2015-01-23 17:51:47 +01:00
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<title>pcre2serialize specification</title>
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<body bgcolor="#FFFFFF" text="#00005A" link="#0066FF" alink="#3399FF" vlink="#2222BB">
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<h1>pcre2serialize man page</h1>
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Return to the <a href="index.html">PCRE2 index page</a>.
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</p>
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<p>
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This page is part of the PCRE2 HTML documentation. It was generated
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automatically from the original man page. If there is any nonsense in it,
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please consult the man page, in case the conversion went wrong.
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<br>
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<ul>
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<li><a name="TOC1" href="#SEC1">SAVING AND RE-USING PRECOMPILED PCRE2 PATTERNS</a>
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2016-06-05 18:05:34 +02:00
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<li><a name="TOC2" href="#SEC2">SECURITY CONCERNS</a>
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<li><a name="TOC3" href="#SEC3">SAVING COMPILED PATTERNS</a>
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<li><a name="TOC4" href="#SEC4">RE-USING PRECOMPILED PATTERNS</a>
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<li><a name="TOC5" href="#SEC5">AUTHOR</a>
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<li><a name="TOC6" href="#SEC6">REVISION</a>
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</ul>
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<br><a name="SEC1" href="#TOC1">SAVING AND RE-USING PRECOMPILED PCRE2 PATTERNS</a><br>
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<P>
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<b>int32_t pcre2_serialize_decode(pcre2_code **<i>codes</i>,</b>
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<b> int32_t <i>number_of_codes</i>, const uint32_t *<i>bytes</i>,</b>
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<b> pcre2_general_context *<i>gcontext</i>);</b>
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<br>
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<br>
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<b>int32_t pcre2_serialize_encode(pcre2_code **<i>codes</i>,</b>
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<b> int32_t <i>number_of_codes</i>, uint32_t **<i>serialized_bytes</i>,</b>
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<b> PCRE2_SIZE *<i>serialized_size</i>, pcre2_general_context *<i>gcontext</i>);</b>
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<br>
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<br>
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<b>void pcre2_serialize_free(uint8_t *<i>bytes</i>);</b>
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<br>
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<br>
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<b>int32_t pcre2_serialize_get_number_of_codes(const uint8_t *<i>bytes</i>);</b>
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<br>
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<br>
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If you are running an application that uses a large number of regular
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expression patterns, it may be useful to store them in a precompiled form
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instead of having to compile them every time the application is run. However,
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if you are using the just-in-time optimization feature, it is not possible to
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save and reload the JIT data, because it is position-dependent. The host on
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which the patterns are reloaded must be running the same version of PCRE2, with
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the same code unit width, and must also have the same endianness, pointer width
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and PCRE2_SIZE type. For example, patterns compiled on a 32-bit system using
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PCRE2's 16-bit library cannot be reloaded on a 64-bit system, nor can they be
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reloaded using the 8-bit library.
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</P>
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<P>
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Note that "serialization" in PCRE2 does not convert compiled patterns to an
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abstract format like Java or .NET serialization. The serialized output is
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really just a bytecode dump, which is why it can only be reloaded in the same
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environment as the one that created it. Hence the restrictions mentioned above.
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Applications that are not statically linked with a fixed version of PCRE2 must
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be prepared to recompile patterns from their sources, in order to be immune to
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PCRE2 upgrades.
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</P>
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<br><a name="SEC2" href="#TOC1">SECURITY CONCERNS</a><br>
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<P>
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2016-06-29 18:52:05 +02:00
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The facility for saving and restoring compiled patterns is intended for use
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within individual applications. As such, the data supplied to
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<b>pcre2_serialize_decode()</b> is expected to be trusted data, not data from
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arbitrary external sources. There is only some simple consistency checking, not
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complete validation of what is being re-loaded. Corrupted data may cause
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undefined results. For example, if the length field of a pattern in the
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serialized data is corrupted, the deserializing code may read beyond the end of
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the byte stream that is passed to it.
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</P>
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<br><a name="SEC3" href="#TOC1">SAVING COMPILED PATTERNS</a><br>
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<P>
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Before compiled patterns can be saved they must be serialized, which in PCRE2
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means converting the pattern to a stream of bytes. A single byte stream may
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contain any number of compiled patterns, but they must all use the same
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character tables. A single copy of the tables is included in the byte stream
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(its size is 1088 bytes). For more details of character tables, see the
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<a href="pcre2api.html#localesupport">section on locale support</a>
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in the
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<a href="pcre2api.html"><b>pcre2api</b></a>
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documentation.
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</P>
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<P>
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The function <b>pcre2_serialize_encode()</b> creates a serialized byte stream
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from a list of compiled patterns. Its first two arguments specify the list,
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being a pointer to a vector of pointers to compiled patterns, and the length of
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the vector. The third and fourth arguments point to variables which are set to
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point to the created byte stream and its length, respectively. The final
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argument is a pointer to a general context, which can be used to specify custom
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memory mangagement functions. If this argument is NULL, <b>malloc()</b> is used
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to obtain memory for the byte stream. The yield of the function is the number
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of serialized patterns, or one of the following negative error codes:
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<pre>
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PCRE2_ERROR_BADDATA the number of patterns is zero or less
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PCRE2_ERROR_BADMAGIC mismatch of id bytes in one of the patterns
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PCRE2_ERROR_MEMORY memory allocation failed
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PCRE2_ERROR_MIXEDTABLES the patterns do not all use the same tables
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PCRE2_ERROR_NULL the 1st, 3rd, or 4th argument is NULL
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</pre>
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PCRE2_ERROR_BADMAGIC means either that a pattern's code has been corrupted, or
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that a slot in the vector does not point to a compiled pattern.
