constellation/internal/image/image.go

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/*
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.CDNRepositoryURL)
if err != nil {
return nil, fmt.Errorf("parsing image version repository URL: %w", err)
}
versionFilename := path.Base(version) + ".json"
url.Path = path.Join(constants.CDNImagePath, 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)
}