Golang gzip reader does not returns the right error.

gzip_bug.go

package main

import (
	"bytes"
	"compress/gzip"
	"errors"
	"fmt"
	"io"
)

// When N < 10  ==> underlying error
// When N >= 10 ==> gzip: invalid header
var N = 10

func main() {
	data := bytes.NewBufferString("some fake data")
	r1 := newUnderlyingReader(data)
	r2, err := gzip.NewReader(r1)
	if err != nil {
		panic(err)
	}

	p := make([]byte, 4096)
	_, err = r2.Read(p)
	fmt.Println(err)
}

type underlyingReader struct {
	r io.Reader
}

func newUnderlyingReader(r io.Reader) *underlyingReader {
	return &underlyingReader{r}
}

func (r *underlyingReader) Read(p []byte) (n int, err error) {
	n = N
	err = errors.New("underlying error")

	return
}