From 071757645ee0f9f15f57e43447d7c234deb062c0 Mon Sep 17 00:00:00 2001
From: Alvaro Herrera <alvherre@alvh.no-ip.org>
Date: Fri, 25 Jun 2021 16:02:00 -0400
Subject: [PATCH v2 2/4] Add PQrequestFlush()

---
 doc/src/sgml/libpq.sgml          | 17 +++++++++++++++
 src/interfaces/libpq/exports.txt |  1 +
 src/interfaces/libpq/fe-exec.c   | 37 ++++++++++++++++++++++++++++++++
 src/interfaces/libpq/libpq-fe.h  |  1 +
 4 files changed, 56 insertions(+)

diff --git a/doc/src/sgml/libpq.sgml b/doc/src/sgml/libpq.sgml
index 7f8a4db089..4d203f51e1 100644
--- a/doc/src/sgml/libpq.sgml
+++ b/doc/src/sgml/libpq.sgml
@@ -5401,6 +5401,23 @@ int PQpipelineSync(PGconn *conn);
       </para>
      </listitem>
     </varlistentry>
+
+    <varlistentry id="libpq-PQrequestFlush">
+     <term><function>PQrequestFlush</function><indexterm><primary>PQrequestFlush</primary></indexterm></term>
+
+      <listitem>
+       <para>
+        Requests the server to flush its output buffer.  The server does
+        that automatically upon <function>PQpipelineSync</function> or
+        any request when not in pipeline mode; this function is useful
+        if results are expected without establishing a synchronization
+        point.  Returns 1 for success and 0 on failure.
+<synopsis>
+int PQrequestFlush(PGconn *conn);
+</synopsis>
+       </para>
+      </listitem>
+     </varlistentry>
    </variablelist>
   </sect2>
 
diff --git a/src/interfaces/libpq/exports.txt b/src/interfaces/libpq/exports.txt
index 824a03ffbd..c616059f58 100644
--- a/src/interfaces/libpq/exports.txt
+++ b/src/interfaces/libpq/exports.txt
@@ -185,3 +185,4 @@ PQpipelineSync            182
 PQpipelineStatus          183
 PQsetTraceFlags           184
 PQmblenBounded              185
+PQrequestFlush            186
diff --git a/src/interfaces/libpq/fe-exec.c b/src/interfaces/libpq/fe-exec.c
index 7bd5b3a7b9..00d744eaa7 100644
--- a/src/interfaces/libpq/fe-exec.c
+++ b/src/interfaces/libpq/fe-exec.c
@@ -3696,6 +3696,43 @@ PQflush(PGconn *conn)
 	return pqFlush(conn);
 }
 
+/*
+ * Send request for server to flush its buffer
+ */
+int
+PQrequestFlush(PGconn *conn)
+{
+	if (!conn)
+		return 0;
+
+	/* Don't try to send if we know there's no live connection. */
+	if (conn->status != CONNECTION_OK)
+	{
+		appendPQExpBufferStr(&conn->errorMessage,
+							 libpq_gettext("no connection to the server\n"));
+		return 0;
+	}
+
+	/* Can't send while already busy, either, unless enqueuing for later */
+	if (conn->asyncStatus != PGASYNC_IDLE &&
+		conn->pipelineStatus == PQ_PIPELINE_OFF)
+	{
+		appendPQExpBufferStr(&conn->errorMessage,
+							 libpq_gettext("another command is already in progress\n"));
+		return false;
+	}
+
+	if (pqPutMsgStart('H', conn) < 0 ||
+		pqPutMsgEnd(conn) < 0)
+	{
+		return 0;
+	}
+	/* XXX useless without a flush ...? */
+	pqFlush(conn);
+
+	return 1;
+}
+
 /*
  * pqPipelineFlush
  *
diff --git a/src/interfaces/libpq/libpq-fe.h b/src/interfaces/libpq/libpq-fe.h
index cc6032b15b..cf7cbe942e 100644
--- a/src/interfaces/libpq/libpq-fe.h
+++ b/src/interfaces/libpq/libpq-fe.h
@@ -496,6 +496,7 @@ extern PGPing PQpingParams(const char *const *keywords,
 
 /* Force the write buffer to be written (or at least try) */
 extern int	PQflush(PGconn *conn);
+extern int	PQrequestFlush(PGconn *conn);
 
 /*
  * "Fast path" interface --- not really recommended for application
-- 
2.30.2