rpc: Add getblockfilter RPC method.

Retrieves and returns block filter and header from index.

src/rpc/blockchain.cpp

@@ -7,6 +7,7 @@
 
 #include <amount.h>
 #include <base58.h>
+#include <blockfilter.h>
 #include <chain.h>
 #include <chainparams.h>
 #include <checkpoints.h>
@@ -14,6 +15,7 @@
 #include <consensus/validation.h>
 #include <core_io.h>
 #include <hash.h>
+#include <index/blockfilterindex.h>
 #include <index/txindex.h>
 #include <key_io.h>
 #include <policy/feerate.h>
@@ -2296,6 +2298,85 @@ UniValue scantxoutset(const JSONRPCRequest& request)
     return result;
 }
 
+static UniValue getblockfilter(const JSONRPCRequest& request)
+{
+    if (request.fHelp || request.params.size() < 1 || request.params.size() > 2) {
+        throw std::runtime_error(
+            RPCHelpMan{"getblockfilter",
+                "\nRetrieve a BIP 157 content filter for a particular block.\n",
+                {
+                    {"blockhash", RPCArg::Type::STR_HEX, RPCArg::Optional::NO, "The hash of the block"},
+                    {"filtertype", RPCArg::Type::STR, /*default*/ "basic", "The type name of the filter"},
+                },
+                RPCResult{
+                    "{\n"
+                    "  \"filter\" : (string) the hex-encoded filter data\n"
+                    "  \"header\" : (string) the hex-encoded filter header\n"
+                    "}\n"
+                },
+                RPCExamples{
+                    HelpExampleCli("getblockfilter", "\"00000000c937983704a73af28acdec37b049d214adbda81d7e2a3dd146f6ed09\" \"basic\"")
+                }
+            }.ToString()
+        );
+    }
+
+    uint256 block_hash = ParseHashV(request.params[0], "blockhash");
+    std::string filtertype_name = "basic";
+    if (!request.params[1].isNull()) {
+        filtertype_name = request.params[1].get_str();
+    }
+
+    BlockFilterType filtertype;
+    if (!BlockFilterTypeByName(filtertype_name, filtertype)) {
+        throw JSONRPCError(RPC_INVALID_ADDRESS_OR_KEY, "Unknown filtertype");
+    }
+
+    BlockFilterIndex* index = GetBlockFilterIndex(filtertype);
+    if (!index) {
+        throw JSONRPCError(RPC_MISC_ERROR, "Index is not enabled for filtertype " + filtertype_name);
+    }
+
+    const CBlockIndex* block_index;
+    bool block_was_connected;
+    {
+        LOCK(cs_main);
+        block_index = LookupBlockIndex(block_hash);
+        if (!block_index) {
+            throw JSONRPCError(RPC_INVALID_ADDRESS_OR_KEY, "Block not found");
+        }
+        block_was_connected = block_index->IsValid(BLOCK_VALID_SCRIPTS);
+    }
+
+    bool index_ready = index->BlockUntilSyncedToCurrentChain();
+
+    BlockFilter filter;
+    uint256 filter_header;
+    if (!index->LookupFilter(block_index, filter) ||
+        !index->LookupFilterHeader(block_index, filter_header)) {
+        int err_code;
+        std::string errmsg = "Filter not found.";
+
+        if (!block_was_connected) {
+            err_code = RPC_INVALID_ADDRESS_OR_KEY;
+            errmsg += " Block was not connected to active chain.";
+        } else if (!index_ready) {
+            err_code = RPC_MISC_ERROR;
+            errmsg += " Block filters are still in the process of being indexed.";
+        } else {
+            err_code = RPC_INTERNAL_ERROR;
+            errmsg += " This error is unexpected and indicates index corruption.";
+        }
+
+        throw JSONRPCError(err_code, errmsg);
+    }
+
+    UniValue ret(UniValue::VOBJ);
+    ret.pushKV("filter", HexStr(filter.GetEncodedFilter()));
+    ret.pushKV("header", filter_header.GetHex());
+    return ret;
+}
+
 // clang-format off
 static const CRPCCommand commands[] =
 { //  category              name                      actor (function)         argNames
@@ -2323,6 +2404,7 @@ static const CRPCCommand commands[] =
 
