Don't repeatedly register cache callbacks in pgoutput plugin.

[pgsql.git] / src / fe_utils / string_utils.c

/*-------------------------------------------------------------------------
 *
 * String-processing utility routines for frontend code
 *
 * Assorted utility functions that are useful in constructing SQL queries
 * and interpreting backend output.
 *
 *
 * Portions Copyright (c) 1996-2019, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 * src/fe_utils/string_utils.c
 *
 *-------------------------------------------------------------------------
 */
#include "postgres_fe.h"

#include <ctype.h>

#include "fe_utils/string_utils.h"

#include "common/keywords.h"


static PQExpBuffer defaultGetLocalPQExpBuffer(void);

/* Globals exported by this file */
int                     quote_all_identifiers = 0;
PQExpBuffer (*getLocalPQExpBuffer) (void) = defaultGetLocalPQExpBuffer;


/*
 * Returns a temporary PQExpBuffer, valid until the next call to the function.
 * This is used by fmtId and fmtQualifiedId.
 *
 * Non-reentrant and non-thread-safe but reduces memory leakage. You can
 * replace this with a custom version by setting the getLocalPQExpBuffer
 * function pointer.
 */
static PQExpBuffer
defaultGetLocalPQExpBuffer(void)
{
        static PQExpBuffer id_return = NULL;

        if (id_return)                          /* first time through? */
        {
                /* same buffer, just wipe contents */
                resetPQExpBuffer(id_return);
        }
        else
        {
                /* new buffer */
                id_return = createPQExpBuffer();
        }

        return id_return;
}

/*
 *      Quotes input string if it's not a legitimate SQL identifier as-is.
 *
 *      Note that the returned string must be used before calling fmtId again,
 *      since we re-use the same return buffer each time.
 */
const char *
fmtId(const char *rawid)
{
        PQExpBuffer id_return = getLocalPQExpBuffer();

        const char *cp;
        bool            need_quotes = false;

        /*
         * These checks need to match the identifier production in scan.l. Don't
         * use islower() etc.
         */
        if (quote_all_identifiers)
                need_quotes = true;
        /* slightly different rules for first character */
        else if (!((rawid[0] >= 'a' && rawid[0] <= 'z') || rawid[0] == '_'))
                need_quotes = true;
        else
        {
                /* otherwise check the entire string */
                for (cp = rawid; *cp; cp++)
                {
                        if (!((*cp >= 'a' && *cp <= 'z')
                                  || (*cp >= '0' && *cp <= '9')
                                  || (*cp == '_')))
                        {
                                need_quotes = true;
                                break;
                        }
                }
        }

        if (!need_quotes)
        {
                /*
                 * Check for keyword.  We quote keywords except for unreserved ones.
                 * (In some cases we could avoid quoting a col_name or type_func_name
                 * keyword, but it seems much harder than it's worth to tell that.)
                 *
                 * Note: ScanKeywordLookup() does case-insensitive comparison, but
                 * that's fine, since we already know we have all-lower-case.
                 */
                int                     kwnum = ScanKeywordLookup(rawid, &ScanKeywords);

                if (kwnum >= 0 && ScanKeywordCategories[kwnum] != UNRESERVED_KEYWORD)
                        need_quotes = true;
        }

        if (!need_quotes)
        {
                /* no quoting needed */
                appendPQExpBufferStr(id_return, rawid);
        }
        else
        {
                appendPQExpBufferChar(id_return, '"');
                for (cp = rawid; *cp; cp++)
                {
                        /*
                         * Did we find a double-quote in the string? Then make this a
                         * double double-quote per SQL99. Before, we put in a
                         * backslash/double-quote pair. - thomas 2000-08-05
                         */
                        if (*cp == '"')
                                appendPQExpBufferChar(id_return, '"');
                        appendPQExpBufferChar(id_return, *cp);
                }
                appendPQExpBufferChar(id_return, '"');
        }

        return id_return->data;
}

/*
 * fmtQualifiedId - construct a schema-qualified name, with quoting as needed.
 *
 * Like fmtId, use the result before calling again.
 *
 * Since we call fmtId and it also uses getLocalPQExpBuffer() we cannot
 * use that buffer until we're finished with calling fmtId().
 */
const char *
fmtQualifiedId(const char *schema, const char *id)
{
        PQExpBuffer id_return;
        PQExpBuffer lcl_pqexp = createPQExpBuffer();

