Plumb a read function up the stack to IDiskQueue

fdbserver/DiskQueue.actor.cpp

@@ -713,6 +713,7 @@ public:
 		}
 		return endLocation();
 	}
+
 	virtual void pop( location upTo ) {
 		ASSERT( !upTo.hi );
 		ASSERT( !recovered || upTo.lo <= endLocation() );
@@ -732,6 +733,8 @@ public:
 		}
 	}
 
+	virtual Future<Standalone<StringRef>> read(location from, location to) { return read(this, from, to); }
+
 	int getMaxPayload() {
 		return Page::maxPayload;
 	}
@@ -1241,6 +1244,8 @@ public:
 
 	virtual location getNextReadLocation() { return queue->getNextReadLocation(); }
 
+	virtual Future<Standalone<StringRef>> read( location start, location end ) { return queue->read( start, end ); }
+
 	virtual location push( StringRef contents ) {
 		pushed = queue->push(contents);
 		return pushed;

fdbserver/IDiskQueue.h

@@ -54,6 +54,7 @@ public:
 	virtual Future<Standalone<StringRef>> readNext( int bytes ) = 0;  // Return the next bytes in the queue (beginning, the first time called, with the first unpopped byte)
 	virtual location getNextReadLocation() = 0;    // Returns a location >= the location of all bytes previously returned by readNext(), and <= the location of all bytes subsequently returned
 
+	virtual Future<Standalone<StringRef>> read( location start, location end ) = 0;
 	virtual location push( StringRef contents ) = 0;  // Appends the given bytes to the byte stream.  Returns a location token representing the *end* of the contents.
 	virtual void pop( location upTo ) = 0;            // Removes all bytes before the given location token from the byte stream.
 	virtual Future<Void> commit() = 0;  // returns when all prior pushes and pops are durable.  If commit does not return (due to close or a crash), any prefix of the pushed bytes and any prefix of the popped bytes may be durable.

fdbserver/LogSystemDiskQueueAdapter.h

@@ -70,6 +70,7 @@ public:
 	virtual Future<bool> initializeRecovery() { return false; }
 	virtual Future<Standalone<StringRef>> readNext( int bytes );
 	virtual IDiskQueue::location getNextReadLocation();
+	virtual Future<Standalone<StringRef>> read( location start, location end ) { ASSERT(false); throw internal_error(); }
 	virtual IDiskQueue::location push( StringRef contents );
 	virtual void pop( IDiskQueue::location upTo );
 	virtual Future<Void> commit();