mbutils.c

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/*-------------------------------------------------------------------------
 *
 * mbutils.c
 *    This file contains functions for encoding conversion.
 *
 * The string-conversion functions in this file share some API quirks.
 * Note the following:
 *
 * The functions return a palloc'd, null-terminated string if conversion
 * is required.  However, if no conversion is performed, the given source
 * string pointer is returned as-is.
 *
 * Although the presence of a length argument means that callers can pass
 * non-null-terminated strings, care is required because the same string
 * will be passed back if no conversion occurs.  Such callers *must* check
 * whether result == src and handle that case differently.
 *
 * If the source and destination encodings are the same, the source string
 * is returned without any verification; it's assumed to be valid data.
 * If that might not be the case, the caller is responsible for validating
 * the string using a separate call to pg_verify_mbstr().  Whenever the
 * source and destination encodings are different, the functions ensure that
 * the result is validly encoded according to the destination encoding.
 *
 *
 * Portions Copyright (c) 1996-2019, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *    src/backend/utils/mb/mbutils.c
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.h"

#include "access/xact.h"
#include "catalog/namespace.h"
#include "mb/pg_wchar.h"
#include "utils/builtins.h"
#include "utils/memutils.h"
#include "utils/syscache.h"

/*
 * We maintain a simple linked list caching the fmgr lookup info for the
 * currently selected conversion functions, as well as any that have been
 * selected previously in the current session.  (We remember previous
 * settings because we must be able to restore a previous setting during
 * transaction rollback, without doing any fresh catalog accesses.)
 *
 * Since we'll never release this data, we just keep it in TopMemoryContext.
 */
typedef struct ConvProcInfo
{
    int         s_encoding;     /* server and client encoding IDs */
    int         c_encoding;
    FmgrInfo    to_server_info; /* lookup info for conversion procs */
    FmgrInfo    to_client_info;
} ConvProcInfo;

static List *ConvProcList = NIL;    /* List of ConvProcInfo */

/*
 * These variables point to the currently active conversion functions,
 * or are NULL when no conversion is needed.
 */
static FmgrInfo *ToServerConvProc = NULL;
static FmgrInfo *ToClientConvProc = NULL;

/*
 * These variables track the currently-selected encodings.
 */
static const pg_enc2name *ClientEncoding = &pg_enc2name_tbl[PG_SQL_ASCII];
static const pg_enc2name *DatabaseEncoding = &pg_enc2name_tbl[PG_SQL_ASCII];
static const pg_enc2name *MessageEncoding = &pg_enc2name_tbl[PG_SQL_ASCII];

/*
 * During backend startup we can't set client encoding because we (a)
 * can't look up the conversion functions, and (b) may not know the database
 * encoding yet either.  So SetClientEncoding() just accepts anything and
 * remembers it for InitializeClientEncoding() to apply later.
 */
static bool backend_startup_complete = false;
static int  pending_client_encoding = PG_SQL_ASCII;


/* Internal functions */
static char *perform_default_encoding_conversion(const char *src,
                                                 int len, bool is_client_to_server);
static int  cliplen(const char *str, int len, int limit);


/*
 * Prepare for a future call to SetClientEncoding.  Success should mean
 * that SetClientEncoding is guaranteed to succeed for this encoding request.
 *
 * (But note that success before backend_startup_complete does not guarantee
 * success after ...)
 *
 * Returns 0 if okay, -1 if not (bad encoding or can't support conversion)
 */
int
PrepareClientEncoding(int encoding)
{
    int         current_server_encoding;
    ListCell   *lc;

    if (!PG_VALID_FE_ENCODING(encoding))
        return -1;

    /* Can't do anything during startup, per notes above */
    if (!backend_startup_complete)
        return 0;

    current_server_encoding = GetDatabaseEncoding();

