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Sergey Lyubka
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README.md
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README.md
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SLRE: Super Light Regular Expression library
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============================================
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SLRE is an ISO C library that implements a subset of Perl regular
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expression syntax. Main features of SLRE are:
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* Written in strict ANSI C'89
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* Small size (compiled x86 code is about 5kB)
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* Uses little stack and does no dynamic memory allocation
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* Provides simple intuitive API
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* Implements most useful subset of Perl regex syntax (see below)
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* Easily extensible. E.g. if one wants to introduce a new
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metacharacter `\i`, meaning "IPv4 address", it is easy to do so with SLRE.
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SLRE is perfect for tasks like parsing network requests, configuration
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files, user input, etc, when libraries like [PCRE](http://pcre.org) are too
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heavyweight for the given task. Developers of embedded systems would benefit
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most.
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## Supported Syntax
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(?i) Must be at the beginning of the regex. Makes match case-insensitive
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^ Match beginning of a buffer
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$ Match end of a buffer
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() Grouping and substring capturing
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\s Match whitespace
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\S Match non-whitespace
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\d Match decimal digit
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+ Match one or more times (greedy)
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+? Match one or more times (non-greedy)
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* Match zero or more times (greedy)
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*? Match zero or more times (non-greedy)
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? Match zero or once (non-greedy)
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x|y Match x or y (alternation operator)
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\meta Match one of the meta character: ^$().[]*+?|\
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\xHH Match byte with hex value 0xHH, e.g. \x4a
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[...] Match any character from set. Ranges like [a-z] are supported
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[^...] Match any character but ones from set
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Under development: Unicode support.
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## API
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int slre_match(const char *regexp, const char *buf, int buf_len,
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struct slre_cap *caps, int num_caps);
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`slre_match()` matches string buffer `buf` of length `buf_len` against
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regular expression `regexp`, which should conform the syntax outlined
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above. If regular expression `regexp` contains brackets, `slre_match()`
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can capture the respective substrings into the array of `struct slre_cap`
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structures:
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/* Stores matched fragment for the expression inside brackets */
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struct slre_cap {
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const char *ptr; /* Points to the matched fragment */
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int len; /* Length of the matched fragment */
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};
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N-th member of the `caps` array will contain fragment that corresponds to the
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N-th opening bracket in the `regex`, N is zero-based. `slre_match()` returns
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number of bytes scanned from the beginning of the string. If return value is
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greater or equal to 0, there is a match. If return value is less then 0, there
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is no match. Negative return codes are as follows:
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#define SLRE_NO_MATCH -1
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#define SLRE_UNEXPECTED_QUANTIFIER -2
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#define SLRE_UNBALANCED_BRACKETS -3
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#define SLRE_INTERNAL_ERROR -4
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#define SLRE_INVALID_CHARACTER_SET -5
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#define SLRE_INVALID_METACHARACTER -6
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#define SLRE_CAPS_ARRAY_TOO_SMALL -7
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#define SLRE_TOO_MANY_BRANCHES -8
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#define SLRE_TOO_MANY_BRACKETS -9
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## Example: parsing HTTP request line
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const char *request = " GET /index.html HTTP/1.0\r\n\r\n";
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struct slre_cap caps[4];
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if (slre_match("^\\s*(\\S+)\\s+(\\S+)\\s+HTTP/(\\d)\\.(\\d)",
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request, strlen(request), caps, 4) > 0) {
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printf("Method: [%.*s], URI: [%.*s]\n",
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caps[0].len, caps[0].ptr,
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caps[1].len, caps[1].ptr);
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} else {
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printf("Error parsing [%s]\n", request);
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}
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## Example: find all URLs in a string
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static const char *str =
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"<img src=\"HTTPS://FOO.COM/x?b#c=tab1\"/> "
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" <a href=\"http://cesanta.com\">some link</a>";
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static const char *regex = "(?i)((https?://)[^\\s/'\"<>]+/?[^\\s'\"<>]*)";
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struct slre_cap caps[2];
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int i, j = 0, str_len = strlen(str);
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while (j < str_len &&
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(i = slre_match(regex, str + j, str_len - j, caps, 2, NULL)) > 0) {
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printf("Found URL: [%.*s]\n", caps[0].len, caps[0].ptr);
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j += i;
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}
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Output:
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Found URL: [HTTPS://FOO.COM/x?b#c=tab1]
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Found URL: [http://cesanta.com]
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# License
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SLRE is released under
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[GNU GPL v.2](http://www.gnu.org/licenses/old-licenses/gpl-2.0.html).
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Businesses have an option to get non-restrictive, royalty-free commercial
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license and professional support from
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[Cesanta Software](http://cesanta.com).
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[Super Light DNS Resolver](https://github.com/cesanta/sldr),
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[Mongoose web server](https://github.com/cesanta/mongoose)
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are other projects by Cesanta Software, developed with the same philosophy
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of functionality and simplicity.
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SLRE documentation is at
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[http://cesanta.com/#docs,SLRE.md](http://cesanta.com/#docs,SLRE.md)
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