        /* Some callers might fail to provide a schema name */
        if (schema && *schema)
        {
                appendPQExpBuffer(lcl_pqexp, "%s.", fmtId(schema));
        }
        appendPQExpBufferStr(lcl_pqexp, fmtId(id));

        id_return = getLocalPQExpBuffer();

        appendPQExpBufferStr(id_return, lcl_pqexp->data);
        destroyPQExpBuffer(lcl_pqexp);

        return id_return->data;
}


/*
 * Format a Postgres version number (in the PG_VERSION_NUM integer format
 * returned by PQserverVersion()) as a string.  This exists mainly to
 * encapsulate knowledge about two-part vs. three-part version numbers.
 *
 * For reentrancy, caller must supply the buffer the string is put in.
 * Recommended size of the buffer is 32 bytes.
 *
 * Returns address of 'buf', as a notational convenience.
 */
char *
formatPGVersionNumber(int version_number, bool include_minor,
                                          char *buf, size_t buflen)
{
        if (version_number >= 100000)
        {
                /* New two-part style */
                if (include_minor)
                        snprintf(buf, buflen, "%d.%d", version_number / 10000,
                                         version_number % 10000);
                else
                        snprintf(buf, buflen, "%d", version_number / 10000);
        }
        else
        {
                /* Old three-part style */
                if (include_minor)
                        snprintf(buf, buflen, "%d.%d.%d", version_number / 10000,
                                         (version_number / 100) % 100,
                                         version_number % 100);
                else
                        snprintf(buf, buflen, "%d.%d", version_number / 10000,
                                         (version_number / 100) % 100);
        }
        return buf;
}


/*
 * Convert a string value to an SQL string literal and append it to
 * the given buffer.  We assume the specified client_encoding and
 * standard_conforming_strings settings.
 *
 * This is essentially equivalent to libpq's PQescapeStringInternal,
 * except for the output buffer structure.  We need it in situations
 * where we do not have a PGconn available.  Where we do,
 * appendStringLiteralConn is a better choice.
 */
void
appendStringLiteral(PQExpBuffer buf, const char *str,
                                        int encoding, bool std_strings)
{
        size_t          length = strlen(str);
        const char *source = str;
        char       *target;

        if (!enlargePQExpBuffer(buf, 2 * length + 2))
                return;

        target = buf->data + buf->len;
        *target++ = '\'';

        while (*source != '\0')
        {
                char            c = *source;
                int                     len;
                int                     i;

                /* Fast path for plain ASCII */
                if (!IS_HIGHBIT_SET(c))
                {
                        /* Apply quoting if needed */
                        if (SQL_STR_DOUBLE(c, !std_strings))
                                *target++ = c;
                        /* Copy the character */
                        *target++ = c;
                        source++;
                        continue;
                }

                /* Slow path for possible multibyte characters */
                len = PQmblen(source, encoding);

                /* Copy the character */
                for (i = 0; i < len; i++)
                {
                        if (*source == '\0')
                                break;
                        *target++ = *source++;
                }

                /*
                 * If we hit premature end of string (ie, incomplete multibyte
                 * character), try to pad out to the correct length with spaces. We
                 * may not be able to pad completely, but we will always be able to
                 * insert at least one pad space (since we'd not have quoted a
                 * multibyte character).  This should be enough to make a string that
                 * the server will error out on.
                 */
                if (i < len)
                {
                        char       *stop = buf->data + buf->maxlen - 2;

                        for (; i < len; i++)
                        {
                                if (target >= stop)
                                        break;
                                *target++ = ' ';
                        }
                        break;
                }
        }

