Make uploads to a resource fail cleanly, keep files of one name apart, and add a drop zone and a file list

[reiern70]

Closes #1670
Closes #1669

Two commits, one per issue; the second builds on the first. The follow-ups from review are folded into the commit they belong to.

Make uploads to a resource fail cleanly and keep files of one name apart (#1670)

• A failed upload calls onUploadFailure() with "The upload failed." (new key uploadToResourceFailed) instead of ending on the error page.
• The field only accepts the resource keys of the limits, of no files selected and of a lost connection. An HTTP status text or an answer that is not JSON reads as a failed upload, instead of throwing MissingResourceException or claiming the file is too large.
• A connection that breaks off before the server answers is reported as uploadConnectionLost, worded "The upload failed: the connection to the server was lost." The key check is the protected getUploadErrorMessage(String), so a subclass can word keys its own script reports.
• The resource no longer sends exception messages to the browser. It logs them as errors, which it did not do at all before.
• The script checks the limits of the field before sending. Files beyond them get the message of the limit and are not uploaded, instead of the server resetting the connection.
• A second upload of the same field is refused while one runs. Before, the two requests shared the progress information in the session, and one of them failed.
• The received files are reported to the field by POST. Before, beyond some 65 files the GET URL exceeded the request line limit of Jetty and Tomcat and onUploadSuccess() was never called.
• FolderUploadsFileManager stores files under random names, so two files with the same name no longer overwrite each other.
• cancel() does nothing once the upload has ended, and a before-send callback returning false keeps the upload from being sent.

Add a drop zone and a file list to uploads to a resource (#1669)

• FileDropZoneBehavior makes any component a drop target for the files of a field. It respects the accept and multiple attributes of the input, leaves folders out, and sets wicket-upload-dragover while files are dragged over it.
• FileListBehavior, on a <ul> or <ol>, lists the files chosen for the next upload, each with a Remove button (key uploadToResourceRemove). With a list and a multiple input, files chosen or dropped add up instead of replacing each other. Uploaded files leave the list, failed ones stay.
• A field without these behaviors works as before.
• The upload-to-resource example shows both. Its styles never applied, because they were in a <head> the page ignores and inline, which the CSP of the examples blocks, so they are in UploadToResourcePage.css now. Its guard against leaving the page during an upload used jQuery and failed under the plain JavaScript engine. Its explanation also says that the limits are checked before anything is sent and that files of one name are kept apart.

API changes and migration

Keeping files of one name apart needs a stored name that travels from the file manager through the browser back to the field, so on master:

• IUploadsFileManager gets store(FileUpload, String), which returns the stored name. save() is deprecated for removal, and Wicket no longer calls it. The default store() calls save(), so an implementation written for save() keeps working, with the old behaviour for files of one name. The default save() throws an UnsupportedOperationException, so a manager that implements neither method fails with a clear message at its first upload rather than with a StackOverflowError.
• AbstractFileUploadResource.saveFiles() returns the stored names, and prepareResponse() and generateJsonResponse() receive them. FileUploadResourceReference.generateFileInfo() receives the stored name as well. These are hooks for subclasses, so the signatures change rather than keeping deprecated ones that would no longer be called: an override fails to compile instead of being skipped silently.
• UploadInfo carries the stored name (getFileName(), new constructor, the old one is deprecated). equals() and hashCode() use it.
• New, additive: FileUploadToResourceField.getUploadErrorMessage(String) is protected, and the constants UPLOAD_FAILED_RESOURCE_KEY and CONNECTION_LOST_RESOURCE_KEY name the keys of a failed upload and of a lost connection.

The full before and after of every change, who has to act and how, is in migration-to-11.md.

There is no OpenRewrite recipe, because none of this is mechanical. Like the other Wicket 11 changes that need manual migration, the note is in the comment of the MigrateToWicket11 recipe in wicket.yml. There is no "Migration to Wicket 11.0" page on the wiki yet. Draft wording for it:

Uploads to a resource (FileUploadToResourceField): implement IUploadsFileManager#store(FileUpload, String) instead of the deprecated save(). It stores the file under a name of its own and returns that name, which getFile(uploadFieldId, fileName) then receives. The name goes to the browser and back, so getFile() must not return a file of another upload field. FolderUploadsFileManager stores files under random names: find them with UploadInfo#getFile() or UploadInfo#getFileName(), not by client file name. Subclasses of AbstractFileUploadResource receive the stored names in saveFiles(), prepareResponse() and generateJsonResponse(), subclasses of FileUploadResourceReference in generateFileInfo(). A failed upload reads "The upload failed." (resource key uploadToResourceFailed) instead of ending on the error page.

No backport: wicket-10.x stays as it is.

Tests

• WicketTester: FileUploadToResourceFieldTest, FileListBehaviorTest, FileDropZoneBehaviorTest, IUploadsFileManagerTest for the defaults of store() and save(), and store() tests in FolderUploadsFileManagerTest.
• QUnit: upload-to-resource.js, run against both the jQuery and the plain JavaScript engine.
• By hand, on the upload-to-resource example in Chrome and Firefox under both engines: files of one name, the limits, a second upload while one runs, cancel, server failures, a connection reset, picks adding up, remove, a real file drop (Chrome) and the leave-page prompt.
• mvn clean install -Pjs-test is green on each of the two commits.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 62.17%. Comparing base (5cbd566) to head (e57325b).

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #1671      +/-   ##
============================================
+ Coverage     61.96%   62.17%   +0.21%     
- Complexity    11285    11311      +26     
============================================
  Files          1250     1253       +3     
  Lines         48437    48455      +18     
  Branches       6796     6796              
============================================
+ Hits          30014    30128     +114     
+ Misses        15729    15632      -97     
- Partials       2694     2695       +1     

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[reiern70]

Note for reviewers: this guard keeps the script from setting itself up a second time when it reaches the page twice, for example once on its own and once in an aggregated bundle.

On master it compared with 'object', which never matches: Wicket.FileUploadToResourceField is a constructor, so typeof gives 'function'. A second run therefore replaced the constructor and all its methods. That did no visible harm while the script kept no state of its own.

This PR gives the script state: lists, the file lists of each field, which FileListBehavior registers through addList(). With the old guard, a second run would start a new, empty lists. Lists registered after it would be invisible to fields created before it, and those fields would stop collecting files. With 'function', the second run returns at once and everything shares one registry.

The 'object' check looks copied from scripts whose namespace is a plain object, such as Wicket.FilesSelected and Wicket.Head, where it is right.

The QUnit test "a second run of the script keeps the field and its lists" in upload-to-resource.js loads the script again. With 'object', all three of its assertions fail.