Refactor CopyOneRowTo

The handling of binary and text formats are quite different here, so
it's more clear to check for the format first and have two separate
loops.

Author: jian he <jian.universality@gmail.com>
Reviewed-by: Ilia Evdokimov, Junwang Zhao
Discussion: https://www.postgresql.org/message-id/CACJufxFzHCeFBQF0M%2BSgk_NwknWuQ4oU7tS1isVeBrbhcKOHkg@mail.gmail.com

src/backend/commands/copyto.c

@@ -902,11 +902,8 @@ DoCopyTo(CopyToState cstate)
 static void
 CopyOneRowTo(CopyToState cstate, TupleTableSlot *slot)
 {
-	bool		need_delim = false;
 	FmgrInfo   *out_functions = cstate->out_functions;
 	MemoryContext oldcontext;
-	ListCell   *cur;
-	char	   *string;
 
 	MemoryContextReset(cstate->rowcontext);
 	oldcontext = MemoryContextSwitchTo(cstate->rowcontext);
@@ -920,29 +917,23 @@ CopyOneRowTo(CopyToState cstate, TupleTableSlot *slot)
 	/* Make sure the tuple is fully deconstructed */
 	slot_getallattrs(slot);
 
-	foreach(cur, cstate->attnumlist)
+	if (!cstate->opts.binary)
 	{
-		int			attnum = lfirst_int(cur);
-		Datum		value = slot->tts_values[attnum - 1];
-		bool		isnull = slot->tts_isnull[attnum - 1];
+		bool		need_delim = false;
 
-		if (!cstate->opts.binary)
+		foreach_int(attnum, cstate->attnumlist)
 		{
+			Datum		value = slot->tts_values[attnum - 1];
+			bool		isnull = slot->tts_isnull[attnum - 1];
+			char	   *string;
+
 			if (need_delim)
 				CopySendChar(cstate, cstate->opts.delim[0]);
 			need_delim = true;
-		}
 
-		if (isnull)
-		{
-			if (!cstate->opts.binary)
+			if (isnull)
 				CopySendString(cstate, cstate->opts.null_print_client);
 			else
-				CopySendInt32(cstate, -1);
-		}
-		else
-		{
-			if (!cstate->opts.binary)
 			{
 				string = OutputFunctionCall(&out_functions[attnum - 1],
 											value);
@@ -952,10 +943,20 @@ CopyOneRowTo(CopyToState cstate, TupleTableSlot *slot)
 				else
 					CopyAttributeOutText(cstate, string);
 			}
+		}
+	}
+	else
+	{
+		foreach_int(attnum, cstate->attnumlist)
+		{
+			Datum		value = slot->tts_values[attnum - 1];
+			bool		isnull = slot->tts_isnull[attnum - 1];
+			bytea	   *outputbytes;
+
+			if (isnull)
+				CopySendInt32(cstate, -1);
 			else
 			{
-				bytea	   *outputbytes;
-
 				outputbytes = SendFunctionCall(&out_functions[attnum - 1],
 											   value);
 				CopySendInt32(cstate, VARSIZE(outputbytes) - VARHDRSZ);