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) 1996-2021, 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;

/*
 * This variable stores the conversion function to convert from UTF-8
 * to the server encoding.  It's NULL if the server encoding *is* UTF-8,
 * or if we lack a conversion function for this.
 */
static FmgrInfo *Utf8ToServerConvProc = 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)
{
    int         current_server_encoding;

    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())));
    }

    /*
     * Also look up the UTF8-to-server conversion function if needed.  Since
     * the server encoding is fixed within any one backend process, we don't
     * have to do this more than once.
     */
    current_server_encoding = GetDatabaseEncoding();
    if (current_server_encoding != PG_UTF8 &&
        current_server_encoding != PG_SQL_ASCII)
    {
        Oid         utf8_to_server_proc;

        Assert(IsTransactionState());
        utf8_to_server_proc =
            FindDefaultConversionProc(PG_UTF8,
                                      current_server_encoding);
        /* If there's no such conversion, just leave the pointer as NULL */
        if (OidIsValid(utf8_to_server_proc))
        {
            FmgrInfo   *finfo;

            finfo = (FmgrInfo *) MemoryContextAlloc(TopMemoryContext,
                                                    sizeof(FmgrInfo));
            fmgr_info_cxt(utf8_to_server_proc, finfo,
                          TopMemoryContext);
            /* Set Utf8ToServerConvProc only after data is fully valid */
            Utf8ToServerConvProc = finfo;
        }
    }
}

/*
 * 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.
     *
     * len * MAX_CONVERSION_GROWTH is typically a vast overestimate of the
     * required space, so it might exceed MaxAllocSize even though the result
     * would actually fit.  We do not want to hand back a result string that
     * exceeds MaxAllocSize, because callers might not cope gracefully --- but
     * if we just allocate more than that, and don't use it, that's fine.
     */
    if ((Size) len >= (MaxAllocHugeSize / (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 = (unsigned char *)
        MemoryContextAllocHuge(CurrentMemoryContext,
                               (Size) len * MAX_CONVERSION_GROWTH + 1);

    (void) OidFunctionCall6(proc,
                            Int32GetDatum(src_encoding),
                            Int32GetDatum(dest_encoding),
                            CStringGetDatum(src),
                            CStringGetDatum(result),
                            Int32GetDatum(len),
                            BoolGetDatum(false));

    /*
     * If the result is large, it's worth repalloc'ing to release any extra
     * space we asked for.  The cutoff here is somewhat arbitrary, but we
     * *must* check when len * MAX_CONVERSION_GROWTH exceeds MaxAllocSize.
     */
    if (len > 1000000)
    {
        Size        resultlen = strlen((char *) result);

        if (resultlen >= MaxAllocSize)
            ereport(ERROR,
                    (errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
                     errmsg("out of memory"),
                     errdetail("String of %d bytes is too long for encoding conversion.",
                               len)));

        result = (unsigned char *) repalloc(result, resultlen + 1);
    }

    return result;
}

/*
 * Convert src string to another encoding.
 *
 * This function has a different API than the other conversion functions.
 * The caller should've looked up the conversion function using
 * FindDefaultConversionProc().  Unlike the other functions, the converted
 * result is not palloc'd.  It is written to the caller-supplied buffer
 * instead.
 *
 * src_encoding   - encoding to convert from
 * dest_encoding  - encoding to convert to
 * src, srclen    - input buffer and its length in bytes
 * dest, destlen  - destination buffer and its size in bytes
 *
 * The output is null-terminated.
 *
 * If destlen < srclen * MAX_CONVERSION_LENGTH + 1, the converted output
 * wouldn't necessarily fit in the output buffer, and the function will not
 * convert the whole input.
 *
 * TODO: The conversion function interface is not great.  Firstly, it
 * would be nice to pass through the destination buffer size to the
 * conversion function, so that if you pass a shorter destination buffer, it
 * could still continue to fill up the whole buffer.  Currently, we have to
 * assume worst case expansion and stop the conversion short, even if there
 * is in fact space left in the destination buffer.  Secondly, it would be
 * nice to return the number of bytes written to the caller, to avoid a call
 * to strlen().
 */
int
pg_do_encoding_conversion_buf(Oid proc,
                              int src_encoding,
                              int dest_encoding,
                              unsigned char *src, int srclen,
                              unsigned char *dest, int destlen,
                              bool noError)
{
    Datum       result;

