func checkFileHasContents(c *gc.C, stor storage.StorageReader, name string, contents []byte, attempt utils.AttemptStrategy) {
	r, err := storage.GetWithRetry(stor, name, attempt)
	c.Assert(err, gc.IsNil)
	c.Check(r, gc.NotNil)
	defer r.Close()

	data, err := ioutil.ReadAll(r)
	c.Check(err, gc.IsNil)
	c.Check(data, gc.DeepEquals, contents)

	url, err := stor.URL(name)
	c.Assert(err, gc.IsNil)

	var resp *http.Response
	for a := attempt.Start(); a.Next(); {
		resp, err = utils.GetValidatingHTTPClient().Get(url)
		c.Assert(err, gc.IsNil)
		if resp.StatusCode != 404 {
			break
		}
		c.Logf("get retrying after earlier get succeeded. *sigh*.")
	}
	c.Assert(err, gc.IsNil)
	data, err = ioutil.ReadAll(resp.Body)
	c.Assert(err, gc.IsNil)
	defer resp.Body.Close()
	c.Assert(resp.StatusCode, gc.Equals, 200, gc.Commentf("error response: %s", data))
	c.Check(data, gc.DeepEquals, contents)
}

func readImageMetadata(stor storage.StorageReader, path string) ([]byte, error) {
	r, err := stor.Get(path)
	if err != nil {
		return nil, err
	}
	defer r.Close()
	return ioutil.ReadAll(r)
}

// ParseMetadataFromStorage loads ImageMetadata from the specified storage reader.
func ParseMetadataFromStorage(c *gc.C, stor storage.StorageReader) []*imagemetadata.ImageMetadata {
	source := storage.NewStorageSimpleStreamsDataSource("test storage reader", stor, "images")

	// Find the simplestreams index file.
	params := simplestreams.ValueParams{
		DataType:      "image-ids",
		ValueTemplate: imagemetadata.ImageMetadata{},
	}
	const requireSigned = false
	indexPath := simplestreams.UnsignedIndex
	indexRef, err := simplestreams.GetIndexWithFormat(
		source, indexPath, "index:1.0", requireSigned, simplestreams.CloudSpec{}, params)
	c.Assert(err, gc.IsNil)
	c.Assert(indexRef.Indexes, gc.HasLen, 1)

	imageIndexMetadata := indexRef.Indexes["com.ubuntu.cloud:custom"]
	c.Assert(imageIndexMetadata, gc.NotNil)

	// Read the products file contents.
	r, err := stor.Get(path.Join("images", imageIndexMetadata.ProductsFilePath))
	defer r.Close()
	c.Assert(err, gc.IsNil)
	data, err := ioutil.ReadAll(r)
	c.Assert(err, gc.IsNil)

	// Parse the products file metadata.
	url, err := source.URL(imageIndexMetadata.ProductsFilePath)
	c.Assert(err, gc.IsNil)
	cloudMetadata, err := simplestreams.ParseCloudMetadata(data, "products:1.0", url, imagemetadata.ImageMetadata{})
	c.Assert(err, gc.IsNil)

	// Collate the metadata.
	imageMetadataMap := make(map[string]*imagemetadata.ImageMetadata)
	var expectedProductIds set.Strings
	var imageVersions set.Strings
	for _, mc := range cloudMetadata.Products {
		for _, items := range mc.Items {
			for key, item := range items.Items {
				imageMetadata := item.(*imagemetadata.ImageMetadata)
				imageMetadataMap[key] = imageMetadata
				imageVersions.Add(key)
				productId := fmt.Sprintf("com.ubuntu.cloud:server:%s:%s", mc.Version, imageMetadata.Arch)
				expectedProductIds.Add(productId)
			}
		}
	}

	// Make sure index's product IDs are all represented in the products metadata.
	sort.Strings(imageIndexMetadata.ProductIds)
	c.Assert(imageIndexMetadata.ProductIds, gc.DeepEquals, expectedProductIds.SortedValues())

	imageMetadata := make([]*imagemetadata.ImageMetadata, len(imageMetadataMap))
	for i, key := range imageVersions.SortedValues() {
		imageMetadata[i] = imageMetadataMap[key]
	}
	return imageMetadata
}

