Moved all the block producer/consumer interfaces to common.

common/block.go

@@ -1,7 +1,31 @@
 package common
 
-// Block data from Minetest database.
-type Block struct {
-	Coord Coord
-	Data  []byte
-}
+import (
+	"errors"
+)
+
+// Error returned if a Producer has run to its end.
+var ErrNoMoreBlocks = errors.New("No more blocks.")
+
+type (
+	// Block data from Minetest database.
+	Block struct {
+		Coord Coord
+		Data  []byte
+	}
+	// BlockProducer is used to over a existing Minetest database
+	// and return its content block by block.
+	BlockProducer interface {
+		// error is ErrNoMoreBlocks if it run out of blocks.
+		Next(*Block) error
+		// Closes the open database connections.
+		Close() error
+	}
+
+	// BlockConsumer is used to store blocks in a new Minetest database.
+	BlockConsumer interface {
+		Consume(*Block) error
+		// Closes the open database connections.
+		Close() error
+	}
+)