    /*
     * Check for cases that require no conversion function.
     */
    if (current_server_encoding == encoding ||
        current_server_encoding == PG_SQL_ASCII ||
        encoding == PG_SQL_ASCII)
        return 0;

    if (IsTransactionState())
    {
        /*
         * If we're in a live transaction, it's safe to access the catalogs,
         * so look up the functions.  We repeat the lookup even if the info is
         * already cached, so that we can react to changes in the contents of
         * pg_conversion.
         */
        Oid         to_server_proc,
                    to_client_proc;
        ConvProcInfo *convinfo;
        MemoryContext oldcontext;

        to_server_proc = FindDefaultConversionProc(encoding,
                                                   current_server_encoding);
        if (!OidIsValid(to_server_proc))
            return -1;
        to_client_proc = FindDefaultConversionProc(current_server_encoding,
                                                   encoding);
        if (!OidIsValid(to_client_proc))
            return -1;

        /*
         * Load the fmgr info into TopMemoryContext (could still fail here)
         */
        convinfo = (ConvProcInfo *) MemoryContextAlloc(TopMemoryContext,
                                                       sizeof(ConvProcInfo));
        convinfo->s_encoding = current_server_encoding;
        convinfo->c_encoding = encoding;
        fmgr_info_cxt(to_server_proc, &convinfo->to_server_info,
                      TopMemoryContext);
        fmgr_info_cxt(to_client_proc, &convinfo->to_client_info,
                      TopMemoryContext);

        /* Attach new info to head of list */
        oldcontext = MemoryContextSwitchTo(TopMemoryContext);
        ConvProcList = lcons(convinfo, ConvProcList);
        MemoryContextSwitchTo(oldcontext);

        /*
         * We cannot yet remove any older entry for the same encoding pair,
         * since it could still be in use.  SetClientEncoding will clean up.
         */

        return 0;               /* success */
    }
    else
    {
        /*
         * If we're not in a live transaction, the only thing we can do is
         * restore a previous setting using the cache.  This covers all
         * transaction-rollback cases.  The only case it might not work for is
         * trying to change client_encoding on the fly by editing
         * postgresql.conf and SIGHUP'ing.  Which would probably be a stupid
         * thing to do anyway.
         */
        foreach(lc, ConvProcList)
        {
            ConvProcInfo *oldinfo = (ConvProcInfo *) lfirst(lc);

            if (oldinfo->s_encoding == current_server_encoding &&
                oldinfo->c_encoding == encoding)
                return 0;
        }

        return -1;              /* it's not cached, so fail */
    }
}

/*
 * Set the active client encoding and set up the conversion-function pointers.
 * PrepareClientEncoding should have been called previously for this encoding.
 *
 * Returns 0 if okay, -1 if not (bad encoding or can't support conversion)
 */
int
SetClientEncoding(int encoding)
{
    int         current_server_encoding;
    bool        found;
    ListCell   *lc;

    if (!PG_VALID_FE_ENCODING(encoding))
        return -1;

    /* Can't do anything during startup, per notes above */
    if (!backend_startup_complete)
    {
        pending_client_encoding = encoding;
        return 0;
    }

    current_server_encoding = GetDatabaseEncoding();

    /*
     * Check for cases that require no conversion function.
     */
    if (current_server_encoding == encoding ||
        current_server_encoding == PG_SQL_ASCII ||
        encoding == PG_SQL_ASCII)
    {
        ClientEncoding = &pg_enc2name_tbl[encoding];
        ToServerConvProc = NULL;
        ToClientConvProc = NULL;
        return 0;
    }

    /*
     * Search the cache for the entry previously prepared by
     * PrepareClientEncoding; if there isn't one, we lose.  While at it,
     * release any duplicate entries so that repeated Prepare/Set cycles don't
     * leak memory.
     */
    found = false;
    foreach(lc, ConvProcList)
    {
        ConvProcInfo *convinfo = (ConvProcInfo *) lfirst(lc);

        if (convinfo->s_encoding == current_server_encoding &&
            convinfo->c_encoding == encoding)
        {
            if (!found)
            {
                /* Found newest entry, so set up */
                ClientEncoding = &pg_enc2name_tbl[encoding];
                ToServerConvProc = &convinfo->to_server_info;
                ToClientConvProc = &convinfo->to_client_info;
                found = true;
            }
            else
            {
                /* Duplicate entry, release it */
                ConvProcList = foreach_delete_current(ConvProcList, lc);
                pfree(convinfo);
            }
        }
    }

    if (found)
        return 0;               /* success */
    else
        return -1;              /* it's not cached, so fail */
}