    /*
     * If the destination buffer is not large enough to hold the result in the
     * worst case, limit the input size passed to the conversion function.
     */
    if ((Size) srclen >= ((destlen - 1) / (Size) MAX_CONVERSION_GROWTH))
        srclen = ((destlen - 1) / (Size) MAX_CONVERSION_GROWTH);

    result = OidFunctionCall6(proc,
                              Int32GetDatum(src_encoding),
                              Int32GetDatum(dest_encoding),
                              CStringGetDatum(src),
                              CStringGetDatum(dest),
                              Int32GetDatum(srclen),
                              BoolGetDatum(noError));
    return DatumGetInt32(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);
    (void) pg_verify_mbstr(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.
     * See comments in pg_do_encoding_conversion.
     */
    if ((Size) len >= (MaxAllocHugeSize / (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 = (char *)
        MemoryContextAllocHuge(CurrentMemoryContext,
                               (Size) len * MAX_CONVERSION_GROWTH + 1);

    FunctionCall6(flinfo,
                  Int32GetDatum(src_encoding),
                  Int32GetDatum(dest_encoding),
                  CStringGetDatum(src),
                  CStringGetDatum(result),
                  Int32GetDatum(len),
                  BoolGetDatum(false));

    /*
     * Release extra space if there might be a lot --- see comments in
     * pg_do_encoding_conversion.
     */
    if (len > 1000000)
    {
        Size        resultlen = strlen(result);

        if (resultlen >= MaxAllocSize)
            ereport(ERROR,
                    (errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
                     errmsg("out of memory"),
                     errdetail("String of %d bytes is too long for encoding conversion.",
                               len)));

        result = (char *) repalloc(result, resultlen + 1);
    }

    return result;
}

/*
 * Convert a single Unicode code point into a string in the server encoding.
 *
 * The code point given by "c" is converted and stored at *s, which must
 * have at least MAX_UNICODE_EQUIVALENT_STRING+1 bytes available.
 * The output will have a trailing '\0'.  Throws error if the conversion
 * cannot be performed.
 *
 * Note that this relies on having previously looked up any required
 * conversion function.  That's partly for speed but mostly because the parser
 * may call this outside any transaction, or in an aborted transaction.
 */
void
pg_unicode_to_server(pg_wchar c, unsigned char *s)
{
    unsigned char c_as_utf8[MAX_MULTIBYTE_CHAR_LEN + 1];
    int         c_as_utf8_len;
    int         server_encoding;

    /*
     * Complain if invalid Unicode code point.  The choice of errcode here is
     * debatable, but really our caller should have checked this anyway.
     */
    if (!is_valid_unicode_codepoint(c))
        ereport(ERROR,
                (errcode(ERRCODE_SYNTAX_ERROR),
                 errmsg("invalid Unicode code point")));

    /* Otherwise, if it's in ASCII range, conversion is trivial */
    if (c <= 0x7F)
    {
        s[0] = (unsigned char) c;
        s[1] = '\0';
        return;
    }

    /* If the server encoding is UTF-8, we just need to reformat the code */
    server_encoding = GetDatabaseEncoding();
    if (server_encoding == PG_UTF8)
    {
        unicode_to_utf8(c, s);
        s[pg_utf_mblen(s)] = '\0';
        return;
    }

    /* For all other cases, we must have a conversion function available */
    if (Utf8ToServerConvProc == NULL)
        ereport(ERROR,
                (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                 errmsg("conversion between %s and %s is not supported",
                        pg_enc2name_tbl[PG_UTF8].name,
                        GetDatabaseEncodingName())));

    /* Construct UTF-8 source string */
    unicode_to_utf8(c, c_as_utf8);
    c_as_utf8_len = pg_utf_mblen(c_as_utf8);
    c_as_utf8[c_as_utf8_len] = '\0';

    /* Convert, or throw error if we can't */
    FunctionCall6(Utf8ToServerConvProc,
                  Int32GetDatum(PG_UTF8),
                  Int32GetDatum(server_encoding),
                  CStringGetDatum(c_as_utf8),
                  CStringGetDatum(s),
                  Int32GetDatum(c_as_utf8_len),
                  BoolGetDatum(false));
}


