wallet: Add ListWalletDir utility

ListWalletDir returns all available wallets in the current wallet directory.

Based on MeshCollider work in pull bitcoin#11485.

src/wallet/walletutil.cpp

@@ -4,6 +4,8 @@
 
 #include <wallet/walletutil.h>
 
+#include <util.h>
+
 fs::path GetWalletDir()
 {
     fs::path path;
@@ -25,3 +27,51 @@ fs::path GetWalletDir()
 
     return path;
 }
+
+static bool IsBerkeleyBtree(const fs::path& path)
+{
+    // A Berkeley DB Btree file has at least 4K.
+    // This check also prevents opening lock files.
+    boost::system::error_code ec;
+    if (fs::file_size(path, ec) < 4096) return false;
+
+    fs::ifstream file(path.string(), std::ios::binary);
+    if (!file.is_open()) return false;
+
+    file.seekg(12, std::ios::beg); // Magic bytes start at offset 12
+    uint32_t data = 0;
+    file.read((char*) &data, sizeof(data)); // Read 4 bytes of file to compare against magic
+
+    // Berkeley DB Btree magic bytes, from:
+    //  https://github.com/file/file/blob/5824af38469ec1ca9ac3ffd251e7afe9dc11e227/magic/Magdir/database#L74-L75
+    //  - big endian systems - 00 05 31 62
+    //  - little endian systems - 62 31 05 00
+    return data == 0x00053162 || data == 0x62310500;
+}
+
+std::vector<fs::path> ListWalletDir()
+{
+    const fs::path wallet_dir = GetWalletDir();
+    std::vector<fs::path> paths;
+
+    for (auto it = fs::recursive_directory_iterator(wallet_dir); it != end(it); ++it) {
+        if (it->status().type() == fs::directory_file && IsBerkeleyBtree(it->path() / "wallet.dat")) {
+            // Found a directory which contains wallet.dat btree file, add it as a wallet.
+            paths.emplace_back(fs::relative(it->path(), wallet_dir));
+        } else if (it.level() == 0 && it->symlink_status().type() == fs::regular_file && IsBerkeleyBtree(it->path())) {
+            if (it->path().filename() == "wallet.dat") {
+                // Found top-level wallet.dat btree file, add top level directory ""
+                // as a wallet.
+                paths.emplace_back();
+            } else {
+                // Found top-level btree file not called wallet.dat. Current bitcoin
+                // software will never create these files but will allow them to be
+                // opened in a shared database environment for backwards compatibility.
+                // Add it to the list of available wallets.
+                paths.emplace_back(fs::relative(it->path(), wallet_dir));
+            }
+        }
+    }
+
+    return paths;
+}

src/wallet/walletutil.h

@@ -5,10 +5,14 @@
 #ifndef BITCOIN_WALLET_WALLETUTIL_H
 #define BITCOIN_WALLET_WALLETUTIL_H
 
-#include <chainparamsbase.h>
-#include <util.h>
+#include <fs.h>
+
+#include <vector>
 
 //! Get the path of the wallet directory.
 fs::path GetWalletDir();
 
+//! Get wallets in wallet directory.
+std::vector<fs::path> ListWalletDir();
+
 #endif // BITCOIN_WALLET_WALLETUTIL_H