Function InitializeClientEncoding

src/backend/utils/mb/mbutils.c:282–332

* Initialize client encoding conversions. * Called from InitPostgres() once during backend startup. */

 *		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