+	SkipNow()
 	Errorf(format string, args ...any)
 	Error(args ...any)
 	Fatalf(format string, args ...any)
@@ -388,6 +432,9 @@ type tb interface {
 	Name() string
 	Logf(format string, args ...any)
 	Log(args ...any)
+	Skipf(format string, args ...any)
+	Skip(args ...any)
+	SkipNow()
 	Errorf(format string, args ...any)
 	Error(args ...any)
 	Fatalf(format string, args ...any)
diff --git a/engine_fuzz_test.go b/engine_fuzz_test.go
new file mode 100644
index 0000000..73db2ed
--- /dev/null
+++ b/engine_fuzz_test.go
@@ -0,0 +1,51 @@
+// Copyright 2022 Gregory Petrosyan <gregory.petrosyan@gmail.com>
+//
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this
+// file, You can obtain one at https://mozilla.org/MPL/2.0/.
+
+package rapid_test
+
+import (
+	"testing"
+
+	. "pgregory.net/rapid"
+)
+
+func checkInt(t *T) {
+	answer := Int().Draw(t, "answer")
+	if answer == 42 {
+		t.Fatalf("fuzzing works")
+	}
+}
+
+func checkSlice(t *T) {
+	slice := SliceOfN(Int(), 5, 5).Draw(t, "slice")
+	if slice[0] < slice[1] && slice[1] < slice[2] && slice[2] < slice[3] && slice[3] < slice[4] {
+		t.Fatalf("fuzzing works")
+	}
+}
+
+func checkString(t *T) {
+	hello := String().Draw(t, "hello")
+	if hello == "world" {
+		t.Fatalf("fuzzing works")
+	}
+}
+
+func TestRapidInt(t *testing.T) {
+	t.Skip()
+	Check(t, checkInt)
+}
+func TestRapidSlice(t *testing.T) {
+	t.Skip()
+	Check(t, checkSlice)
+}
+func TestRapidString(t *testing.T) {
+	t.Skip()
+	Check(t, checkString)
+}
+
+func FuzzInt(f *testing.F)    { f.Fuzz(MakeFuzz(checkInt)) }
+func FuzzSlice(f *testing.F)  { f.Fuzz(MakeFuzz(checkSlice)) }
+func FuzzString(f *testing.F) { f.Fuzz(MakeFuzz(checkString)) }