As we now always use Library through a shared_ptr, we can make `Library`
not copiable and not movable.
So we can move back the data in `Library`, we don't care about move
constructor.
The why of this mutex is in `Library` is a bit complex.
It has been introduced in c2927ce when there was only `Library` and no
`std::unique_ptr<Impl>`.
As introducing the mutex imply implementing the move constructor, we have
split all data in `LibraryBase` (and keep a default move constructor here)
and add the mutex in `Library` (and implement a simple move constructor).
Later, in 090c2fd, we have move the `LibraryBase` to `Library::Impl`
(which should have been `Library::Data`).
So at the end, `Library::Impl` is never moved. We can move the `mutex` in
it and still simply implement move constructor for `Library`.
Created a generic function multipleQuery which takes:
1. string (representing a comma separated list)
2. param (the value to query on using Xapian).
Category and language query will use this function.
From now on, the `lang` parameter of the /catalog/search,
/catalog/v2/entries, and /catalog/v2/partial_entries endpoints is
interpreted as a comma-separated list of languages.
libzim's search is not thread safe (mainly because xapian is not).
So we must protect our search objects from multi thread calls.
The best way to do this is to associate a mutex to the `zim::Searcher`
and lock the searcher each time we access object derivated from the
searcher (search, results, iterator, ...)
As we still create a `Reader` in the deprecated code of `Library`,
we need a way to create a reader without raising a deprecated warning.
So we create a another constructor with a dummy argument and we use it.
Library became thread-safe with the exception of `getBookById()`
and `getBookByPath()` methods - thread safety in those accessors is
rendered meaningless by their return type (they return a reference
to a book which can be removed any time later by another thread).
Introducing a mutex in `Library` necessitates manually implementing the
move constructor and assignment operator. It's better to still delegate
that work to the compiler to eliminate any possibility of bugs when new
data members are added to `Library`. The trick is to move the data into
an auxiliary class `LibraryBase` and derive `Library` from it.
After switching to Xapian-based search in the library/catalog, an empty
query stopped acting as a match-all query. This commit restores the old
behaviour in that regard.
Catalog filtering should now be case/diacritics insensitive for all
fields. However it is not validated for language, name and category
fields, and is validated for tags, creator & publisher only for text
supplied in the filter (but not for values read from the book).
Catalog filtering by titles/description was sensitive to diacritics
present in the query string. Fixed that.
Also enhanced the unit test to validate the insensitivity to diacritics
present in either the title/description or the query string.
Matthieu Gautier
Nikhil Tanwar
Veloman Yunkan
Maneesh P M