        /* Write the terminating quote and NUL character. */
        *target++ = '\'';
        *target = '\0';

        buf->len = target - buf->data;
}


/*
 * Convert a string value to an SQL string literal and append it to
 * the given buffer.  Encoding and string syntax rules are as indicated
 * by current settings of the PGconn.
 */
void
appendStringLiteralConn(PQExpBuffer buf, const char *str, PGconn *conn)
{
        size_t          length = strlen(str);

        /*
         * XXX This is a kluge to silence escape_string_warning in our utility
         * programs.  It should go away someday.
         */
        if (strchr(str, '\\') != NULL && PQserverVersion(conn) >= 80100)
        {
                /* ensure we are not adjacent to an identifier */
                if (buf->len > 0 && buf->data[buf->len - 1] != ' ')
                        appendPQExpBufferChar(buf, ' ');
                appendPQExpBufferChar(buf, ESCAPE_STRING_SYNTAX);
                appendStringLiteral(buf, str, PQclientEncoding(conn), false);
                return;
        }
        /* XXX end kluge */

        if (!enlargePQExpBuffer(buf, 2 * length + 2))
                return;
        appendPQExpBufferChar(buf, '\'');
        buf->len += PQescapeStringConn(conn, buf->data + buf->len,
                                                                   str, length, NULL);
        appendPQExpBufferChar(buf, '\'');
}


/*
 * Convert a string value to a dollar quoted literal and append it to
 * the given buffer. If the dqprefix parameter is not NULL then the
 * dollar quote delimiter will begin with that (after the opening $).
 *
 * No escaping is done at all on str, in compliance with the rules
 * for parsing dollar quoted strings.  Also, we need not worry about
 * encoding issues.
 */
void
appendStringLiteralDQ(PQExpBuffer buf, const char *str, const char *dqprefix)
{
        static const char suffixes[] = "_XXXXXXX";
        int                     nextchar = 0;
        PQExpBuffer delimBuf = createPQExpBuffer();

        /* start with $ + dqprefix if not NULL */
        appendPQExpBufferChar(delimBuf, '$');
        if (dqprefix)
                appendPQExpBufferStr(delimBuf, dqprefix);

        /*
         * Make sure we choose a delimiter which (without the trailing $) is not
         * present in the string being quoted. We don't check with the trailing $
         * because a string ending in $foo must not be quoted with $foo$.
         */
        while (strstr(str, delimBuf->data) != NULL)
        {
                appendPQExpBufferChar(delimBuf, suffixes[nextchar++]);
                nextchar %= sizeof(suffixes) - 1;
        }

        /* add trailing $ */
        appendPQExpBufferChar(delimBuf, '$');

        /* quote it and we are all done */
        appendPQExpBufferStr(buf, delimBuf->data);
        appendPQExpBufferStr(buf, str);
        appendPQExpBufferStr(buf, delimBuf->data);

        destroyPQExpBuffer(delimBuf);
}


/*
 * Convert a bytea value (presented as raw bytes) to an SQL string literal
 * and append it to the given buffer.  We assume the specified
 * standard_conforming_strings setting.
 *
 * This is needed in situations where we do not have a PGconn available.
 * Where we do, PQescapeByteaConn is a better choice.
 */
void
appendByteaLiteral(PQExpBuffer buf, const unsigned char *str, size_t length,
                                   bool std_strings)
{
        const unsigned char *source = str;
        char       *target;

        static const char hextbl[] = "0123456789abcdef";

        /*
         * This implementation is hard-wired to produce hex-format output. We do
         * not know the server version the output will be loaded into, so making
         * an intelligent format choice is impossible.  It might be better to
         * always use the old escaped format.
         */
        if (!enlargePQExpBuffer(buf, 2 * length + 5))
                return;

        target = buf->data + buf->len;
        *target++ = '\'';
        if (!std_strings)
                *target++ = '\\';
        *target++ = '\\';
        *target++ = 'x';

        while (length-- > 0)
        {
                unsigned char c = *source++;

