constellation/internal/versionsapi/fetcher/fetcher.go

/*
Copyright (c) Edgeless Systems GmbH

SPDX-License-Identifier: AGPL-3.0-only
*/

package fetcher

import (
	"context"
	"encoding/json"
	"fmt"
	"net/http"

	"github.com/edgelesssys/constellation/v2/internal/versionsapi"
)

// Fetcher fetches versions API resources.
//
// The fetcher is used to get information from the versions API without having to
// authenticate with AWS. It is the interface that should be used in user-facing
// application code most of the time.
type Fetcher struct {
	httpc httpc
}

// NewFetcher returns a new Fetcher.
func NewFetcher() *Fetcher {
	return &Fetcher{
		httpc: http.DefaultClient,
	}
}

// FetchVersionList fetches the given version list from the versions API.
func (f *Fetcher) FetchVersionList(ctx context.Context, list versionsapi.List) (versionsapi.List, error) {
	return fetch(ctx, f.httpc, list)
}

// FetchVersionLatest fetches the latest version from the versions API.
func (f *Fetcher) FetchVersionLatest(ctx context.Context, latest versionsapi.Latest) (versionsapi.Latest, error) {
	return fetch(ctx, f.httpc, latest)
}

// FetchImageInfo fetches the given image info from the versions API.
func (f *Fetcher) FetchImageInfo(ctx context.Context, imageInfo versionsapi.ImageInfo) (versionsapi.ImageInfo, error) {
	return fetch(ctx, f.httpc, imageInfo)
}

type apiObject interface {
	ValidateRequest() error
	Validate() error
	URL() (string, error)
}

func fetch[T apiObject](ctx context.Context, c httpc, obj T) (T, error) {
	if err := obj.ValidateRequest(); err != nil {
		return *new(T), fmt.Errorf("validating request for %T: %w", obj, err)
	}

	url, err := obj.URL()
	if err != nil {
		return *new(T), fmt.Errorf("getting URL for %T: %w", obj, err)
	}

	req, err := http.NewRequestWithContext(ctx, http.MethodGet, url, http.NoBody)
	if err != nil {
		return *new(T), fmt.Errorf("creating request for %T: %w", obj, err)
	}

	resp, err := c.Do(req)
	if err != nil {
		return *new(T), fmt.Errorf("sending request for %T: %w", obj, err)
	}
	defer resp.Body.Close()
	switch resp.StatusCode {
	case http.StatusOK:
	case http.StatusNotFound:
		return *new(T), &NotFoundError{fmt.Errorf("requesting resource at %s returned status code 404", url)}
	default:
		return *new(T), fmt.Errorf("unexpected status code %d while requesting resource", resp.StatusCode)
	}

	var newObj T
	if err := json.NewDecoder(resp.Body).Decode(&newObj); err != nil {
		return *new(T), fmt.Errorf("decoding %T: %w", obj, err)
	}

	if newObj.Validate() != nil {
		return *new(T), fmt.Errorf("received invalid %T: %w", newObj, newObj.Validate())
	}

	return newObj, nil
}

// NotFoundError is an error that is returned when a resource is not found.
type NotFoundError struct {
	err error
}

func (e *NotFoundError) Error() string {
	return fmt.Sprintf("the requested resource was not found: %s", e.err.Error())
}

func (e *NotFoundError) Unwrap() error {
	return e.err
}

type httpc interface {
	Do(req *http.Request) (*http.Response, error)
}