stringutils.c

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/*
 * psql - the PostgreSQL interactive terminal
 *
 * Copyright (c) 2000-2026, PostgreSQL Global Development Group
 *
 * src/bin/psql/stringutils.c
 */
#include "postgres_fe.h"
 
#include <ctype.h>
 
#include "common.h"
#include "stringutils.h"
 
 
/*
 * Replacement for strtok() (a.k.a. poor man's flex)
 *
 * Splits a string into tokens, returning one token per call, then NULL
 * when no more tokens exist in the given string.
 *
 * The calling convention is similar to that of strtok, but with more
 * frammishes.
 *
 * s -          string to parse, if NULL continue parsing the last string
 * whitespace - set of whitespace characters that separate tokens
 * delim -      set of non-whitespace separator characters (or NULL)
 * quote -      set of characters that can quote a token (NULL if none)
 * escape -     character that can quote quotes (0 if none)
 * e_strings -  if true, treat E'...' syntax as a valid token
 * del_quotes - if true, strip quotes from the returned token, else return
 *              it exactly as found in the string
 * encoding -   the active character-set encoding
 *
 * Characters in 'delim', if any, will be returned as single-character
 * tokens unless part of a quoted token.
 *
 * Double occurrences of the quoting character are always taken to represent
 * a single quote character in the data.  If escape isn't 0, then escape
 * followed by anything (except \0) is a data character too.
 *
 * The combination of e_strings and del_quotes both true is not currently
 * handled.  This could be fixed but it's not needed anywhere at the moment.
 *
 * Note that the string s is _not_ overwritten in this implementation.
 *
 * NB: it's okay to vary delim, quote, and escape from one call to the
 * next on a single source string, but changing whitespace is a bad idea
 * since you might lose data.
 */
char *
strtokx(const char *s,
        const char *whitespace,
        const char *delim,
        const char *quote,
        char escape,
        bool e_strings,
        bool del_quotes,
        int encoding)
{
    static char *storage = NULL;    /* store the local copy of the users
                                     * string here */
    static char *string = NULL; /* pointer into storage where to continue on
                                 * next call */
 
    /* variously abused variables: */
    unsigned int offset;
    char       *start;
    char       *p;
 
    if (s)
    {
        free(storage);
 
        /*
         * We may need extra space to insert delimiter nulls for adjacent
         * tokens.  2X the space is a gross overestimate, but it's unlikely
         * that this code will be used on huge strings anyway.
         */
        storage = pg_malloc(2 * strlen(s) + 1);
        strcpy(storage, s);
        string = storage;
    }
 
    if (!storage)
        return NULL;
 
    /* skip leading whitespace */
    offset = strspn(string, whitespace);
    start = &string[offset];
 
    /* end of string reached? */
    if (*start == '\0')
    {
        /* technically we don't need to free here, but we're nice */
        free(storage);
        storage = NULL;
        string = NULL;
        return NULL;
    }
 
    /* test if delimiter character */
    if (delim && strchr(delim, *start))
    {
        /*
         * If not at end of string, we need to insert a null to terminate the
         * returned token.  We can just overwrite the next character if it
         * happens to be in the whitespace set ... otherwise move over the
         * rest of the string to make room.  (This is why we allocated extra
         * space above).
         */
        p = start + 1;
        if (*p != '\0')
        {
            if (!strchr(whitespace, *p))
                memmove(p + 1, p, strlen(p) + 1);
            *p = '\0';
            string = p + 1;
        }
        else
        {
            /* at end of string, so no extra work */
            string = p;
        }
 
        return start;
    }
 
    /* check for E string */
    p = start;
    if (e_strings &&
        (*p == 'E' || *p == 'e') &&
        p[1] == '\'')
    {
        quote = "'";
        escape = '\\';          /* if std strings before, not any more */
        p++;
    }
 
    /* test if quoting character */
    if (quote && strchr(quote, *p))
    {
        /* okay, we have a quoted token, now scan for the closer */
        char        thisquote = *p++;
 
        for (; *p; p += PQmblenBounded(p, encoding))
        {
            if (*p == escape && p[1] != '\0')
                p++;            /* process escaped anything */
            else if (*p == thisquote && p[1] == thisquote)
                p++;            /* process doubled quote */
            else if (*p == thisquote)
            {
                p++;            /* skip trailing quote */
                break;
            }
        }
 
