--- /dev/null
+.. _chimera:
+
+#######
+Chimera
+#######
+
+This section describes Chimera library.
+
+************
+Introduction
+************
+
+Chimera is a software regular expression matching engine that is a hybrid of
+Hyperscan and PCRE. The design goals of Chimera are to fully support PCRE
+syntax as well as to take advantage of the high performance nature of Hyperscan.
+
+Chimera inherits the design guideline of Hyperscan with C APIs for compilation
+and scanning.
+
+The Chimera API itself is composed of two major components:
+
+===========
+Compilation
+===========
+
+These functions take a group of regular expressions, along with identifiers and
+option flags, and compile them into an immutable database that can be used by
+the Chimera scanning API. This compilation process performs considerable
+analysis and optimization work in order to build a database that will match
+the given expressions efficiently.
+
+See :ref:`chcompile` for more details
+
+========
+Scanning
+========
+
+Once a Chimera database has been created, it can be used to scan data in memory.
+Chimera only supports block mode in which we scan a single contiguous block in
+memory.
+
+Matches are delivered to the application via a user-supplied callback function
+that is called synchronously for each match.
+
+For a given database, Chimera provides several guarantees:
+
+* No memory allocations occur at runtime with the exception of scratch space
+ allocation, it should be done ahead of time for performance-critical
+ applications:
+
+ - **Scratch space**: temporary memory used for internal data at scan time.
+ Structures in scratch space do not persist beyond the end of a single scan
+ call.
+
+* The size of the scratch space required for a given database is fixed and
+ determined at database compile time. This means that the memory requirement
+ of the application are known ahead of time, and the scratch space can be
+ pre-allocated if required for performance reasons.
+
+* Any pattern that has successfully been compiled by the Chimera compiler can
+ be scanned against any input. There could be internal resource limits or
+ other limitations caused by PCRE at runtime that could cause a scan call to
+ return an error.
+
+.. note:: Chimera is designed to have the same matching behavior as PCRE,
+ including greedy/ungreedy, capturing, etc. Chimera reports both
+ **start offset** and **end offset** for each match like PCRE. Different
+ from the fashion of reporting all matches in Hyperscan, Chimera only reports
+ non-overlapping matches. For example, the pattern :regexp:`/foofoo/` will
+ match ``foofoofoofoo`` at offsets (0, 6) and (6, 12).
+
+.. note:: Since Chimera is a hybrid of Hyperscan and PCRE in order to support
+ full PCRE syntax, there will be extra performance overhead compared to
+ Hyperscan-only solution. Please always use Hyperscan for better performance
+ unless you must need full PCRE syntax support.
+
+See :ref:`chruntime` for more details
+
+************
+Requirements
+************
+
+The PCRE library (http://pcre.org/) version 8.41 is required for Chimera.
+
+.. note:: Since Chimera needs to reference PCRE internal function, please place PCRE source
+ directory under Hyperscan root directory in order to build Chimera.
+
+Beside this, both hardware and software requirements of Chimera are the same to Hyperscan.
+See :ref:`hardware` and :ref:`software` for more details.
+
+.. note:: Building Hyperscan will automatically generate Chimera library.
+ Currently only static library is supported for Chimera, so please
+ use static build type when configure CMake build options.
+
+.. _chcompile:
+
+******************
+Compiling Patterns
+******************
+
+===================
+Building a Database
+===================
+
+The Chimera compiler API accepts regular expressions and converts them into a
+compiled pattern database that can then be used to scan data.
+
+The API provides two functions that compile regular expressions into
+databases:
+
+#. :c:func:`ch_compile`: compiles a single expression into a pattern database.
+
+#. :c:func:`ch_compile_multi`: compiles an array of expressions into a pattern
+ database. All of the supplied patterns will be scanned for concurrently at
+ scan time, with user-supplied identifiers returned when they match.
+
+#. :c:func:`ch_compile_ext_multi`: compiles an array of expressions as above,
+ but allows PCRE match limits to be specified for each expression.
+
+Compilation allows the Chimera library to analyze the given pattern(s) and
+pre-determine how to scan for these patterns in an optimized fashion using
+Hyperscan and PCRE.
+
+===============
+Pattern Support
+===============
+
+Chimera fully supports the pattern syntax used by the PCRE library ("libpcre"),
+described at <http://www.pcre.org/>.The version of PCRE used to validate
+Chimera's interpretation of this syntax is 8.41.
+
+=========
+Semantics
+=========
+
+Chimera supports the exact same semantics of PCRE library. Moreover, it supports
+multiple simultaneous pattern matching like Hyperscan and the multiple matches
+will be reported in order by end offset.
+
+.. _chruntime:
+
+*********************
+Scanning for Patterns
+*********************
+
+Chimera provides scan function with ``ch_scan``.
+
+================
+Handling Matches
+================
+
+``ch_scan`` will call a user-supplied callback function when a match
+is found. This function has the following signature:
+
+ .. doxygentypedef:: ch_match_event_handler
+ :outline:
+ :no-link:
+
+The *id* argument will be set to the identifier for the matching expression
+provided at compile time, and the *from* argument will be set to the
+start-offset of the match the *to* argument will be set to the end-offset
+of the match. The *captured* stores offsets of entire pattern match as well as
+captured subexpressions. The *size* will be set to the number of valid entries in
+the *captured*.
