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## General
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This is CppCMS future proofing release:
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- CppCMS moved to C++11 by default and now requires a compiler that supports it
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- Templates compiler and unit-tests support both python 2.7 and python >= 3.5
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- Lots of booster API had become an alias to C++11 libraries
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- Improved HTTP support - now it is first class citizen and not debugging tool over CGI protocol. The improvements include:
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- HTTP/1.1
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- keep-alive support
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- Reqiest pipelining
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- Chunked transfer encoding
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- HTTP response now generated directly rather than being converted from CGI output stream.
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- Performance improvement in environment variables handling and HTTP general
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## Breaking Changes
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- All references to `std::auto_ptr` were replaced by `std::unique_ptr` since `auto_ptr` was deprecated and removed in C++17.
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- Booster API become alias for std equivalents
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- `shared_ptr`, `weak_ptr`, `enable_shared_from_this`
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- `static_pointer_cast`, `dynamic_pointer_cast`, `const_pointer_cast`
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- all `booster::system` now refers to std system library: `error_category`, `system_category`, `error_code`, `system_error`
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- `function`
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- `thread`, `mutex`, `recursive_mutex`, `conditional_variable`, `unique_lock`
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Since some interfaces of C++ standard library functions may differ from ones appear in booster these changes may break some code
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## Additional Changes
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- `cppcms_tmpl_cc` now uses `std::begin/end`, `std::rbegin/rend` to iterate over containers
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- Now it is possible to use `std::regex` instead of PCRE, it has some performance penalty and lack UTF-8 support but it is good option to eliminate some dependencies - for example on Windows.
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- `zlib` dependency optional it does not remove file based session storage.
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- `atomic_counter` - uses `std::atomic` internally
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- Many (but not all) APIs that require dynamic parameters size are now using to C++11 variadic templates
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## Requirements Updates
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- C++11 enabled compiler, tested on gcc>=4.8, clang >=3.8, msvc 2017 (2015 probably will work as well)
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- Python 2.7 or >= 3.5
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- Relaxed requirement of PCRE
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- Relaxed requirement of zlib
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## Things Not Taken from Standard Library and C++11
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- `booster::regex` there were several reasons:
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1. CppCMS uses PCRE that allows to refer to a string as UTF-8, for example matching "." with code point rather than byte. It is a useful functionality that absent from `std::regex`.
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2. `std::regex` - level of implementation is still quite poor on some older C++11 compilers, for example gcc-4.8 does not support them at all, clang-4.0/libc++ fails to match properly some patterns.
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3. Performance of PCRE is much better
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4. It was impossible to use `std::smatch`/`std::cmatch` with custom regex engine since they do not provide an API to build them externally so I couldn't just create PCRE based regular expression with standard `std::cmatch`. This is significant limitation of the standard C++ library.
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Also I added an option to use `std::regex` engine inside `booster::regex` to simplify build on some environments and reduce dependency on external libraries. But outside the API of `booster::regex` remained exactly the same.
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- `std::shared_mutex`, `std::recursive_shared_mutex` - also C++14 provides `std::shared_mutex` it lacks support of recursive one. So I decided to keep existing implementation and stick to C++11
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- Use of variadic templates in `url_mapper` and `url_dispatcher`. Also C++11 variadic templates are fantastic feature some of the tasks remained quite complicated, for example implementing `sum(int... args)` isn't something simple at all (`url_dispatcher` need ints)
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Performing some per-parameter operations and passing them as pack to another function is complex as well. It was somewhat addressed in C++17 but still the benefit of re-implementing existing and working solution is minute in comparison to complexity of implementation and finally the code readability and maintainability
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