percentrepl.c

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/*-------------------------------------------------------------------------
 *
 * percentrepl.c
 *    Common routines to replace percent placeholders in strings
 *
 * Portions Copyright (c) 1996-2025, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *    src/common/percentrepl.c
 *
 *-------------------------------------------------------------------------
 */
 
#ifndef FRONTEND
#include "postgres.h"
#else
#include "postgres_fe.h"
#include "common/logging.h"
#endif
 
#include "common/percentrepl.h"
#include "lib/stringinfo.h"
 
/*
 * replace_percent_placeholders
 *
 * Replace percent-letter placeholders in input string with the supplied
 * values.  For example, to replace %f with foo and %b with bar, call
 *
 * replace_percent_placeholders(instr, "param_name", "bf", bar, foo);
 *
 * The return value is palloc'd.
 *
 * "%%" is replaced by a single "%".
 *
 * This throws an error for an unsupported placeholder or a "%" at the end of
 * the input string.
 *
 * A value may be NULL.  If the corresponding placeholder is found in the
 * input string, it will be treated as if an unsupported placeholder was used.
 * This allows callers to share a "letters" specification but vary the
 * actually supported placeholders at run time.
 *
 * This functions is meant for cases where all the values are readily
 * available or cheap to compute and most invocations will use most values
 * (for example for archive_command).  Also, it requires that all values are
 * strings.  It won't be a good match for things like log prefixes or prompts
 * that use a mix of data types and any invocation will only use a few of the
 * possible values.
 *
 * param_name is the name of the underlying GUC parameter, for error
 * reporting.  At the moment, this function is only used for GUC parameters.
 * If other kinds of uses were added, the error reporting would need to be
 * revised.
 */
char *
replace_percent_placeholders(const char *instr, const char *param_name, const char *letters,...)
{
    StringInfoData result;
 
    initStringInfo(&result);
 
    for (const char *sp = instr; *sp; sp++)
    {
        if (*sp == '%')
        {
            if (sp[1] == '%')
            {
                /* Convert %% to a single % */
                sp++;
                appendStringInfoChar(&result, *sp);
            }
            else if (sp[1] == '\0')
            {
                /* Incomplete escape sequence, expected a character afterward */
#ifdef FRONTEND
                pg_log_error("invalid value for parameter \"%s\": \"%s\"", param_name, instr);
                pg_log_error_detail("String ends unexpectedly after escape character \"%%\".");
                exit(1);
#else
                ereport(ERROR,
                        errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                        errmsg("invalid value for parameter \"%s\": \"%s\"", param_name, instr),
                        errdetail("String ends unexpectedly after escape character \"%%\"."));
#endif
            }
            else
            {
                /* Look up placeholder character */
                bool        found = false;
                va_list     ap;
 
                sp++;
 
                va_start(ap, letters);
                for (const char *lp = letters; *lp; lp++)
                {
                    char       *val = va_arg(ap, char *);
 
                    if (*sp == *lp)
                    {
                        if (val)
                        {
                            appendStringInfoString(&result, val);
                            found = true;
                        }
                        /* If val is NULL, we will report an error. */
                        break;
                    }
                }
                va_end(ap);
                if (!found)
                {
                    /* Unknown placeholder */
#ifdef FRONTEND
                    pg_log_error("invalid value for parameter \"%s\": \"%s\"", param_name, instr);
                    pg_log_error_detail("String contains unexpected placeholder \"%%%c\".", *sp);
                    exit(1);
#else
                    ereport(ERROR,
                            errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                            errmsg("invalid value for parameter \"%s\": \"%s\"", param_name, instr),
                            errdetail("String contains unexpected placeholder \"%%%c\".", *sp));
#endif
                }
            }
        }
        else
        {
            appendStringInfoChar(&result, *sp);
        }
    }
 
    return result.data;
}