/*
 * Initialize client encoding conversions.
 *      Called from InitPostgres() once during backend startup.
 */
void
InitializeClientEncoding(void)
{
    Assert(!backend_startup_complete);
    backend_startup_complete = true;

    if (PrepareClientEncoding(pending_client_encoding) < 0 ||
        SetClientEncoding(pending_client_encoding) < 0)
    {
        /*
         * Oops, the requested conversion is not available. We couldn't fail
         * before, but we can now.
         */
        ereport(FATAL,
                (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                 errmsg("conversion between %s and %s is not supported",
                        pg_enc2name_tbl[pending_client_encoding].name,
                        GetDatabaseEncodingName())));
    }
}

/*
 * returns the current client encoding
 */
int
pg_get_client_encoding(void)
{
    return ClientEncoding->encoding;
}

/*
 * returns the current client encoding name
 */
const char *
pg_get_client_encoding_name(void)
{
    return ClientEncoding->name;
}

/*
 * Convert src string to another encoding (general case).
 *
 * See the notes about string conversion functions at the top of this file.
 */
unsigned char *
pg_do_encoding_conversion(unsigned char *src, int len,
                          int src_encoding, int dest_encoding)
{
    unsigned char *result;
    Oid         proc;

    if (len <= 0)
        return src;             /* empty string is always valid */

    if (src_encoding == dest_encoding)
        return src;             /* no conversion required, assume valid */

    if (dest_encoding == PG_SQL_ASCII)
        return src;             /* any string is valid in SQL_ASCII */

    if (src_encoding == PG_SQL_ASCII)
    {
        /* No conversion is possible, but we must validate the result */
        (void) pg_verify_mbstr(dest_encoding, (const char *) src, len, false);
        return src;
    }

    if (!IsTransactionState())  /* shouldn't happen */
        elog(ERROR, "cannot perform encoding conversion outside a transaction");

    proc = FindDefaultConversionProc(src_encoding, dest_encoding);
    if (!OidIsValid(proc))
        ereport(ERROR,
                (errcode(ERRCODE_UNDEFINED_FUNCTION),
                 errmsg("default conversion function for encoding \"%s\" to \"%s\" does not exist",
                        pg_encoding_to_char(src_encoding),
                        pg_encoding_to_char(dest_encoding))));

    /*
     * Allocate space for conversion result, being wary of integer overflow
     */
    if ((Size) len >= (MaxAllocSize / (Size) MAX_CONVERSION_GROWTH))
        ereport(ERROR,
                (errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
                 errmsg("out of memory"),
                 errdetail("String of %d bytes is too long for encoding conversion.",
                           len)));

    result = palloc(len * MAX_CONVERSION_GROWTH + 1);

    OidFunctionCall5(proc,
                     Int32GetDatum(src_encoding),
                     Int32GetDatum(dest_encoding),
                     CStringGetDatum(src),
                     CStringGetDatum(result),
                     Int32GetDatum(len));
    return result;
}

/*
 * Convert string to encoding encoding_name. The source
 * encoding is the DB encoding.
 *
 * BYTEA convert_to(TEXT string, NAME encoding_name) */
Datum
pg_convert_to(PG_FUNCTION_ARGS)
{
    Datum       string = PG_GETARG_DATUM(0);
    Datum       dest_encoding_name = PG_GETARG_DATUM(1);
    Datum       src_encoding_name = DirectFunctionCall1(namein,
                                                        CStringGetDatum(DatabaseEncoding->name));
    Datum       result;

    /*
     * pg_convert expects a bytea as its first argument. We're passing it a
     * text argument here, relying on the fact that they are both in fact
     * varlena types, and thus structurally identical.
     */
    result = DirectFunctionCall3(pg_convert, string,
                                 src_encoding_name, dest_encoding_name);

    PG_RETURN_DATUM(result);
}

/*
 * Convert string from encoding encoding_name. The destination
 * encoding is the DB encoding.
 *
 * TEXT convert_from(BYTEA string, NAME encoding_name) */
Datum
pg_convert_from(PG_FUNCTION_ARGS)
{
    Datum       string = PG_GETARG_DATUM(0);
    Datum       src_encoding_name = PG_GETARG_DATUM(1);
    Datum       dest_encoding_name = DirectFunctionCall1(namein,
                                                         CStringGetDatum(DatabaseEncoding->name));
    Datum       result;

    result = DirectFunctionCall3(pg_convert, string,
                                 src_encoding_name, dest_encoding_name);

