Add fail over utility functions

These functions should be used by providers to centrally manage lists of
servers. Servers are grouped into services and each service has it's own
list of servers. If, however, you will try to add a same server into two
different services, they will share a common structure. This means that
a host will only be resolved once.

1 files changed, 106 insertions, 0 deletions

diff --git a/server/providers/fail_over.h b/server/providers/fail_over.h
new file mode 100644
index 000000000..b6e2f2f7b
--- /dev/null
+++ b/server/providers/fail_over.h
@@ -0,0 +1,106 @@
+#ifndef __FAIL_OVER_H__
+#define __FAIL_OVER_H__
+
+#include <stdbool.h>
+#include <talloc.h>
+
+/* Some forward declarations that don't have to do anything with fail over. */
+struct hostent;
+struct resolv_ctx;
+struct tevent_context;
+struct tevent_req;
+
+enum port_status {
+    PORT_NEUTRAL,    /* We didn't try this port yet. */
+    PORT_WORKING,    /* This port was reported to work. */
+    PORT_NOT_WORKING /* This port was reported to not work. */
+};
+
+enum server_status {
+    SERVER_NAME_NOT_RESOLVED, /* We didn't yet resolved the host name. */
+    SERVER_RESOLVING_NAME,    /* Name resolving is in progress. */
+    SERVER_NAME_RESOLVED,     /* We resolved the host name but didn't try to connect. */
+    SERVER_WORKING,           /* We successfully connected to the server. */
+    SERVER_NOT_WORKING        /* We tried and failed to connect to the server. */
+};
+
+struct fo_ctx;
+struct fo_service;
+struct fo_server;
+
+/*
+ * Create a new fail over context. The 'retry_timeout' argument specifies the
+ * duration in seconds of how long a server or port will be considered
+ * non-working after being marked as such.
+ */
+struct fo_ctx *fo_context_init(TALLOC_CTX *mem_ctx,
+                               time_t retry_timeout);
+
+/*
+ * Create a new service structure for 'ctx', saving it to the location pointed
+ * to by '_service'. The needed memory will be allocated from 'ctx'.
+ * Service name will be set to 'name'.
+ */
+int fo_new_service(struct fo_ctx *ctx,
+                   const char *name,
+                   struct fo_service **_service);
+
+/*
+ * Look up service named 'name' from the 'ctx' service list. Target of
+ * '_service' will be set to the service if it was found.
+ */
+int fo_get_service(struct fo_ctx *ctx,
+                   const char *name,
+                   struct fo_service **_service);
+
+/*
+ * Adds a server 'name' to the 'service'. Port 'port' will be used for
+ * connection. If 'name' is NULL, no server resolution will be done.
+ */
+int fo_add_server(struct fo_service *service,
+                  const char *name,
+                  int port,
+                  void *user_data);
+
+/*
+ * Request the first server from the service's list of servers. It is only
+ * considered if it is not marked as not working (or the retry interval already
+ * passed). If the server address wasn't resolved yet, it will be done.
+ */
+struct tevent_req *fo_resolve_service_send(TALLOC_CTX *mem_ctx,
+                                           struct tevent_context *ev,
+                                           struct resolv_ctx *resolv,
+                                           struct fo_service *service);
+
+int fo_resolve_service_recv(struct tevent_req *req,
+                            struct fo_server **server);
+
+/*
+ * Set feedback about 'server'. Caller should use this to indicate a problem
+ * with the server itself, not only with the service on that server. This
+ * should be used, for example, when the IP address of the server can't be
+ * reached. This setting can affect other services as well, since they can
+ * share the same server.
+ */
+void fo_set_server_status(struct fo_server *server,
+                          enum server_status status);
+
+/*
+ * Set feedback about the port status. This function should be used when
+ * the server itself is working but the service is not. When status is set
+ * to PORT_WORKING, 'server' is also marked as an "active server" for it's
+ * service. When the next fo_resolve_service_send() function is called, this
+ * server will be preferred. This will hold as long as it is not marked as
+ * not-working.
+ */
+void fo_set_port_status(struct fo_server *server,
+                        enum port_status status);
+
+
+void *fo_get_server_user_data(struct fo_server *server);
+
+int fo_get_server_port(struct fo_server *server);
+
+struct hostent *fo_get_server_hostent(struct fo_server *server);
+
+#endif /* !__FAIL_OVER_H__ */