// ReadList returns a List of the tools in store with the given major.minor version.
// If minorVersion = -1, then only majorVersion is considered.
// If store contains no such tools, it returns ErrNoMatches.
func ReadList(stor storage.StorageReader, toolsDir string, majorVersion, minorVersion int) (coretools.List, error) {
	if minorVersion >= 0 {
		logger.Debugf("reading v%d.%d tools", majorVersion, minorVersion)
	} else {
		logger.Debugf("reading v%d.* tools", majorVersion)
	}
	storagePrefix := storagePrefix(toolsDir)
	names, err := storage.List(stor, storagePrefix)
	if err != nil {
		return nil, err
	}
	var list coretools.List
	var foundAnyTools bool
	for _, name := range names {
		name = filepath.ToSlash(name)
		if !strings.HasPrefix(name, storagePrefix) || !strings.HasSuffix(name, toolSuffix) {
			continue
		}
		var t coretools.Tools
		vers := name[len(storagePrefix) : len(name)-len(toolSuffix)]
		if t.Version, err = version.ParseBinary(vers); err != nil {
			logger.Debugf("failed to parse version %q: %v", vers, err)
			continue
		}
		foundAnyTools = true
		// Major version must match specified value.
		if t.Version.Major != majorVersion {
			continue
		}
		// If specified minor version value supplied, minor version must match.
		if minorVersion >= 0 && t.Version.Minor != minorVersion {
			continue
		}
		logger.Debugf("found %s", vers)
		if t.URL, err = stor.URL(name); err != nil {
			return nil, err
		}
		list = append(list, &t)
		// Older versions of Juju only know about ppc64, so add metadata for that arch.
		if t.Version.Arch == arch.PPC64EL {
			legacyPPC64Tools := t
			legacyPPC64Tools.Version.Arch = arch.LEGACY_PPC64
			list = append(list, &legacyPPC64Tools)
		}
	}
	if len(list) == 0 {
		if foundAnyTools {
			return nil, coretools.ErrNoMatches
		}
		return nil, ErrNoTools
	}
	return list, nil
}

// ReadList returns a List of the tools in store with the given major.minor version.
// If minorVersion = -1, then only majorVersion is considered.
// If store contains no such tools, it returns ErrNoMatches.
func ReadList(stor storage.StorageReader, majorVersion, minorVersion int) (coretools.List, error) {
	if minorVersion >= 0 {
		logger.Debugf("reading v%d.%d tools", majorVersion, minorVersion)
	} else {
		logger.Debugf("reading v%d.* tools", majorVersion)
	}
	names, err := storage.List(stor, toolPrefix)
	if err != nil {
		return nil, err
	}
	var list coretools.List
	var foundAnyTools bool
	for _, name := range names {
		if !strings.HasPrefix(name, toolPrefix) || !strings.HasSuffix(name, toolSuffix) {
			continue
		}
		var t coretools.Tools
		vers := name[len(toolPrefix) : len(name)-len(toolSuffix)]
		if t.Version, err = version.ParseBinary(vers); err != nil {
			logger.Debugf("failed to parse version %q: %v", vers, err)
			continue
		}
		foundAnyTools = true
		// Major version must match specified value.
		if t.Version.Major != majorVersion {
			continue
		}
		// If specified minor version value supplied, minor version must match.
		if minorVersion >= 0 && t.Version.Minor != minorVersion {
			continue
		}
		logger.Debugf("found %s", vers)
		if t.URL, err = stor.URL(name); err != nil {
			return nil, err
		}
		list = append(list, &t)
	}
	if len(list) == 0 {
		if foundAnyTools {
			return nil, coretools.ErrNoMatches
		}
		return nil, ErrNoTools
	}
	return list, nil
}

func checkFileHasContents(c *gc.C, stor storage.StorageReader, name string, contents []byte) {
	r, err := storage.Get(stor, name)
	c.Assert(err, gc.IsNil)
	c.Check(r, gc.NotNil)
	defer r.Close()
	data, err := ioutil.ReadAll(r)
	c.Check(err, gc.IsNil)
	c.Check(data, gc.DeepEquals, contents)

	url, err := stor.URL(name)
	c.Assert(err, gc.IsNil)
	resp, err := http.Get(url)
	c.Assert(err, gc.IsNil)
	data, err = ioutil.ReadAll(resp.Body)
	c.Assert(err, gc.IsNil)
	defer resp.Body.Close()
	c.Assert(resp.StatusCode, gc.Equals, http.StatusOK, gc.Commentf("error response: %s", data))
	c.Check(data, gc.DeepEquals, contents)
}

