zip archive invalid but works with other utilities

[cpuguy83]

What version of Go are you using (go version)?

$ go version
go version go1.16.2 darwin/amd64

Does this issue reproduce with the latest release?

What operating system and processor architecture are you using (go env)?

go env Output

$ go env
GO111MODULE=""
GOARCH="amd64"
GOBIN="/Users/cpuguy83/go/bin"
GOCACHE="/Users/cpuguy83/Library/Caches/go-build"
GOENV="/Users/cpuguy83/Library/Application Support/go/env"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="darwin"
GOINSECURE=""
GOMODCACHE="/Users/cpuguy83/go/pkg/mod"
GONOPROXY=""
GONOSUMDB=""
GOOS="darwin"
GOPATH="/Users/cpuguy83/go"
GOPRIVATE=""
GOPROXY="https://proxy.golang.org,direct"
GOROOT="/usr/local/Cellar/go/1.16.2/libexec"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/usr/local/Cellar/go/1.16.2/libexec/pkg/tool/darwin_amd64"
GOVCS=""
GOVERSION="go1.16.2"
GCCGO="gccgo"
AR="ar"
CC="clang"
CXX="clang++"
CGO_ENABLED="1"
GOMOD="/Users/cpuguy83/dev/gh-actions-downloader/go.mod"
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
PKG_CONFIG="pkg-config"
GOGCCFLAGS="-fPIC -arch x86_64 -m64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fdebug-prefix-map=/var/folders/h0/019q23y92j58nhjw33nyjd1h0000gn/T/go-build2038630442=/tmp/go-build -gno-record-gcc-switches -fno-common"

What did you do?

I have this zip archive (linked to the source here, but also attached to the issue below) which archive/zip says is invalid.
This is created by github actions artifact uploader.

TestResults MacOS.zip

What did you expect to see?

Maybe at least details on what makes it invalid but genereally I'd expect a way to make it work since other zip utilities seem to be OK with it.

What did you see instead?

zip.NewReader gives me:

zip: not a valid zip file

[ianlancetaylor]

I downloaded your zip file and ran this program. It worked for me, in that zip.OpenReader did not return an error.

Show us your Go code.

package main

import (
	"archive/zip"
	"fmt"
	"os"
)

func main() {
	_, err := zip.OpenReader(os.Args[1])
	if err != nil {
		fmt.Println(err)
	}
}

[cpuguy83]

Note that "client" here is from google/go-github and client.Do writes the response into f.
On the particular job I am downloading artifacts for there are several artifacts that are all fine, its this one that it doesn't like.

	u, resp, err := client.Actions.DownloadArtifact(ctx, a.org, a.repo, a.ID, false)
	if err != nil {
		type ghErr struct {
			Message string `json:"message"`
		}
		e := &ghErr{}
		json.NewDecoder(io.LimitReader(resp.Body, 32*1024)).Decode(e)
		return errors.Wrapf(err, "error getting url to download artifact: %s", e.Message)
	}
	resp.Body.Close()

	req, err := http.NewRequestWithContext(ctx, http.MethodGet, u.String(), nil)
	if err != nil {
		return err
	}

	if err := os.MkdirAll(dir, 0700); err != nil {
		return errors.Wrap(err, "error creating artifact dir")
	}

	f, err := os.OpenFile(filepath.Join(dir, a.Name)+".zip", os.O_CREATE|os.O_RDWR|os.O_TRUNC, 0600)
	if err != nil {
		return errors.Wrap(err, "error creating save file")
	}
	defer f.Close()

	resp, err = client.Do(ctx, req, f)
	if err != nil {
		return err
	}
	defer resp.Body.Close()

	if _, err := f.Seek(0, io.SeekStart); err != nil {
		return errors.Wrap(err, "error seeking back to save file start")
	}

	r, err := zip.NewReader(f, a.Size)
	if err != nil {
		return errors.Wrapf(err, "error making zip reader from file %s", f.Name())
	}
	if err := unzipGo(r, a, dir); err != nil {
		return err
	}

Working on a utility to download github actions artifacts... I'll post full code to a repo soon just need to clean up some hardcoded things first.

[ianlancetaylor]

r, err := zip.NewReader(f, a.Size)

What is a.Size?

[cpuguy83]

Oh... that's it! Github is reporting the wrong size for the file.
If I change that to the position f was at before I reset it (which I realize I don't need to do also...) it works.

[cpuguy83]

❤️ Sorry for the noise.