Docker send credentials to docker.io when registry URL doesn't contain a host but has a scheme and a path

[Ingvin]

Description

Found in Gitlab CI that if registry URL doesn't contain host but has scheme and path docker will try to login to registry-1.docker.io. This is happening when hostname is in env variable and this variable is empty.

I have this problem with Docker on Ubuntu 20.04 but I think OS isn't relevant to this issue.
Tested versions:

• Docker version 24.0.5, build 24.0.5-0ubuntu1~20.04.1
• Docker version 26.1.1, build 4cf5afa
  Also tested with podman as daemon and run docker:latest image with hash sha256:8bd6302a909f6f2ed9a17058cce2d83442bddb9e65c974352c2ba485a1e6d7ba and with podman there is no problem.

Reproduce

Docker daemon + docker image:

1. sudo docker run -it --rm --privileged -v /var/run/docker.sock:/var/run/docker.sock docker:latest ash
2. export REGISTRY_LOGIN="test" REGISTRY_PASS="test"
3. docker login "https:///repository/docker/" -u "$REGISTRY_LOGIN" -p "$REGISTRY_PASS"

Error response from daemon: Get "https://registry-1.docker.io/v2/": unauthorized: incorrect username or password

Podman daemon + docker image:

1. systemctl start --user podman.socket Run podman socket as user (rootless)
2. podman run -it --rm --privileged -v $XDG_RUNTIME_DIR/podman/podman.sock:/var/run/docker.sock:Z docker:latest ash
3. export REGISTRY_LOGIN="test" REGISTRY_PASS="test"
4. docker login "https:///repository/docker/" -u "$REGISTRY_LOGIN" -p "$REGISTRY_PASS"

Error response from daemon: login attempt to  failed with status: authenticating creds for "": pinging container registry : Get "https:///v2/": http: no Host in request URL

Expected behavior

Docker has to check URL for empty hostname and show error about invalid address instead of fallback to registry-1.docker.io

docker version

Client: Docker Engine - Community
 Version:           26.1.1
 API version:       1.45
 Go version:        go1.21.9
 Git commit:        4cf5afa
 Built:             Tue Apr 30 11:48:20 2024
 OS/Arch:           linux/amd64
 Context:           default

Server: Docker Engine - Community
 Engine:
  Version:          26.1.1
  API version:      1.45 (minimum version 1.24)
  Go version:       go1.21.9
  Git commit:       ac2de55
  Built:            Tue Apr 30 11:48:20 2024
  OS/Arch:          linux/amd64
  Experimental:     false
 containerd:
  Version:          1.6.31
  GitCommit:        e377cd56a71523140ca6ae87e30244719194a521
 runc:
  Version:          1.1.12
  GitCommit:        v1.1.12-0-g51d5e94
 docker-init:
  Version:          0.19.0
  GitCommit:        de40ad0

docker info

Client: Docker Engine - Community
 Version:    26.1.1
 Context:    default
 Debug Mode: false
 Plugins:
  buildx: Docker Buildx (Docker Inc.)
    Version:  v0.14.0
    Path:     /usr/libexec/docker/cli-plugins/docker-buildx
  compose: Docker Compose (Docker Inc.)
    Version:  v2.27.0
    Path:     /usr/libexec/docker/cli-plugins/docker-compose

Server:
 Containers: 0
  Running: 0
  Paused: 0
  Stopped: 0
 Images: 3
 Server Version: 26.1.1
 Storage Driver: overlay2
  Backing Filesystem: extfs
  Supports d_type: true
  Using metacopy: false
  Native Overlay Diff: true
  userxattr: false
 Logging Driver: json-file
 Cgroup Driver: cgroupfs
 Cgroup Version: 1
 Plugins:
  Volume: local
  Network: bridge host ipvlan macvlan null overlay
  Log: awslogs fluentd gcplogs gelf journald json-file local splunk syslog
 Swarm: inactive
 Runtimes: io.containerd.runc.v2 runc
 Default Runtime: runc
 Init Binary: docker-init
 containerd version: e377cd56a71523140ca6ae87e30244719194a521
 runc version: v1.1.12-0-g51d5e94
 init version: de40ad0
 Security Options:
  apparmor
  seccomp
   Profile: builtin
 Kernel Version: 5.4.0-167-generic
 Operating System: Ubuntu 20.04.6 LTS
 OSType: linux
 Architecture: x86_64
 CPUs: 2
 Total Memory: 3.741GiB
 Name: test-ubuntu
 ID: 3a3c7d87-cb84-40bd-a2a9-7aa2986e2754
 Docker Root Dir: /var/lib/docker
 Debug Mode: true
  File Descriptors: 25
  Goroutines: 41
  System Time: 2024-05-03T19:19:47.644464025Z
  EventsListeners: 0
 Experimental: false
 Insecure Registries:
  127.0.0.0/8
 Live Restore Enabled: false

WARNING: No swap limit support

Additional Info

No response