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, 3 insertions, 0 deletions

diff --git a/src/server.h b/src/server.h
index 8e4d8d902..471e8c72a 100644
--- a/src/server.h
+++ b/src/server.h
@@ -3162,6 +3162,7 @@ void migrateCommand(client *c);
 void askingCommand(client *c);
 void readonlyCommand(client *c);
 void readwriteCommand(client *c);
+int verifyDumpPayload(unsigned char *p, size_t len, uint16_t *rdbver_ptr);
 void dumpCommand(client *c);
 void objectCommand(client *c);
 void memoryCommand(client *c);
@@ -3182,6 +3183,8 @@ void functionInfoCommand(client *c);
 void functionListCommand(client *c);
 void functionHelpCommand(client *c);
 void functionFlushCommand(client *c);
+void functionRestoreCommand(client *c);
+void functionDumpCommand(client *c);
 void timeCommand(client *c);
 void bitopCommand(client *c);
 void bitcountCommand(client *c);