wallet: Add MakeDatabase function

New function is not currently called but will be called in upcoming commits. It
moves database path checking, and existence checking, and already-loaded
checking, and verification into a single function so this logic does not need
to be repeated all over higher level wallet code, and so higher level code does
not need to change when SQLite support is added in
https://github.com/bitcoin/bitcoin/pull/19077. This also lets higher level
wallet code make fewer assumptions about the contents of wallet directories.

This commit just adds the new function and does not change behavior in any way.

src/wallet/bdb.cpp

@@ -824,3 +824,35 @@ std::unique_ptr<DatabaseBatch> BerkeleyDatabase::MakeBatch(const char* mode, boo
 {
     return MakeUnique<BerkeleyBatch>(*this, mode, flush_on_close);
 }
+
+bool ExistsBerkeleyDatabase(const fs::path& path)
+{
+    fs::path env_directory;
+    std::string data_filename;
+    SplitWalletPath(path, env_directory, data_filename);
+    return IsBerkeleyBtree(env_directory / data_filename);
+}
+
+std::unique_ptr<BerkeleyDatabase> MakeBerkeleyDatabase(const fs::path& path, const DatabaseOptions& options, DatabaseStatus& status, bilingual_str& error)
+{
+    std::unique_ptr<BerkeleyDatabase> db;
+    {
+        LOCK(cs_db); // Lock env.m_databases until insert in BerkeleyDatabase constructor
+        std::string data_filename;
+        std::shared_ptr<BerkeleyEnvironment> env = GetWalletEnv(path, data_filename);
+        if (env->m_databases.count(data_filename)) {
+            error = Untranslated(strprintf("Refusing to load database. Data file '%s' is already loaded.", (env->Directory() / data_filename).string()));
+            status = DatabaseStatus::FAILED_ALREADY_LOADED;
+            return nullptr;
+        }
+        db = MakeUnique<BerkeleyDatabase>(std::move(env), std::move(data_filename));
+    }
+
+    if (options.verify && !db->Verify(error)) {
+        status = DatabaseStatus::FAILED_VERIFY;
+        return nullptr;
+    }
+
+    status = DatabaseStatus::SUCCESS;
+    return db;
+}

src/wallet/bdb.h

@@ -90,6 +90,9 @@ std::shared_ptr<BerkeleyEnvironment> GetWalletEnv(const fs::path& wallet_path, s
 /** Return whether a BDB wallet database is currently loaded. */
 bool IsBDBWalletLoaded(const fs::path& wallet_path);
 
+/** Check format of database file */
+bool IsBerkeleyBtree(const fs::path& path);
+
 class BerkeleyBatch;
 
 /** An instance of this class represents one database.
@@ -224,4 +227,10 @@ public:
 
 std::string BerkeleyDatabaseVersion();
 
+//! Check if Berkeley database exists at specified path.
+bool ExistsBerkeleyDatabase(const fs::path& path);
+
+//! Return object giving access to Berkeley database at specified path.
+std::unique_ptr<BerkeleyDatabase> MakeBerkeleyDatabase(const fs::path& path, const DatabaseOptions& options, DatabaseStatus& status, bilingual_str& error);
+
 #endif // BITCOIN_WALLET_BDB_H

src/wallet/db.h

@@ -195,4 +195,26 @@ public:
     std::unique_ptr<DatabaseBatch> MakeBatch(const char* mode = "r+", bool flush_on_close = true) override { return MakeUnique<DummyBatch>(); }
 };
 
+enum class DatabaseFormat {
+    BERKELEY,
+};
+
+struct DatabaseOptions {
+    bool require_existing = false;
+    bool require_create = false;
+    bool verify = true;
+};
+
+enum class DatabaseStatus {
+    SUCCESS,
+    FAILED_BAD_PATH,
+    FAILED_BAD_FORMAT,
+    FAILED_ALREADY_LOADED,
+    FAILED_ALREADY_EXISTS,
+    FAILED_NOT_FOUND,
+    FAILED_VERIFY,
+};
+
+std::unique_ptr<WalletDatabase> MakeDatabase(const fs::path& path, const DatabaseOptions& options, DatabaseStatus& status, bilingual_str& error);
+
 #endif // BITCOIN_WALLET_DB_H

src/wallet/walletdb.cpp

@@ -13,6 +13,8 @@
 #include <util/bip32.h>
 #include <util/system.h>
 #include <util/time.h>
+#include <util/translation.h>
+#include <wallet/bdb.h>
 #include <wallet/wallet.h>
 
 #include <atomic>
@@ -993,6 +995,43 @@ bool WalletBatch::TxnAbort()
     return m_batch->TxnAbort();
 }
 
+std::unique_ptr<WalletDatabase> MakeDatabase(const fs::path& path, const DatabaseOptions& options, DatabaseStatus& status, bilingual_str& error)
+{
+    bool exists;
+    try {
+        exists = fs::symlink_status(path).type() != fs::file_not_found;
+    } catch (const fs::filesystem_error& e) {
+        error = Untranslated(strprintf("Failed to access database path '%s': %s", path.string(), fsbridge::get_filesystem_error_message(e)));
+        status = DatabaseStatus::FAILED_BAD_PATH;
+        return nullptr;
+    }
+
+    Optional<DatabaseFormat> format;
+    if (exists) {
+        if (ExistsBerkeleyDatabase(path)) {
+            format = DatabaseFormat::BERKELEY;
+        }
+    } else if (options.require_existing) {
+        error = Untranslated(strprintf("Failed to load database path '%s'. Path does not exist.", path.string()));
+        status = DatabaseStatus::FAILED_NOT_FOUND;
+        return nullptr;
+    }
+
+    if (!format && options.require_existing) {
+        error = Untranslated(strprintf("Failed to load database path '%s'. Data is not in recognized format.", path.string()));
+        status = DatabaseStatus::FAILED_BAD_FORMAT;
+        return nullptr;
+    }
+
+    if (format && options.require_create) {
+        error = Untranslated(strprintf("Failed to create database path '%s'. Database already exists.", path.string()));
+        status = DatabaseStatus::FAILED_ALREADY_EXISTS;
+        return nullptr;
+    }
+
+    return MakeBerkeleyDatabase(path, options, status, error);
+}
+
 bool IsWalletLoaded(const fs::path& wallet_path)
 {
     return IsBDBWalletLoaded(wallet_path);

src/wallet/walletutil.cpp

@@ -29,7 +29,7 @@ fs::path GetWalletDir()
     return path;
 }
 
-static bool IsBerkeleyBtree(const fs::path& path)
+bool IsBerkeleyBtree(const fs::path& path)
 {
     if (!fs::exists(path)) return false;