Merge bitcoin/bitcoin#21056: rpc: Add a `-rpcwaittimeout` parameter to limit time spent waiting

b9e76f1bf0 rpc: Add test for -rpcwaittimeout (Christian Decker)
f76cb10d7d rpc: Prefix rpcwaittimeout error with details on its nature (Christian Decker)
c490e17ef6 doc: Add release notes for the `-rpcwaittimeout` cli parameter (Christian Decker)
a7fcc8eb59 rpc: Add a `-rpcwaittimeout` parameter to limit time spent waiting (Christian Decker)

Pull request description:

  Adds a new numeric `-rpcwaittimeout` that can be used to limit the
  time we spend waiting on the RPC server to appear. This is used by
  downstream projects to provide a bit of slack when `bitcoind`s RPC
  interface is not available right away.

  This makes the `-rpcwait` argument more useful, since we can now limit
  how long we'll ultimately wait, before potentially giving up and reporting
  an error to the caller. It was discussed in the context of the BTCPayServer
  wanting to have c-lightning wait for the RPC interface to become available
  but still have the option of giving up eventually ([4355]).

  I checked with laanwj whether this is already possible ([comment]), and
  whether this would be a welcome change. Initially I intended to repurpose
  the (optional) argument to `-rpcwait`, however I decided against it since it
  would potentially break existing configurations, using things like `rpcwait=1`,
  or `rpcwait=true` (the former would have an unintended short timeout, when
  old behavior was to wait indefinitely).

  ~Due to its simplicity I didn't implement a test for it yet, but if that's desired I
  can provide one.~ Test was added during reviews.

  [4355]: https://github.com/ElementsProject/lightning/issues/4355
  [comment]: https://github.com/ElementsProject/lightning/issues/4355#issuecomment-768288261

ACKs for top commit:
  laanwj:
    Code review ACK b9e76f1bf0
  promag:
    ACK b9e76f1bf0.

Tree-SHA512: 3cd6728038ec7ca7c35c2e7ccb213bfbe963f99a49bb48bbc1e511c4dd23d9957c04f9af1f8ec57120e47b26eaf580b46817b099d5fc5083c98da7aa92db8638

doc/release-notes-21056.md

@@ -0,0 +1,6 @@
+New bitcoin-cli settings
+------------------------
+
+- A new `-rpcwaittimeout` argument to `bitcoin-cli` sets the timeout
+  in seconds to use with `-rpcwait`. If the timeout expires,
+  `bitcoin-cli` will report a failure. (#21056)

src/bitcoin-cli.cpp

@@ -40,6 +40,7 @@ UrlDecodeFn* const URL_DECODE = urlDecode;
 