     { "blockchain",         "preciousblock",          &preciousblock,          {"blockhash"} },
     { "blockchain",         "scantxoutset",           &scantxoutset,           {"action", "scanobjects"} },
+    { "blockchain",         "getblockfilter",         &getblockfilter,         {"blockhash", "filtertype"} },
 
     /* Not shown in help */
     { "hidden",             "invalidateblock",        &invalidateblock,        {"blockhash"} },

test/functional/rpc_getblockfilter.py

@@ -0,0 +1,59 @@
+#!/usr/bin/env python3
+# Copyright (c) 2018 The Bitcoin Core developers
+# Distributed under the MIT software license, see the accompanying
+# file COPYING or http://www.opensource.org/licenses/mit-license.php.
+"""Test the getblockfilter RPC."""
+
+from test_framework.test_framework import BitcoinTestFramework
+from test_framework.util import (
+    assert_equal, assert_is_hex_string, assert_raises_rpc_error,
+    connect_nodes, disconnect_nodes, sync_blocks
+    )
+
+FILTER_TYPES = ["basic"]
+
+class GetBlockFilterTest(BitcoinTestFramework):
+    def set_test_params(self):
+        self.setup_clean_chain = True
+        self.num_nodes = 2
+        self.extra_args = [["-blockfilterindex"], []]
+
+    def run_test(self):
+        # Create two chains by disconnecting nodes 0 & 1, mining, then reconnecting
+        disconnect_nodes(self.nodes[0], 1)
+
+        self.nodes[0].generate(3)
+        self.nodes[1].generate(4)
+
+        assert_equal(self.nodes[0].getblockcount(), 3)
+        chain0_hashes = [self.nodes[0].getblockhash(block_height) for block_height in range(4)]
+
+        # Reorg node 0 to a new chain
+        connect_nodes(self.nodes[0], 1)
+        sync_blocks(self.nodes)
+
+        assert_equal(self.nodes[0].getblockcount(), 4)
+        chain1_hashes = [self.nodes[0].getblockhash(block_height) for block_height in range(4)]
+
+        # Test getblockfilter returns a filter for all blocks and filter types on active chain
+        for block_hash in chain1_hashes:
+            for filter_type in FILTER_TYPES:
+                result = self.nodes[0].getblockfilter(block_hash, filter_type)
+                assert_is_hex_string(result['filter'])
+
+        # Test getblockfilter returns a filter for all blocks and filter types on stale chain
+        for block_hash in chain0_hashes:
+            for filter_type in FILTER_TYPES:
+                result = self.nodes[0].getblockfilter(block_hash, filter_type)
+                assert_is_hex_string(result['filter'])
+
+        # Test getblockfilter with unknown block
+        bad_block_hash = "0123456789abcdef" * 4
+        assert_raises_rpc_error(-5, "Block not found", self.nodes[0].getblockfilter, bad_block_hash, "basic")
+
+        # Test getblockfilter with undefined filter type
+        genesis_hash = self.nodes[0].getblockhash(0)
+        assert_raises_rpc_error(-5, "Unknown filtertype", self.nodes[0].getblockfilter, genesis_hash, "unknown")
+
+if __name__ == '__main__':
+    GetBlockFilterTest().main()

test/functional/test_runner.py

@@ -144,6 +144,7 @@ BASE_SCRIPTS = [
     'wallet_txn_doublespend.py',
     'wallet_txn_clone.py --mineblock',
     'feature_notifications.py',
+    'rpc_getblockfilter.py',
     'rpc_invalidateblock.py',
     'feature_rbf.py',
     'mempool_packages.py',