[dev.fuzz] internal/fuzz: support corpus file encoding/decoding

Change-Id: Id245ce5f154557f1744210e7d7f061d08901c746
Reviewed-on: https://go-review.googlesource.com/c/go/+/290951
Trust: Katie Hockman <katie@golang.org>
Run-TryBot: Katie Hockman <katie@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Jay Conrod <jayconrod@google.com>

src/internal/fuzz/encoding_test.go

@@ -0,0 +1,115 @@
+// Copyright 2021 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package fuzz
+
+import (
+	"strings"
+	"testing"
+)
+
+func TestUnmarshalMarshal(t *testing.T) {
+	var tests = []struct {
+		in string
+		ok bool
+	}{
+		{
+			in: "int(1234)",
+			ok: false, // missing version
+		},
+		{
+			in: `version 1
+string("a"bcad")`,
+			ok: false, // malformed
+		},
+		{
+			in: `version 1
+int()`,
+			ok: false, // empty value
+		},
+		{
+			in: `version 1
+uint(-32)`,
+			ok: false, // invalid negative uint
+		},
+		{
+			in: `version 1
+int8(1234456)`,
+			ok: false, // int8 too large
+		},
+		{
+			in: `version 1
+int(20*5)`,
+			ok: false, // expression in int value
+		},
+		{
+			in: `version 1
+int(--5)`,
+			ok: false, // expression in int value
+		},
+		{
+			in: `version 1
+bool(0)`,
+			ok: false, // malformed bool
+		},
+		{
+			in: `version 1
+byte('aa)`,
+			ok: false, // malformed byte
+		},
+		{
+			in: `version 1
+byte('☃')`,
+			ok: false, // byte out of range
+		},
+		{
+			in: `version 1
+string("extra")
+[]byte("spacing")  
+    `,
+			ok: true,
+		},
+		{
+			in: `version 1
+int(-23)
+int8(-2)
+int64(2342425)
+uint(1)
+uint16(234)
+uint32(352342)
+uint64(123)
+rune('œ')
+byte('K')
+byte('ÿ')
+[]byte("hello¿")
+[]byte("a")
+bool(true)
+string("hello\\xbd\\xb2=\\xbc ⌘")
+float64(-12.5)
+float32(2.5)`,
+			ok: true,
+		},
+	}
+	for _, test := range tests {
+		t.Run(test.in, func(t *testing.T) {
+			vals, err := unmarshalCorpusFile([]byte(test.in))
+			if test.ok && err != nil {
+				t.Fatalf("unmarshal unexpected error: %v", err)
+			} else if !test.ok && err == nil {
+				t.Fatalf("unmarshal unexpected success")
+			}
+			if !test.ok {
+				return // skip the rest of the test
+			}
+			newB := marshalCorpusFile(vals...)
+			if err != nil {
+				t.Fatalf("marshal unexpected error: %v", err)
+			}
+			want := strings.TrimSpace(test.in)
+			if want != string(newB) {
+				t.Errorf("values changed after unmarshal then marshal\nbefore: %q\nafter:  %q", want, newB)
+			}
+		})
+	}
+}