Add a lot of documentation

copy_data.go

@@ -11,14 +11,20 @@ type CopyData struct {
 	Data []byte
 }
 
-func (*CopyData) Backend()  {}
+// Backend identifies this message as sendable by the PostgreSQL backend.
+func (*CopyData) Backend() {}
+
+// Frontend identifies this message as sendable by a PostgreSQL frontend.
 func (*CopyData) Frontend() {}
 
+// Decode decodes src into dst. src must contain the complete message with the exception of the initial 1 byte message
+// type identifier and 4 byte message length.
 func (dst *CopyData) Decode(src []byte) error {
 	dst.Data = src
 	return nil
 }
 
+// Encode encodes src into dst. dst will include the 1 byte message type identifier and the 4 byte message length.
 func (src *CopyData) Encode(dst []byte) []byte {
 	dst = append(dst, 'd')
 	dst = pgio.AppendInt32(dst, int32(4+len(src.Data)))
@@ -26,6 +32,7 @@ func (src *CopyData) Encode(dst []byte) []byte {
 	return dst
 }
 
+// MarshalJSON implements encoding/json.Marshaler.
 func (src *CopyData) MarshalJSON() ([]byte, error) {
 	return json.Marshal(struct {
 		Type string