[PATCH 2/5] lib: API to retrieve database revision and UUID

[David Bremner <david@tethera.net>]

From: Austin Clements <aclements@csail.mit.edu>

This exposes the committed database revision to library users along
with a UUID that can be used to detect when revision numbers are no
longer comparable (e.g., because the database has been replaced).
---
 lib/database-private.h         |  1 +
 lib/database.cc                | 11 +++++++++++
 lib/notmuch.h                  | 18 ++++++++++++++++++
 test/T570-revision-tracking.sh | 37 +++++++++++++++++++++++++++++++++++++
 test/test-lib.sh               |  5 +++++
 5 files changed, 72 insertions(+)
 create mode 100755 test/T570-revision-tracking.sh

diff --git a/lib/database-private.h b/lib/database-private.h
index 5c5a2bb..4e93257 100644
--- a/lib/database-private.h
+++ b/lib/database-private.h
@@ -170,6 +170,7 @@ struct _notmuch_database {
      * under a higher revision number, which can be generated with
      * notmuch_database_new_revision. */
     unsigned long revision;
+    const char *uuid;
 
     Xapian::QueryParser *query_parser;
     Xapian::TermGenerator *term_gen;
diff --git a/lib/database.cc b/lib/database.cc
index 52e2e8f..fc78769 100644
--- a/lib/database.cc
+++ b/lib/database.cc
@@ -992,6 +992,8 @@ notmuch_database_open_verbose (const char *path,
 	    notmuch->revision = 0;
 	else
 	    notmuch->revision = Xapian::sortable_unserialise (last_mod);
+	notmuch->uuid = talloc_strdup (
+	    notmuch, notmuch->xapian_db->get_uuid ().c_str ());
 
 	notmuch->query_parser = new Xapian::QueryParser;
 	notmuch->term_gen = new Xapian::TermGenerator;
@@ -1666,6 +1668,15 @@ DONE:
     return NOTMUCH_STATUS_SUCCESS;
 }
 
+unsigned long
+notmuch_database_get_revision (notmuch_database_t *notmuch,
+				const char **uuid)
+{
+    if (uuid)
+	*uuid = notmuch->uuid;
+    return notmuch->revision;
+}
+
 /* We allow the user to use arbitrarily long paths for directories. But
  * we have a term-length limit. So if we exceed that, we'll use the
  * SHA-1 of the path for the database term.
diff --git a/lib/notmuch.h b/lib/notmuch.h
index 421c19d..a7ac012 100644
--- a/lib/notmuch.h
+++ b/lib/notmuch.h
@@ -468,6 +468,24 @@ notmuch_status_t
 notmuch_database_end_atomic (notmuch_database_t *notmuch);
 
 /**
+ * Return the committed database revision and UUID.
+ *
+ * The database revision number increases monotonically with each
+ * commit to the database.  Hence, all messages and message changes
+ * committed to the database (that is, visible to readers) have a last
+ * modification revision <= the committed database revision.  Any
+ * messages committed in the future will be assigned a modification
+ * revision > the committed database revision.
+ *
+ * The UUID is a NUL-terminated opaque string that uniquely identifies
+ * this database.  Two revision numbers are only comparable if they
+ * have the same database UUID.
+ */
+unsigned long
+notmuch_database_get_revision (notmuch_database_t *notmuch,
+				const char **uuid);
+
+/**
  * Retrieve a directory object from the database for 'path'.
  *
  * Here, 'path' should be a path relative to the path of 'database'
diff --git a/test/T570-revision-tracking.sh b/test/T570-revision-tracking.sh
new file mode 100755
index 0000000..e0a5703
--- /dev/null
+++ b/test/T570-revision-tracking.sh
@@ -0,0 +1,37 @@
+#!/usr/bin/env bash
+test_description="database revision tracking"
+
+. ./test-lib.sh || exit 1
+
+add_email_corpus
+
+test_begin_subtest "notmuch_database_get_revision"
+test_C ${MAIL_DIR} <<'EOF'
+#include <stdio.h>
+#include <string.h>
+#include <notmuch.h>
+int main (int argc, char** argv)
+{
+   notmuch_database_t *db;
+   notmuch_status_t stat;
+   unsigned long revision;
+   const char *uuid;
+
+   unsigned long rev;
+
+   stat = notmuch_database_open (argv[1], NOTMUCH_DATABASE_MODE_READ_ONLY, &db);
+   if (stat)
+       fputs ("open failed\n", stderr);
+   revision = notmuch_database_get_revision (db, &uuid);
+   printf("%s\t%lu\n", uuid, revision);
+}
+EOF
+notmuch_uuid_sanitize < OUTPUT > CLEAN
+cat <<'EOF' >EXPECTED
+== stdout ==
+UUID	53
+== stderr ==
+EOF
+test_expect_equal_file EXPECTED CLEAN
+
+test_done
diff --git a/test/test-lib.sh b/test/test-lib.sh
index 0bf7163..126911f 100644
--- a/test/test-lib.sh
+++ b/test/test-lib.sh
@@ -720,6 +720,11 @@ notmuch_date_sanitize ()
     sed \
 	-e 's/^Date: Fri, 05 Jan 2001 .*0000/Date: GENERATED_DATE/'
 }
+
+notmuch_uuid_sanitize ()
+{
+    sed 's/[0-9a-f]\{8\}-[0-9a-f]\{4\}-[0-9a-f]\{4\}-[0-9a-f]\{4\}-[0-9a-f]\{12\}/UUID/g'
+}
 # End of notmuch helper functions
 
 # Use test_set_prereq to tell that a particular prerequisite is available.
-- 
2.1.4