Add a "Consensus diff manager" module.

This module's job is to remember old consensus documents, to
calculate their diffs on demand, and to .

There are some incomplete points in this code; I've marked them with
"XXXX". I intend to fix them in separate commits, since I believe
doing it in separate commits will make the branch easier to review.

1 files changed, 38 insertions, 0 deletions

diff --git a/src/or/consdiffmgr.h b/src/or/consdiffmgr.h
new file mode 100644
index 0000000000..860e055bb5
--- /dev/null
+++ b/src/or/consdiffmgr.h
@@ -0,0 +1,38 @@
+/* Copyright (c) 2017, The Tor Project, Inc. */
+/* See LICENSE for licensing information */
+
+#ifndef TOR_CONSDIFFMGR_H
+#define TOR_CONSDIFFMGR_H
+
+/**
+ * Possible outcomes from trying to look up a given consensus diff.
+ */
+typedef enum consdiff_status_t {
+  CONSDIFF_AVAILABLE,
+  CONSDIFF_NOT_FOUND,
+  CONSDIFF_IN_PROGRESS,
+} consdiff_status_t;
+
+typedef struct consdiff_cfg_t {
+  uint32_t cache_max_age_hours;
+  uint32_t cache_max_num;
+} consdiff_cfg_t;
+
+struct consensus_cache_entry_t; // from conscache.h
+
+int consdiffmgr_add_consensus(const char *consensus,
+                              const networkstatus_t *as_parsed);
+
+consdiff_status_t consdiffmgr_find_diff_from(
+                           struct consensus_cache_entry_t **entry_out,
+                           consensus_flavor_t flavor,
+                           int digest_type,
+                           const uint8_t *digest,
+                           size_t digestlen);
+void consdiffmgr_rescan(void);
+int consdiffmgr_cleanup(void);
+void consdiffmgr_configure(const consdiff_cfg_t *cfg);
+void consdiffmgr_free_all(void);
+
+#endif
+