// migrateCustomImageMetadata copies uploaded image metadata from provider
// storage to environment storage, preserving paths.
func migrateCustomImageMetadata(st *state.State, agentConfig agent.Config) error {
	logger.Debugf("migrating custom image metadata to environment storage")
	estor := newStateStorage(st.EnvironUUID(), st.MongoSession())

	// Local and manual provider host storage on the state server's
	// filesystem, and serve via HTTP storage. The storage worker
	// doesn't run yet, so we just open the files directly.
	var pstor storage.StorageReader
	providerType := agentConfig.Value(agent.ProviderType)
	if providerType == provider.Local || provider.IsManual(providerType) {
		storageDir := agentConfig.Value(agent.StorageDir)
		var err error
		pstor, err = filestorage.NewFileStorageReader(storageDir)
		if err != nil {
			return errors.Annotate(err, "cannot get local filesystem storage reader")
		}
	} else {
		var err error
		pstor, err = environs.LegacyStorage(st)
		if errors.IsNotSupported(err) {
			return nil
		} else if err != nil {
			return errors.Annotate(err, "cannot get provider storage")
		}
	}

	paths, err := pstor.List(storage.BaseImagesPath)
	if err != nil {
		return err
	}
	for _, path := range paths {
		logger.Infof("migrating image metadata at path %q", path)
		data, err := readImageMetadata(pstor, path)
		if err != nil {
			return errors.Annotate(err, "failed to read image metadata")
		}
		err = estor.Put(path, bytes.NewReader(data), int64(len(data)))
		if err != nil {
			return errors.Annotate(err, "failed to write image metadata")
		}
	}
	return nil
}

// ParseMetadataFromStorage loads ImageMetadata from the specified storage reader.
func ParseMetadataFromStorage(c *gc.C, stor storage.StorageReader) []*imagemetadata.ImageMetadata {
	imageIndexMetadata, source := ParseIndexMetadataFromStorage(c, stor)
	c.Assert(imageIndexMetadata, gc.NotNil)

	// Read the products file contents.
	r, err := stor.Get(path.Join("images", imageIndexMetadata.ProductsFilePath))
	defer r.Close()
	c.Assert(err, jc.ErrorIsNil)
	data, err := ioutil.ReadAll(r)
	c.Assert(err, jc.ErrorIsNil)

	// Parse the products file metadata.
	url, err := source.URL(imageIndexMetadata.ProductsFilePath)
	c.Assert(err, jc.ErrorIsNil)
	cloudMetadata, err := simplestreams.ParseCloudMetadata(data, "products:1.0", url, imagemetadata.ImageMetadata{})
	c.Assert(err, jc.ErrorIsNil)

	// Collate the metadata.
	imageMetadataMap := make(map[string]*imagemetadata.ImageMetadata)
	expectedProductIds, imageVersions := make(set.Strings), make(set.Strings)
	for _, mc := range cloudMetadata.Products {
		for _, items := range mc.Items {
			for key, item := range items.Items {
				imageMetadata := item.(*imagemetadata.ImageMetadata)
				imageMetadataMap[key] = imageMetadata
				imageVersions.Add(key)
				productId := fmt.Sprintf("com.ubuntu.cloud:server:%s:%s", mc.Version, imageMetadata.Arch)
				expectedProductIds.Add(productId)
			}
		}
	}

