configuration: Add utility functions to backup/restore config.

Signed-off-by: Mathieu Borderé <[email protected]>

src/configuration.c

@@ -349,4 +349,43 @@ void configurationTrace(const struct raft *r, struct raft_configuration *c, cons
     }
     tracef("=== CONFIG END ===");
 }
+
+int configurationBackupCurrent(struct raft *r)
+{
+    int rv;
+    struct raft_configuration current;
+
+    /* Copy the configuration to an intermediate configuration because the copy
+     * can fail and we don't want to be left without the previous configuration. */
+    configurationInit(&current);
+    rv = configurationCopy(&r->configuration, &current);
+    if (rv != 0) {
+        return rv;
+    }
+    configurationClose(&r->configuration_previous);
+    r->configuration_previous = current;
+    return 0;
+}
+
+int configurationRestorePrevious(struct raft *r)
+{
+    int rv;
+    struct raft_configuration prev;
+
+    if (r->configuration_previous.n == 0) {
+        tracef("There is no previous configuration.");
+        return RAFT_INVALID;
+    }
+
+    /* Copy the configuration to an intermediate configuration because the copy
+     * can fail and we don't want to be left without a configuration. */
+    configurationInit(&prev);
+    rv = configurationCopy(&r->configuration_previous, &prev);
+    if (rv != 0) {
+        return rv;
+    }
+    configurationClose(&r->configuration);
+    r->configuration = prev;
+    return 0;
+}
 #undef tracef

src/configuration.h

@@ -63,4 +63,11 @@ int configurationDecode(const struct raft_buffer *buf,
 
 /* Output the configuration to the raft tracer */
 void configurationTrace(const struct raft *r, struct raft_configuration *c, const char *msg);
+
+/* Replaces the previous configuration with a copy of the current configuration */
+int configurationBackupCurrent(struct raft *r);
+
+/* Replaces the current configuration with a copy of the previous configuration. */
+int configurationRestorePrevious(struct raft *r);
+
 #endif /* CONFIGURATION_H_ */