                *target++ = hextbl[(c >> 4) & 0xF];
                *target++ = hextbl[c & 0xF];
        }

        /* Write the terminating quote and NUL character. */
        *target++ = '\'';
        *target = '\0';

        buf->len = target - buf->data;
}


/*
 * Append the given string to the shell command being built in the buffer,
 * with shell-style quoting as needed to create exactly one argument.
 *
 * Forbid LF or CR characters, which have scant practical use beyond designing
 * security breaches.  The Windows command shell is unusable as a conduit for
 * arguments containing LF or CR characters.  A future major release should
 * reject those characters in CREATE ROLE and CREATE DATABASE, because use
 * there eventually leads to errors here.
 *
 * appendShellString() simply prints an error and dies if LF or CR appears.
 * appendShellStringNoError() omits those characters from the result, and
 * returns false if there were any.
 */
void
appendShellString(PQExpBuffer buf, const char *str)
{
        if (!appendShellStringNoError(buf, str))
        {
                fprintf(stderr,
                                _("shell command argument contains a newline or carriage return: \"%s\"\n"),
                                str);
                exit(EXIT_FAILURE);
        }
}

bool
appendShellStringNoError(PQExpBuffer buf, const char *str)
{
#ifdef WIN32
        int                     backslash_run_length = 0;
#endif
        bool            ok = true;
        const char *p;

        /*
         * Don't bother with adding quotes if the string is nonempty and clearly
         * contains only safe characters.
         */
        if (*str != '\0' &&
                strspn(str, "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789-_./:") == strlen(str))
        {
                appendPQExpBufferStr(buf, str);
                return ok;
        }

#ifndef WIN32
        appendPQExpBufferChar(buf, '\'');
        for (p = str; *p; p++)
        {
                if (*p == '\n' || *p == '\r')
                {
                        ok = false;
                        continue;
                }

                if (*p == '\'')
                        appendPQExpBufferStr(buf, "'\"'\"'");
                else
                        appendPQExpBufferChar(buf, *p);
        }
        appendPQExpBufferChar(buf, '\'');
#else                                                   /* WIN32 */

        /*
         * A Windows system() argument experiences two layers of interpretation.
         * First, cmd.exe interprets the string.  Its behavior is undocumented,
         * but a caret escapes any byte except LF or CR that would otherwise have
         * special meaning.  Handling of a caret before LF or CR differs between
         * "cmd.exe /c" and other modes, and it is unusable here.
         *
         * Second, the new process parses its command line to construct argv (see
         * https://msdn.microsoft.com/en-us/library/17w5ykft.aspx).  This treats
         * backslash-double quote sequences specially.
         */
        appendPQExpBufferStr(buf, "^\"");
        for (p = str; *p; p++)
        {
                if (*p == '\n' || *p == '\r')
                {
                        ok = false;
                        continue;
                }

                /* Change N backslashes before a double quote to 2N+1 backslashes. */
                if (*p == '"')
                {
                        while (backslash_run_length)
                        {
                                appendPQExpBufferStr(buf, "^\\");
                                backslash_run_length--;
                        }
                        appendPQExpBufferStr(buf, "^\\");
                }
                else if (*p == '\\')
                        backslash_run_length++;
                else
                        backslash_run_length = 0;

                /*
                 * Decline to caret-escape the most mundane characters, to ease
                 * debugging and lest we approach the command length limit.
                 */
                if (!((*p >= 'a' && *p <= 'z') ||
                          (*p >= 'A' && *p <= 'Z') ||
                          (*p >= '0' && *p <= '9')))
                        appendPQExpBufferChar(buf, '^');
                appendPQExpBufferChar(buf, *p);
        }

