Error: "unexpected end of JSON input" from CreateNetwork()

[KIVagant]

Hello. I'm getting the error from network.CreateNetwork():

unexpected end of JSON input

I feel like it is produced by the line:
https://github.com/fsouza/go-dockerclient/blob/main/network.go#L181

       if err := json.NewDecoder(resp.Body).Decode(&cnr); err != nil {
		return nil, err
	}

I see how the network is being created in Docker, but I cannot get the proper response back from the function.

It would be nice to have a debug mode to check the actual response.

Package Version:

github.com/fsouza/go-dockerclient v0.0.0-20170929173952-199e3d903f17

Docker version:

Docker Desktop Community, OSX, 2.3.0.5 (48029) stable
Engine: 19.03.12

Update: I found what caused this specific issue (or more how to fix it):

echo '{}' > ~/.dockercfg

Pretty funny that an empty ~/.dockercfg prevents the network from being created. Anyway it would be nice to get a message printed to stderr (at least in "debug" mode).

[fsouza]

@KIVagant can you share a reproducer? Are you sure the error is on the CresteNetwork call and not on the client instantiation? 🤔

[fsouza]

About adding debug information, generally a library shouldn't touch stdout and stderr, what we need is a better error message with more context x)

[kivagant-ba]

can you share a reproducer?

In my case the code is called by another tool, but the error appeared when I had an empty ~/.dockercfg. But you are right that it is not about this specific issue but about how to understand what's wrong when an issue appears. My workmate guessed what could cause this and saved a lot of time for me. Some debug info in any form would be a life saver.

[fsouza]

Gotcha. Yeah, CreateNetwork never tries to read .dockercfg, as that file contains auth configuration that's used to authenticate with the daemon or docker registries, something not required in the CreateNetwork call.

For example, this succeeds:

％ :>~/.dockercfg
％ cat cnetwork.go
package main

import (
        "fmt"

        docker "github.com/fsouza/go-dockerclient"
)

func main() {
        client, err := docker.NewClientFromEnv()
        if err != nil {
                panic(err)
        }
        network, err := client.CreateNetwork(docker.CreateNetworkOptions{
                Name: "somenetwork",
        })
        if err != nil {
                panic(err)
        }
        fmt.Printf("%#v", network)
}
％ go run ./cnetwork.go
&docker.Network{Name:"somenetwork", ID:"2fdd4a546e6f3a501b7b7569e69bd75073c1e88399ccb1dc41ac00ce8e5bb879", Scope:"", Driver:"", IPAM:docker.IPAMOptions{Driver:"", Config:[]docker.IPAMConfig(nil), Options:map[string]string(nil)}, Containers:map[string]docker.Endpoint(nil), Options:map[string]string(nil), Internal:false, EnableIPv6:false, Labels:map[string]string(nil)}                                                                                                           
％ docker network ls
NETWORK ID          NAME                DRIVER              SCOPE
bf4523465f64        bridge              bridge              local
21e74eb3d047        host                host                local
38813c67793b        none                null                local
2fdd4a546e6f        somenetwork         bridge              local

But this would fail:

package main

import (
	"fmt"

	docker "github.com/fsouza/go-dockerclient"
)

func main() {
	authConfigs, err := docker.NewAuthConfigurationsFromDockerCfg()
	if err != nil {
		panic(err)
	}
	fmt.Println(authConfigs)
}

[kivagant-ba]

I saw the error coming from CreateNetwork, so I don't know what to say about the examples.

[fsouza]

How do you know the error was coming from CreateNetwork? Can you share the part of the code that calls CreateNetwork and the client creation?

[kivagant-ba]

I was able to configure a debugger the code and now I can confirm your assumption.

This is a "stack trace" that produces the error:

# somewhere in the tool code:
   authConfigs, err := docker.NewAuthConfigurationsFromDockerCfg()

# /Users/yevhen.hlotov/go/pkg/mod/github.com/fsouza/go-dockerclient@v0.0.0-20170929173952-199e3d903f17/auth.go:82
# (NewAuthConfigurationsFromDockerCfg)
// It tries to open ~/.docker/config.json
        for _, path := range pathsToTry {
		auths, err = NewAuthConfigurationsFromFile(path) // HERE (1st try)
		if err == nil {
			return auths, nil
		}
	}

# go/pkg/mod/github.com/fsouza/go-dockerclient@v0.0.0-20170929173952-199e3d903f17/auth.go:127
		userpass := strings.SplitN(string(data), ":", 2)
		if len(userpass) != 2 {
                       // First error appears here, but it does not caused any issues:
			return nil, ErrCannotParseDockercfg
		}

# go/pkg/mod/github.com/fsouza/go-dockerclient@v0.0.0-20170929173952-199e3d903f17/auth.go:56 (NewAuthConfigurationsFromFile)

	return NewAuthConfigurations(r)

# go/pkg/mod/github.com/fsouza/go-dockerclient@v0.0.0-20170929173952-199e3d903f17/auth.go:83

for _, path := range pathsToTry {
		auths, err = NewAuthConfigurationsFromFile(path)
		if err == nil { // THE CHECK cannot be passed and it goes to another try in the loop and opens the empty ~/.dockercfg
			return auths, nil
		}
	}

# go/pkg/mod/github.com/fsouza/go-dockerclient@v0.0.0-20170929173952-199e3d903f17/auth.go:120 (parseDockerConfig)
// And finally it dies here
        if err := json.Unmarshal(byteData, &confs); err != nil {
		return nil, err
	}

[kivagant-ba]

This is the new latest version of the code:

https://github.com/fsouza/go-dockerclient/blob/main/auth.go#L198

var confs map[string]dockerConfig
	if err := json.Unmarshal(byteData, &confs); err != nil {
		return nil, err
	}

I guess a "if not empty" check could fix this.

[fsouza]

Yeah, I know the origin of the error, this is what I shared above. It's just not in the path of CreateNetwork, so I was wondering if something was off 🤔

Can definitely improve the error message.