feat: check for Docker connectivity on install (#38)

Fixes #30

pkgmgr/docker.go

@@ -16,6 +16,7 @@ package pkgmgr
 
 import (
 	"context"
+	"errors"
 	"fmt"
 	"io"
 	"log/slog"
@@ -28,6 +29,20 @@ import (
 	"github.com/docker/go-connections/nat"
 )
 
+const (
+	dockerInstallError = `could not contact Docker daemon
+
+Docker is required to be already installed and running. Please refer to the following pages for more information
+about how to install Docker.
+
+ * https://docs.docker.com/get-docker/
+ * https://docs.docker.com/engine/install/
+
+If Docker is already installed but the socket is not in a standard location, you can use the DOCKER_HOST environment
+variable to point to it.
+`
+)
+
 type DockerService struct {
 	client        *client.Client
 	logger        *slog.Logger
@@ -287,6 +302,7 @@ func (d *DockerService) getClient() (*client.Client, error) {
 	if d.client == nil {
 		tmpClient, err := client.NewClientWithOpts(
 			client.WithAPIVersionNegotiation(),
+			client.WithHostFromEnv(),
 		)
 		if err != nil {
 			return nil, err
@@ -295,3 +311,11 @@ func (d *DockerService) getClient() (*client.Client, error) {
 	}
 	return d.client, nil
 }
+
+func CheckDockerConnectivity() error {
+	tmpDockerService := &DockerService{}
+	if _, err := tmpDockerService.getClient(); err != nil {
+		return errors.New(dockerInstallError)
+	}
+	return nil
+}

pkgmgr/error.go

@@ -34,3 +34,6 @@ var ErrContextNotExist = errors.New("context does not exist")
 
 // ErrContextAlreadyExists is returned when creating a context with a name that is already in use
 var ErrContextAlreadyExists = errors.New("specified context already exists")
+
+// ErrContainerAlreadyExists is returned when creating a new container with a name that is already in use
+var ErrContainerAlreadyExists = errors.New("specified container already exists")

pkgmgr/package.go

@@ -30,12 +30,21 @@ type Package struct {
 
 func (p Package) install(cfg Config, context string) error {
 	pkgName := fmt.Sprintf("%s-%s-%s", p.Name, p.Version, context)
+	// Run pre-flight checks
 	for _, installStep := range p.InstallSteps {
 		// Make sure only one install method is specified per install step
 		if installStep.Docker != nil &&
 			installStep.File != nil {
 			return ErrMultipleInstallMethods
 		}
+		if installStep.Docker != nil {
+			if err := installStep.Docker.preflight(cfg, pkgName); err != nil {
+				return fmt.Errorf("pre-flight check failed: %s", err)
+			}
+		}
+	}
+	// Perform install
+	for _, installStep := range p.InstallSteps {
 		if installStep.Docker != nil {
 			if err := installStep.Docker.install(cfg, pkgName); err != nil {
 				return err
@@ -91,6 +100,21 @@ type PackageInstallStepDocker struct {
 	Ports         []string          `yaml:"ports,omitempty"`
 }
 
+func (p *PackageInstallStepDocker) preflight(cfg Config, pkgName string) error {
+	if err := CheckDockerConnectivity(); err != nil {
+		return err
+	}
+	containerName := fmt.Sprintf("%s-%s", pkgName, p.ContainerName)
+	svc, err := NewDockerServiceFromContainerName(containerName, cfg.Logger)
+	if err != nil {
+		return err
+	}
+	if svc != nil {
+		return ErrContainerAlreadyExists
+	}
+	return nil
+}
+
 func (p *PackageInstallStepDocker) install(cfg Config, pkgName string) error {
 	containerName := fmt.Sprintf("%s-%s", pkgName, p.ContainerName)
 	svc := DockerService{