Add new line after writing block to hex file. (#10984)

* add new line after writing block to hex file.

* refactor for testability

* correct import

* better error reporting, code formatting

* multiline imports

* docs

* better docs, move type to common types, merge ImportBlocks and ExportBlocks

* tabs over spaces

* correct test imports

* Apply suggestions from code review

Co-Authored-By: David <dvdplm@gmail.com>

* correct typo

* fixed test import

ethcore/client-traits/src/lib.rs

@@ -55,6 +55,7 @@ use trace::{
 	localized::LocalizedTrace,
 	VMTrace,
 };
+use common_types::data_format::DataFormat;
 use vm::{LastHashes, Schedule};
 
 use common_types::snapshot::Progress;
@@ -510,3 +511,29 @@ pub trait ChainNotify: Send + Sync {
 		// does nothing by default
 	}
 }
+
+/// Provides a method for importing/exporting blocks
+pub trait ImportExportBlocks {
+    /// Export blocks to destination, with the given from, to and format argument.
+    /// destination could be a file or stdout.
+    /// If the format is hex, each block is written on a new line.
+    /// For binary exports, all block data is written to the same line.
+	fn export_blocks<'a>(
+        &self,
+        destination: Box<dyn std::io::Write + 'a>,
+        from: BlockId,
+        to: BlockId,
+        format: Option<DataFormat>
+    ) -> Result<(), String>;
+
+	/// Import blocks from destination, with the given format argument
+	/// Source could be a file or stdout.
+	/// For hex format imports, it attempts to read the blocks on a line by line basis.
+	/// For binary format imports, reads the 8 byte RLP header in order to decode the block
+	/// length to be read.
+	fn import_blocks<'a>(
+		&self,
+		source: Box<dyn std::io::Read + 'a>,
+		format: Option<DataFormat>
+	) -> Result<(), String>;
+}