src/cmd/go/testdata/script/test_fuzz_minimize_interesting.txt

[short] skip
[!fuzz-instrumented] skip

# Test that when an interesting value is discovered (one that expands coverage),
# the fuzzing engine minimizes it before writing it to the cache.
#
# The program below starts with a seed value of length 100, but more coverage
# will be found for any value other than the seed. We should end with a value
# in the cache of length 1 (the minimizer currently does not produce empty
# strings). check_cache.go confirms that.
#
# We would like to verify that ALL values in the cache were minimized to a
# length of 1, but this isn't always possible when new coverage is found in
# functions called by testing or internal/fuzz in the background.

go test -c -fuzz=.  # Build using shared build cache for speed.
env GOCACHE=$WORK/gocache
exec ./fuzz.test$GOEXE -test.fuzzcachedir=$GOCACHE/fuzz -test.fuzz=FuzzMinCache -test.fuzztime=1000x
go run check_cache/check_cache.go $GOCACHE/fuzz/FuzzMinCache

# Test that minimization occurs for a crash that appears while minimizing a
# newly found interesting input. There must be only one worker for this test to
# be flaky like we want.
! exec ./fuzz.test$GOEXE -test.fuzzcachedir=$GOCACHE/fuzz -test.fuzz=FuzzMinimizerCrashInMinimization -test.run=^$ -test.fuzztime=10000x -test.parallel=1
! stdout '^ok'
stdout -count=1 'got the minimum size!'
stdout -count=1 'bad input'
stdout FAIL
# Check that the input written to testdata will reproduce the error, and is the
# smallest possible.
go run check_testdata/check_testdata.go FuzzMinimizerCrashInMinimization 1

# Test that a nonrecoverable error that occurs while minimizing an interesting
# input is reported correctly.
! exec ./fuzz.test$GOEXE -test.fuzzcachedir=$GOCACHE/fuzz -test.fuzz=FuzzMinimizerNonrecoverableCrashInMinimization -test.run=^$ -test.fuzztime=10000x -test.parallel=1
! stdout '^ok'
stdout -count=1 'fuzzing process hung or terminated unexpectedly while minimizing'
stdout -count=1 'EOF'
stdout FAIL
# Check that the input written to testdata will reproduce the error.
go run check_testdata/check_testdata.go FuzzMinimizerNonrecoverableCrashInMinimization 1

-- go.mod --
module fuzz

go 1.17
-- y.go --
package fuzz

import (
	"bytes"
	"io"
)

func Y(w io.Writer, s string) {
	if !bytes.Equal([]byte(s), []byte("y")) {
		w.Write([]byte("not equal"))
	}
}
-- fuzz_test.go --
package fuzz

import (
	"bytes"
	"os"
	"testing"
)

func FuzzMinimizerCrashInMinimization(f *testing.F) {
	seed := bytes.Repeat([]byte{255}, 100)
	f.Add(seed)
	f.Fuzz(func(t *testing.T, b []byte) {
		if bytes.Equal(seed, b) {
			return
		}
		t.Error("bad input")
		if len(b) == 1 {
			t.Error("got the minimum size!")
		}
	})
}

var fuzzing bool

func FuzzMinimizerNonrecoverableCrashInMinimization(f *testing.F) {
	seed := bytes.Repeat([]byte{255}, 100)
	f.Add(seed)
	f.Fuzz(func(t *testing.T, b []byte) {
		if bytes.Equal(seed, b) {
			return
		} else if len(b) == 1 {
			os.Exit(1)
		}
	})
}

func FuzzMinCache(f *testing.F) {
	seed := bytes.Repeat([]byte("a"), 20)
	f.Add(seed)
	f.Fuzz(func(t *testing.T, buf []byte) {
		if bytes.Equal(buf, seed) {
			return
		}
	})
}
-- check_testdata/check_testdata.go --
//go:build ignore
// +build ignore

// check_testdata.go checks that the string written
// is not longer than the provided length.
package main

import (
	"bytes"
	"fmt"
	"io/ioutil"
	"os"
	"path/filepath"
	"regexp"
	"strconv"
)

func main() {
	wantLen, err := strconv.Atoi(os.Args[2])
	if err != nil {
		fmt.Fprintln(os.Stderr, err)
		os.Exit(1)
	}
	testName := os.Args[1]
	dir := filepath.Join("testdata/fuzz", testName)

	files, err := ioutil.ReadDir(dir)
	if err != nil {
		fmt.Fprintln(os.Stderr, err)
		os.Exit(1)
	}

	if len(files) == 0 {
		fmt.Fprintf(os.Stderr, "expect at least one failure to be written to testdata\n")
		os.Exit(1)
	}

	for _, f := range files {
		data, err := ioutil.ReadFile(filepath.Join(dir, f.Name()))
		if err != nil {
			panic(err)
		}
		var containsVal bool
		for _, line := range bytes.Split(data, []byte("\n")) {
			m := valRe.FindSubmatch(line)
			if m == nil {
				continue
			}
			containsVal = true
			s, err := strconv.Unquote(string(m[1]))
			if err != nil {
				panic(err)
			}
			if len(s) != wantLen {
				fmt.Fprintf(os.Stderr, "expect length %d, got %d (%q)\n", wantLen, len(s), line)
				os.Exit(1)
			}
		}
		if !containsVal {
			fmt.Fprintln(os.Stderr, "corpus file contained no values")
			os.Exit(1)
		}
	}
}

var valRe = regexp.MustCompile(`^\[\]byte\(([^)]+)\)$`)

-- check_cache/check_cache.go --
//go:build ignore
// +build ignore

// check_cache.go checks that each file in the cached corpus has a []byte
// of length at most 1. This verifies that at least one cached input is minimized.
package main

import (
	"bytes"
	"fmt"
	"os"
	"path/filepath"
	"regexp"
	"strconv"
)

func main() {
	dir := os.Args[1]
	ents, err := os.ReadDir(dir)
	if err != nil {
		fmt.Fprintln(os.Stderr, err)
		os.Exit(1)
	}
	for _, ent := range ents {
		name := filepath.Join(dir, ent.Name())
		if good, err := checkCacheFile(name); err != nil {
			fmt.Fprintln(os.Stderr, err)
			os.Exit(1)
		} else if good {
			os.Exit(0)
		}
	}
	fmt.Fprintln(os.Stderr, "no cached inputs were minimized")
	os.Exit(1)
}

func checkCacheFile(name string) (good bool, err error) {
	data, err := os.ReadFile(name)
	if err != nil {
		return false, err
	}
	for _, line := range bytes.Split(data, []byte("\n")) {
		m := valRe.FindSubmatch(line)
		if m == nil {
			continue
		}
		if s, err := strconv.Unquote(string(m[1])); err != nil {
			return false, err
		} else if len(s) <= 1 {
			return true, nil
		}
	}
	return false, nil
}

var valRe = regexp.MustCompile(`^\[\]byte\(([^)]+)\)$`)