Move bulk of FS flush code to db.py

More logically belongs there.
Have servers use the flushed DB height not the block processor's height.
Get all headers only from disk.

server/block_processor.py

@@ -10,7 +10,6 @@
 
 import array
 import asyncio
-import itertools
 import os
 from struct import pack, unpack
 import time
@@ -438,47 +437,11 @@ class BlockProcessor(server.db.DB):
 
     def fs_flush(self):
         '''Flush the things stored on the filesystem.'''
-        blocks_done = len(self.headers)
-        prior_tx_count = (self.tx_counts[self.fs_height]
-                          if self.fs_height >= 0 else 0)
-        cur_tx_count = self.tx_counts[-1] if self.tx_counts else 0
-        txs_done = cur_tx_count - prior_tx_count
-
-        assert self.fs_height + blocks_done == self.height
-        assert len(self.tx_hashes) == blocks_done
-        assert len(self.tx_counts) == self.height + 1
-        assert cur_tx_count == self.tx_count, \
-            'cur: {:,d} new: {:,d}'.format(cur_tx_count, self.tx_count)
-
-        # First the headers
-        headers = b''.join(self.headers)
-        header_len = self.coin.HEADER_LEN
-        self.headers_file.seek((self.fs_height + 1) * header_len)
-        self.headers_file.write(headers)
-        self.headers_file.flush()
-
-        # Then the tx counts
-        self.txcount_file.seek((self.fs_height + 1) * self.tx_counts.itemsize)
-        self.txcount_file.write(self.tx_counts[self.fs_height + 1:])
-        self.txcount_file.flush()
-
-        # Finally the hashes
-        hashes = memoryview(b''.join(itertools.chain(*self.tx_hashes)))
-        assert len(hashes) % 32 == 0
-        assert len(hashes) // 32 == txs_done
-        cursor = 0
-        file_pos = prior_tx_count * 32
-        while cursor < len(hashes):
-            file_num, offset = divmod(file_pos, self.tx_hash_file_size)
-            size = min(len(hashes) - cursor, self.tx_hash_file_size - offset)
-            filename = 'hashes{:04d}'.format(file_num)
-            with self.open_file(filename, create=True) as f:
-                f.seek(offset)
-                f.write(hashes[cursor:cursor + size])
-            cursor += size
-            file_pos += size
-
-        os.sync()
+        assert self.fs_height + len(self.headers) == self.height
+        assert self.tx_count == self.tx_counts[-1] if self.tx_counts else 0
+
+        self.fs_update(self.fs_height, self.headers, self.tx_hashes)
+
         self.fs_height = self.height
         self.fs_tx_count = self.tx_count
         self.tx_hashes = []
@@ -824,23 +787,6 @@ class BlockProcessor(server.db.DB):
         self.db_height = self.height
         self.db_tip = self.tip
 
-    def read_headers(self, start, count):
-        # Read some from disk
-        disk_count = min(count, max(0, self.fs_height + 1 - start))
-        result = self.fs_read_headers(start, disk_count)
-        count -= disk_count
-        start += disk_count
-
-        # The rest from memory
-        if count:
-            start -= self.fs_height + 1
-            if not (count >= 0 and start + count <= len(self.headers)):
-                raise ChainError('{:,d} headers starting at {:,d} not on disk'
-                                 .format(count, start))
-            result += b''.join(self.headers[start: start + count])
-
-        return result
-
     def get_tx_hash(self, tx_num):
         '''Returns the tx_hash and height of a tx number.'''
         tx_hash, tx_height = self.fs_tx_hash(tx_num)

server/db.py

@@ -10,6 +10,7 @@
 
 import array
 import ast
+import itertools
 import os
 from struct import pack, unpack
 from bisect import bisect_right
@@ -117,7 +118,6 @@ class DB(LoggedClass):
             self.logger.info('sync time so far: {}'
                              .format(formatted_time(self.wall_time)))
 