 static const char DEFAULT_RPCCONNECT[] = "127.0.0.1";
 static const int DEFAULT_HTTP_CLIENT_TIMEOUT=900;
+static constexpr int DEFAULT_WAIT_CLIENT_TIMEOUT = 0;
 static const bool DEFAULT_NAMED=false;
 static const int CONTINUE_EXECUTION=-1;
 static constexpr int8_t UNKNOWN_NETWORK{-1};
@@ -73,6 +74,7 @@ static void SetupCliArgs(ArgsManager& argsman)
     argsman.AddArg("-rpcport=<port>", strprintf("Connect to JSON-RPC on <port> (default: %u, testnet: %u, signet: %u, regtest: %u)", defaultBaseParams->RPCPort(), testnetBaseParams->RPCPort(), signetBaseParams->RPCPort(), regtestBaseParams->RPCPort()), ArgsManager::ALLOW_ANY | ArgsManager::NETWORK_ONLY, OptionsCategory::OPTIONS);
     argsman.AddArg("-rpcuser=<user>", "Username for JSON-RPC connections", ArgsManager::ALLOW_ANY, OptionsCategory::OPTIONS);
     argsman.AddArg("-rpcwait", "Wait for RPC server to start", ArgsManager::ALLOW_ANY, OptionsCategory::OPTIONS);
+    argsman.AddArg("-rpcwaittimeout=<n>", strprintf("Timeout in seconds to wait for the RPC server to start, or 0 for no timeout. (default: %d)", DEFAULT_WAIT_CLIENT_TIMEOUT), ArgsManager::ALLOW_INT, OptionsCategory::OPTIONS);
     argsman.AddArg("-rpcwallet=<walletname>", "Send RPC for non-default wallet on RPC server (needs to exactly match corresponding -wallet option passed to bitcoind). This changes the RPC endpoint used, e.g. http://127.0.0.1:8332/wallet/<walletname>", ArgsManager::ALLOW_ANY, OptionsCategory::OPTIONS);
     argsman.AddArg("-stdin", "Read extra arguments from standard input, one per line until EOF/Ctrl-D (recommended for sensitive information such as passphrases). When combined with -stdinrpcpass, the first line from standard input is used for the RPC password.", ArgsManager::ALLOW_ANY, OptionsCategory::OPTIONS);
     argsman.AddArg("-stdinrpcpass", "Read RPC password from standard input as a single line. When combined with -stdin, the first line from standard input is used for the RPC password. When combined with -stdinwalletpassphrase, -stdinrpcpass consumes the first line, and -stdinwalletpassphrase consumes the second.", ArgsManager::ALLOW_ANY, OptionsCategory::OPTIONS);
@@ -794,6 +796,9 @@ static UniValue ConnectAndCallRPC(BaseRequestHandler* rh, const std::string& str
     UniValue response(UniValue::VOBJ);
     // Execute and handle connection failures with -rpcwait.
     const bool fWait = gArgs.GetBoolArg("-rpcwait", false);
+    const int timeout = gArgs.GetArg("-rpcwaittimeout", DEFAULT_WAIT_CLIENT_TIMEOUT);
+    const int64_t deadline = GetTime<std::chrono::seconds>().count() + timeout;
+
     do {
         try {
             response = CallRPC(rh, strMethod, args, rpcwallet);
@@ -804,11 +809,12 @@ static UniValue ConnectAndCallRPC(BaseRequestHandler* rh, const std::string& str
                 }
             }
             break; // Connection succeeded, no need to retry.
-        } catch (const CConnectionFailed&) {
+        } catch (const CConnectionFailed& e) {
-            if (fWait) {
+            const int64_t now = GetTime<std::chrono::seconds>().count();
-                UninterruptibleSleep(std::chrono::milliseconds{1000});
+            if (fWait && (timeout <= 0 || now < deadline)) {
+                UninterruptibleSleep(std::chrono::seconds{1});
             } else {
-                throw;
+                throw CConnectionFailed(strprintf("timeout on transient error: %s", e.what()));
             }
         }
     } while (fWait);

test/functional/interface_bitcoin_cli.py

@@ -10,10 +10,12 @@ from test_framework.blocktools import COINBASE_MATURITY
 from test_framework.test_framework import BitcoinTestFramework
 from test_framework.util import (
     assert_equal,
+    assert_greater_than_or_equal,
     assert_raises_process_error,
     assert_raises_rpc_error,
     get_auth_cookie,
 )
+import time
 
 # The block reward of coinbaseoutput.nValue (50) BTC/block matures after
 # COINBASE_MATURITY (100) blocks. Therefore, after mining 101 blocks we expect
@@ -248,6 +250,12 @@ class TestBitcoinCli(BitcoinTestFramework):
         self.nodes[0].wait_for_rpc_connection()
         assert_equal(blocks, BLOCKS + 25)
 
+        self.log.info("Test -rpcwait option waits at most -rpcwaittimeout seconds for startup")
+        self.stop_node(0)  # stop the node so we time out
+        start_time = time.time()
+        assert_raises_process_error(1, "Could not connect to the server", self.nodes[0].cli('-rpcwait', '-rpcwaittimeout=5').echo)
+        assert_greater_than_or_equal(time.time(), start_time + 5)
+
 
 if __name__ == '__main__':
     TestBitcoinCli().main()