fetch-pack: introduce negotiator API

Introduce the new files fetch-negotiator.{h,c}, which contains an API
behind which the details of negotiation are abstracted. Currently, only
one algorithm is available: the existing one.

This patch is written to be easily reviewed: static functions are
moved verbatim from fetch-pack.c to negotiator/default.c, and it can be
seen that the lines replaced by negotiator->X() calls are present in the
X() functions respectively.

Signed-off-by: Jonathan Tan <jonathantanmy@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 57 insertions, 0 deletions

diff --git a/fetch-negotiator.h b/fetch-negotiator.h
new file mode 100644
index 0000000000..b1290aa9c6
--- /dev/null
+++ b/fetch-negotiator.h
@@ -0,0 +1,57 @@
+#ifndef FETCH_NEGOTIATOR
+#define FETCH_NEGOTIATOR
+
+struct commit;
+
+/*
+ * An object that supplies the information needed to negotiate the contents of
+ * the to-be-sent packfile during a fetch.
+ *
+ * To set up the negotiator, call fetch_negotiator_init(), then known_common()
+ * (0 or more times), then add_tip() (0 or more times).
+ *
+ * Then, when "have" lines are required, call next(). Call ack() to report what
+ * the server tells us.
+ *
+ * Once negotiation is done, call release(). The negotiator then cannot be used
+ * (unless reinitialized with fetch_negotiator_init()).
+ */
+struct fetch_negotiator {
+	/*
+	 * Before negotiation starts, indicate that the server is known to have
+	 * this commit.
+	 */
+	void (*known_common)(struct fetch_negotiator *, struct commit *);
+
+	/*
+	 * Once this function is invoked, known_common() cannot be invoked any
+	 * more.
+	 *
+	 * Indicate that this commit and all its ancestors are to be checked
+	 * for commonality with the server.
+	 */
+	void (*add_tip)(struct fetch_negotiator *, struct commit *);
+
+	/*
+	 * Once this function is invoked, known_common() and add_tip() cannot
+	 * be invoked any more.
+	 *
+	 * Return the next commit that the client should send as a "have" line.
+	 */
+	const struct object_id *(*next)(struct fetch_negotiator *);
+
+	/*
+	 * Inform the negotiator that the server has the given commit. This
+	 * method must only be called on commits returned by next().
+	 */
+	int (*ack)(struct fetch_negotiator *, struct commit *);
+
+	void (*release)(struct fetch_negotiator *);
+
+	/* internal use */
+	void *data;
+};
+
+void fetch_negotiator_init(struct fetch_negotiator *negotiator);
+
+#endif