solution: delegate bitcoin balance request to another upstream, if data is unavailable locally

src/test/groovy/io/emeraldpay/dshackle/config/UpstreamsConfigReaderSpec.groovy

@@ -92,6 +92,7 @@ class UpstreamsConfigReaderSpec extends Specification {
         with(act.upstreams.get(0)) {
             id == "local"
             chain == "bitcoin"
+            options == null || options.providesBalance == false
             connection instanceof UpstreamsConfig.BitcoinConnection
             with((UpstreamsConfig.BitcoinConnection) connection) {
                 rpc != null
@@ -119,6 +120,7 @@ class UpstreamsConfigReaderSpec extends Specification {
         with(act.upstreams.get(0)) {
             id == "local"
             chain == "bitcoin"
+            options.providesBalance == true
             connection instanceof UpstreamsConfig.BitcoinConnection
             with((UpstreamsConfig.BitcoinConnection) connection) {
                 rpc != null

src/test/groovy/io/emeraldpay/dshackle/rpc/TrackBitcoinAddressSpec.groovy

@@ -259,6 +259,7 @@ class TrackBitcoinAddressSpec extends Specification {
         }
         MultistreamHolder upstreams = new MultistreamHolderMock(Chain.BITCOIN, upstream)
         TrackBitcoinAddress track = new TrackBitcoinAddress(upstreams)
+        track.setBalanceAvailability(Chain.BITCOIN, true)
 
         when:
         def resp = track.subscribe(BlockchainOuterClass.BalanceRequest.newBuilder()
@@ -285,6 +286,5 @@ class TrackBitcoinAddressSpec extends Specification {
                 }
                 .expectComplete()
                 .verify(Duration.ofSeconds(1))
-
     }
 }

src/test/groovy/io/emeraldpay/dshackle/upstream/grpc/RemoteCapabilitiesSpec.groovy

@@ -0,0 +1,32 @@
+package io.emeraldpay.dshackle.upstream.grpc
+
+import io.emeraldpay.api.proto.BlockchainOuterClass
+import io.emeraldpay.dshackle.upstream.Capability
+import spock.lang.Specification
+
+class RemoteCapabilitiesSpec extends Specification {
+
+    def "parse from remote - all"() {
+        setup:
+        def remote = BlockchainOuterClass.DescribeChain.newBuilder()
+                .addCapabilities(BlockchainOuterClass.Capabilities.CAP_CALLS)
+                .addCapabilities(BlockchainOuterClass.Capabilities.CAP_NONE)
+                .addCapabilities(BlockchainOuterClass.Capabilities.CAP_BALANCE)
+                .build()
+        when:
+        def act = RemoteCapabilities.extract(remote)
+        then:
+        act == [Capability.BALANCE, Capability.RPC].toSet()
+    }
+
+    def "parse from remote - only call"() {
+        setup:
+        def remote = BlockchainOuterClass.DescribeChain.newBuilder()
+                .addCapabilities(BlockchainOuterClass.Capabilities.CAP_CALLS)
+                .build()
+        when:
+        def act = RemoteCapabilities.extract(remote)
+        then:
+        act == [Capability.RPC].toSet()
+    }
+}

src/test/resources/upstreams-bitcoin-esplora.yaml

@@ -9,6 +9,8 @@ defaults:
 upstreams:
   - id: local
     chain: bitcoin
+    options:
+      balance: true
     connection:
       bitcoin:
         rpc: