#regex #glibc #libgnurx #regcomp #regexec

sys gnurx-sys

Regular expression functionality from glibc extracted into a separate library, for Win32

4 releases

0.2.0 Nov 6, 2020
0.1.2 Nov 2, 2020
0.1.1 Nov 2, 2020
0.1.0 Nov 2, 2020

#27 in Windows APIs

LGPL-2.1-or-later

325KB
8K SLoC

C 8K SLoC // 0.1% comments Rust 273 SLoC // 0.5% comments

crates.io docs.rs license

gnurx-sys: Unsafe Rust bindings for libgnurx

This is the regex functionality from glibc extracted into a separate library, for Win32. See the README of the C library.

regcomp(), regexec(), regerror() and regfree() are POSIX regex functions. They conform to POSIX.1-2001 and POSIX.1-2008 standards. They are defined as follows:

extern "C" {
    pub fn regcomp(
        preg: *mut regex_t,
        pattern: *const c_char,
        cflags: c_int,
    ) -> c_int;

    pub fn regexec(
        preg: *const regex_t,
        string: *const c_char,
        nmatch: usize,
        pmatch: *mut regmatch_t,
        eflags: c_int,
    ) -> c_int;

    pub fn regerror(
        errcode: c_int,
        preg: *const regex_t,
        errbuf: *mut c_char,
        errbuf_size: usize,
    ) -> usize;

    pub fn regfree(preg: *mut regex_t);
}

POSIX regex compiling

regcomp() is used to compile a regular expression into a form that is suitable for subsequent regexec() searches.

regcomp() is supplied with preg, a pointer to a pattern buffer storage area; pattern, a pointer to the null-terminated string and cflags, flags used to determine the type of compilation.

All regular expression searching must be done via a compiled pattern buffer, thus regexec() must always be supplied with the address of a regcomp() initialized pattern buffer.

cflags may be the bitwise-or of zero or more of the following:

  • REG_EXTENDED: Use POSIX Extended Regular Expression syntax when interpreting regex. If not set, POSIX Basic Regular Expression syntax is used.

  • REG_ICASE: Do not differentiate case. Subsequent regexec() searches using this pattern buffer will be case insensitive.

  • REG_NOSUB: Do not report position of matches. The nmatch and pmatch arguments to regexec() are ignored if the pattern buffer supplied was compiled with this flag set.

  • REG_NEWLINE: Match-any-character operators don't match a newline.

    • A nonmatching list ([^...]) not containing a newline does not match a newline.
    • Match-beginning-of-line operator (^) matches the empty string immediately after a newline, regardless of whether eflags, the execution flags of regexec(), contains REG_NOTBOL.
    • Match-end-of-line operator ($) matches the empty string immediately before a newline, regardless of whether eflags contains REG_NOTEOL.

POSIX regex matching

regexec() is used to match a null-terminated string against the precompiled pattern buffer, preg. nmatch and pmatch are used to provide information regarding the location of any matches. eflags may be the bitwise-or of one or both of REG_NOTBOL and REG_NOTEOL which cause changes in matching behavior described below:

  • REG_NOTBOL: The match-beginning-of-line operator always fails to match (but see the compilation flag REG_NEWLINE above). This flag may be used when different portions of a string are passed to regexec() and the beginning of the string should not be interpreted as the beginning of the line.

  • REG_NOTEOL: The match-end-of-line operator always fails to match (but see the compilation flag REG_NEWLINE above).

Byte offsets

Unless REG_NOSUB was set for the compilation of the pattern buffer, it is possible to obtain match addressing information.

pmatch must be dimensioned to have at least nmatch elements. These are filled in by regexec() with substring match addresses. The offsets of the subexpression starting at the ith open parenthesis are stored in pmatch[i].

The entire regular expression's match addresses are stored in pmatch[0]. (Note that to return the offsets of N subexpression matches, nmatch must be at least N + 1.)

Any unused structure elements will contain the value -1.

The regmatch_t structure which is the type of pmatch is defined as:

pub struct regmatch_t {
    pub rm_so: regoff_t,
    pub rm_eo: regoff_t,
}

Each rm_so element that is not -1 indicates the start offset of the next largest substring match within the string.