	// Make sure index's product IDs are all represented in the products metadata.
	sort.Strings(imageIndexMetadata.ProductIds)
	c.Assert(imageIndexMetadata.ProductIds, gc.DeepEquals, expectedProductIds.SortedValues())

	imageMetadata := make([]*imagemetadata.ImageMetadata, len(imageMetadataMap))
	for i, key := range imageVersions.SortedValues() {
		imageMetadata[i] = imageMetadataMap[key]
	}
	return imageMetadata
}

func fetchToolsArchive(stor storage.StorageReader, toolsDir string, agentTools *tools.Tools) ([]byte, error) {
	r, err := stor.Get(envtools.StorageName(agentTools.Version, toolsDir))
	if err != nil {
		return nil, err
	}
	defer r.Close()

	var buf bytes.Buffer
	hash, size, err := utils.ReadSHA256(io.TeeReader(r, &buf))
	if err != nil {
		return nil, err
	}
	if hash != agentTools.SHA256 {
		return nil, errors.New("hash mismatch")
	}
	if size != agentTools.Size {
		return nil, errors.New("size mismatch")
	}
	return buf.Bytes(), nil
}

// ParseMetadataFromStorage loads ToolsMetadata from the specified storage reader.
func ParseMetadataFromStorage(c *gc.C, stor storage.StorageReader, stream string, expectMirrors bool) []*tools.ToolsMetadata {
	source := storage.NewStorageSimpleStreamsDataSource("test storage reader", stor, "tools")
	params := simplestreams.ValueParams{
		DataType:      tools.ContentDownload,
		ValueTemplate: tools.ToolsMetadata{},
	}

	const requireSigned = false
	indexPath := simplestreams.UnsignedIndex("v1", 2)
	mirrorsPath := simplestreams.MirrorsPath("v1")
	indexRef, err := simplestreams.GetIndexWithFormat(
		source, indexPath, "index:1.0", mirrorsPath, requireSigned, simplestreams.CloudSpec{}, params)
	c.Assert(err, jc.ErrorIsNil)

	toolsIndexMetadata := indexRef.Indexes[tools.ToolsContentId(stream)]
	c.Assert(toolsIndexMetadata, gc.NotNil)

	// Read the products file contents.
	r, err := stor.Get(path.Join("tools", toolsIndexMetadata.ProductsFilePath))
	defer r.Close()
	c.Assert(err, jc.ErrorIsNil)
	data, err := ioutil.ReadAll(r)
	c.Assert(err, jc.ErrorIsNil)

	url, err := source.URL(toolsIndexMetadata.ProductsFilePath)
	c.Assert(err, jc.ErrorIsNil)
	cloudMetadata, err := simplestreams.ParseCloudMetadata(data, "products:1.0", url, tools.ToolsMetadata{})
	c.Assert(err, jc.ErrorIsNil)

	toolsMetadataMap := make(map[string]*tools.ToolsMetadata)
	expectedProductIds := make(set.Strings)
	toolsVersions := make(set.Strings)
	for _, mc := range cloudMetadata.Products {
		for _, items := range mc.Items {
			for key, item := range items.Items {
				toolsMetadata := item.(*tools.ToolsMetadata)
				toolsMetadataMap[key] = toolsMetadata
				toolsVersions.Add(key)
				seriesVersion, err := series.SeriesVersion(toolsMetadata.Release)
				if err != nil {
					c.Assert(err, jc.Satisfies, series.IsUnknownSeriesVersionError)
				}
				productId := fmt.Sprintf("com.ubuntu.juju:%s:%s", seriesVersion, toolsMetadata.Arch)
				expectedProductIds.Add(productId)
			}
		}
	}

	// Make sure index's product IDs are all represented in the products metadata.
	sort.Strings(toolsIndexMetadata.ProductIds)
	c.Assert(toolsIndexMetadata.ProductIds, gc.DeepEquals, expectedProductIds.SortedValues())

	toolsMetadata := make([]*tools.ToolsMetadata, len(toolsMetadataMap))
	for i, key := range toolsVersions.SortedValues() {
		toolsMetadata[i] = toolsMetadataMap[key]
	}

	if expectMirrors {
		r, err = stor.Get(path.Join("tools", simplestreams.UnsignedMirror("v1")))
		c.Assert(err, jc.ErrorIsNil)
		defer r.Close()
		data, err = ioutil.ReadAll(r)
		c.Assert(err, jc.ErrorIsNil)
		c.Assert(string(data), jc.Contains, `"mirrors":`)
		c.Assert(string(data), jc.Contains, tools.ToolsContentId(stream))
		c.Assert(err, jc.ErrorIsNil)
	}
	return toolsMetadata
}