doc: \copy can get data values \. and end-of-input confused

Reported-by: Svante Richter

Discussion: https://postgr.es/m/fcd57e4-8f23-4c3e-a5db-2571d09208e2@beta.fastmail.com

Backpatch-through: 11

doc/src/sgml/ref/psql-ref.sgml

@@ -1082,6 +1082,10 @@ testdb=>
         destination, because all data must pass through the client/server
         connection.  For large amounts of data the <acronym>SQL</acronym>
         command might be preferable.
+        Also, because of this pass-through method, <literal>\copy
+        ... from</literal> in <acronym>CSV</acronym> mode will erroneously
+        treat a <literal>\.</literal> data value alone on a line as an
+        end-of-input marker.
         </para>
         </tip>
 

src/bin/psql/copy.c

@@ -629,6 +629,7 @@ handleCopyIn(PGconn *conn, FILE *copystream, bool isbinary, PGresult **res)
 						 * This code erroneously assumes '\.' on a line alone
 						 * inside a quoted CSV string terminates the \copy.
 						 * https://www.postgresql.org/message-id/E1TdNVQ-0001ju-GO@wrigleys.postgresql.org
+						 * https://www.postgresql.org/message-id/bfcd57e4-8f23-4c3e-a5db-2571d09208e2@beta.fastmail.com
 						 */
 						if ((linelen == 3 && memcmp(fgresult, "\\.\n", 3) == 0) ||
 							(linelen == 4 && memcmp(fgresult, "\\.\r\n", 4) == 0))