diff --git a/src/backend/commands/copyfromparse.c b/src/backend/commands/copyfromparse.c
index df6ea33ff14..6b40a379ee5 100644
--- a/src/backend/commands/copyfromparse.c
+++ b/src/backend/commands/copyfromparse.c
@@ -163,7 +163,7 @@ static pg_always_inline bool NextCopyFromRawFieldsInternal(CopyFromState cstate,
 
 
 /* Low-level communications functions */
-static int	CopyGetData(CopyFromState cstate, void *databuf,
+int			CopyGetData(CopyFromState cstate, void *databuf,
 						int minread, int maxread);
 static inline bool CopyGetInt32(CopyFromState cstate, int32 *val);
 static inline bool CopyGetInt16(CopyFromState cstate, int16 *val);
@@ -245,7 +245,7 @@ ReceiveCopyBinaryHeader(CopyFromState cstate)
  *
  * NB: no data conversion is applied here.
  */
-static int
+int
 CopyGetData(CopyFromState cstate, void *databuf, int minread, int maxread)
 {
 	int			bytesread = 0;
diff --git a/src/backend/commands/copyto.c b/src/backend/commands/copyto.c
index af2aab18234..fb9013e8622 100644
--- a/src/backend/commands/copyto.c
+++ b/src/backend/commands/copyto.c
@@ -82,10 +82,10 @@ static void CopyToBinaryEnd(CopyToState cstate);
 /* Low-level communications functions */
 static void SendCopyBegin(CopyToState cstate);
 static void SendCopyEnd(CopyToState cstate);
-static void CopySendData(CopyToState cstate, const void *databuf, int datasize);
+/* exported for custom formats, see copyapi.h */
 static void CopySendString(CopyToState cstate, const char *str);
 static void CopySendChar(CopyToState cstate, char c);
-static void CopySendEndOfRow(CopyToState cstate);
+
 static void CopySendTextLikeEndOfRow(CopyToState cstate);
 static void CopySendInt32(CopyToState cstate, int32 val);
 static void CopySendInt16(CopyToState cstate, int16 val);
@@ -513,7 +513,7 @@ SendCopyEnd(CopyToState cstate)
  * NB: no data conversion is applied by these functions
  *----------
  */
-static void
+void
 CopySendData(CopyToState cstate, const void *databuf, int datasize)
 {
 	appendBinaryStringInfo(cstate->fe_msgbuf, databuf, datasize);
@@ -531,7 +531,7 @@ CopySendChar(CopyToState cstate, char c)
 	appendStringInfoCharMacro(cstate->fe_msgbuf, c);
 }
 
-static void
+void
 CopySendEndOfRow(CopyToState cstate)
 {
 	StringInfo	fe_msgbuf = cstate->fe_msgbuf;
diff --git a/src/include/commands/copyapi.h b/src/include/commands/copyapi.h
index f1924424df8..361a707fdef 100644
--- a/src/include/commands/copyapi.h
+++ b/src/include/commands/copyapi.h
@@ -145,4 +145,17 @@ extern void RegisterCopyCustomFormat(const char *name, const CopyToRoutine *to,
 
 extern const CopyCustomFormatEntry *GetCopyCustomFormatRoutines(const char *name);
 
+/*
+ * Low-level I/O for custom formats.
+ *
+ * A format implementation has to move bytes to and from whatever the COPY is
+ * attached to (a file, a PROGRAM, the frontend, or a callback), and only these
+ * know how to do that.  Without them an extension can register a format but
+ * cannot implement one.
+ */
+extern void CopySendData(CopyToState cstate, const void *databuf, int datasize);
+extern void CopySendEndOfRow(CopyToState cstate);
+extern int	CopyGetData(CopyFromState cstate, void *databuf,
+						int minread, int maxread);
+
 #endif							/* COPYAPI_H */