/* 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));
}

Datum
PG_char_to_encoding(PG_FUNCTION_ARGS)
{
    Name        s = PG_GETARG_NAME(0);

    PG_RETURN_INT32(pg_char_to_encoding(NameStr(*s)));
}

Datum
PG_encoding_to_char(PG_FUNCTION_ARGS)
{
    int32       encoding = PG_GETARG_INT32(0);
    const char *encoding_name = pg_encoding_to_char(encoding);

    return DirectFunctionCall1(namein, CStringGetDatum(encoding_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;
}


/*
 * Generic character incrementer function.
 *
 * Not knowing anything about the properties of the encoding in use, we just
 * keep incrementing the last byte until we get a validly-encoded result,
 * or we run out of values to try.  We don't bother to try incrementing
 * higher-order bytes, so there's no growth in runtime for wider characters.
 * (If we did try to do that, we'd need to consider the likelihood that 255
 * is not a valid final byte in the encoding.)
 */
static bool
pg_generic_charinc(unsigned char *charptr, int len)
{
    unsigned char *lastbyte = charptr + len - 1;
    mbchar_verifier mbverify;

    /* We can just invoke the character verifier directly. */
    mbverify = pg_wchar_table[GetDatabaseEncoding()].mbverifychar;

    while (*lastbyte < (unsigned char) 255)
    {
        (*lastbyte)++;
        if ((*mbverify) (charptr, len) == len)
            return true;
    }

    return false;
}

/*
 * UTF-8 character incrementer function.
 *
 * For a one-byte character less than 0x7F, we just increment the byte.
 *
 * For a multibyte character, every byte but the first must fall between 0x80
 * and 0xBF; and the first byte must be between 0xC0 and 0xF4.  We increment
 * the last byte that's not already at its maximum value.  If we can't find a
 * byte that's less than the maximum allowable value, we simply fail.  We also
 * need some special-case logic to skip regions used for surrogate pair
 * handling, as those should not occur in valid UTF-8.
 *
 * Note that we don't reset lower-order bytes back to their minimums, since
 * we can't afford to make an exhaustive search (see make_greater_string).
 */
static bool
pg_utf8_increment(unsigned char *charptr, int length)
{
    unsigned char a;
    unsigned char limit;

    switch (length)
    {
        default:
            /* reject lengths 5 and 6 for now */
            return false;
        case 4:
            a = charptr[3];
            if (a < 0xBF)
            {
                charptr[3]++;
                break;
            }
            /* FALL THRU */
        case 3:
            a = charptr[2];
            if (a < 0xBF)
            {
                charptr[2]++;
                break;
            }
            /* FALL THRU */
        case 2:
            a = charptr[1];
            switch (*charptr)
            {
                case 0xED:
                    limit = 0x9F;
                    break;
                case 0xF4:
                    limit = 0x8F;
                    break;
                default:
                    limit = 0xBF;
                    break;
            }
            if (a < limit)
            {
                charptr[1]++;
                break;
            }
            /* FALL THRU */
        case 1:
            a = *charptr;
            if (a == 0x7F || a == 0xDF || a == 0xEF || a == 0xF4)
                return false;
            charptr[0]++;
            break;
    }

    return true;
}

/*
 * EUC-JP character incrementer function.
 *
 * If the sequence starts with SS2 (0x8e), it must be a two-byte sequence
 * representing JIS X 0201 characters with the second byte ranging between
 * 0xa1 and 0xdf.  We just increment the last byte if it's less than 0xdf,
 * and otherwise rewrite the whole sequence to 0xa1 0xa1.
 *
 * If the sequence starts with SS3 (0x8f), it must be a three-byte sequence
 * in which the last two bytes range between 0xa1 and 0xfe.  The last byte
 * is incremented if possible, otherwise the second-to-last byte.
 *
 * If the sequence starts with a value other than the above and its MSB
 * is set, it must be a two-byte sequence representing JIS X 0208 characters
 * with both bytes ranging between 0xa1 and 0xfe.  The last byte is
 * incremented if possible, otherwise the second-to-last byte.
 *
 * Otherwise, the sequence is a single-byte ASCII character. It is
 * incremented up to 0x7f.
 */
static bool
pg_eucjp_increment(unsigned char *charptr, int length)
{
    unsigned char c1,
                c2;
    int         i;

