pg: support for copy sql commands (#9272)

vlib/pg/pg.v

@@ -1,11 +1,17 @@
 module pg
 
+import io
+
 #flag -lpq
 #flag linux -I/usr/include/postgresql
 #flag darwin -I/opt/local/include/postgresql11
 #flag windows -I @VROOT/thirdparty/pg/include
 #flag windows -L @VROOT/thirdparty/pg/win64
+
+// PostgreSQL Source Code
+// https://doxygen.postgresql.org/libpq-fe_8h.html
 #include <libpq-fe.h>
+
 pub struct DB {
 mut:
 	conn &C.PGconn
@@ -16,7 +22,8 @@ pub mut:
 	vals []string
 }
 
-struct C.PGResult
+struct C.PGResult {
+}
 
 pub struct Config {
 pub:
@@ -41,12 +48,25 @@ fn C.PQntuples(&C.PGResult) int
 
 fn C.PQnfields(&C.PGResult) int
 
-fn C.PQexec(voidptr) &C.PGResult
+fn C.PQexec(voidptr, byteptr) &C.PGResult
 
-fn C.PQexecParams(voidptr) &C.PGResult
+// Params:
+// const Oid *paramTypes
+// const char *const *paramValues
+// const int *paramLengths
+// const int *paramFormats
+fn C.PQexecParams(conn voidptr, command byteptr, nParams int, paramTypes int, paramValues byteptr, paramLengths int, paramFormats int, resultFormat int) &C.PGResult
+
+fn C.PQputCopyData(conn voidptr, buffer byteptr, nbytes int) int
+
+fn C.PQputCopyEnd(voidptr, int) int
+
+fn C.PQgetCopyData(conn voidptr, buffer &byteptr, async int) int
 
 fn C.PQclear(&C.PGResult) voidptr
 
+fn C.PQfreemem(voidptr)
+
 fn C.PQfinish(voidptr)
 
 // connect makes a new connection to the database server using
@@ -114,7 +134,7 @@ pub fn (db DB) q_int(query string) ?int {
 	return val.int()
 }
 
-// q_int submit a command to the database server and
+// q_string submit a command to the database server and
 // returns an the first field in the first tuple
 // as a string. If no row is found or on
 // command failure, an error is returned
@@ -189,3 +209,67 @@ fn (db DB) handle_error_or_result(res voidptr, elabel string) ?[]Row {
 	}
 	return res_to_rows(res)
 }
+
+// copy_expert execute COPY commands
+// https://www.postgresql.org/docs/9.5/libpq-copy.html
+pub fn (db DB) copy_expert(query string, file io.ReaderWriter) ?int {
+	res := C.PQexec(db.conn, query.str)
+	status := C.PQresultStatus(res)
+
+	defer {
+		C.PQclear(res)
+	}
+
+	e := unsafe { C.PQerrorMessage(db.conn).vstring() }
+	if e != '' {
+		return error('pg copy error:\n$e')
+	}
+
+	if status == C.PGRES_COPY_IN {
+		mut buf := []byte{len: 4 * 1024}
+		for {
+			n := file.read(mut buf) or {
+				msg := 'pg copy error: Failed to read from input'
+				C.PQputCopyEnd(db.conn, msg.str)
+				return err
+			}
+			if n <= 0 {
+				break
+			}
+
+			code := C.PQputCopyData(db.conn, buf.data, n)
+			if code == -1 {
+				return error('pg copy error: Failed to send data, code=$code')
+			}
+		}
+
+		code := C.PQputCopyEnd(db.conn, 0)
+
+		if code != 1 {
+			return error('pg copy error: Failed to finish copy command, code: $code')
+		}
+	} else if status == C.PGRES_COPY_OUT {
+		for {
+			address := byteptr(0)
+			n_bytes := C.PQgetCopyData(db.conn, &address, 0)
+			if n_bytes > 0 {
+				mut local_buf := []byte{len: n_bytes}
+				unsafe { C.memcpy(byteptr(local_buf.data), address, n_bytes) }
+				file.write(local_buf) or {
+					C.PQfreemem(address)
+					return err
+				}
+			} else if n_bytes == -1 {
+				break
+			} else if n_bytes == -2 {
+				// consult PQerrorMessage for the reason
+				return error('pg copy error: read error')
+			}
+			if address != 0 {
+				C.PQfreemem(address)
+			}
+		}
+	}
+
+	return 0
+}