added a new protobuf for paginating txo results

v2/proto/page.proto

@@ -0,0 +1,72 @@
+// Page message can represent the results of
+// paginated queries to a server which return
+// transactions and outputs. This should be
+// enough to cover just about every blockchain
+// type in LBRY: claims, supports, payments, etc.
+//
+// Assembling Result Page
+// 
+// To prevent unnecessarily duplicating the same
+// raw TX many times if the result is TXOs in
+// the same transaction, the Page is split between
+// a list of `txos` (pointers) and a list of `txs`
+// (actual raw transactions). To assemble the page,
+//
+//  1) Loop over all `txs`, parsing them into a TX
+//     object as desired and adding them into a
+//     mapping keyed by "tx hash -> TX object". 
+//
+//  2) Create a new list to hold the page results.
+//
+//  3) Loop over all `txos` adding it along with the
+//     TX retrieved from previously created TX mapping.
+//     Optionally, lookup and include the channel `txo`
+//     using the same process.
+//
+//  4) You should now have a list of TXOs with their
+//     associated TX and for claims in a channel also
+//     associated channel TXO and TX.
+//
+// If the Page object is used strictly to return a list
+// of TXs then the `txos` attribute will be empty. The
+// semantics of which field is being paginated (`txos` vs
+// `txs`) is determined in context of the RPC API. An
+// RPC method such as `get_transactions` is likely to
+// be paginating the `txs` list.
+//
+syntax = "proto3";
+
+package pb;
+
+message Page {
+  repeated Output txos = 1;
+  repeated Transaction txs = 2;
+  uint32 total = 3;
+  uint32 offset = 4;
+}
+
+message Output {
+  // pointer to an output in one of the Page.txs
+  bytes tx_hash = 1;
+  uint32 nout = 2;
+
+  // if this output is a stream claim in a
+  // channel, this is a pointer to an output
+  // representing that channel (should be
+  // available in Page.txs)
+  Output channel = 3;
+}
+
+message Transaction {
+  // entire raw transaction
+  bytes tx = 1;
+
+  // height progression
+  //   -1: in mempool but has unconfirmed inputs
+  //    0: in mempool and all inputs confirmed
+  // +num: confirmed in a specific block (height)
+  int32 height = 2;
+
+  // position in block from top, only if height > 0
+  uint32 position = 3;
+}