    c1 = *charptr;

    switch (c1)
    {
        case SS2:               /* JIS X 0201 */
            if (length != 2)
                return false;

            c2 = charptr[1];

            if (c2 >= 0xdf)
                charptr[0] = charptr[1] = 0xa1;
            else if (c2 < 0xa1)
                charptr[1] = 0xa1;
            else
                charptr[1]++;
            break;

        case SS3:               /* JIS X 0212 */
            if (length != 3)
                return false;

            for (i = 2; i > 0; i--)
            {
                c2 = charptr[i];
                if (c2 < 0xa1)
                {
                    charptr[i] = 0xa1;
                    return true;
                }
                else if (c2 < 0xfe)
                {
                    charptr[i]++;
                    return true;
                }
            }

            /* Out of 3-byte code region */
            return false;

        default:
            if (IS_HIGHBIT_SET(c1)) /* JIS X 0208? */
            {
                if (length != 2)
                    return false;

                for (i = 1; i >= 0; i--)
                {
                    c2 = charptr[i];
                    if (c2 < 0xa1)
                    {
                        charptr[i] = 0xa1;
                        return true;
                    }
                    else if (c2 < 0xfe)
                    {
                        charptr[i]++;
                        return true;
                    }
                }

                /* Out of 2 byte code region */
                return false;
            }
            else
            {                   /* ASCII, single byte */
                if (c1 > 0x7e)
                    return false;
                (*charptr)++;
            }
            break;
    }

    return true;
}

/*
 * get the character incrementer for the encoding for the current database
 */
mbcharacter_incrementer
pg_database_encoding_character_incrementer(void)
{
    /*
     * Eventually it might be best to add a field to pg_wchar_table[], but for
     * now we just use a switch.
     */
    switch (GetDatabaseEncoding())
    {
        case PG_UTF8:
            return pg_utf8_increment;

        case PG_EUC_JP:
            return pg_eucjp_increment;

        default:
            return pg_generic_charinc;
    }
}

/*
 * fetch maximum length of the encoding for the current database
 */
int
pg_database_encoding_max_length(void)
{
    return pg_wchar_table[GetDatabaseEncoding()].maxmblen;
}

/*
 * Verify mbstr to make sure that it is validly encoded in the current
 * database encoding.  Otherwise same as pg_verify_mbstr().
 */
bool
pg_verifymbstr(const char *mbstr, int len, bool noError)
{
    return pg_verify_mbstr(GetDatabaseEncoding(), mbstr, len, noError);
}

/*
 * Verify mbstr to make sure that it is validly encoded in the specified
 * encoding.
 */
bool
pg_verify_mbstr(int encoding, const char *mbstr, int len, bool noError)
{
    int         oklen;

    Assert(PG_VALID_ENCODING(encoding));

    oklen = pg_wchar_table[encoding].mbverifystr((const unsigned char *) mbstr, len);
    if (oklen != len)
    {
        if (noError)
            return false;
        report_invalid_encoding(encoding, mbstr + oklen, len - oklen);
    }
    return true;
}

/*
 * Verify mbstr to make sure that it is validly encoded in the specified
 * encoding.
 *
 * mbstr is not necessarily zero terminated; length of mbstr is
 * specified by len.
 *
 * If OK, return length of string in the encoding.
 * If a problem is found, return -1 when noError is
 * true; when noError is false, ereport() a descriptive message.
 *
 * Note: We cannot use the faster encoding-specific mbverifystr() function
 * here, because we need to count the number of characters in the string.
 */
int
pg_verify_mbstr_len(int encoding, const char *mbstr, int len, bool noError)
{
    mbchar_verifier mbverifychar;
    int         mb_len;

    Assert(PG_VALID_ENCODING(encoding));

    /*
     * In single-byte encodings, we need only reject nulls (\0).
     */
    if (pg_encoding_max_length(encoding) <= 1)
    {
        const char *nullpos = memchr(mbstr, 0, len);

        if (nullpos == NULL)
            return len;
        if (noError)
            return -1;
        report_invalid_encoding(encoding, nullpos, 1);
    }

    /* fetch function pointer just once */
    mbverifychar = pg_wchar_table[encoding].mbverifychar;

    mb_len = 0;

    while (len > 0)
    {
        int         l;