    /*
     * pg_convert returns a bytea, which we in turn return as text, relying on
     * the fact that they are both in fact varlena types, and thus
     * structurally identical. Although not all bytea values are valid text,
     * in this case it will be because we've told pg_convert to return one
     * that is valid as text in the current database encoding.
     */
    PG_RETURN_DATUM(result);
}

/*
 * Convert string between two arbitrary encodings.
 *
 * BYTEA convert(BYTEA string, NAME src_encoding_name, NAME dest_encoding_name)
 */
Datum
pg_convert(PG_FUNCTION_ARGS)
{
    bytea      *string = PG_GETARG_BYTEA_PP(0);
    char       *src_encoding_name = NameStr(*PG_GETARG_NAME(1));
    int         src_encoding = pg_char_to_encoding(src_encoding_name);
    char       *dest_encoding_name = NameStr(*PG_GETARG_NAME(2));
    int         dest_encoding = pg_char_to_encoding(dest_encoding_name);
    const char *src_str;
    char       *dest_str;
    bytea      *retval;
    int         len;

    if (src_encoding < 0)
        ereport(ERROR,
                (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                 errmsg("invalid source encoding name \"%s\"",
                        src_encoding_name)));
    if (dest_encoding < 0)
        ereport(ERROR,
                (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                 errmsg("invalid destination encoding name \"%s\"",
                        dest_encoding_name)));

    /* make sure that source string is valid */
    len = VARSIZE_ANY_EXHDR(string);
    src_str = VARDATA_ANY(string);
    pg_verify_mbstr_len(src_encoding, src_str, len, false);

    /* perform conversion */
    dest_str = (char *) pg_do_encoding_conversion((unsigned char *) unconstify(char *, src_str),
                                                  len,
                                                  src_encoding,
                                                  dest_encoding);

    /* update len if conversion actually happened */
    if (dest_str != src_str)
        len = strlen(dest_str);

    /*
     * build bytea data type structure.
     */
    retval = (bytea *) palloc(len + VARHDRSZ);
    SET_VARSIZE(retval, len + VARHDRSZ);
    memcpy(VARDATA(retval), dest_str, len);

    if (dest_str != src_str)
        pfree(dest_str);

    /* free memory if allocated by the toaster */
    PG_FREE_IF_COPY(string, 0);

    PG_RETURN_BYTEA_P(retval);
}

/*
 * get the length of the string considered as text in the specified
 * encoding. Raises an error if the data is not valid in that
 * encoding.
 *
 * INT4 length (BYTEA string, NAME src_encoding_name)
 */
Datum
length_in_encoding(PG_FUNCTION_ARGS)
{
    bytea      *string = PG_GETARG_BYTEA_PP(0);
    char       *src_encoding_name = NameStr(*PG_GETARG_NAME(1));
    int         src_encoding = pg_char_to_encoding(src_encoding_name);
    const char *src_str;
    int         len;
    int         retval;

    if (src_encoding < 0)
        ereport(ERROR,
                (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                 errmsg("invalid encoding name \"%s\"",
                        src_encoding_name)));

    len = VARSIZE_ANY_EXHDR(string);
    src_str = VARDATA_ANY(string);

    retval = pg_verify_mbstr_len(src_encoding, src_str, len, false);

    PG_RETURN_INT32(retval);
}

/*
 * Get maximum multibyte character length in the specified encoding.
 *
 * Note encoding is specified numerically, not by name as above.
 */
Datum
pg_encoding_max_length_sql(PG_FUNCTION_ARGS)
{
    int         encoding = PG_GETARG_INT32(0);

    if (PG_VALID_ENCODING(encoding))
        PG_RETURN_INT32(pg_wchar_table[encoding].maxmblen);
    else
        PG_RETURN_NULL();
}

/*
 * Convert client encoding to server encoding.
 *
 * See the notes about string conversion functions at the top of this file.
 */
char *
pg_client_to_server(const char *s, int len)
{
    return pg_any_to_server(s, len, ClientEncoding->encoding);
}