        /*
         * Change N backslashes at end of argument to 2N backslashes, because they
         * precede the double quote that terminates the argument.
         */
        while (backslash_run_length)
        {
                appendPQExpBufferStr(buf, "^\\");
                backslash_run_length--;
        }
        appendPQExpBufferStr(buf, "^\"");
#endif                                                  /* WIN32 */

        return ok;
}


/*
 * Append the given string to the buffer, with suitable quoting for passing
 * the string as a value in a keyword/value pair in a libpq connection string.
 */
void
appendConnStrVal(PQExpBuffer buf, const char *str)
{
        const char *s;
        bool            needquotes;

        /*
         * If the string is one or more plain ASCII characters, no need to quote
         * it. This is quite conservative, but better safe than sorry.
         */
        needquotes = true;
        for (s = str; *s; s++)
        {
                if (!((*s >= 'a' && *s <= 'z') || (*s >= 'A' && *s <= 'Z') ||
                          (*s >= '0' && *s <= '9') || *s == '_' || *s == '.'))
                {
                        needquotes = true;
                        break;
                }
                needquotes = false;
        }

        if (needquotes)
        {
                appendPQExpBufferChar(buf, '\'');
                while (*str)
                {
                        /* ' and \ must be escaped by to \' and \\ */
                        if (*str == '\'' || *str == '\\')
                                appendPQExpBufferChar(buf, '\\');

                        appendPQExpBufferChar(buf, *str);
                        str++;
                }
                appendPQExpBufferChar(buf, '\'');
        }
        else
                appendPQExpBufferStr(buf, str);
}


/*
 * Append a psql meta-command that connects to the given database with the
 * then-current connection's user, host and port.
 */
void
appendPsqlMetaConnect(PQExpBuffer buf, const char *dbname)
{
        const char *s;
        bool complex;

        /*
         * If the name is plain ASCII characters, emit a trivial "\connect "foo"".
         * For other names, even many not technically requiring it, skip to the
         * general case.  No database has a zero-length name.
         */
        complex = false;

        for (s = dbname; *s; s++)
        {
                if (*s == '\n' || *s == '\r')
                {
                        fprintf(stderr,
                                        _("database name contains a newline or carriage return: \"%s\"\n"),
                                        dbname);
                        exit(EXIT_FAILURE);
                }

                if (!((*s >= 'a' && *s <= 'z') || (*s >= 'A' && *s <= 'Z') ||
                          (*s >= '0' && *s <= '9') || *s == '_' || *s == '.'))
                {
                        complex = true;
                }
        }

        appendPQExpBufferStr(buf, "\\connect ");
        if (complex)
        {
                PQExpBufferData connstr;

                initPQExpBuffer(&connstr);
                appendPQExpBuffer(&connstr, "dbname=");
                appendConnStrVal(&connstr, dbname);

                appendPQExpBuffer(buf, "-reuse-previous=on ");

                /*
                 * As long as the name does not contain a newline, SQL identifier
                 * quoting satisfies the psql meta-command parser.  Prefer not to
                 * involve psql-interpreted single quotes, which behaved differently
                 * before PostgreSQL 9.2.
                 */
                appendPQExpBufferStr(buf, fmtId(connstr.data));

                termPQExpBuffer(&connstr);
        }
        else
                appendPQExpBufferStr(buf, fmtId(dbname));
        appendPQExpBufferChar(buf, '\n');
}


/*
 * Deconstruct the text representation of a 1-dimensional Postgres array
 * into individual items.
 *
 * On success, returns true and sets *itemarray and *nitems to describe
 * an array of individual strings.  On parse failure, returns false;
 * *itemarray may exist or be NULL.
 *
 * NOTE: free'ing itemarray is sufficient to deallocate the working storage.
 */
bool
parsePGArray(const char *atext, char ***itemarray, int *nitems)
{
        int                     inputlen;
        char      **items;
        char       *strings;
        int                     curitem;

