Allow users to have multiple wallets in bitcoind (#1334)

* Change the bitcoind RPC URL to use the default wallet named ""

README.md

@@ -48,7 +48,8 @@ You will find detailed guides and frequently asked questions there.
 :warning: Eclair requires Bitcoin Core 0.17.1 or higher. If you are upgrading an existing wallet, you need to create a new address and send all your funds to that address.
 
 Eclair needs a _synchronized_, _segwit-ready_, **_zeromq-enabled_**, _wallet-enabled_, _non-pruning_, _tx-indexing_ [Bitcoin Core](https://github.com/bitcoin/bitcoin) node.
-Eclair will use any BTC it finds in the Bitcoin Core wallet to fund any channels you choose to open. Eclair will return BTC from closed channels to this wallet. 
+Eclair will use any BTC it finds in the default Bitcoin Core wallet to fund any channels you choose to open. Eclair will return BTC from closed channels to this wallet. You can have multiple Bitcoin Core wallets but make sure that the default one is always available.
+Any BTC found in the wallet can be used to fund the channels you choose to open and the BTC from closed channels will return to this wallet. 
 You can configure your Bitcoin Node to use either `p2sh-segwit` addresses or `bech32` addresses, Eclair is compatible with both modes.
 If your Bitcoin Core wallet has "non-segwit UTXOs" (outputs that are neither `p2sh-segwit` or `bech32`), you must send them to a `p2sh-segwit` or `bech32` address.
 

eclair-core/src/main/scala/fr/acinq/eclair/blockchain/bitcoind/rpc/BasicBitcoinJsonRPCClient.scala

@@ -43,7 +43,7 @@ class BasicBitcoinJsonRPCClient(user: String, password: String, host: String = "
     KamonExt.timeFuture("bitcoin.rpc.basic.invoke.time") {
     for {
       res <- sttp
-        .post(uri"$scheme://$host:$port")
+        .post(uri"$scheme://$host:$port/wallet/") // wallet/ specifies to use the default bitcoind wallet, named ""
         .body(requests)
         .auth.basic(user, password)
         .response(asJson[Seq[JsonRPCResponse]])