/*
 * Convert any encoding to server encoding.
 *
 * See the notes about string conversion functions at the top of this file.
 *
 * Unlike the other string conversion functions, this will apply validation
 * even if encoding == DatabaseEncoding->encoding.  This is because this is
 * used to process data coming in from outside the database, and we never
 * want to just assume validity.
 */
char *
pg_any_to_server(const char *s, int len, int encoding)
{
    if (len <= 0)
        return unconstify(char *, s);   /* empty string is always valid */

    if (encoding == DatabaseEncoding->encoding ||
        encoding == PG_SQL_ASCII)
    {
        /*
         * No conversion is needed, but we must still validate the data.
         */
        (void) pg_verify_mbstr(DatabaseEncoding->encoding, s, len, false);
        return unconstify(char *, s);
    }

    if (DatabaseEncoding->encoding == PG_SQL_ASCII)
    {
        /*
         * No conversion is possible, but we must still validate the data,
         * because the client-side code might have done string escaping using
         * the selected client_encoding.  If the client encoding is ASCII-safe
         * then we just do a straight validation under that encoding.  For an
         * ASCII-unsafe encoding we have a problem: we dare not pass such data
         * to the parser but we have no way to convert it.  We compromise by
         * rejecting the data if it contains any non-ASCII characters.
         */
        if (PG_VALID_BE_ENCODING(encoding))
            (void) pg_verify_mbstr(encoding, s, len, false);
        else
        {
            int         i;

            for (i = 0; i < len; i++)
            {
                if (s[i] == '\0' || IS_HIGHBIT_SET(s[i]))
                    ereport(ERROR,
                            (errcode(ERRCODE_CHARACTER_NOT_IN_REPERTOIRE),
                             errmsg("invalid byte value for encoding \"%s\": 0x%02x",
                                    pg_enc2name_tbl[PG_SQL_ASCII].name,
                                    (unsigned char) s[i])));
            }
        }
        return unconstify(char *, s);
    }

    /* Fast path if we can use cached conversion function */
    if (encoding == ClientEncoding->encoding)
        return perform_default_encoding_conversion(s, len, true);

    /* General case ... will not work outside transactions */
    return (char *) pg_do_encoding_conversion((unsigned char *) unconstify(char *, s),
                                              len,
                                              encoding,
                                              DatabaseEncoding->encoding);
}

/*
 * Convert server encoding to client encoding.
 *
 * See the notes about string conversion functions at the top of this file.
 */
char *
pg_server_to_client(const char *s, int len)
{
    return pg_server_to_any(s, len, ClientEncoding->encoding);
}

/*
 * Convert server encoding to any encoding.
 *
 * See the notes about string conversion functions at the top of this file.
 */
char *
pg_server_to_any(const char *s, int len, int encoding)
{
    if (len <= 0)
        return unconstify(char *, s);   /* empty string is always valid */

    if (encoding == DatabaseEncoding->encoding ||
        encoding == PG_SQL_ASCII)
        return unconstify(char *, s);   /* assume data is valid */

    if (DatabaseEncoding->encoding == PG_SQL_ASCII)
    {
        /* No conversion is possible, but we must validate the result */
        (void) pg_verify_mbstr(encoding, s, len, false);
        return unconstify(char *, s);
    }

    /* Fast path if we can use cached conversion function */
    if (encoding == ClientEncoding->encoding)
        return perform_default_encoding_conversion(s, len, false);

    /* General case ... will not work outside transactions */
    return (char *) pg_do_encoding_conversion((unsigned char *) unconstify(char *, s),
                                              len,
                                              DatabaseEncoding->encoding,
                                              encoding);
}

/*
 *  Perform default encoding conversion using cached FmgrInfo. Since
 *  this function does not access database at all, it is safe to call
 *  outside transactions.  If the conversion has not been set up by
 *  SetClientEncoding(), no conversion is performed.
 */
static char *
perform_default_encoding_conversion(const char *src, int len,
                                    bool is_client_to_server)
{
    char       *result;
    int         src_encoding,
                dest_encoding;
    FmgrInfo   *flinfo;

    if (is_client_to_server)
    {
        src_encoding = ClientEncoding->encoding;
        dest_encoding = DatabaseEncoding->encoding;
        flinfo = ToServerConvProc;
    }
    else
    {
        src_encoding = DatabaseEncoding->encoding;
        dest_encoding = ClientEncoding->encoding;
        flinfo = ToClientConvProc;
    }

    if (flinfo == NULL)
        return unconstify(char *, src);