        /*
         * We expect input in the form of "{item,item,item}" where any item is
         * either raw data, or surrounded by double quotes (in which case embedded
         * characters including backslashes and quotes are backslashed).
         *
         * We build the result as an array of pointers followed by the actual
         * string data, all in one malloc block for convenience of deallocation.
         * The worst-case storage need is not more than one pointer and one
         * character for each input character (consider "{,,,,,,,,,,}").
         */
        *itemarray = NULL;
        *nitems = 0;
        inputlen = strlen(atext);
        if (inputlen < 2 || atext[0] != '{' || atext[inputlen - 1] != '}')
                return false;                   /* bad input */
        items = (char **) malloc(inputlen * (sizeof(char *) + sizeof(char)));
        if (items == NULL)
                return false;                   /* out of memory */
        *itemarray = items;
        strings = (char *) (items + inputlen);

        atext++;                                        /* advance over initial '{' */
        curitem = 0;
        while (*atext != '}')
        {
                if (*atext == '\0')
                        return false;           /* premature end of string */
                items[curitem] = strings;
                while (*atext != '}' && *atext != ',')
                {
                        if (*atext == '\0')
                                return false;   /* premature end of string */
                        if (*atext != '"')
                                *strings++ = *atext++;  /* copy unquoted data */
                        else
                        {
                                /* process quoted substring */
                                atext++;
                                while (*atext != '"')
                                {
                                        if (*atext == '\0')
                                                return false;   /* premature end of string */
                                        if (*atext == '\\')
                                        {
                                                atext++;
                                                if (*atext == '\0')
                                                        return false;   /* premature end of string */
                                        }
                                        *strings++ = *atext++;  /* copy quoted data */
                                }
                                atext++;
                        }
                }
                *strings++ = '\0';
                if (*atext == ',')
                        atext++;
                curitem++;
        }
        if (atext[1] != '\0')
                return false;                   /* bogus syntax (embedded '}') */
        *nitems = curitem;
        return true;
}


/*
 * Format a reloptions array and append it to the given buffer.
 *
 * "prefix" is prepended to the option names; typically it's "" or "toast.".
 *
 * Returns false if the reloptions array could not be parsed (in which case
 * nothing will have been appended to the buffer), or true on success.
 *
 * Note: this logic should generally match the backend's flatten_reloptions()
 * (in adt/ruleutils.c).
 */
bool
appendReloptionsArray(PQExpBuffer buffer, const char *reloptions,
                                          const char *prefix, int encoding, bool std_strings)
{
        char      **options;
        int                     noptions;
        int                     i;

        if (!parsePGArray(reloptions, &options, &noptions))
        {
                if (options)
                        free(options);
                return false;
        }

        for (i = 0; i < noptions; i++)
        {
                char       *option = options[i];
                char       *name;
                char       *separator;
                char       *value;

                /*
                 * Each array element should have the form name=value.  If the "=" is
                 * missing for some reason, treat it like an empty value.
                 */
                name = option;
                separator = strchr(option, '=');
                if (separator)
                {
                        *separator = '\0';
                        value = separator + 1;
                }
                else
                        value = "";

                if (i > 0)
                        appendPQExpBufferStr(buffer, ", ");
                appendPQExpBuffer(buffer, "%s%s=", prefix, fmtId(name));

                /*
                 * In general we need to quote the value; but to avoid unnecessary
                 * clutter, do not quote if it is an identifier that would not need
                 * quoting.  (We could also allow numbers, but that is a bit trickier
                 * than it looks --- for example, are leading zeroes significant?  We
                 * don't want to assume very much here about what custom reloptions
                 * might mean.)
                 */
                if (strcmp(fmtId(value), value) == 0)
                        appendPQExpBufferStr(buffer, value);
                else
                        appendStringLiteral(buffer, value, encoding, std_strings);
        }

        if (options)
                free(options);

