Move /src to /subprojects

This will facilitate breaking up Nix into multiple packages for each
component with Meson.

subprojects/libstore/common-ssh-store-config.hh

@@ -0,0 +1,62 @@
+#pragma once
+///@file
+
+#include "store-api.hh"
+
+namespace nix {
+
+class SSHMaster;
+
+struct CommonSSHStoreConfig : virtual StoreConfig
+{
+    using StoreConfig::StoreConfig;
+
+    CommonSSHStoreConfig(std::string_view scheme, std::string_view host, const Params & params);
+
+    const Setting<Path> sshKey{this, "", "ssh-key",
+        "Path to the SSH private key used to authenticate to the remote machine."};
+
+    const Setting<std::string> sshPublicHostKey{this, "", "base64-ssh-public-host-key",
+        "The public host key of the remote machine."};
+
+    const Setting<bool> compress{this, false, "compress",
+        "Whether to enable SSH compression."};
+
+    const Setting<std::string> remoteStore{this, "", "remote-store",
+        R"(
+          [Store URL](@docroot@/store/types/index.md#store-url-format)
+          to be used on the remote machine. The default is `auto`
+          (i.e. use the Nix daemon or `/nix/store` directly).
+        )"};
+
+    /**
+     * The `parseURL` function supports both IPv6 URIs as defined in
+     * RFC2732, but also pure addresses. The latter one is needed here to
+     * connect to a remote store via SSH (it's possible to do e.g. `ssh root@::1`).
+     *
+     * When initialized, the following adjustments are made:
+     *
+     * - If the URL looks like `root@[::1]` (which is allowed by the URL parser and probably
+     *   needed to pass further flags), it
+     *   will be transformed into `root@::1` for SSH (same for `[::1]` -> `::1`).
+     *
+     * - If the URL looks like `root@::1` it will be left as-is.
+     *
+     * - In any other case, the string will be left as-is.
+     *
+     * Will throw an error if `connStr` is empty too.
+     */
+    std::string host;
+
+    /**
+     * Small wrapper around `SSHMaster::SSHMaster` that gets most
+     * arguments from this configuration.
+     *
+     * See that constructor for details on the remaining two arguments.
+     */
+    SSHMaster createSSHMaster(
+        bool useMaster,
+        Descriptor logFD = INVALID_DESCRIPTOR);
+};
+
+}