CLI: use global image version field

- Restructure config by removing CSP-specific image references
- Add global image field
- Download image lookup table on create
- Download QEMU image on QEMU create

internal/image/image.go

@@ -0,0 +1,161 @@
+/*
+Copyright (c) Edgeless Systems GmbH
+
+SPDX-License-Identifier: AGPL-3.0-only
+*/
+
+package image
+
+import (
+	"context"
+	"encoding/json"
+	"fmt"
+	"io"
+	"net/http"
+	"net/url"
+	"os"
+	"path"
+	"path/filepath"
+	"strings"
+
+	"github.com/edgelesssys/constellation/v2/internal/cloud/cloudprovider"
+	"github.com/edgelesssys/constellation/v2/internal/config"
+	"github.com/edgelesssys/constellation/v2/internal/constants"
+	"github.com/spf13/afero"
+)
+
+// imageLookupTable is a lookup table for image references.
+//
+// Example:
+//
+//	{
+//	  "aws": {
+//	    "us-west-2": "ami-0123456789abcdef0"
+//	  },
+//	  "azure": {
+//	    "cvm": "cvm-image-id"
+//	  },
+//	  "gcp": {
+//	    "sev-es": "projects/<project>/global/images/<image>"
+//	  },
+//	  "qemu": {
+//	    "default": "https://cdn.example.com/image.raw"
+//	  }
+//	}
+type imageLookupTable map[string]map[string]string
+
+// getReference returns the image reference for a given CSP and image variant.
+func (l *imageLookupTable) getReference(csp, variant string) (string, error) {
+	if l == nil {
+		return "", fmt.Errorf("image lookup table is nil")
+	}
+	if _, ok := (*l)[csp]; !ok {
+		return "", fmt.Errorf("image not available for CSP %q", csp)
+	}
+	if _, ok := (*l)[csp][variant]; !ok {
+		return "", fmt.Errorf("image not available for variant %q", variant)
+	}
+	return (*l)[csp][variant], nil
+}
+
+// Fetcher fetches image references using a lookup table.
+type Fetcher struct {
+	httpc httpc
+	fs    *afero.Afero
+}
+
+// New returns a new image fetcher.
+func New() *Fetcher {
+	return &Fetcher{
+		httpc: http.DefaultClient,
+		fs:    &afero.Afero{Fs: afero.NewOsFs()},
+	}
+}
+
+// FetchReference fetches the image reference for a given image version uid, CSP and image variant.
+func (f *Fetcher) FetchReference(ctx context.Context, config *config.Config) (string, error) {
+	provider := config.GetProvider()
+	variant, err := variant(provider, config)
+	if err != nil {
+		return "", err
+	}
+	return f.fetch(ctx, provider, config.Image, variant)
+}
+
+// fetch fetches the image reference for a given image version uid, CSP and image variant.
+func (f *Fetcher) fetch(ctx context.Context, csp cloudprovider.Provider, version, variant string) (string, error) {
+	raw, err := getFromFile(f.fs, version)
+	if err != nil && os.IsNotExist(err) {
+		raw, err = getFromURL(ctx, f.httpc, version)
+	}
+	if err != nil {
+		return "", fmt.Errorf("fetching image reference: %w", err)
+	}
+	lut := make(imageLookupTable)
+	if err := json.Unmarshal(raw, &lut); err != nil {
+		return "", fmt.Errorf("decoding image reference: %w", err)
+	}
+	return lut.getReference(strings.ToLower(csp.String()), variant)
+}
+
+// variant returns the image variant for a given CSP and configuration.
+func variant(provider cloudprovider.Provider, config *config.Config) (string, error) {
+	switch provider {
+	case cloudprovider.AWS:
+		return config.Provider.AWS.Region, nil
+	case cloudprovider.Azure:
+		if *config.Provider.Azure.ConfidentialVM {
+			return "cvm", nil
+		}
+		return "trustedlaunch", nil
+
+	case cloudprovider.GCP:
+		return "sev-es", nil
+	case cloudprovider.QEMU:
+		return "default", nil
+	default:
+		return "", fmt.Errorf("unsupported provider: %s", provider)
+	}
+}
+
+func getFromFile(fs *afero.Afero, version string) ([]byte, error) {
+	version = filepath.Base(version)
+	return fs.ReadFile(version + ".json")
+}
+
+// getFromURL fetches the image lookup table from a URL.
+func getFromURL(ctx context.Context, client httpc, version string) ([]byte, error) {
+	url, err := url.Parse(constants.ImageVersionRepositoryURL)
+	if err != nil {
+		return nil, fmt.Errorf("parsing image version repository URL: %w", err)
+	}
+	versionFilename := path.Base(version) + ".json"
+	url.Path = path.Join("constellation/v1/images", versionFilename)
+	req, err := http.NewRequestWithContext(ctx, http.MethodGet, url.String(), http.NoBody)
+	if err != nil {
+		return nil, err
+	}
+
+	resp, err := client.Do(req)
+	if err != nil {
+		return nil, err
+	}
+	defer resp.Body.Close()
+	if resp.StatusCode != http.StatusOK {
+		switch resp.StatusCode {
+		case http.StatusNotFound:
+			return nil, fmt.Errorf("image %q does not exist", version)
+		default:
+			return nil, fmt.Errorf("unexpected status code %d", resp.StatusCode)
+		}
+	}
+	content, err := io.ReadAll(resp.Body)
+	if err != nil {
+		return nil, err
+	}
+	return content, nil
+}
+
+type httpc interface {
+	Do(req *http.Request) (*http.Response, error)
+}