        return true;
}


/*
 * processSQLNamePattern
 *
 * Scan a wildcard-pattern string and generate appropriate WHERE clauses
 * to limit the set of objects returned.  The WHERE clauses are appended
 * to the already-partially-constructed query in buf.  Returns whether
 * any clause was added.
 *
 * conn: connection query will be sent to (consulted for escaping rules).
 * buf: output parameter.
 * pattern: user-specified pattern option, or NULL if none ("*" is implied).
 * have_where: true if caller already emitted "WHERE" (clauses will be ANDed
 * onto the existing WHERE clause).
 * force_escape: always quote regexp special characters, even outside
 * double quotes (else they are quoted only between double quotes).
 * schemavar: name of query variable to match against a schema-name pattern.
 * Can be NULL if no schema.
 * namevar: name of query variable to match against an object-name pattern.
 * altnamevar: NULL, or name of an alternative variable to match against name.
 * visibilityrule: clause to use if we want to restrict to visible objects
 * (for example, "pg_catalog.pg_table_is_visible(p.oid)").  Can be NULL.
 *
 * Formatting note: the text already present in buf should end with a newline.
 * The appended text, if any, will end with one too.
 */
bool
processSQLNamePattern(PGconn *conn, PQExpBuffer buf, const char *pattern,
                                          bool have_where, bool force_escape,
                                          const char *schemavar, const char *namevar,
                                          const char *altnamevar, const char *visibilityrule)
{
        PQExpBufferData schemabuf;
        PQExpBufferData namebuf;
        int                     encoding = PQclientEncoding(conn);
        bool            inquotes;
        const char *cp;
        int                     i;
        bool            added_clause = false;

#define WHEREAND() \
        (appendPQExpBufferStr(buf, have_where ? "  AND " : "WHERE "), \
         have_where = true, added_clause = true)

        if (pattern == NULL)
        {
                /* Default: select all visible objects */
                if (visibilityrule)
                {
                        WHEREAND();
                        appendPQExpBuffer(buf, "%s\n", visibilityrule);
                }
                return added_clause;
        }

        initPQExpBuffer(&schemabuf);
        initPQExpBuffer(&namebuf);

        /*
         * Parse the pattern, converting quotes and lower-casing unquoted letters.
         * Also, adjust shell-style wildcard characters into regexp notation.
         *
         * We surround the pattern with "^(...)$" to force it to match the whole
         * string, as per SQL practice.  We have to have parens in case the string
         * contains "|", else the "^" and "$" will be bound into the first and
         * last alternatives which is not what we want.
         *
         * Note: the result of this pass is the actual regexp pattern(s) we want
         * to execute.  Quoting/escaping into SQL literal format will be done
         * below using appendStringLiteralConn().
         */
        appendPQExpBufferStr(&namebuf, "^(");

        inquotes = false;
        cp = pattern;

        while (*cp)
        {
                char            ch = *cp;

                if (ch == '"')
                {
                        if (inquotes && cp[1] == '"')
                        {
                                /* emit one quote, stay in inquotes mode */
                                appendPQExpBufferChar(&namebuf, '"');
                                cp++;
                        }
                        else
                                inquotes = !inquotes;
                        cp++;
                }
                else if (!inquotes && isupper((unsigned char) ch))
                {
                        appendPQExpBufferChar(&namebuf,
                                                                  pg_tolower((unsigned char) ch));
                        cp++;
                }
                else if (!inquotes && ch == '*')
                {
                        appendPQExpBufferStr(&namebuf, ".*");
                        cp++;
                }
                else if (!inquotes && ch == '?')
                {
                        appendPQExpBufferChar(&namebuf, '.');
                        cp++;
                }
                else if (!inquotes && ch == '.')
                {
                        /* Found schema/name separator, move current pattern to schema */
                        resetPQExpBuffer(&schemabuf);
                        appendPQExpBufferStr(&schemabuf, namebuf.data);
                        resetPQExpBuffer(&namebuf);
                        appendPQExpBufferStr(&namebuf, "^(");
                        cp++;
                }
                else if (ch == '$')
                {
                        /*
                         * Dollar is always quoted, whether inside quotes or not. The
                         * reason is that it's allowed in SQL identifiers, so there's a
                         * significant use-case for treating it literally, while because
                         * we anchor the pattern automatically there is no use-case for
                         * having it possess its regexp meaning.
                         */
                        appendPQExpBufferStr(&namebuf, "\\$");
                        cp++;
                }
                else
                {
                        /*
                         * Ordinary data character, transfer to pattern
                         *
                         * Inside double quotes, or at all times if force_escape is true,
                         * quote regexp special characters with a backslash to avoid
                         * regexp errors.  Outside quotes, however, let them pass through
                         * as-is; this lets knowledgeable users build regexp expressions
                         * that are more powerful than shell-style patterns.
                         */
                        if ((inquotes || force_escape) &&
                                strchr("|*+?()[]{}.^$\\", ch))
                                appendPQExpBufferChar(&namebuf, '\\');
                        i = PQmblen(cp, encoding);
                        while (i-- && *cp)
                        {
                                appendPQExpBufferChar(&namebuf, *cp);
                                cp++;
                        }
                }
        }

