transport: make transport vtable more private

Move the definition of the transport-specific functions provided by
transports, whether declared in transport.c or transport-helper.c, into
an internal header. This means that transport-using code (as opposed to
transport-declaring code) can no longer access these functions (without
importing the internal header themselves), making it clear that they
should use the transport_*() functions instead, and also allowing the
interface between the transport mechanism and an individual transport to
independently evolve.

This is superficially a reversal of commit 824d5776c3f2 ("Refactor
struct transport_ops inlined into struct transport", 2007-09-19).
However, the scope of the involved variables was neither affected nor
discussed in that commit, and I think that the advantages in making
those functions more private outweigh the advantages described in that
commit's commit message. A minor additional point is that the code has
gotten more complicated since then, in that the function-pointer
variables are potentially mutated twice (once initially and once if
transport_take_over() is invoked), increasing the value of corralling
them into their own struct.

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

1 files changed, 61 insertions, 0 deletions

diff --git a/transport-internal.h b/transport-internal.h
new file mode 100644
index 0000000000..3c1a29d727
--- /dev/null
+++ b/transport-internal.h
@@ -0,0 +1,61 @@
+#ifndef TRANSPORT_INTERNAL_H
+#define TRANSPORT_INTERNAL_H
+
+struct ref;
+struct transport;
+
+struct transport_vtable {
+	/**
+	 * Returns 0 if successful, positive if the option is not
+	 * recognized or is inapplicable, and negative if the option
+	 * is applicable but the value is invalid.
+	 **/
+	int (*set_option)(struct transport *connection, const char *name,
+			  const char *value);
+	/**
+	 * Returns a list of the remote side's refs. In order to allow
+	 * the transport to try to share connections, for_push is a
+	 * hint as to whether the ultimate operation is a push or a fetch.
+	 *
+	 * If the transport is able to determine the remote hash for
+	 * the ref without a huge amount of effort, it should store it
+	 * in the ref's old_sha1 field; otherwise it should be all 0.
+	 **/
+	struct ref *(*get_refs_list)(struct transport *transport, int for_push);
+
+	/**
+	 * Fetch the objects for the given refs. Note that this gets
+	 * an array, and should ignore the list structure.
+	 *
+	 * If the transport did not get hashes for refs in
+	 * get_refs_list(), it should set the old_sha1 fields in the
+	 * provided refs now.
+	 **/
+	int (*fetch)(struct transport *transport, int refs_nr, struct ref **refs);
+
+	/**
+	 * Push the objects and refs. Send the necessary objects, and
+	 * then, for any refs where peer_ref is set and
+	 * peer_ref->new_oid is different from old_oid, tell the
+	 * remote side to update each ref in the list from old_oid to
+	 * peer_ref->new_oid.
+	 *
+	 * Where possible, set the status for each ref appropriately.
+	 *
+	 * The transport must modify new_sha1 in the ref to the new
+	 * value if the remote accepted the change. Note that this
+	 * could be a different value from peer_ref->new_oid if the
+	 * process involved generating new commits.
+	 **/
+	int (*push_refs)(struct transport *transport, struct ref *refs, int flags);
+	int (*connect)(struct transport *connection, const char *name,
+		       const char *executable, int fd[2]);
+
+	/** get_refs_list(), fetch(), and push_refs() can keep
+	 * resources (such as a connection) reserved for further
+	 * use. disconnect() releases these resources.
+	 **/
+	int (*disconnect)(struct transport *connection);
+};
+
+#endif