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</P>
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<P>
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Once a set of patterns has been serialized you can save the data in any
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appropriate manner. Here is sample code that compiles two patterns and writes
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them to a file. It assumes that the variable <i>fd</i> refers to a file that is
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open for output. The error checking that should be present in a real
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application has been omitted for simplicity.
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<pre>
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int errorcode;
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uint8_t *bytes;
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PCRE2_SIZE erroroffset;
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PCRE2_SIZE bytescount;
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pcre2_code *list_of_codes[2];
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list_of_codes[0] = pcre2_compile("first pattern",
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PCRE2_ZERO_TERMINATED, 0, &errorcode, &erroroffset, NULL);
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list_of_codes[1] = pcre2_compile("second pattern",
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PCRE2_ZERO_TERMINATED, 0, &errorcode, &erroroffset, NULL);
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errorcode = pcre2_serialize_encode(list_of_codes, 2, &bytes,
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&bytescount, NULL);
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errorcode = fwrite(bytes, 1, bytescount, fd);
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</pre>
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Note that the serialized data is binary data that may contain any of the 256
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possible byte values. On systems that make a distinction between binary and
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non-binary data, be sure that the file is opened for binary output.
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</P>
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<P>
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Serializing a set of patterns leaves the original data untouched, so they can
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still be used for matching. Their memory must eventually be freed in the usual
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way by calling <b>pcre2_code_free()</b>. When you have finished with the byte
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stream, it too must be freed by calling <b>pcre2_serialize_free()</b>.
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</P>
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<br><a name="SEC4" href="#TOC1">RE-USING PRECOMPILED PATTERNS</a><br>
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<P>
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In order to re-use a set of saved patterns you must first make the serialized
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byte stream available in main memory (for example, by reading from a file). The
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management of this memory block is up to the application. You can use the
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<b>pcre2_serialize_get_number_of_codes()</b> function to find out how many
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compiled patterns are in the serialized data without actually decoding the
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patterns:
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<pre>
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uint8_t *bytes = <serialized data>;
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int32_t number_of_codes = pcre2_serialize_get_number_of_codes(bytes);
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</pre>
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The <b>pcre2_serialize_decode()</b> function reads a byte stream and recreates
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the compiled patterns in new memory blocks, setting pointers to them in a
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vector. The first two arguments are a pointer to a suitable vector and its
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length, and the third argument points to a byte stream. The final argument is a
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pointer to a general context, which can be used to specify custom memory
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mangagement functions for the decoded patterns. If this argument is NULL,
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<b>malloc()</b> and <b>free()</b> are used. After deserialization, the byte
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stream is no longer needed and can be discarded.
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<pre>
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int32_t number_of_codes;
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pcre2_code *list_of_codes[2];
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uint8_t *bytes = <serialized data>;
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int32_t number_of_codes =
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pcre2_serialize_decode(list_of_codes, 2, bytes, NULL);
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</pre>
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If the vector is not large enough for all the patterns in the byte stream, it
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is filled with those that fit, and the remainder are ignored. The yield of the
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function is the number of decoded patterns, or one of the following negative
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error codes:
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<pre>
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PCRE2_ERROR_BADDATA second argument is zero or less
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PCRE2_ERROR_BADMAGIC mismatch of id bytes in the data
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PCRE2_ERROR_BADMODE mismatch of code unit size or PCRE2 version
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PCRE2_ERROR_BADSERIALIZEDDATA other sanity check failure
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PCRE2_ERROR_MEMORY memory allocation failed
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PCRE2_ERROR_NULL first or third argument is NULL
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</pre>
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PCRE2_ERROR_BADMAGIC may mean that the data is corrupt, or that it was compiled
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on a system with different endianness.
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</P>
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<P>
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Decoded patterns can be used for matching in the usual way, and must be freed
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by calling <b>pcre2_code_free()</b>. However, be aware that there is a potential
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race issue if you are using multiple patterns that were decoded from a single
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byte stream in a multithreaded application. A single copy of the character
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tables is used by all the decoded patterns and a reference count is used to
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arrange for its memory to be automatically freed when the last pattern is
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freed, but there is no locking on this reference count. Therefore, if you want
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to call <b>pcre2_code_free()</b> for these patterns in different threads, you
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must arrange your own locking, and ensure that <b>pcre2_code_free()</b> cannot
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be called by two threads at the same time.
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</P>
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<P>
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If a pattern was processed by <b>pcre2_jit_compile()</b> before being
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serialized, the JIT data is discarded and so is no longer available after a
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save/restore cycle. You can, however, process a restored pattern with
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<b>pcre2_jit_compile()</b> if you wish.
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</P>
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<br><a name="SEC5" href="#TOC1">AUTHOR</a><br>
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<P>
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Philip Hazel
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<br>
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University Computing Service
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<br>
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Cambridge, England.
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<br>
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</P>
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2016-06-05 18:05:34 +02:00
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<br><a name="SEC6" href="#TOC1">REVISION</a><br>
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2015-01-23 17:51:47 +01:00
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<P>
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2018-06-27 19:20:58 +02:00
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Last updated: 27 June 2018
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<br>
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2018-06-27 19:20:58 +02:00
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Copyright © 1997-2018 University of Cambridge.
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<br>
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<p>
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Return to the <a href="index.html">PCRE2 index page</a>.
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</p>
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