        /*
         * Now decide what we need to emit.  We may run under a hostile
         * search_path, so qualify EVERY name.  Note there will be a leading "^("
         * in the patterns in any case.
         *
         * We want the regex matches to use the database's default collation where
         * collation-sensitive behavior is required (for example, which characters
         * match '\w').  That happened by default before PG v12, but if the server
         * is >= v12 then we need to force it through explicit COLLATE clauses,
         * otherwise the "C" collation attached to "name" catalog columns wins.
         */
        if (namebuf.len > 2)
        {
                /* We have a name pattern, so constrain the namevar(s) */

                appendPQExpBufferStr(&namebuf, ")$");
                /* Optimize away a "*" pattern */
                if (strcmp(namebuf.data, "^(.*)$") != 0)
                {
                        WHEREAND();
                        if (altnamevar)
                        {
                                appendPQExpBuffer(buf,
                                                                  "(%s OPERATOR(pg_catalog.~) ", namevar);
                                appendStringLiteralConn(buf, namebuf.data, conn);
                                if (PQserverVersion(conn) >= 120000)
                                        appendPQExpBufferStr(buf, " COLLATE pg_catalog.default");
                                appendPQExpBuffer(buf,
                                                                  "\n        OR %s OPERATOR(pg_catalog.~) ",
                                                                  altnamevar);
                                appendStringLiteralConn(buf, namebuf.data, conn);
                                if (PQserverVersion(conn) >= 120000)
                                        appendPQExpBufferStr(buf, " COLLATE pg_catalog.default");
                                appendPQExpBufferStr(buf, ")\n");
                        }
                        else
                        {
                                appendPQExpBuffer(buf, "%s OPERATOR(pg_catalog.~) ", namevar);
                                appendStringLiteralConn(buf, namebuf.data, conn);
                                if (PQserverVersion(conn) >= 120000)
                                        appendPQExpBufferStr(buf, " COLLATE pg_catalog.default");
                                appendPQExpBufferChar(buf, '\n');
                        }
                }
        }

        if (schemabuf.len > 2)
        {
                /* We have a schema pattern, so constrain the schemavar */

                appendPQExpBufferStr(&schemabuf, ")$");
                /* Optimize away a "*" pattern */
                if (strcmp(schemabuf.data, "^(.*)$") != 0 && schemavar)
                {
                        WHEREAND();
                        appendPQExpBuffer(buf, "%s OPERATOR(pg_catalog.~) ", schemavar);
                        appendStringLiteralConn(buf, schemabuf.data, conn);
                        if (PQserverVersion(conn) >= 120000)
                                appendPQExpBufferStr(buf, " COLLATE pg_catalog.default");
                        appendPQExpBufferChar(buf, '\n');
                }
        }
        else
        {
                /* No schema pattern given, so select only visible objects */
                if (visibilityrule)
                {
                        WHEREAND();
                        appendPQExpBuffer(buf, "%s\n", visibilityrule);
                }
        }

        termPQExpBuffer(&schemabuf);
        termPQExpBuffer(&namebuf);

        return added_clause;
#undef WHEREAND
}