Add blockchain.block.headers RPC call

docs/PROTOCOL.rst

@@ -927,14 +927,50 @@ Get a list of features and services supported by the server.
 Protocol Version 1.2
 --------------------
 
-Protocol version 1.2 is the same as version `1.1` except for the
+Protocol version 1.2 introduces new methods `blockcahin.block.get_chunk`,
-addition of a new method `mempool.get_fee_histogram`.
+`mempool.get_fee_histogram`.
 
-All methods with taking addresses are deprecated, and will be removed
+`blockchain.block.get_chunk` and all methods beginning
-at some point in the future.  You should update your code to use
+ `blockchain.address.` are deprecated and support will be removed in
-`Script Hashes`_ and the scripthash methods introduced in protocol 1.1
+ some future protocol version.  You should update your code to use
-instead.
+ `blockchain.block.headers` and `Script Hashes`_ with the scripthash
+ methods introduced in protocol 1.1 instead.
 
+blockchain.block.headers
+========================
+
+Return concatenated block headers as hexadecimal from the main chain.
+
+  blockchain.block.headers(**start_height**, **count**)
+
+  **start_height**
+
+    The height of the first header requested, a non-negative integer.
+
+  **count**
+
+    The number of headers requested, a non-negative integer.
+
+**Response**
+
+    A dictionary with at least 3 members:
+
+* **count**
+
+    The number of headers returned, between zero and the number
+    requested.  If the chain has not extended sufficiently far, only
+    the available headers will be returned.  If more headers than
+    **max** were requested at most **max** will be returned.
+
+* **hex**
+
+    The binary block headers concatenated together as hexadecimal
+    strings, in order.
+
+* **max**
+
+    The maximum number of headers the server will return in a single
+    request.
 
 mempool.get_fee_histogram
 =========================

server/controller.py

@@ -747,13 +747,16 @@ class Controller(ServerBase):
 
         return await self.run_in_executor(job)
 
-    def get_chunk(self, index):
+    def block_headers(self, start_height, count):
-        '''Return header chunk as hex.  Index is a non-negative integer.'''
+        '''Read count block headers starting at start_height; both
-        chunk_size = self.coin.CHUNK_SIZE
+        must be non-negative.
-        start_height = index * chunk_size
+
-        count = chunk_size
+        The return value is (hex, n), where hex is the hex encoding of
-        headers, n = self.bp.read_headers(start_height, count).hex()
+        the concatenated headers, and n is the number of headers read
-        return headers
+        (0 <= n <= count).
+        '''
+        headers, n = self.bp.read_headers(start_height, count)
+        return headers.hex(), n
 
     # Client RPC "blockchain" command handlers
 

server/session.py

@@ -25,6 +25,8 @@ class SessionBase(JSONSession):
     sessions.
     '''
 
+    MAX_CHUNK_SIZE = 2016
+
     def __init__(self, controller, kind):
         # Force v2 as a temporary hack for old Coinomi wallets
         # Remove in April 2017
@@ -255,13 +257,17 @@ class ElectrumX(SessionBase):
         return self.env.server_features()
 
     def block_headers(self, start_height, count):
-        '''Return concatenated block headers as hex for the main chain;
+        '''Return count concatenated block headers as hex for the main chain;
-        count headers starting at start_height.
+        starting at start_height.
 
-        start_height and count must be non-negative integers.'''
+        start_height and count must be non-negative integers.  At most
+        MAX_CHUNK_SIZE headers will be returned.
+        '''
         start_height = self.controller.non_negative_integer(start_height)
         count = self.controller.non_negative_integer(count)
-        return self.controller.block_headers(start_height, count).hex()
+        count = min(count, self.MAX_CHUNK_SIZE)
+        hex_str, n =  self.controller.block_headers(start_height, count)
+        return {'hex': hex_str, 'count': n, 'max': self.MAX_CHUNK_SIZE}
 
     def block_get_chunk(self, index):
         '''Return a chunk of block headers as a hexadecimal string.
@@ -270,9 +276,8 @@ class ElectrumX(SessionBase):
         index = self.controller.non_negative_integer(index)
         chunk_size = self.coin.CHUNK_SIZE
         start_height = index * chunk_size
-        count = chunk_size
+        hex_str, n =  self.controller.block_headers(start_height, chunk_size)
-
+        return hex_str
-        return self.controller.block_headers(start_height, count).hex()
 
     def block_get_chunk(self, index):
         '''Return a chunk of block headers as a hexadecimal string.
@@ -462,7 +467,9 @@ class ElectrumX(SessionBase):
         if ptuple >= (1, 2):
             # New handler as of 1.2
             handlers.update({
-                'mempool.get_fee_histogram': controller.mempool_get_fee_histogram,
+                'mempool.get_fee_histogram':
+                controller.mempool_get_fee_histogram,
+                'blockchain.block.headers': self.block_headers,
             })
 
         self.electrumx_handlers = handlers