1 This file defines the "sync API", an interface to the syncer 2 backend that exposes (1) the core functionality of maintaining a consistent 3 local snapshot of a hierarchical object set; (2) a means to transactionally 4 access and modify those objects; (3) a means to control client/server 5 synchronization tasks, namely: pushing local object modifications to a 6 server, pulling nonlocal object modifications from a server to this client, 7 and resolving conflicts that may arise between the two; and (4) an 8 abstraction of some external functionality that is to be provided by the 9 host environment. 10 11 This interface is used as the entry point into the syncer backend 12 when the backend is compiled as a library and embedded in another 13 application. A goal for this interface layer is to depend on very few 14 external types, so that an application can use the sync backend 15 without introducing a dependency on specific types. A non-goal is to 16 have binary compatibility across versions or compilers; this allows the 17 interface to use C++ classes. An application wishing to use the sync API 18 should ideally compile the syncer backend and this API as part of the 19 application's own build, to avoid e.g. mismatches in calling convention, 20 structure padding, or name mangling that could arise if there were a 21 compiler mismatch. 22 23 The schema of the objects in the sync domain is based on the model, which 24 is essentially a hierarchy of items and folders similar to a filesystem, 25 but with a few important differences. The sync API contains fields 26 such as URL to easily allow the embedding application to store web 27 browser bookmarks. Also, the sync API allows duplicate titles in a parent. 28 Consequently, it does not support looking up an object by title 29 and parent, since such a lookup is not uniquely determined. Lastly, 30 unlike a filesystem model, objects in the Sync API model have a strict 31 ordering within a parent; the position is manipulable by callers, and 32 children of a node can be enumerated in the order of their position. 33
