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container.go
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container.go
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package s3
import (
"bytes"
"io"
"strings"
"github.com/aws/aws-sdk-go/aws"
"github.com/aws/aws-sdk-go/aws/awserr"
"github.com/aws/aws-sdk-go/service/s3"
"github.com/aws/aws-sdk-go/service/s3/s3manager"
"github.com/google/uuid"
"github.com/pkg/errors"
"gomodules.xyz/stow"
)
// Amazon S3 bucket contains a creation date and a name.
type container struct {
// name is needed to retrieve items.
name string
// client is responsible for performing the requests.
client *s3.S3
// region describes the AWS Availability Zone of the S3 Bucket.
region string
customEndpoint string
}
// ID returns a string value which represents the name of the container.
func (c *container) ID() string {
return c.name
}
// Name returns a string value which represents the name of the container.
func (c *container) Name() string {
return c.name
}
// Item returns a stow.Item instance of a container based on the name of the container and the key representing. The
// retrieved item only contains metadata about the object. This ensures that only the minimum amount of information is
// transferred. Calling item.Open() will actually do a get request and open a stream to read from.
func (c *container) Item(id string) (stow.Item, error) {
return c.getItem(id)
}
// Items sends a request to retrieve a list of items that are prepended with
// the prefix argument. The 'cursor' variable facilitates pagination.
func (c *container) Browse(prefix, delimiter, cursor string, count int) (*stow.ItemPage, error) {
itemLimit := int64(count)
params := &s3.ListObjectsV2Input{
Bucket: aws.String(c.Name()),
StartAfter: &cursor,
MaxKeys: &itemLimit,
Prefix: &prefix,
}
response, err := c.client.ListObjectsV2(params)
if err != nil {
return nil, errors.Wrap(err, "Items, listing objects")
}
prefixes := make([]string, len(response.CommonPrefixes))
for i, prefix := range response.CommonPrefixes {
prefixes[i] = *prefix.Prefix
}
containerItems := make([]stow.Item, 0, len(response.Contents)) // Allocate space for the Item slice.
for _, object := range response.Contents {
if *object.StorageClass == "GLACIER" {
continue
}
etag := cleanEtag(*object.ETag) // Copy etag value and remove the strings.
object.ETag = &etag // Assign the value to the object field representing the item.
newItem := &item{
container: c,
client: c.client,
properties: properties{
ETag: object.ETag,
Key: object.Key,
LastModified: object.LastModified,
Owner: object.Owner,
Size: object.Size,
StorageClass: object.StorageClass,
},
}
containerItems = append(containerItems, newItem)
}
// Create a marker and determine if the list of items to retrieve is complete.
// If not, the last file is the input to the value of after which item to start
startAfter := ""
if *response.IsTruncated {
startAfter = containerItems[len(containerItems)-1].Name()
}
return &stow.ItemPage{Prefixes: prefixes, Items: containerItems, Cursor: startAfter}, nil
}
// Items sends a request to retrieve a list of items that are prepended with
// the prefix argument. The 'cursor' variable facilitates pagination.
func (c *container) Items(prefix, cursor string, count int) ([]stow.Item, string, error) {
page, err := c.Browse(prefix, "", cursor, count)
if err != nil {
return nil, "", err
}
return page.Items, page.Cursor, err
}
func (c *container) RemoveItem(id string) error {
params := &s3.DeleteObjectInput{
Bucket: aws.String(c.Name()),
Key: aws.String(id),
}
_, err := c.client.DeleteObject(params)
if err != nil {
return errors.Wrapf(err, "RemoveItem, deleting object %+v", params)
}
return nil
}
// Put sends a request to upload content to the container. The arguments
// received are the name of the item (S3 Object), a reader representing the
// content, and the size of the file. Many more attributes can be given to the
// file, including metadata. Keeping it simple for now.
func (c *container) Put(name string, r io.Reader, size int64, metadata map[string]interface{}) (stow.Item, error) {
// Convert map[string]interface{} to map[string]*string
mdPrepped, err := prepMetadata(metadata)
if err != nil {
return nil, errors.Wrap(err, "unable to create or update item, preparing metadata")
}
uploader := s3manager.NewUploaderWithClient(c.client)
_, err = uploader.Upload(&s3manager.UploadInput{
Bucket: aws.String(c.name), // Required
Key: aws.String(name), // Required
Body: r,
Metadata: mdPrepped, // map[string]*string
})
if err != nil {
return nil, errors.Wrap(err, "PutObject, putting object")
}
i, err := c.client.HeadObject(&s3.HeadObjectInput{
Key: aws.String(name),
Bucket: aws.String(c.name),
})
var etag string
if i.ETag != nil && err == nil {
etag = cleanEtag(*i.ETag)
}
// Some fields are empty because this information isn't included in the response.
