pcre2serialize (3) - Linux Manuals
pcre2serialize: Perl-compatible regular expressions (revised API)
NAME
PCRE2 - Perl-compatible regular expressions (revised API)
SAVING AND RE-USING PRECOMPILED PCRE2 PATTERNS
int32_t pcre2_serialize_decode(pcre2_code **codes, int32_t number_of_codes, const uint32_t *bytes, pcre2_general_context *gcontext); int32_t pcre2_serialize_encode(pcre2_code **codes, int32_t number_of_codes, uint32_t **serialized_bytes, PCRE2_SIZE *serialized_size, pcre2_general_context *gcontext); void pcre2_serialize_free(uint8_t *bytes); int32_t pcre2_serialize_get_number_of_codes(const uint8_t *bytes);
If you are running an application that uses a large number of regular expression patterns, it may be useful to store them in a precompiled form instead of having to compile them every time the application is run. However, if you are using the just-in-time optimization feature, it is not possible to save and reload the JIT data, because it is position-dependent. The host on which the patterns are reloaded must be running the same version of PCRE2, with the same code unit width, and must also have the same endianness, pointer width and PCRE2_SIZE type. For example, patterns compiled on a 32-bit system using PCRE2's 16-bit library cannot be reloaded on a 64-bit system, nor can they be reloaded using the 8-bit library.
Note that "serialization" in PCRE2 does not convert compiled patterns to an abstract format like Java or .NET serialization. The serialized output is really just a bytecode dump, which is why it can only be reloaded in the same environment as the one that created it. Hence the restrictions mentioned above. Applications that are not statically linked with a fixed version of PCRE2 must be prepared to recompile patterns from their sources, in order to be immune to PCRE2 upgrades.
SECURITY CONCERNS
The facility for saving and restoring compiled patterns is intended for use within individual applications. As such, the data supplied to pcre2_serialize_decode() is expected to be trusted data, not data from arbitrary external sources. There is only some simple consistency checking, not complete validation of what is being re-loaded. Corrupted data may cause undefined results. For example, if the length field of a pattern in the serialized data is corrupted, the deserializing code may read beyond the end of the byte stream that is passed to it.
SAVING COMPILED PATTERNS
Before compiled patterns can be saved they must be serialized, which in PCRE2 means converting the pattern to a stream of bytes. A single byte stream may contain any number of compiled patterns, but they must all use the same character tables. A single copy of the tables is included in the byte stream (its size is 1088 bytes). For more details of character tables, see the section on locale support in the pcre2api documentation.
The function pcre2_serialize_encode() creates a serialized byte stream from a list of compiled patterns. Its first two arguments specify the list, being a pointer to a vector of pointers to compiled patterns, and the length of the vector. The third and fourth arguments point to variables which are set to point to the created byte stream and its length, respectively. The final argument is a pointer to a general context, which can be used to specify custom memory mangagement functions. If this argument is NULL, malloc() is used to obtain memory for the byte stream. The yield of the function is the number of serialized patterns, or one of the following negative error codes:
PCRE2_ERROR_BADMAGIC means either that a pattern's code has been corrupted, or
that a slot in the vector does not point to a compiled pattern.
Once a set of patterns has been serialized you can save the data in any
appropriate manner. Here is sample code that compiles two patterns and writes
them to a file. It assumes that the variable fd refers to a file that is
open for output. The error checking that should be present in a real
application has been omitted for simplicity.
Note that the serialized data is binary data that may contain any of the 256
possible byte values. On systems that make a distinction between binary and
non-binary data, be sure that the file is opened for binary output.
Serializing a set of patterns leaves the original data untouched, so they can
still be used for matching. Their memory must eventually be freed in the usual
way by calling pcre2_code_free(). When you have finished with the byte
stream, it too must be freed by calling pcre2_serialize_free(). If this
function is called with a NULL argument, it returns immediately without doing
anything.
In order to re-use a set of saved patterns you must first make the serialized
byte stream available in main memory (for example, by reading from a file). The
management of this memory block is up to the application. You can use the
pcre2_serialize_get_number_of_codes() function to find out how many
compiled patterns are in the serialized data without actually decoding the
patterns:
The pcre2_serialize_decode() function reads a byte stream and recreates
the compiled patterns in new memory blocks, setting pointers to them in a
vector. The first two arguments are a pointer to a suitable vector and its
length, and the third argument points to a byte stream. The final argument is a
pointer to a general context, which can be used to specify custom memory
mangagement functions for the decoded patterns. If this argument is NULL,
malloc() and free() are used. After deserialization, the byte
stream is no longer needed and can be discarded.
If the vector is not large enough for all the patterns in the byte stream, it
is filled with those that fit, and the remainder are ignored. The yield of the
function is the number of decoded patterns, or one of the following negative
error codes:
PCRE2_ERROR_BADMAGIC may mean that the data is corrupt, or that it was compiled
on a system with different endianness.
Decoded patterns can be used for matching in the usual way, and must be freed
by calling pcre2_code_free(). However, be aware that there is a potential
race issue if you are using multiple patterns that were decoded from a single
byte stream in a multithreaded application. A single copy of the character
tables is used by all the decoded patterns and a reference count is used to
arrange for its memory to be automatically freed when the last pattern is
freed, but there is no locking on this reference count. Therefore, if you want
to call pcre2_code_free() for these patterns in different threads, you
must arrange your own locking, and ensure that pcre2_code_free() cannot
be called by two threads at the same time.
If a pattern was processed by pcre2_jit_compile() before being
serialized, the JIT data is discarded and so is no longer available after a
save/restore cycle. You can, however, process a restored pattern with
pcre2_jit_compile() if you wish.
RE-USING PRECOMPILED PATTERNS
AUTHOR
Philip Hazel
University Computing Service
Cambridge, England.
REVISION
Last updated: 27 June 2018
Copyright (c) 1997-2018 University of Cambridge.