-
     def write_state(self, batch):
         '''Write chain state to the batch.'''
         state = {
@@ -142,7 +142,51 @@ class DB(LoggedClass):
                 return open(filename, 'wb+')
             raise
 
-    def fs_read_headers(self, start, count):
+    def fs_update(self, fs_height, headers, block_tx_hashes):
+        '''Write headers, the tx_count array and block tx hashes to disk.
+
+        Their first height is fs_height.  No recorded DB state is
+        updated.  These arrays are all append only, so in a crash we
+        just pick up again from the DB height.
+        '''
+        blocks_done = len(self.headers)
+        new_height = fs_height + blocks_done
+        prior_tx_count = (self.tx_counts[fs_height] if fs_height >= 0 else 0)
+        cur_tx_count = self.tx_counts[-1] if self.tx_counts else 0
+        txs_done = cur_tx_count - prior_tx_count
+
+        assert len(self.tx_hashes) == blocks_done
+        assert len(self.tx_counts) == new_height + 1
+
+        # First the headers
+        self.headers_file.seek((fs_height + 1) * self.coin.HEADER_LEN)
+        self.headers_file.write(b''.join(headers))
+        self.headers_file.flush()
+
+        # Then the tx counts
+        self.txcount_file.seek((fs_height + 1) * self.tx_counts.itemsize)
+        self.txcount_file.write(self.tx_counts[fs_height + 1:])
+        self.txcount_file.flush()
+
+        # Finally the hashes
+        hashes = memoryview(b''.join(itertools.chain(*block_tx_hashes)))
+        assert len(hashes) % 32 == 0
+        assert len(hashes) // 32 == txs_done
+        cursor = 0
+        file_pos = prior_tx_count * 32
+        while cursor < len(hashes):
+            file_num, offset = divmod(file_pos, self.tx_hash_file_size)
+            size = min(len(hashes) - cursor, self.tx_hash_file_size - offset)
+            filename = 'hashes{:04d}'.format(file_num)
+            with self.open_file(filename, create=True) as f:
+                f.seek(offset)
+                f.write(hashes[cursor:cursor + size])
+            cursor += size
+            file_pos += size
+
+        os.sync()
+
+    def read_headers(self, start, count):
         '''Requires count >= 0.'''
         # Read some from disk
         disk_count = min(count, self.db_height + 1 - start)
@@ -172,7 +216,7 @@ class DB(LoggedClass):
             return f.read(32), tx_height
 
     def fs_block_hashes(self, height, count):
-        headers = self.fs_read_headers(height, count)
+        headers = self.read_headers(height, count)
         # FIXME: move to coins.py
         hlen = self.coin.HEADER_LEN
         return [self.coin.header_hash(header)

server/protocol.py

@@ -311,7 +311,8 @@ class ServerManager(util.LoggedClass):
         for session in self.sessions:
             if isinstance(session, ElectrumX):
                 # Use a tuple to distinguish from JSON
-                session.messages.put_nowait((self.bp.height, touched, cache))
+                triple = (self.bp.db_height, touched, cache)
+                session.messages.put_nowait(triple)
 
     async def shutdown(self):
         '''Call to shutdown the servers.  Returns when done.'''
@@ -377,7 +378,7 @@ class ServerManager(util.LoggedClass):
     async def rpc_getinfo(self, params):
         '''The RPC 'getinfo' call.'''
         return {
-            'blocks': self.bp.height,
+            'blocks': self.bp.db_height,
             'peers': len(self.irc.peers),
             'sessions': self.session_count(),
             'watched': self.subscription_count,
@@ -592,8 +593,8 @@ class ElectrumX(Session):
                              .format(self.peername(), len(matches)))
 
     def height(self):
-        '''Return the block processor's current height.'''
-        return self.bp.height
+        '''Return the current flushed database height.'''
+        return self.bp.db_height
 
     def current_electrum_header(self):
         '''Used as response to a headers subscription request.'''