command/Partition: add command "partition" to switch to another partition

doc/protocol.xml

@@ -2368,6 +2368,20 @@ OK
       </para>
 
       <variablelist>
+        <varlistentry id="command_partition">
+          <term>
+            <cmdsynopsis>
+              <command>partition</command>
+              <arg choice="req"><replaceable>NAME</replaceable></arg>
+            </cmdsynopsis>
+          </term>
+          <listitem>
+            <para>
+              Switch the client to a different partition.
+            </para>
+          </listitem>
+        </varlistentry>
+
         <varlistentry id="command_listpartitions">
           <term>
             <cmdsynopsis>

src/command/AllCommands.cxx

@@ -137,6 +137,7 @@ static constexpr struct command commands[] = {
 	{ "next", PERMISSION_CONTROL, 0, 0, handle_next },
 	{ "notcommands", PERMISSION_NONE, 0, 0, handle_not_commands },
 	{ "outputs", PERMISSION_READ, 0, 0, handle_devices },
+	{ "partition", PERMISSION_READ, 1, 1, handle_partition },
 	{ "password", PERMISSION_NONE, 1, 1, handle_password },
 	{ "pause", PERMISSION_CONTROL, 0, 1, handle_pause },
 	{ "ping", PERMISSION_NONE, 0, 0, handle_ping },

src/command/PartitionCommands.cxx

@@ -29,6 +29,21 @@
 #include "util/CharUtil.hxx"
 
 CommandResult
+handle_partition(Client &client, Request request, Response &response)
+{
+	const char *name = request.front();
+	auto &instance = client.GetInstance();
+	auto *partition = instance.FindPartition(name);
+	if (partition == nullptr) {
+		response.Error(ACK_ERROR_NO_EXIST, "partition does not exist");
+		return CommandResult::ERROR;
+	}
+
+	client.SetPartition(*partition);
+	return CommandResult::OK;
+}
+
+CommandResult
 handle_listpartitions(Client &client, Request, Response &r)
 {
 	for (const auto &partition : client.GetInstance().partitions) {

src/command/PartitionCommands.hxx

@@ -27,6 +27,9 @@ class Request;
 class Response;
 
 CommandResult
+handle_partition(Client &client, Request request, Response &response);
+
+CommandResult
 handle_listpartitions(Client &client, Request request, Response &response);
 
 CommandResult