// May have to involve sending a request if we want more specific information.
// Keeping it simple for now.
// s3.Object info: https://github.com/aws/aws-sdk-go/blob/master/service/s3/api.go#L7092-L7107
// Response: https://github.com/aws/aws-sdk-go/blob/master/service/s3/api.go#L8193-L8227
newItem := &item{
container: c,
client: c.client,
properties: properties{
ETag: &etag,
Key: &name,
Size: &size,
//LastModified *time.Time
//Owner *s3.Owner
//StorageClass *string
},
}
return newItem, nil
}
// Region returns a string representing the region/availability zone of the container.
func (c *container) Region() string {
return c.region
}
// A request to retrieve a single item includes information that is more specific than
// a PUT. Instead of doing a request within the PUT, make this method available so that the
// request can be made by the field retrieval methods when necessary. This is the case for
// fields that are left out, such as the object's last modified date. This also needs to be
// done only once since the requested information is retained.
// May be simpler to just stick it in PUT and and do a request every time, please vouch
// for this if so.
func (c *container) getItem(id string) (*item, error) {
params := &s3.HeadObjectInput{
Bucket: aws.String(c.name),
Key: aws.String(id),
}
res, err := c.client.HeadObject(params)
if err != nil {
// stow needs ErrNotFound to pass the test but amazon returns an opaque error
if aerr, ok := err.(awserr.Error); ok && aerr.Code() == "NotFound" {
return nil, stow.ErrNotFound
}
return nil, errors.Wrap(err, "getItem, getting the object")
}
etag := cleanEtag(*res.ETag) // etag string value contains quotations. Remove them.
md, err := parseMetadata(res.Metadata)
if err != nil {
return nil, errors.Wrap(err, "unable to retrieve Item information, parsing metadata")
}
i := &item{
container: c,
client: c.client,
properties: properties{
ETag: &etag,
Key: &id,
LastModified: res.LastModified,
Owner: nil, // not returned in the response.
Size: res.ContentLength,
StorageClass: res.StorageClass,
Metadata: md,
},
}
return i, nil
}
// Remove quotation marks from beginning and end. This includes quotations that
// are escaped. Also removes leading `W/` from prefix for weak Etags.
//
// Based on the Etag spec, the full etag value (<FULL ETAG VALUE>) can include:
// - W/"<ETAG VALUE>"
// - "<ETAG VALUE>"
// - ""
// Source: https://tools.ietf.org/html/rfc7232#section-2.3
//
// Based on HTTP spec, forward slash is a separator and must be enclosed in
// quotes to be used as a valid value. Hence, the returned value may include:
// - "<FULL ETAG VALUE>"
// - \"<FULL ETAG VALUE>\"
// Source: https://www.w3.org/Protocols/rfc2616/rfc2616-sec2.html#sec2.2
//
// This function contains a loop to check for the presence of the three possible
// filler characters and strips them, resulting in only the Etag value.
func cleanEtag(etag string) string {
for {
// Check if the filler characters are present
if strings.HasPrefix(etag, `\"`) {
etag = strings.Trim(etag, `\"`)
} else if strings.HasPrefix(etag, `"`) {
etag = strings.Trim(etag, `"`)
} else if strings.HasPrefix(etag, `W/`) {
etag = strings.Replace(etag, `W/`, "", 1)
} else {
break
}
}
return etag
}
// prepMetadata parses a raw map into the native type required by S3 to set metadata (map[string]*string).
// TODO: validation for key values. This function also assumes that the value of a key value pair is a string.
func prepMetadata(md map[string]interface{}) (map[string]*string, error) {
m := make(map[string]*string, len(md))
for key, value := range md {
strValue, valid := value.(string)
if !valid {
return nil, errors.Errorf(`value of key '%s' in metadata must be of type string`, key)
}
m[key] = aws.String(strValue)
}
return m, nil
}
// The first letter of a dash separated key value is capitalized, so perform a ToLower on it.
// This Key transformation of returning lowercase is consistent with other locations..
func parseMetadata(md map[string]*string) (map[string]interface{}, error) {
m := make(map[string]interface{}, len(md))
for key, value := range md {
k := strings.ToLower(key)
m[k] = *value
}
return m, nil
}
func (c *container) HasWriteAccess() error {
// TODO: Use https://docs.aws.amazon.com/AmazonS3/latest/API/RESTBucketGETpolicy.html ?
r := bytes.NewReader([]byte("CheckBucketAccess"))
item, err := c.Put(".trash/"+uuid.New().String(), r, r.Size(), nil)
if err != nil {
return err
}
if err := c.RemoveItem(item.ID()); err != nil {
return err
}
return nil
}