SLRE: Super Light Regular Expression library

SLRE is an ISO C library that implements a subset of Perl regular expression syntax. Main features of SLRE are:

• Written in strict ISO C, conforming to ANSI C'89
• Small size (compiled x86 code is about 4kB)
• Uses little stack and does no dynamic memory allocation
• Provides intuitive simple API
• Implements most useful subset of Perl regex syntax (see below)
• Production quality, extensively unit-tested
• Easily extensible. E.g. if one wants to introduce a new metacharacter \i, meaning "IPv4 address", it is easy to do so with SLRE.

SLRE is perfect for tasks like parsing network requests, configuration files, user input, etc, when libraries like PCRE are too heavyweight for the given task. Developers of embedded systems would benefit most.

Supported Syntax

^        Match beginning of a buffer
$        Match end of a buffer
()       Grouping and substring capturing
\s       Match whitespace
\S       Match non-whitespace
\d       Match decimal digit
+        Match one or more times (greedy)
+?       Match one or more times (non-greedy)
*        Match zero or more times (greedy)
*?       Match zero or more times (non-greedy)
?        Match zero or once
x|y      Match x or y (alternation operator)
\meta    Match one of the meta character: ^$().[]*+?|\
\xHH     Match byte with hex value 0xHH

Not yet supported but in progress:

[...]    Match any character from set. A-Z like ranges supported
[^...]   Match any character but ones from set

API

int slre_match(const char *regexp, const char *buf, int buf_len,
               struct slre_cap *caps, const char **error_msg);

slre_match() matches string buffer buf of length buf_len against regular expression regexp, which should conform the syntax outlined above. If regular expression regexp contains brackets, slre_match() will capture the respective substrings. Array of captures, caps, must have at least as many elements as number of bracket pairs in the regexp.

slre_match() returns 0 if there is no match found. Otherwise, it returns the number scanned bytes from the beginning of the string. This way, it is easy to do repetitive matches. Hint: if it is required to know the exact matched substring, enclose regexp in a brackets and specify caps, which should be an array of following structures:

struct slre_cap {
  const char *ptr;  /* Points to the matched fragment */
  int len;          /* Length of the matched fragment */
};

Example: parsing HTTP request

const char *error_msg, *request = " GET /index.html HTTP/1.0\r\n\r\n";
struct slre_cap caps[4];

if (slre_match("^\\s*(\\S+)\\s+(\\S+)\\s+HTTP/(\\d)\\.(\\d)",
               request, strlen(request), caps, &error_msg)) {
  printf("Method: [%.*s], URI: [%.*s]\n",
         caps[0].len, caps[0].ptr,
         caps[1].len, caps[1].ptr);
} else {
  printf("Error parsing [%s]: [%s]\n", request, error_msg);
}