        /*
         * If not at end of string, we need to insert a null to terminate the
         * returned token.  See notes above.
         */
        if (*p != '\0')
        {
            if (!strchr(whitespace, *p))
                memmove(p + 1, p, strlen(p) + 1);
            *p = '\0';
            string = p + 1;
        }
        else
        {
            /* at end of string, so no extra work */
            string = p;
        }
 
        /* Clean up the token if caller wants that */
        if (del_quotes)
            strip_quotes(start, thisquote, escape, encoding);
 
        return start;
    }
 
    /*
     * Otherwise no quoting character.  Scan till next whitespace, delimiter
     * or quote.  NB: at this point, *start is known not to be '\0',
     * whitespace, delim, or quote, so we will consume at least one character.
     */
    offset = strcspn(start, whitespace);
 
    if (delim)
    {
        unsigned int offset2 = strcspn(start, delim);
 
        if (offset > offset2)
            offset = offset2;
    }
 
    if (quote)
    {
        unsigned int offset2 = strcspn(start, quote);
 
        if (offset > offset2)
            offset = offset2;
    }
 
    p = start + offset;
 
    /*
     * If not at end of string, we need to insert a null to terminate the
     * returned token.  See notes above.
     */
    if (*p != '\0')
    {
        if (!strchr(whitespace, *p))
            memmove(p + 1, p, strlen(p) + 1);
        *p = '\0';
        string = p + 1;
    }
    else
    {
        /* at end of string, so no extra work */
        string = p;
    }
 
    return start;
}
 
 
/*
 * strip_quotes
 *
 * Remove quotes from the string at *source.  Leading and trailing occurrences
 * of 'quote' are removed; embedded double occurrences of 'quote' are reduced
 * to single occurrences; if 'escape' is not 0 then 'escape' removes special
 * significance of next character.
 *
 * Note that the source string is overwritten in-place.
 */
void
strip_quotes(char *source, char quote, char escape, int encoding)
{
    char       *src;
    char       *dst;
 
    Assert(source != NULL);
    Assert(quote != '\0');
 
    src = dst = source;
 
    if (*src && *src == quote)
        src++;                  /* skip leading quote */
 
    while (*src)
    {
        char        c = *src;
        int         i;
 
        if (c == quote && src[1] == '\0')
            break;              /* skip trailing quote */
        else if (c == quote && src[1] == quote)
            src++;              /* process doubled quote */
        else if (c == escape && src[1] != '\0')
            src++;              /* process escaped character */
 
        i = PQmblenBounded(src, encoding);
        while (i--)
            *dst++ = *src++;
    }
 
    *dst = '\0';
}
 
 
/*
 * quote_if_needed
 *
 * Opposite of strip_quotes().  If "source" denotes itself literally without
 * quoting or escaping, returns NULL.  Otherwise, returns a malloc'd copy with
 * quoting and escaping applied:
 *
 * source -         string to parse
 * entails_quote -  any of these present?  need outer quotes
 * quote -          doubled within string, affixed to both ends
 * escape -         doubled within string
 * force_quote -    if true, quote the output even if it doesn't "need" it
 * encoding -       the active character-set encoding
 *
 * Do not use this as a substitute for PQescapeStringConn().  Use it for
 * strings to be parsed by strtokx() or psql_scan_slash_option().
 */
char *
quote_if_needed(const char *source, const char *entails_quote,
                char quote, char escape, bool force_quote,
                int encoding)
{
    const char *src;
    char       *ret;
    char       *dst;
    bool        need_quotes = force_quote;
 
    Assert(source != NULL);
    Assert(quote != '\0');
 
    src = source;
    dst = ret = pg_malloc(2 * strlen(src) + 3); /* excess */
 
    *dst++ = quote;
 
    while (*src)
    {
        char        c = *src;
        int         i;
 
        if (c == quote)
        {
            need_quotes = true;
            *dst++ = quote;
        }
        else if (c == escape)
        {
            need_quotes = true;
            *dst++ = escape;
        }
        else if (strchr(entails_quote, c))
            need_quotes = true;
 
        i = PQmblenBounded(src, encoding);
        while (i--)
            *dst++ = *src++;
    }
 
    *dst++ = quote;
    *dst = '\0';
 
    if (!need_quotes)
    {
        free(ret);
        ret = NULL;
    }
 
    return ret;
}