protoparse: panic when parsing empty file

[bradleyjkemp]

Hi, found this panic when trying to parse an empty file. The error seems to be in github.com/jhump/protoreflect/desc/protoparse/parser.go:559 where lx.err is nil so no error is returned but lx.res is also nil so a nil pointer dereference occurs later when this is accessed.

To reproduce just try to parse any empty file or use the following self-contained example:

package main

import (
	"bytes"
	"io"
	"io/ioutil"

	"github.com/jhump/protoreflect/desc/protoparse"
)

func main() {
	protoparse.Parser{
		Accessor: func(filename string) (io.ReadCloser, error) {
			return ioutil.NopCloser(bytes.NewBuffer(nil)), nil
		},
	}.ParseFiles("this_crashes.proto")
}

Stack trace:

panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x20 pc=0x1243e81]

goroutine 1 [running]:
github.com/jhump/protoreflect/desc/protoparse.(*parseResult).createFileDescriptor(0xc00000acc0, 0x130cc9e, 0xa, 0x0, 0x134cf60, 0xc000022c00)
	$GOPATH/src/github.com/jhump/protoreflect/desc/protoparse/parser.go:597 +0x151
github.com/jhump/protoreflect/desc/protoparse.createParseResult(0x130cc9e, 0xa, 0x0, 0x1672048, 0xc0000b5b20, 0xc0000b5b18)
	$GOPATH/src/github.com/jhump/protoreflect/desc/protoparse/parser.go:588 +0xb4
github.com/jhump/protoreflect/desc/protoparse.parseProto(0x130cc9e, 0xa, 0x1672048, 0xc0001179e0, 0xc000117900, 0x0, 0x200000, 0x4220000)
	$GOPATH/src/github.com/jhump/protoreflect/desc/protoparse/parser.go:571 +0x1fd
github.com/jhump/protoreflect/desc/protoparse.parseProtoFiles.func1(0x134d0e0, 0xc0001179e0, 0xc0000b5c00, 0xc000117900, 0xc0000b5ce8, 0xc0000b5c10)
	$GOPATH/src/github.com/jhump/protoreflect/desc/protoparse/parser.go:383 +0xd9
github.com/jhump/protoreflect/desc/protoparse.parseProtoFiles(0xc0000752c0, 0xc0000b5e68, 0x1, 0x1, 0xc0000a0000, 0xc0000b5ce8, 0x1550ea0, 0xc000000300)
	$GOPATH/src/github.com/jhump/protoreflect/desc/protoparse/parser.go:384 +0x3af
github.com/jhump/protoreflect/desc/protoparse.Parser.ParseFilesButDoNotLink(0x0, 0x0, 0x0, 0x0, 0xc0000752c0, 0x0, 0xc0000b5e68, 0x1, 0x1, 0x12ac2a0, ...)
	$GOPATH/src/github.com/jhump/protoreflect/desc/protoparse/parser.go:237 +0x13c
github.com/jhump/protoreflect/desc/protoparse.Fuzz(0x4220000, 0x0, 0x200000, 0x4)
	$GOPATH/src/github.com/jhump/protoreflect/desc/protoparse/fuzz.go:20 +0x151
go-fuzz-dep.Main(0xc0000b5f80, 0x1, 0x1)
	/var/folders/6m/r713l1xj6_dcykbx21svs09h0000gp/T/go-fuzz-build315933473/goroot/src/go-fuzz-dep/main.go:36 +0x1b6
main.main()
	/var/folders/6m/r713l1xj6_dcykbx21svs09h0000gp/T/go-fuzz-build315933473/gopath/src/github.com/jhump/protoreflect/desc/protoparse/go.fuzz.main/main.go:15 +0x52
exit status 2

(I also created a simple fuzzing harness for both ParseFiles and ParseFilesButDoNotLink but go-fuzz didn't find any other panics so far)

[jhump]

Thanks for the report, @bradleyjkemp!