Merge bitcoin#22789: external_signer: improve fingerprint matching logic (stop on first match)

d047ed7 external_signer: improve fingerprint matching logic (stop on first match) (Sebastian Falbesoner)

Pull request description:

  The fingerprint matching logic in `ExternalSigner::SignTransaction` currently always iterates all inputs of a PSBT, even after a match has already been found. I guess the reason for that is not that it was not thought of, but rather the fact that breaking out of a nested loop is simply not possible (at least not without adding ugly constructs like gotos or extra state variables).
  This PR fixes this by using `std::any_of` from C++'s standard library, see http://www.cplusplus.com/reference/algorithm/any_of/

ACKs for top commit:
  lsilva01:
    Code Review ACK bitcoin@d047ed7
  Sjors:
    utACK d047ed7
  Zero-1729:
    crACK d047ed7
  mjdietzx:
    Code review ACK d047ed7
  hebasto:
    ACK d047ed7, I have reviewed the code and it looks OK, I agree it can be merged.

Tree-SHA512: 447e7c0c6a5b5549a2c09d52e55ba4146302c1a06e4d96de11f6945d09f98c89129cba221202dff7e0718e01a83dd173b9f19b1f02b6be228978f3f6e35d8096

Author: laanwj

src/external_signer.cpp

@@ -9,6 +9,7 @@
 #include <util/system.h>
 #include <external_signer.h>
 
+#include <algorithm>
 #include <stdexcept>
 #include <string>
 #include <vector>
@@ -75,15 +76,14 @@ bool ExternalSigner::SignTransaction(PartiallySignedTransaction& psbtx, std::str
     ssTx << psbtx;
 
     // Check if signer fingerprint matches any input master key fingerprint
-    bool match = false;
-    for (unsigned int i = 0; i < psbtx.inputs.size(); ++i) {
-        const PSBTInput& input = psbtx.inputs[i];
+    auto matches_signer_fingerprint = [&](const PSBTInput& input) {
         for (const auto& entry : input.hd_keypaths) {
-            if (m_fingerprint == strprintf("%08x", ReadBE32(entry.second.fingerprint))) match = true;
+            if (m_fingerprint == strprintf("%08x", ReadBE32(entry.second.fingerprint))) return true;
         }
-    }
+        return false;
+    };
 
-    if (!match) {
+    if (!std::any_of(psbtx.inputs.begin(), psbtx.inputs.end(), matches_signer_fingerprint)) {
         error = "Signer fingerprint " + m_fingerprint + " does not match any of the inputs:\n" + EncodeBase64(ssTx.str());
         return false;
     }