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+#ifndef GIT_SIMPLE_IPC_H
+#define GIT_SIMPLE_IPC_H
+
+/*
+ * See Documentation/technical/api-simple-ipc.txt
+ */
+
+#ifdef SUPPORTS_SIMPLE_IPC
+#include "pkt-line.h"
+
+/*
+ * Simple IPC Client Side API.
+ */
+
+enum ipc_active_state {
+	/*
+	 * The pipe/socket exists and the daemon is waiting for connections.
+	 */
+	IPC_STATE__LISTENING = 0,
+
+	/*
+	 * The pipe/socket exists, but the daemon is not listening.
+	 * Perhaps it is very busy.
+	 * Perhaps the daemon died without deleting the path.
+	 * Perhaps it is shutting down and draining existing clients.
+	 * Perhaps it is dead, but other clients are lingering and
+	 * still holding a reference to the pathname.
+	 */
+	IPC_STATE__NOT_LISTENING,
+
+	/*
+	 * The requested pathname is bogus and no amount of retries
+	 * will fix that.
+	 */
+	IPC_STATE__INVALID_PATH,
+
+	/*
+	 * The requested pathname is not found.  This usually means
+	 * that there is no daemon present.
+	 */
+	IPC_STATE__PATH_NOT_FOUND,
+
+	IPC_STATE__OTHER_ERROR,
+};
+
+struct ipc_client_connect_options {
+	/*
+	 * Spin under timeout if the server is running but can't
+	 * accept our connection yet.  This should always be set
+	 * unless you just want to poke the server and see if it
+	 * is alive.
+	 */
+	unsigned int wait_if_busy:1;
+
+	/*
+	 * Spin under timeout if the pipe/socket is not yet present
+	 * on the file system.  This is useful if we just started
+	 * the service and need to wait for it to become ready.
+	 */
+	unsigned int wait_if_not_found:1;
+
+	/*
+	 * Disallow chdir() when creating a Unix domain socket.
+	 */
+	unsigned int uds_disallow_chdir:1;
+};
+
+#define IPC_CLIENT_CONNECT_OPTIONS_INIT { \
+	.wait_if_busy = 0, \
+	.wait_if_not_found = 0, \
+	.uds_disallow_chdir = 0, \
+}
+
+/*
+ * Determine if a server is listening on this named pipe or socket using
+ * platform-specific logic.  This might just probe the filesystem or it
+ * might make a trivial connection to the server using this pathname.
+ */
+enum ipc_active_state ipc_get_active_state(const char *path);
+
+struct ipc_client_connection {
+	int fd;
+};
+
+/*
+ * Try to connect to the daemon on the named pipe or socket.
+ *
+ * Returns IPC_STATE__LISTENING and a connection handle.
+ *
+ * Otherwise, returns info to help decide whether to retry or to
+ * spawn/respawn the server.
+ */
+enum ipc_active_state ipc_client_try_connect(
+	const char *path,
+	const struct ipc_client_connect_options *options,
+	struct ipc_client_connection **p_connection);
+
+void ipc_client_close_connection(struct ipc_client_connection *connection);
+
+/*
+ * Used by the client to synchronously send and receive a message with
+ * the server on the provided client connection.
+ *
+ * Returns 0 when successful.
+ *
+ * Calls error() and returns non-zero otherwise.
+ */
+int ipc_client_send_command_to_connection(
+	struct ipc_client_connection *connection,
+	const char *message, struct strbuf *answer);
+
+/*
+ * Used by the client to synchronously connect and send and receive a
+ * message to the server listening at the given path.
+ *
+ * Returns 0 when successful.
+ *
+ * Calls error() and returns non-zero otherwise.
+ */
+int ipc_client_send_command(const char *path,
+			    const struct ipc_client_connect_options *options,
+			    const char *message, struct strbuf *answer);
+
+/*
+ * Simple IPC Server Side API.
+ */
+
+struct ipc_server_reply_data;
+
+typedef int (ipc_server_reply_cb)(struct ipc_server_reply_data *,
+				  const char *response,
+				  size_t response_len);
+
+/*
+ * Prototype for an application-supplied callback to process incoming
+ * client IPC messages and compose a reply.  The `application_cb` should
+ * use the provided `reply_cb` and `reply_data` to send an IPC response
+ * back to the client.  The `reply_cb` callback can be called multiple
+ * times for chunking purposes.  A reply message is optional and may be
+ * omitted if not necessary for the application.
+ *
+ * The return value from the application callback is ignored.
+ * The value `SIMPLE_IPC_QUIT` can be used to shutdown the server.
+ */
+typedef int (ipc_server_application_cb)(void *application_data,
+					const char *request,
+					ipc_server_reply_cb *reply_cb,
+					struct ipc_server_reply_data *reply_data);
+
+#define SIMPLE_IPC_QUIT -2
+
+/*
+ * Opaque instance data to represent an IPC server instance.
+ */
+struct ipc_server_data;
+
+/*
+ * Control parameters for the IPC server instance.
+ * Use this to hide platform-specific settings.
+ */
+struct ipc_server_opts
+{
+	int nr_threads;
+
+	/*
+	 * Disallow chdir() when creating a Unix domain socket.
+	 */
+	unsigned int uds_disallow_chdir:1;
+};
+
+/*
+ * Start an IPC server instance in one or more background threads
+ * and return a handle to the pool.
+ *
+ * Returns 0 if the asynchronous server pool was started successfully.
+ * Returns -1 if not.
+ * Returns -2 if we could not startup because another server is using
+ * the socket or named pipe.
+ *
+ * When a client IPC message is received, the `application_cb` will be
+ * called (possibly on a random thread) to handle the message and
+ * optionally compose a reply message.
+ */
+int ipc_server_run_async(struct ipc_server_data **returned_server_data,
+			 const char *path, const struct ipc_server_opts *opts,
+			 ipc_server_application_cb *application_cb,
+			 void *application_data);
+
+/*
+ * Gently signal the IPC server pool to shutdown.  No new client
+ * connections will be accepted, but existing connections will be
+ * allowed to complete.
+ */
+int ipc_server_stop_async(struct ipc_server_data *server_data);
+
+/*
+ * Block the calling thread until all threads in the IPC server pool
+ * have completed and been joined.
+ */
+int ipc_server_await(struct ipc_server_data *server_data);
+
+/*
+ * Close and free all resource handles associated with the IPC server
+ * pool.
+ */
+void ipc_server_free(struct ipc_server_data *server_data);
+
+/*
+ * Run an IPC server instance and block the calling thread of the
+ * current process.  It does not return until the IPC server has
+ * either shutdown or had an unrecoverable error.
+ *
+ * The IPC server handles incoming IPC messages from client processes
+ * and may use one or more background threads as necessary.
+ *
+ * Returns 0 after the server has completed successfully.
+ * Returns -1 if the server cannot be started.
+ * Returns -2 if we could not startup because another server is using
+ * the socket or named pipe.
+ *
+ * When a client IPC message is received, the `application_cb` will be
+ * called (possibly on a random thread) to handle the message and
+ * optionally compose a reply message.
+ *
+ * Note that `ipc_server_run()` is a synchronous wrapper around the
+ * above asynchronous routines.  It effectively hides all of the
+ * server state and thread details from the caller and presents a
+ * simple synchronous interface.
+ */
+int ipc_server_run(const char *path, const struct ipc_server_opts *opts,
+		   ipc_server_application_cb *application_cb,
+		   void *application_data);
+
+#endif /* SUPPORTS_SIMPLE_IPC */
+#endif /* GIT_SIMPLE_IPC_H */