docs: update libpq's PQputCopyData and PQputCopyEnd

Clarify the meaning of libpq return values for PQputCopyData and
PQputCopyEnd, particularly in non-blocking mode.

Report by Robert Haas

diff --git a/doc/src/sgml/libpq.sgml b/doc/src/sgml/libpq.sgml
index de272c5c53d602c520e0c9090a79a9edd2d597bc..ad104a3a58115e0a7f02ad007035a9fa487a17e2 100644 (file)
--- a/doc/src/sgml/libpq.sgml
+++ b/doc/src/sgml/libpq.sgml
@@ -4318,8 +4318,8 @@ int PQsetnonblocking(PGconn *conn, int arg);
       
        In the nonblocking state, calls to
        PQsendQuery, PQputline,
-       PQputnbytes, and
-       PQendcopy will not block but instead return
+       PQputnbytes, PQputCopyData,
+       and PQendcopy will not block but instead return
        an error if they need to be called again.
       
 
@@ -4961,9 +4961,9 @@ int PQputCopyData(PGconn *conn,
       
        Transmits the COPY data in the specified
        buffer, of length nbytes, to the server.
-       The result is 1 if the data was sent, zero if it was not sent
-       because the attempt would block (this case is only possible if the
-       connection is in nonblocking mode), or -1 if an error occurred.
+       The result is 1 if the data was queued, zero if it was not queued
+       because of full buffers (this will only happen in nonblocking mode),
+       or -1 if an error occurred.
        (Use PQerrorMessage to retrieve details if
        the return value is -1.  If the value is zero, wait for write-ready
        and try again.)
@@ -5009,13 +5009,18 @@ int PQputCopyEnd(PGconn *conn,
        connections.)
       
 
-      
-       The result is 1 if the termination data was sent, zero if it was
-       not sent because the attempt would block (this case is only possible
-       if the connection is in nonblocking mode), or -1 if an error
-       occurred.  (Use PQerrorMessage to retrieve
-       details if the return value is -1.  If the value is zero, wait for
-       write-ready and try again.)
+       
+       The result is 1 if the termination message was sent; or in
+       nonblocking mode, this may only indicate that the termination
+       message was successfully queued.  (In nonblocking mode, to be
+       certain that the data has been sent, you should next wait for
+       write-ready and call PQflush, repeating until it
+       returns zero.)  Zero indicates that the function could not queue
+       the termination message because of full buffers; this will only
+       happen in nonblocking mode.  (In this case, wait for
+       write-ready and try the PQputCopyEnd call
+       again.)  If a hard error occurs, -1 is returned; you can use
+       PQerrorMessage to retrieve details.