testing: "unknown encoding version" error / provide documentation on the fuzz input file format

[kevinburke]

I'm trying to seed inputs to the fuzzer by adding files to testdata/fuzz, per the documentation.

Here is my test file (for package github.com/kevinburke/ssh_config):

package ssh_config

import (
	"bytes"
	"testing"
)

func FuzzDecode(f *testing.F) {
	f.Fuzz(func(t *testing.T, in []byte) {
		_, err := Decode(bytes.NewReader(in))
		if err != nil {
			t.Fatalf("decode %q: %v", string(in), err)
		}
	})
}

Per the documentation, I tried copying existing files in testdata/config1 and testdata/config2 to testdata/fuzz/Decode. This failed because I should have put them in testdata/fuzz/FuzzDecode but that (repetition of the word "fuzz") wasn't obvious to me from the docs.

I then tried running the fuzzer on Go tip (629ffeb) and got:

--- FAIL: FuzzDecode (0.00s)
    fuzz_test.go:9: "testdata/fuzz/FuzzDecode/config1": unmarshal: unknown encoding version: Host localhost 127.0.0.1 # A comment at the end of a host line.
        "testdata/fuzz/FuzzDecode/config2": unmarshal: unknown encoding version: #	$OpenBSD: ssh_config,v 1.30 2016/02/20 23:06:23 sobrado Exp $

I'm not sure how to resolve that. The docs that I saw (the blog post and in src/testing/testing.go) didn't mention anything about a version format for seed files, and the error message does not explain how to resolve the issue.

I also tried searching Google for information if other people had run into the error, and didn't find any.

Updates #49229.

[thanm]

@katiehockman

[katiehockman]

Thanks @kevinburke for reporting this. The corpus files do have a specific version format, and binary files can be converted using https://github.com/golang/tools/blob/master/cmd/file2fuzz/main.go.

We still need to document this, so I can leave this open for documentation purposes.

[katiehockman]

I'm going to close this as a dupe of #48717, since at this point it is going to be a doc change.