The relative rm_eo element indicates the end offset of the match, which is the offset of the first character after the matching text.

POSIX error reporting

regerror() is used to turn the error codes that can be returned by both regcomp() and regexec() into error message strings.

regerror() is passed the error code, errcode, the pattern buffer, preg, a pointer to a character string buffer, errbuf, and the size of the string buffer, errbuf_size.

It returns the size of the errbuf required to contain the null-terminated error message string. If both errbuf and errbuf_size are nonzero, errbuf is filled in with the first errbuf_size - 1 characters of the error message and a terminating null byte (\0).

POSIX pattern buffer freeing

Supplying regfree() with a precompiled pattern buffer, preg will free the memory allocated to the pattern buffer by the compiling process, regcomp().

Return values and errors

regcomp() returns zero for a successful compilation. On failure, it returns one of the following errors (see reg_errcode_t):

  • REG_BADBR: Invalid use of back reference operator.
  • REG_BADPAT: Invalid use of pattern operators such as group or list.
  • REG_BADRPT: Invalid use of repetition operators such as using * as the first character.
  • REG_EBRACE: Un-matched brace interval operators.
  • REG_EBRACK: Un-matched bracket list operators.
  • REG_ECOLLATE: Invalid collating element.
  • REG_ECTYPE: Unknown character class name.
  • REG_EEND: Nonspecific error. This is not defined by POSIX.2.
  • REG_EESCAPE: Trailing backslash.
  • REG_EPAREN: Un-matched parenthesis group operators.
  • REG_ERANGE: Invalid use of the range operator; for example, the ending point of the range occurs prior to the starting point.
  • REG_ESIZE: Compiled regular expression requires a pattern buffer larger than 64Kb. This is not defined by POSIX.2.
  • REG_ESPACE: The regex routines ran out of memory.
  • REG_ESUBREG: Invalid back reference to a subexpression.

regexec() returns zero for a successful match or REG_NOMATCH for failure.

Thread safety

  • regcomp() and regexec() are thread-safe only if the process locale is not modified during the call.
  • regerror() is thread-safe only if the process environment is not modified during the call.
  • regfree() is thread-safe.

Supported environment variables

This crate depends on some environment variables, and variants of those. For each environment variable (e.g., CC), the following are the accepted variants of it:

  • <var>_<target>, e.g., CC_x86_64-pc-windows-gnu.
  • <var>_<target-with-underscores>, e.g., CC_x86_64_pc_windows_gnu.
  • TARGET_<var>, e.g., TARGET_CC.
  • <var>, e.g., CC.

The following environment variables (and their variants) affect how this crate is built:

  • GNURX_LIB_DIR_PREFIX
  • CC
  • CFLAGS
  • AR
  • ARFLAGS

Linking options

By default, this crate builds libgnurx from sources and links statically against it.

In order to change this behavior, and instruct this crate to dynamically link against an externally built libgnurx-0.dll library, please define the environment variable GNURX_LIB_DIR_PREFIX (or any of its variants) when building. The value of GNURX_LIB_DIR_PREFIX needs to be the absolute prefix path where the library is installed. The libgnurx header files are expected to reside in <GNURX_LIB_DIR_PREFIX>/include/, and the shared library should reside in <GNURX_LIB_DIR_PREFIX>/bin/.

Depending on this crate

This crate provides the following variables to other crates that depend on it:

  • DEP_GNURX_INCLUDE: Path of the directory where library C header files reside.
  • DEP_GNURX_LIB: Path of the directory where the library binary resides.

Platform-specific notes

This crate supports only the following target platforms:

  • x86_64-pc-windows-gnu.
  • i686-pc-windows-gnu.

This is due to the nature of the libgnurx library.

Versioning

This project adheres to Semantic Versioning. The CHANGELOG.md file details notable changes over time.

License

Copyright (c) 2020 Koutheir Attouchi.

See the LICENSE.md file at the top-level directory of this distribution.

Licensed under the LGPL version 2.1 license, or any later version thereof. This file may not be copied, modified, or distributed except according to those terms.

Dependencies

~0–1.5MB
~32K SLoC