+
+The match callback function has the capability to continue or halt scanning
+by returning different values.
+
+See :c:type:`ch_match_event_handler` for more information.
+
+=======================
+Handling Runtime Errors
+=======================
+
+``ch_scan`` will call a user-supplied callback function when a runtime error
+occurs in libpcre. This function has the following signature:
+
+ .. doxygentypedef:: ch_error_event_handler
+ :outline:
+ :no-link:
+
+The *id* argument will be set to the identifier for the matching expression
+provided at compile time.
+
+The match callback function has the capability to either halt scanning or
+continue scanning for the next pattern.
+
+See :c:type:`ch_error_event_handler` for more information.
+
+=============
+Scratch Space
+=============
+
+While scanning data, Chimera needs a small amount of temporary memory to store
+on-the-fly internal data. This amount is unfortunately too large to fit on the
+stack, particularly for embedded applications, and allocating memory dynamically
+is too expensive, so a pre-allocated "scratch" space must be provided to the
+scanning functions.
+
+The function :c:func:`ch_alloc_scratch` allocates a large enough region of
+scratch space to support a given database. If the application uses multiple
+databases, only a single scratch region is necessary: in this case, calling
+:c:func:`ch_alloc_scratch` on each database (with the same ``scratch`` pointer)
+will ensure that the scratch space is large enough to support scanning against
+any of the given databases.
+
+While the Chimera library is re-entrant, the use of scratch spaces is not.
+For example, if by design it is deemed necessary to run recursive or nested
+scanning (say, from the match callback function), then an additional scratch
+space is required for that context.
+
+In the absence of recursive scanning, only one such space is required per thread
+and can (and indeed should) be allocated before data scanning is to commence.
+
+In a scenario where a set of expressions are compiled by a single "master"
+thread and data will be scanned by multiple "worker" threads, the convenience
+function :c:func:`ch_clone_scratch` allows multiple copies of an existing
+scratch space to be made for each thread (rather than forcing the caller to pass
+all the compiled databases through :c:func:`ch_alloc_scratch` multiple times).
+
+For example:
+
+.. code-block:: c
+
+ ch_error_t err;
+ ch_scratch_t *scratch_prototype = NULL;
+ err = ch_alloc_scratch(db, &scratch_prototype);
+ if (err != CH_SUCCESS) {
+ printf("ch_alloc_scratch failed!");
+ exit(1);
+ }
+
+ ch_scratch_t *scratch_thread1 = NULL;
+ ch_scratch_t *scratch_thread2 = NULL;
+
+ err = ch_clone_scratch(scratch_prototype, &scratch_thread1);
+ if (err != CH_SUCCESS) {
+ printf("ch_clone_scratch failed!");
+ exit(1);
+ }
+ err = ch_clone_scratch(scratch_prototype, &scratch_thread2);
+ if (err != CH_SUCCESS) {
+ printf("ch_clone_scratch failed!");
+ exit(1);
+ }
+
+ ch_free_scratch(scratch_prototype);
+
+ /* Now two threads can both scan against database db,
+ each with its own scratch space. */
+
+
+=================
+Custom Allocators
+=================
+
+By default, structures used by Chimera at runtime (scratch space, etc) are
+allocated with the default system allocators, usually
+``malloc()`` and ``free()``.
+
+The Chimera API provides a facility for changing this behaviour to support
+applications that use custom memory allocators.
+
+These functions are:
+
+- :c:func:`ch_set_database_allocator`, which sets the allocate and free functions
+ used for compiled pattern databases.
+- :c:func:`ch_set_scratch_allocator`, which sets the allocate and free
+ functions used for scratch space.
+- :c:func:`ch_set_misc_allocator`, which sets the allocate and free functions
+ used for miscellaneous data, such as compile error structures and
+ informational strings.
+
+The :c:func:`ch_set_allocator` function can be used to set all of the custom
+allocators to the same allocate/free pair.
+
+
+************************
+API Reference: Constants
+************************
+
+===========
+Error Codes
+===========
+
+.. doxygengroup:: CH_ERROR
+ :content-only:
+ :no-link:
+
+=============
+Pattern flags
+=============
+
+.. doxygengroup:: CH_PATTERN_FLAG
+ :content-only:
+ :no-link:
+
+==================
+Compile mode flags
+==================
+
+.. doxygengroup:: CH_MODE_FLAG
+ :content-only:
+ :no-link:
+
+
+********************
+API Reference: Files
+********************
+
+==========
+File: ch.h
+==========
+
+.. doxygenfile:: ch.h
+
+=================
+File: ch_common.h
+=================
+
+.. doxygenfile:: ch_common.h
+
+==================
+File: ch_compile.h
+==================
+
+.. doxygenfile:: ch_compile.h
+
+==================
+File: ch_runtime.h
+==================
+
+.. doxygenfile:: ch_runtime.h
projects / thirdparty / vectorscan.git / commitdiff
