Merge bitcoin/bitcoin#23004: multiprocess: add interfaces::ExternalSigner class

a032fa30d282fa69c304e0afd1f95f67c55d22e3 multiprocess: add interfaces::ExternalSigner class (Russell Yanofsky)

Pull request description:

  Add `interfaces::ExternalSigner` class to let signer objects be passed between processes and let signer code run in the original process where the object was created.

  ---

  This PR is part of the [process separation project](https://github.com/bitcoin/bitcoin/projects/10).

ACKs for top commit:
  laanwj:
    Concept and code review ACK a032fa30d282fa69c304e0afd1f95f67c55d22e3
  hebasto:
    re-ACK a032fa30d282fa69c304e0afd1f95f67c55d22e3

Tree-SHA512: 99a729fb3a64d010e142cc778a9f1f358e58345b77faaf2664de7d2277715d59df3352326e8f0f2a6628038670eaa4556310a549079fb28af6d2eeb05aea1460

1 files changed, 18 insertions, 3 deletions

diff --git a/src/node/interfaces.cpp b/src/node/interfaces.cpp
index 192caf7994..9b4ba8eb97 100644
--- a/src/node/interfaces.cpp
+++ b/src/node/interfaces.cpp
@@ -67,6 +67,17 @@ using interfaces::WalletClient;
 
 namespace node {
 namespace {
+#ifdef ENABLE_EXTERNAL_SIGNER
+class ExternalSignerImpl : public interfaces::ExternalSigner
+{
+public:
+    ExternalSignerImpl(::ExternalSigner signer) : m_signer(std::move(signer)) {}
+    std::string getName() override { return m_signer.m_name; }
+private:
+    ::ExternalSigner m_signer;
+};
+#endif
+
 class NodeImpl : public Node
 {
 private:
@@ -172,14 +183,18 @@ public:
         }
         return false;
     }
-    std::vector<ExternalSigner> externalSigners() override
+    std::vector<std::unique_ptr<interfaces::ExternalSigner>> listExternalSigners() override
     {
 #ifdef ENABLE_EXTERNAL_SIGNER
         std::vector<ExternalSigner> signers = {};
         const std::string command = gArgs.GetArg("-signer", "");
-        if (command == "") return signers;
+        if (command == "") return {};
         ExternalSigner::Enumerate(command, signers, Params().NetworkIDString());
-        return signers;
+        std::vector<std::unique_ptr<interfaces::ExternalSigner>> result;
+        for (auto& signer : signers) {
+            result.emplace_back(std::make_unique<ExternalSignerImpl>(std::move(signer)));
+        }
+        return result;
 #else
         // This result is indistinguishable from a successful call that returns
         // no signers. For the current GUI this doesn't matter, because the wallet