Shell: add rpc to retrieve live blocks

src/lib_shell/block_directory.ml

@@ -54,6 +54,14 @@ let build_raw_rpc_directory
     return (State.Block.hash block)
   end ;
 
+  register0 S.live_blocks begin fun block () () ->
+    Chain_traversal.live_blocks
+      block
+      (State.Block.max_operations_ttl block)
+    >>= fun (live_blocks, _) ->
+    return live_blocks
+  end ;
+
   (* block header *)
 
   register0 S.header begin fun block () () ->

src/lib_shell_services/block_services.ml

@@ -76,6 +76,7 @@ type chain_prefix = unit * chain
 type prefix = chain_prefix * block
 let chain_path = RPC_path.(root / "chains" /: chain_arg)
 let mempool_path p = RPC_path.(p / "mempool")
+let live_blocks_path p = RPC_path.(p / "live_blocks")
 let dir_path : (chain_prefix, chain_prefix) RPC_path.t =
   RPC_path.(open_root / "blocks")
 let path = RPC_path.(dir_path /: blocks_arg)
@@ -664,6 +665,16 @@ module Make(Proto : PROTO)(Next_proto : PROTO) = struct
 
     end
 
+    let live_blocks =
+      RPC_service.get_service
+        ~description:"List the ancestors of the given block which, if \
+                      referred to as the branch in an operation \
+                      header, are recent enough for that operation to \
+                      be included in the current block."
+        ~query: RPC_query.empty
+        ~output: Block_hash.Set.encoding
+        RPC_path.(live_blocks_path open_root)
+
   end
 
   let path = RPC_path.prefix chain_path path
@@ -845,6 +856,11 @@ module Make(Proto : PROTO)(Next_proto : PROTO) = struct
 
   end
 
+  let live_blocks ctxt =
+    let f = make_call0 S.live_blocks ctxt in
+    fun ?(chain = `Main) ?(block = `Head 0) () ->
+      f chain block () ()
+
 end
 
 module Fake_protocol = struct

src/lib_shell_services/block_services.mli

@@ -33,6 +33,7 @@ type prefix = (unit * chain) * block
 val dir_path: (chain_prefix, chain_prefix) RPC_path.t
 val path: (chain_prefix, chain_prefix * block) RPC_path.t
 val mempool_path : ('a, 'b) RPC_path.t -> ('a, 'b) RPC_path.t
+val live_blocks_path : ('a, 'b) RPC_path.t -> ('a, 'b) RPC_path.t
 
 type operation_list_quota = {
   max_size: int ;
@@ -236,6 +237,12 @@ module Make(Proto : PROTO)(Next_proto : PROTO) : sig
 
   end
 
+  val live_blocks:
+    #simple ->
+    ?chain:chain ->
+    ?block:block ->
+    unit -> Block_hash.Set.t tzresult Lwt.t
+
   module S : sig
 
     val hash:
@@ -376,6 +383,11 @@ module Make(Proto : PROTO)(Next_proto : PROTO) : sig
 
     end
 
+    val live_blocks:
+      ([ `GET ], prefix,
+       prefix, unit, unit,
+       Block_hash.Set.t) RPC_service.t
+
   end
 
 end