v3-0002-handle-zero-errno-generally.patch

diff --git a/src/backend/libpq/pqcomm.c b/src/backend/libpq/pqcomm.c
index 2802efc63f..0084a9bf13 100644
--- a/src/backend/libpq/pqcomm.c
+++ b/src/backend/libpq/pqcomm.c
@@ -936,6 +936,8 @@ pq_recvbuf(void)
 	{
 		int			r;
 
+		errno = 0;
+
 		r = secure_read(MyProcPort, PqRecvBuffer + PqRecvLength,
 						PQ_RECV_BUFFER_SIZE - PqRecvLength);
 
@@ -948,10 +950,13 @@ pq_recvbuf(void)
 			 * Careful: an ereport() that tries to write to the client would
 			 * cause recursion to here, leading to stack overflow and core
 			 * dump!  This message must go *only* to the postmaster log.
+			 *
+			 * If errno is zero, assume it's EOF and let the caller complain.
 			 */
-			ereport(COMMERROR,
-					(errcode_for_socket_access(),
-					 errmsg("could not receive data from client: %m")));
+			if (errno != 0)
+				ereport(COMMERROR,
+						(errcode_for_socket_access(),
+						 errmsg("could not receive data from client: %m")));
 			return EOF;
 		}
 		if (r == 0)
@@ -1028,6 +1033,8 @@ pq_getbyte_if_available(unsigned char *c)
 	/* Put the socket into non-blocking mode */
 	socket_set_nonblocking(true);
 
+	errno = 0;
+
 	r = secure_read(MyProcPort, c, 1);
 	if (r < 0)
 	{
@@ -1044,10 +1051,13 @@ pq_getbyte_if_available(unsigned char *c)
 			 * Careful: an ereport() that tries to write to the client would
 			 * cause recursion to here, leading to stack overflow and core
 			 * dump!  This message must go *only* to the postmaster log.
+			 *
+			 * If errno is zero, assume it's EOF and let the caller complain.
 			 */
-			ereport(COMMERROR,
-					(errcode_for_socket_access(),
-					 errmsg("could not receive data from client: %m")));
+			if (errno != 0)
+				ereport(COMMERROR,
+						(errcode_for_socket_access(),
+						 errmsg("could not receive data from client: %m")));
 			r = EOF;
 		}
 	}
diff --git a/src/interfaces/libpq/fe-secure.c b/src/interfaces/libpq/fe-secure.c
index bd72a87bbb..b2430362a9 100644
--- a/src/interfaces/libpq/fe-secure.c
+++ b/src/interfaces/libpq/fe-secure.c
@@ -211,6 +211,8 @@ pqsecure_raw_read(PGconn *conn, void *ptr, size_t len)
 	int			result_errno = 0;
 	char		sebuf[PG_STRERROR_R_BUFLEN];
 
+	SOCK_ERRNO_SET(0);
+
 	n = recv(conn->sock, ptr, len, 0);
 
 	if (n < 0)
@@ -237,6 +239,11 @@ pqsecure_raw_read(PGconn *conn, void *ptr, size_t len)
 										"\tbefore or while processing the request.");
 				break;
 
+			case 0:
+				/* If errno didn't get set, treat it as regular EOF */
+				n = 0;
+				break;
+
 			default:
 				libpq_append_conn_error(conn, "could not receive data from server: %s",
 										SOCK_STRERROR(result_errno,