libpq_version.diff

diff --git a/doc/src/sgml/libpq.sgml b/doc/src/sgml/libpq.sgml
index c502439..a776df4 100644
--- a/doc/src/sgml/libpq.sgml
+++ b/doc/src/sgml/libpq.sgml
@@ -5359,6 +5359,50 @@ void *PQresultAlloc(PGresult *res, size_t nBytes);
     </listitem>
    </varlistentry>
 
+   <varlistentry id="libpq-pqlibversion">
+    <term>
+     <function>PQlibVersion</function>
+     <indexterm>
+      <primary>PQlibVersion</primary>
+      <seealso>PQserverVersion</seealso>
+     </indexterm>
+    </term>
+
+    <listitem>
+     <para>
+      Return the version of <productname>libpq</> that is being used.
+<synopsis>
+int PQlibVersion(void);
+</synopsis>
+     </para>
+
+     <para>
+      The result value of this function can be used to determine, at
+      runtime, if a specific functionality is available in the currently
+      loaded version of libpq. Examples of this include whether specific
+      connection options are available for <function>PQconnectdb</> and
+      the new <type>bytea</> encoding in PostgreSQL 9.0 that requires
+      libpq version 9.0 or later to work.
+     </para>
+
+     <para>
+      The number is formed by converting the major, minor, and revision
+      numbers into two-decimal-digit numbers and appending them together.
+      For example, version 9.1 will be returned as 90100, and version
+      9.1.2 will be returned as 90102 (leading zeroes are not shown).
+     </para>
+
+     <note>
+      <para>
+       This function appeared in <productname>PostgreSQL</> version 9.1, so
+       it cannot be used to detect required functionality in earlier
+       versions, since linking to it will create a load time dependency
+       on version 9.1.
+      </para>
+     </note>
+    </listitem>
+   </varlistentry>
+
   </variablelist>
 
  </sect1>
diff --git a/src/interfaces/libpq/exports.txt b/src/interfaces/libpq/exports.txt
index a6c73af..1af8df6 100644
--- a/src/interfaces/libpq/exports.txt
+++ b/src/interfaces/libpq/exports.txt
@@ -159,3 +159,4 @@ PQconnectdbParams         156
 PQconnectStartParams      157
 PQping                    158
 PQpingParams              159
+PQlibVersion              160
diff --git a/src/interfaces/libpq/fe-misc.c b/src/interfaces/libpq/fe-misc.c
index 24ab7cf..999f60b 100644
--- a/src/interfaces/libpq/fe-misc.c
+++ b/src/interfaces/libpq/fe-misc.c
@@ -66,6 +66,14 @@ static int pqSocketCheck(PGconn *conn, int forRead, int forWrite,
 			  time_t end_time);
 static int	pqSocketPoll(int sock, int forRead, int forWrite, time_t end_time);
 
+/*
+ * PQlibVersion: return the libpq version number
+ */
+int
+PQlibVersion(void)
+{
+	return PG_VERSION_NUM;
+}
 
 /*
  * fputnbytes: print exactly N bytes to a file
diff --git a/src/interfaces/libpq/libpq-fe.h b/src/interfaces/libpq/libpq-fe.h
index 271afed..6075ea8 100644
--- a/src/interfaces/libpq/libpq-fe.h
+++ b/src/interfaces/libpq/libpq-fe.h
@@ -547,6 +547,9 @@ extern int	lo_export(PGconn *conn, Oid lobjId, const char *filename);
 
 /* === in fe-misc.c === */
 
+/* Get the version of the libpq library in use */
+extern int	PQlibVersion(void);
+
 /* Determine length of multibyte encoded char at *s */
 extern int	PQmblen(const char *s, int encoding);