    /*
     * Allocate space for conversion result, being wary of integer overflow
     */
    if ((Size) len >= (MaxAllocSize / (Size) MAX_CONVERSION_GROWTH))
        ereport(ERROR,
                (errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
                 errmsg("out of memory"),
                 errdetail("String of %d bytes is too long for encoding conversion.",
                           len)));

    result = palloc(len * MAX_CONVERSION_GROWTH + 1);

    FunctionCall5(flinfo,
                  Int32GetDatum(src_encoding),
                  Int32GetDatum(dest_encoding),
                  CStringGetDatum(src),
                  CStringGetDatum(result),
                  Int32GetDatum(len));
    return result;
}


/* convert a multibyte string to a wchar */
int
pg_mb2wchar(const char *from, pg_wchar *to)
{
    return pg_wchar_table[DatabaseEncoding->encoding].mb2wchar_with_len((const unsigned char *) from, to, strlen(from));
}

/* convert a multibyte string to a wchar with a limited length */
int
pg_mb2wchar_with_len(const char *from, pg_wchar *to, int len)
{
    return pg_wchar_table[DatabaseEncoding->encoding].mb2wchar_with_len((const unsigned char *) from, to, len);
}

/* same, with any encoding */
int
pg_encoding_mb2wchar_with_len(int encoding,
                              const char *from, pg_wchar *to, int len)
{
    return pg_wchar_table[encoding].mb2wchar_with_len((const unsigned char *) from, to, len);
}

/* convert a wchar string to a multibyte */
int
pg_wchar2mb(const pg_wchar *from, char *to)
{
    return pg_wchar_table[DatabaseEncoding->encoding].wchar2mb_with_len(from, (unsigned char *) to, pg_wchar_strlen(from));
}

/* convert a wchar string to a multibyte with a limited length */
int
pg_wchar2mb_with_len(const pg_wchar *from, char *to, int len)
{
    return pg_wchar_table[DatabaseEncoding->encoding].wchar2mb_with_len(from, (unsigned char *) to, len);
}

/* same, with any encoding */
int
pg_encoding_wchar2mb_with_len(int encoding,
                              const pg_wchar *from, char *to, int len)
{
    return pg_wchar_table[encoding].wchar2mb_with_len(from, (unsigned char *) to, len);
}

/* returns the byte length of a multibyte character */
int
pg_mblen(const char *mbstr)
{
    return pg_wchar_table[DatabaseEncoding->encoding].mblen((const unsigned char *) mbstr);
}

/* returns the display length of a multibyte character */
int
pg_dsplen(const char *mbstr)
{
    return pg_wchar_table[DatabaseEncoding->encoding].dsplen((const unsigned char *) mbstr);
}

/* returns the length (counted in wchars) of a multibyte string */
int
pg_mbstrlen(const char *mbstr)
{
    int         len = 0;

    /* optimization for single byte encoding */
    if (pg_database_encoding_max_length() == 1)
        return strlen(mbstr);

    while (*mbstr)
    {
        mbstr += pg_mblen(mbstr);
        len++;
    }
    return len;
}

/* returns the length (counted in wchars) of a multibyte string
 * (not necessarily NULL terminated)
 */
int
pg_mbstrlen_with_len(const char *mbstr, int limit)
{
    int         len = 0;

    /* optimization for single byte encoding */
    if (pg_database_encoding_max_length() == 1)
        return limit;

    while (limit > 0 && *mbstr)
    {
        int         l = pg_mblen(mbstr);

        limit -= l;
        mbstr += l;
        len++;
    }
    return len;
}

/*
 * returns the byte length of a multibyte string
 * (not necessarily NULL terminated)
 * that is no longer than limit.
 * this function does not break multibyte character boundary.
 */
int
pg_mbcliplen(const char *mbstr, int len, int limit)
{
    return pg_encoding_mbcliplen(DatabaseEncoding->encoding, mbstr,
                                 len, limit);
}

