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Overview ¶
Package uploader manages media files uploaded to a server. The files are assumed to be destined to belong to a parent database object, such as a slideshow, with the files being uploaded asynchronously from a form that modifies the parent. The parent need not exist at the time of upload, and a log is used to maintain consistency between the database and the media files.
Images are resized to fit within limits specified by the server. Videos are converted to MP4 format. Thumbnails are generated for both images and videos.
Note that files are given revision numbers for these reasons: (1) A different name forces browsers to fetch the updated file after its content has been changed. (2) It allows us to upload an file without overwriting the current one, and then forget it if the update form is not submitted. (3) The committed state of an object may be displayed with its files, while a new state is being prepared.
uploader maintains consistency between the parent object and the media files it references, with these limitations:
- Object saved before EndSave is completed : there is a brief period when new media files cannot be displayed. ## Can I check?
- After object saved, and before the bind operation, there is a brief period where it references new files and has deleted files removed, but still references the previous versions of updated files.
Use the uploader as follows:
(1) A web request is received to create or update a parent object: call Begin and add the transaction code as a hidden field in the form. Use NameFromFile to extract the media names shown to users from the media file names.
(2) A media file is uploaded via an AJAX request: call Save with the transaction code. Images are resized and thumbnails generated asynchronously to the request.
(3) A parent object is created, updated or deleted: call SetParent to associate the transaction code with the object. Use CleanName to sanitise user names for media, and use MediaType to check that uploaded file types are acceptable. If the media name is new or changed, call FileFromName to get the file name to be stored in the database. (Changed versions for existing names are handled in step 5.) Call tx.SetNext ensure the next step will be executed, commit the change to the database.
(4) Call DoNext. The uploader waits for any uploads to be processed, and then calls the operation specified by etx.SetNext.
(5) Handle the parent bind request from DoNext.
(i) Call StartBind to begin updating references between the parent and the media files.
(ii) For each media file referenced by the parent, call Bind.File, and record any new or updated references. Save the parent in the database.
(6) After the parent update has been committed, call Bind.End. Any existing files not listed by Bind will be deleted.
When deleting an object, call StartBind (with no request code), delete the object and then call EndBind.
Use Thumbnail to get the file name for a thumbnail image corresponding to a media file.
Index ¶
- Constants
- Variables
- func CleanName(name string) string
- func FileFromName(id etx.TxId, name string) string
- func NameFromFile(fileName string) (string, string, int)
- func Thumbnail(filename string) string
- type Bind
- type DB
- type OpOrphans
- type Uploader
- func (up *Uploader) Begin() (string, error)
- func (up *Uploader) DoNext(tx etx.TxId)
- func (up *Uploader) ForOperation(opType int) etx.Op
- func (up *Uploader) Initialise(log *log.Logger, db DB, tm *etx.TM)
- func (up *Uploader) MediaType(name string) int
- func (up *Uploader) Name() string
- func (up *Uploader) Operation(id etx.TxId, opType int, op etx.Op)
- func (up *Uploader) Save(fh *multipart.FileHeader, tx etx.TxId) (err error, byClient bool)
- func (up *Uploader) StartBind(parentId int64, tx etx.TxId) *Bind
- func (up *Uploader) Stop()
- func (up *Uploader) ValidCode(tx etx.TxId) bool
Constants ¶
const ( MediaImage = 1 MediaVideo = 2 MediaAudio = 3 )
Variables ¶
var WebFiles embed.FS
WebFiles are the package's web resources (templates and static files)
Functions ¶
func CleanName ¶
CleanName removes unwanted characters from a filename, to make it safe for display and storage. From https://stackoverflow.com/questions/54461423/efficient-way-to-remove-all-non-alphanumeric-characters-from-large-text. ## This is far more restrictive than we need.
func FileFromName ¶
FileFromName returns a stored file name from a user's name for a newly uploaded file. The owner is a transaction code, because the parent object may not exist yet. It has no revision number, so it doesn't overwrite a previous copy yet.
func NameFromFile ¶
NameFromFile returns the owner ID, media file name and revision from a file name. If the revision is 0, the owner is the request, otherwise the owner is a parent object.
Types ¶
type Bind ¶ added in v0.9.0
type Bind struct {
// contains filtered or unexported fields
}
Context for a sequence of bind calls.
type DB ¶ added in v0.9.0
type DB interface {
Begin() func() // start transaction and return commit function
}
DB is an interface to the database manager that handles parent transactions.
type OpOrphans ¶ added in v0.9.0
type OpOrphans struct {
// contains filtered or unexported fields
}
type Uploader ¶
type Uploader struct {
// parameters
FilePath string
MaxW int
MaxH int
ThumbW int
ThumbH int
MaxAge time.Duration // maximum time for a parent update
SnapshotAt time.Duration // snapshot time in video (-ve for none)
AudioTypes []string
VideoPackage string // software for video processing: ffmpeg, or a docker-hosted implementation of ffmpeg, for debugging
VideoTypes []string
// contains filtered or unexported fields
}
Uploader holds the parameters and state for uploading files. Typically only one is needed.
func (*Uploader) Begin ¶ added in v0.9.0
Begin returns an identifier for an update that may include a set of uploads. It expects that a database transaction (needed to write redo records) has been started.
func (*Uploader) DoNext ¶ added in v0.9.0
DoNext executes the parent's operation specified by etx.SetNext, when all uploaded images have been saved.
func (*Uploader) Initialise ¶ added in v0.9.0
Initialise starts the file uploader.
func (*Uploader) MediaType ¶ added in v0.9.0
MediaType returns the media type. It is 0 if not accepted.
func (*Uploader) Save ¶
Save decodes an uploaded file, and schedules it to be saved in the filesystem.
Source Files