Better error messages for invalid addresses

This commit addresses #20809.

We add an additional 'error' property in the result of 'validateaddress' in case the address is not valid that gives a short description of why the address in invalid. We also change the error message returned by 'getaddressinfo' in case the address is invalid.

src/key_io.cpp

@@ -12,6 +12,9 @@
 #include <assert.h>
 #include <string.h>
 
+/// Maximum witness length for Bech32 addresses.
+static constexpr std::size_t BECH32_WITNESS_PROG_MAX_LEN = 40;
+
 namespace {
 class DestinationEncoder
 {
@@ -65,10 +68,11 @@ public:
     std::string operator()(const CNoDestination& no) const { return {}; }
 };
 
-CTxDestination DecodeDestination(const std::string& str, const CChainParams& params)
+CTxDestination DecodeDestination(const std::string& str, const CChainParams& params, std::string& error_str)
 {
     std::vector<unsigned char> data;
     uint160 hash;
+    error_str = "";
     if (DecodeBase58Check(str, data, 21)) {
         // base58-encoded Bitcoin addresses.
         // Public-key-hash-addresses have version 0 (or 111 testnet).
@@ -85,10 +89,21 @@ CTxDestination DecodeDestination(const std::string& str, const CChainParams& par
             std::copy(data.begin() + script_prefix.size(), data.end(), hash.begin());
             return ScriptHash(hash);
         }
+
+        // Set potential error message.
+        // This message may be changed if the address can also be interpreted as a Bech32 address.
+        error_str = "Invalid prefix for Base58-encoded address";
     }
     data.clear();
     auto bech = bech32::Decode(str);
-    if (bech.second.size() > 0 && bech.first == params.Bech32HRP()) {
+    if (bech.second.size() > 0) {
+        error_str = "";
+
+        if (bech.first != params.Bech32HRP()) {
+            error_str = "Invalid prefix for Bech32 address";
+            return CNoDestination();
+        }
+
         // Bech32 decoding
         int version = bech.second[0]; // The first 5 bit symbol is the witness version (0-16)
         // The rest of the symbols are converted witness program bytes.
@@ -109,11 +124,21 @@ CTxDestination DecodeDestination(const std::string& str, const CChainParams& par
                         return scriptid;
                     }
                 }
+
+                error_str = "Invalid Bech32 v0 address data size";
                 return CNoDestination();
             }
-            if (version > 16 || data.size() < 2 || data.size() > 40) {
+
+            if (version > 16) {
+                error_str = "Invalid Bech32 address witness version";
                 return CNoDestination();
             }
+
+            if (data.size() < 2 || data.size() > BECH32_WITNESS_PROG_MAX_LEN) {
+                error_str = "Invalid Bech32 address data size";
+                return CNoDestination();
+            }
+
             WitnessUnknown unk;
             unk.version = version;
             std::copy(data.begin(), data.end(), unk.program);
@@ -121,6 +146,10 @@ CTxDestination DecodeDestination(const std::string& str, const CChainParams& par
             return unk;
         }
     }
+
+    // Set error message if address can't be interpreted as Base58 or Bech32.
+    if (error_str.empty()) error_str = "Invalid address format";
+
     return CNoDestination();
 }
 } // namespace
@@ -208,14 +237,21 @@ std::string EncodeDestination(const CTxDestination& dest)
     return std::visit(DestinationEncoder(Params()), dest);
 }
 
+CTxDestination DecodeDestination(const std::string& str, std::string& error_msg)
+{
+    return DecodeDestination(str, Params(), error_msg);
+}
+
 CTxDestination DecodeDestination(const std::string& str)
 {
-    return DecodeDestination(str, Params());
+    std::string error_msg;
+    return DecodeDestination(str, error_msg);
 }
 
 bool IsValidDestinationString(const std::string& str, const CChainParams& params)
 {
-    return IsValidDestination(DecodeDestination(str, params));
+    std::string error_msg;
+    return IsValidDestination(DecodeDestination(str, params, error_msg));
 }
 
 bool IsValidDestinationString(const std::string& str)