        /* fast path for ASCII-subset characters */
        if (!IS_HIGHBIT_SET(*mbstr))
        {
            if (*mbstr != '\0')
            {
                mb_len++;
                mbstr++;
                len--;
                continue;
            }
            if (noError)
                return -1;
            report_invalid_encoding(encoding, mbstr, len);
        }

        l = (*mbverifychar) ((const unsigned char *) mbstr, len);

        if (l < 0)
        {
            if (noError)
                return -1;
            report_invalid_encoding(encoding, mbstr, len);
        }

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

/*
 * check_encoding_conversion_args: check arguments of a conversion function
 *
 * "expected" arguments can be either an encoding ID or -1 to indicate that
 * the caller will check whether it accepts the ID.
 *
 * Note: the errors here are not really user-facing, so elog instead of
 * ereport seems sufficient.  Also, we trust that the "expected" encoding
 * arguments are valid encoding IDs, but we don't trust the actuals.
 */
void
check_encoding_conversion_args(int src_encoding,
                               int dest_encoding,
                               int len,
                               int expected_src_encoding,
                               int expected_dest_encoding)
{
    if (!PG_VALID_ENCODING(src_encoding))
        elog(ERROR, "invalid source encoding ID: %d", src_encoding);
    if (src_encoding != expected_src_encoding && expected_src_encoding >= 0)
        elog(ERROR, "expected source encoding \"%s\", but got \"%s\"",
             pg_enc2name_tbl[expected_src_encoding].name,
             pg_enc2name_tbl[src_encoding].name);
    if (!PG_VALID_ENCODING(dest_encoding))
        elog(ERROR, "invalid destination encoding ID: %d", dest_encoding);
    if (dest_encoding != expected_dest_encoding && expected_dest_encoding >= 0)
        elog(ERROR, "expected destination encoding \"%s\", but got \"%s\"",
             pg_enc2name_tbl[expected_dest_encoding].name,
             pg_enc2name_tbl[dest_encoding].name);
    if (len < 0)
        elog(ERROR, "encoding conversion length must not be negative");
}

/*
 * report_invalid_encoding: complain about invalid multibyte character
 *
 * note: len is remaining length of string, not length of character;
 * len must be greater than zero, as we always examine the first byte.
 */
void
report_invalid_encoding(int encoding, const char *mbstr, int len)
{
    int         l = pg_encoding_mblen(encoding, mbstr);
    char        buf[8 * 5 + 1];
    char       *p = buf;
    int         j,
                jlimit;

    jlimit = Min(l, len);
    jlimit = Min(jlimit, 8);    /* prevent buffer overrun */

    for (j = 0; j < jlimit; j++)
    {
        p += sprintf(p, "0x%02x", (unsigned char) mbstr[j]);
        if (j < jlimit - 1)
            p += sprintf(p, " ");
    }

    ereport(ERROR,
            (errcode(ERRCODE_CHARACTER_NOT_IN_REPERTOIRE),
             errmsg("invalid byte sequence for encoding \"%s\": %s",
                    pg_enc2name_tbl[encoding].name,
                    buf)));
}

/*
 * report_untranslatable_char: complain about untranslatable character
 *
 * note: len is remaining length of string, not length of character;
 * len must be greater than zero, as we always examine the first byte.
 */
void
report_untranslatable_char(int src_encoding, int dest_encoding,
                           const char *mbstr, int len)
{
    int         l = pg_encoding_mblen(src_encoding, mbstr);
    char        buf[8 * 5 + 1];
    char       *p = buf;
    int         j,
                jlimit;

    jlimit = Min(l, len);
    jlimit = Min(jlimit, 8);    /* prevent buffer overrun */

    for (j = 0; j < jlimit; j++)
    {
        p += sprintf(p, "0x%02x", (unsigned char) mbstr[j]);
        if (j < jlimit - 1)
            p += sprintf(p, " ");
    }

    ereport(ERROR,
            (errcode(ERRCODE_UNTRANSLATABLE_CHARACTER),
             errmsg("character with byte sequence %s in encoding \"%s\" has no equivalent in encoding \"%s\"",
                    buf,
                    pg_enc2name_tbl[src_encoding].name,
                    pg_enc2name_tbl[dest_encoding].name)));
}


#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                          /* WIN32 */