Add FUNCTION DUMP and RESTORE. (#9938)

Follow the conclusions to support Functions in redis cluster (#9899)

Added 2 new FUNCTION sub-commands:
1. `FUNCTION DUMP` - dump a binary payload representation of all the functions.
2. `FUNCTION RESTORE <PAYLOAD> [FLUSH|APPEND|REPLACE]` - give the binary payload extracted
   using `FUNCTION DUMP`, restore all the functions on the given payload. Restore policy can be given to
   control how to handle existing functions (default is APPEND):
   * FLUSH: delete all existing functions.
   * APPEND: appends the restored functions to the existing functions. On collision, abort.
   * REPLACE: appends the restored functions to the existing functions. On collision,
     replace the old function with the new function.

Modify `redis-cli --cluster add-node` to use `FUNCTION DUMP` to get existing functions from
one of the nodes in the cluster, and `FUNCTION RESTORE` to load the same set of functions
to the new node. `redis-cli` will execute this step before sending the `CLUSTER MEET` command
to the new node. If `FUNCTION DUMP` returns an error, assume the current Redis version do not
support functions and skip `FUNCTION RESTORE`. If `FUNCTION RESTORE` fails, abort and do not send
the `CLUSTER MEET` command. If the new node already contains functions (before the `FUNCTION RESTORE`
is sent), abort and do not add the node to the cluster. Test was added to verify
`redis-cli --cluster add-node` works as expected. 

1 files changed, 2 insertions, 0 deletions

diff --git a/src/rdb.h b/src/rdb.h
index 66496bcec..5942c4333 100644
--- a/src/rdb.h
+++ b/src/rdb.h
@@ -169,7 +169,9 @@ int rdbSaveBinaryFloatValue(rio *rdb, float val);
 int rdbLoadBinaryFloatValue(rio *rdb, float *val);
 int rdbLoadRio(rio *rdb, int rdbflags, rdbSaveInfo *rsi);
 int rdbLoadRioWithLoadingCtx(rio *rdb, int rdbflags, rdbSaveInfo *rsi, rdbLoadingCtx *rdb_loading_ctx);
+int rdbFunctionLoad(rio *rdb, int ver, functionsCtx* functions_ctx, int rdbflags, sds *err);
 int rdbSaveRio(rio *rdb, int *error, int rdbflags, rdbSaveInfo *rsi);
+int functionsSaveRio(rio *rdb);
 rdbSaveInfo *rdbPopulateSaveInfo(rdbSaveInfo *rsi);
 
 #endif