feat: Auto detect the use of Podman from DOCKER_HOST (#982)

* feat: Autodetect the use of Podman if no provider is set, and DOCKER_HOST contains podman.sock

Updated documentation
Unit tests for auto-detection of ProviderPodman

Co-authored-by: Manuel de la Peña <social.mdelapenya@gmail.com>

* Cleanup linter issues

* Use `t.Setenv()` in tests

* Fix the spelling of reap

---------

Co-authored-by: Manuel de la Peña <social.mdelapenya@gmail.com>
Co-authored-by: Manuel de la Peña <mdelapenya@gmail.com>

docs/system_requirements/using_podman.md

@@ -1,19 +1,18 @@
 # Using Podman instead of Docker
 
 _Testcontainers for Go_ supports the use of Podman (rootless or rootful) instead of Docker.
-In most scenarios no special setup is required.
+
+In most scenarios no special setup is required in _Testcontainers for Go_.
 _Testcontainers for Go_ will automatically discover the socket based on the `DOCKER_HOST` or the `TC_HOST` environment variables.
 Alternatively you can configure the host with a `.testcontainers.properties` file.
-The discovered Docker host is also taken into account when starting a reaper container.
-
-There's currently only one special case where additional configuration is necessary: complex container network scenarios.
+The discovered Docker host is taken into account when starting a reaper container.
+The discovered socket is used to detect the use of Podman.
 
 By default _Testcontainers for Go_ takes advantage of the default network settings both Docker and Podman are applying to newly created containers.
 It only intervenes in scenarios where a `ContainerRequest` specifies networks and does not include the default network of the current container provider.
 Unfortunately the default network for Docker is called _bridge_ where the default network in Podman is called _podman_.
-It is not even possible to create a network called _bridge_ with Podman as Podman does not allow creating a network with the same name as an already existing network mode.
 
-In such scenarios it is possible to explicitly make use of the `ProviderPodman` like so:
+In complex container network scenarios it may be required to explicitly make use of the `ProviderPodman` like so:
 
 ```go
 
@@ -36,4 +35,47 @@ func TestSomething(t *testing.T) {
 }
 ```
 
-The `ProviderPodman` configures the `DockerProvider` with the correct default network for Podman to ensure also complex network scenarios are working as with Docker.
+The `ProviderPodman` configures the `DockerProvider` with the correct default network for Podman to ensure complex network scenarios are working as with Docker.
+
+## Podman socket activation
+
+The reaper container needs to connect to the docker daemon to reap containers, so the podman socket service must be started:
+```shell
+> systemctl --user start podman.socket
+```
+
+## Fedora
+
+`DOCKER_HOST` environment variable must be set
+
+```
+> export DOCKER_HOST=unix://$XDG_RUNTIME_DIR/podman/podman.sock
+```
+
+SELinux may require a custom policy be applied to allow the reaper container to connect to and write to a socket. Once you experience the se-linux error, you can run the following commands to create and install a custom policy.
+
+```
+> sudo ausearch -c 'app' --raw | audit2allow -M my-podman
+> sudo semodule -i my-podman.pp
+```
+
+The resulting my-podman.te file should look something like this:
+```
+module my-podman2 1.0;
+
+require {
+        type user_tmp_t;
+        type container_runtime_t;
+        type container_t;
+        class sock_file write;
+        class unix_stream_socket connectto;
+}
+
+#============= container_t ==============
+allow container_t container_runtime_t:unix_stream_socket connectto;
+allow container_t user_tmp_t:sock_file write;
+
+```
+
+**NOTE: It will take two rounds of installing a policy, then experiencing the next se-linux issue, install new policy, etc...**
+

provider.go

@@ -4,11 +4,14 @@ import (
 	"context"
 	"errors"
 	"fmt"
+	"os"
+	"strings"
 )
 
 // possible provider types
 const (
-	ProviderDocker ProviderType = iota // Docker is default = 0
+	ProviderDefault ProviderType = iota // default will auto-detect provider from DOCKER_HOST environment variable
+	ProviderDocker
 	ProviderPodman
 )
 
@@ -97,8 +100,13 @@ func (t ProviderType) GetProvider(opts ...GenericProviderOption) (GenericProvide
 		o.ApplyGenericTo(opt)
 	}
 
-	switch t {
-	case ProviderDocker:
+	pt := t
+	if pt == ProviderDefault && strings.Contains(os.Getenv("DOCKER_HOST"), "podman.sock") {
+		pt = ProviderPodman
+	}
+
+	switch pt {
+	case ProviderDefault, ProviderDocker:
 		providerOptions := append(Generic2DockerOptions(opts...), WithDefaultBridgeNetwork(Bridge))
 		provider, err := NewDockerProvider(providerOptions...)
 		if err != nil {

provider_test.go

@@ -0,0 +1,74 @@
+package testcontainers
+
+import (
+	"testing"
+)
+
+func TestProviderTypeGetProviderAutodetect(t *testing.T) {
+	const dockerSocket = "unix:///var/run/docker.sock"
+	const podmanSocket = "unix://$XDG_RUNTIME_DIR/podman/podman.sock"
+
+	tests := []struct {
+		name       string
+		tr         ProviderType
+		DockerHost string
+		want       string
+		wantErr    bool
+	}{
+		{
+			name:       "default provider without podman.socket",
+			tr:         ProviderDefault,
+			DockerHost: dockerSocket,
+			want:       Bridge,
+		},
+		{
+			name:       "default provider with podman.socket",
+			tr:         ProviderDefault,
+			DockerHost: podmanSocket,
+			want:       Podman,
+		},
+		{
+			name:       "docker provider without podman.socket",
+			tr:         ProviderDocker,
+			DockerHost: dockerSocket,
+			want:       Bridge,
+		},
+		{
+			// Explicitly setting Docker provider should not be overridden by auto-detect
+			name:       "docker provider with podman.socket",
+			tr:         ProviderDocker,
+			DockerHost: podmanSocket,
+			want:       Bridge,
+		},
+		{
+			name:       "Podman provider without podman.socket",
+			tr:         ProviderPodman,
+			DockerHost: dockerSocket,
+			want:       Podman,
+		},
+		{
+			name:       "Podman provider with podman.socket",
+			tr:         ProviderPodman,
+			DockerHost: podmanSocket,
+			want:       Podman,
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			t.Setenv("DOCKER_HOST", tt.DockerHost)
+
+			got, err := tt.tr.GetProvider()
+			if (err != nil) != tt.wantErr {
+				t.Errorf("ProviderType.GetProvider() error = %v, wantErr %v", err, tt.wantErr)
+				return
+			}
+			provider, ok := got.(*DockerProvider)
+			if !ok {
+				t.Fatalf("ProviderType.GetProvider() = %T, want %T", got, &DockerProvider{})
+			}
+			if provider.defaultBridgeNetworkName != tt.want {
+				t.Errorf("ProviderType.GetProvider() = %v, want %v", provider.defaultBridgeNetworkName, tt.want)
+			}
+		})
+	}
+}