/*
 * pg_mbcliplen with specified encoding
 */
int
pg_encoding_mbcliplen(int encoding, const char *mbstr,
                      int len, int limit)
{
    mblen_converter mblen_fn;
    int         clen = 0;
    int         l;

    /* optimization for single byte encoding */
    if (pg_encoding_max_length(encoding) == 1)
        return cliplen(mbstr, len, limit);

    mblen_fn = pg_wchar_table[encoding].mblen;

    while (len > 0 && *mbstr)
    {
        l = (*mblen_fn) ((const unsigned char *) mbstr);
        if ((clen + l) > limit)
            break;
        clen += l;
        if (clen == limit)
            break;
        len -= l;
        mbstr += l;
    }
    return clen;
}

/*
 * Similar to pg_mbcliplen except the limit parameter specifies the
 * character length, not the byte length.
 */
int
pg_mbcharcliplen(const char *mbstr, int len, int limit)
{
    int         clen = 0;
    int         nch = 0;
    int         l;

    /* optimization for single byte encoding */
    if (pg_database_encoding_max_length() == 1)
        return cliplen(mbstr, len, limit);

    while (len > 0 && *mbstr)
    {
        l = pg_mblen(mbstr);
        nch++;
        if (nch > limit)
            break;
        clen += l;
        len -= l;
        mbstr += l;
    }
    return clen;
}

/* mbcliplen for any single-byte encoding */
static int
cliplen(const char *str, int len, int limit)
{
    int         l = 0;

    len = Min(len, limit);
    while (l < len && str[l])
        l++;
    return l;
}

void
SetDatabaseEncoding(int encoding)
{
    if (!PG_VALID_BE_ENCODING(encoding))
        elog(ERROR, "invalid database encoding: %d", encoding);

    DatabaseEncoding = &pg_enc2name_tbl[encoding];
    Assert(DatabaseEncoding->encoding == encoding);
}

void
SetMessageEncoding(int encoding)
{
    /* Some calls happen before we can elog()! */
    Assert(PG_VALID_ENCODING(encoding));

    MessageEncoding = &pg_enc2name_tbl[encoding];
    Assert(MessageEncoding->encoding == encoding);
}

#ifdef ENABLE_NLS
/*
 * Make one bind_textdomain_codeset() call, translating a pg_enc to a gettext
 * codeset.  Fails for MULE_INTERNAL, an encoding unknown to gettext; can also
 * fail for gettext-internal causes like out-of-memory.
 */
static bool
raw_pg_bind_textdomain_codeset(const char *domainname, int encoding)
{
    bool        elog_ok = (CurrentMemoryContext != NULL);
    int         i;

    for (i = 0; pg_enc2gettext_tbl[i].name != NULL; i++)
    {
        if (pg_enc2gettext_tbl[i].encoding == encoding)
        {
            if (bind_textdomain_codeset(domainname,
                                        pg_enc2gettext_tbl[i].name) != NULL)
                return true;

            if (elog_ok)
                elog(LOG, "bind_textdomain_codeset failed");
            else
                write_stderr("bind_textdomain_codeset failed");

            break;
        }
    }

    return false;
}

/*
 * Bind a gettext message domain to the codeset corresponding to the database
 * encoding.  For SQL_ASCII, instead bind to the codeset implied by LC_CTYPE.
 * Return the MessageEncoding implied by the new settings.
 *
 * On most platforms, gettext defaults to the codeset implied by LC_CTYPE.
 * When that matches the database encoding, we don't need to do anything.  In
 * CREATE DATABASE, we enforce or trust that the locale's codeset matches the
 * database encoding, except for the C locale.  (On Windows, we also permit a
 * discrepancy under the UTF8 encoding.)  For the C locale, explicitly bind
 * gettext to the right codeset.
 *
 * On Windows, gettext defaults to the Windows ANSI code page.  This is a
 * convenient departure for software that passes the strings to Windows ANSI
 * APIs, but we don't do that.  Compel gettext to use database encoding or,
 * failing that, the LC_CTYPE encoding as it would on other platforms.
 *
 * This function is called before elog() and palloc() are usable.
 */
int
pg_bind_textdomain_codeset(const char *domainname)
{
    bool        elog_ok = (CurrentMemoryContext != NULL);
    int         encoding = GetDatabaseEncoding();
    int         new_msgenc;

