(core) move home server into core

Summary: This moves enough server material into core to run a home server.  The data engine is not yet incorporated (though in manual testing it works when ported).

Test Plan: existing tests pass

Reviewers: dsagal

Reviewed By: dsagal

Differential Revision: https://phab.getgrist.com/D2552

app/common/uploads.ts

@@ -0,0 +1,44 @@
+/**
+ * Code and declarations shared by browser and server-side code for handling uploads.
+ *
+ * Browser code has several functions available in app/client/lib/uploads.ts which return an
+ * UploadResult that represents an upload. An upload may contain multiple files.
+ *
+ * An upload is identified by a numeric uploadId which is unique within an UploadSet. An UploadSet
+ * is collection of uploads tied to a browser session (as maintained by app/server/lib/Client).
+ * When the session ends, all uploads are cleaned up.
+ *
+ * The uploadId is useful to identify the upload to the server, which can then consume the actual
+ * files there. It may also be used to clean up the upload once it is no longer needed.
+ *
+ * Files within an upload can be identified by their index in UploadResult.files array. The
+ * origName available for files is not guaranteed to be unique.
+ *
+ * Implementation detail: The upload is usually a temporary directory on the server, but may be a
+ * collection of non-temporary files when files are selected using Electron's native file picker.
+ */
+
+/**
+ * Represents a single upload, containing one or more files. Empty uploads are never created.
+ */
+export interface UploadResult {
+  uploadId: number;
+  files: FileUploadResult[];
+}
+
+/**
+ * Represents a single file within an upload. This is the only information made available to the
+ * browser. (In particular, while the server knows also the actual path of the file on the server,
+ * the browser has no need for it and should not know it.)
+ */
+export interface FileUploadResult {
+  origName: string;     // The filename that the user reports for the file (not guaranteed unique).
+  size: number;         // The size of the file in bytes.
+  ext: string;          // The extension of the file, starting with "."
+}
+
+/**
+ * Path where the server accepts POST requests with uploads.  Don't include a leading / so that
+ * the page's <base> will be respected.
+ */
+export const UPLOAD_URL_PATH = 'uploads';