#ifndef WIN32
    const char *ctype = setlocale(LC_CTYPE, NULL);

    if (pg_strcasecmp(ctype, "C") == 0 || pg_strcasecmp(ctype, "POSIX") == 0)
#endif
        if (encoding != PG_SQL_ASCII &&
            raw_pg_bind_textdomain_codeset(domainname, encoding))
            return encoding;

    new_msgenc = pg_get_encoding_from_locale(NULL, elog_ok);
    if (new_msgenc < 0)
        new_msgenc = PG_SQL_ASCII;

#ifdef WIN32
    if (!raw_pg_bind_textdomain_codeset(domainname, new_msgenc))
        /* On failure, the old message encoding remains valid. */
        return GetMessageEncoding();
#endif

    return new_msgenc;
}
#endif

/*
 * The database encoding, also called the server encoding, represents the
 * encoding of data stored in text-like data types.  Affected types include
 * cstring, text, varchar, name, xml, and json.
 */
int
GetDatabaseEncoding(void)
{
    return DatabaseEncoding->encoding;
}

const char *
GetDatabaseEncodingName(void)
{
    return DatabaseEncoding->name;
}

Datum
getdatabaseencoding(PG_FUNCTION_ARGS)
{
    return DirectFunctionCall1(namein, CStringGetDatum(DatabaseEncoding->name));
}

Datum
pg_client_encoding(PG_FUNCTION_ARGS)
{
    return DirectFunctionCall1(namein, CStringGetDatum(ClientEncoding->name));
}

/*
 * gettext() returns messages in this encoding.  This often matches the
 * database encoding, but it differs for SQL_ASCII databases, for processes
 * not attached to a database, and under a database encoding lacking iconv
 * support (MULE_INTERNAL).
 */
int
GetMessageEncoding(void)
{
    return MessageEncoding->encoding;
}

#ifdef WIN32
/*
 * Convert from MessageEncoding to a palloc'ed, null-terminated utf16
 * string. The character length is also passed to utf16len if not
 * null. Returns NULL iff failed. Before MessageEncoding initialization, "str"
 * should be ASCII-only; this will function as though MessageEncoding is UTF8.
 */
WCHAR *
pgwin32_message_to_UTF16(const char *str, int len, int *utf16len)
{
    int         msgenc = GetMessageEncoding();
    WCHAR      *utf16;
    int         dstlen;
    UINT        codepage;

    if (msgenc == PG_SQL_ASCII)
        /* No conversion is possible, and SQL_ASCII is never utf16. */
        return NULL;

    codepage = pg_enc2name_tbl[msgenc].codepage;

    /*
     * Use MultiByteToWideChar directly if there is a corresponding codepage,
     * or double conversion through UTF8 if not.  Double conversion is needed,
     * for example, in an ENCODING=LATIN8, LC_CTYPE=C database.
     */
    if (codepage != 0)
    {
        utf16 = (WCHAR *) palloc(sizeof(WCHAR) * (len + 1));
        dstlen = MultiByteToWideChar(codepage, 0, str, len, utf16, len);
        utf16[dstlen] = (WCHAR) 0;
    }
    else
    {
        char       *utf8;

        /*
         * XXX pg_do_encoding_conversion() requires a transaction.  In the
         * absence of one, hope for the input to be valid UTF8.
         */
        if (IsTransactionState())
        {
            utf8 = (char *) pg_do_encoding_conversion((unsigned char *) str,
                                                      len,
                                                      msgenc,
                                                      PG_UTF8);
            if (utf8 != str)
                len = strlen(utf8);
        }
        else
            utf8 = (char *) str;

        utf16 = (WCHAR *) palloc(sizeof(WCHAR) * (len + 1));
        dstlen = MultiByteToWideChar(CP_UTF8, 0, utf8, len, utf16, len);
        utf16[dstlen] = (WCHAR) 0;

        if (utf8 != str)
            pfree(utf8);
    }

    if (dstlen == 0 && len > 0)
    {
        pfree(utf16);
        return NULL;            /* error */
    }

    if (utf16len)
        *utf16len = dstlen;
    return utf16;
}

#endif