The error is "PoW too low to compete with other messages"
This has been previously reported in #7144
Solution: prevent the move semantics
The source of the error is in PoolHandle.relay
implementation for NetPoolHandle.
Because of the move semantics, `res` variable is in fact
copied (as it implements Copy) into the closure and for
that reason, the returned result is always `false.
* whisper skeleton
* basic message store
* rallying and message logic
* pass host info to network protocol handlers
* choose who starts rally based on node key
* module reshuffling
* mining messages
* prune messages by low PoW until below size target
* associated error type for ethkey generators and `OsRng` generator
* beginnings of RPC
* generic message handler for whisper
* reshuffle code order
* standard payload encoding and decoding
* basic crypto
* minor restructuring of net code
* implement shh_post
* merge?
* implement filters
* rand trait for hash types
* filter RPCs for whisper
* symmetric encryption of payload
* pub-sub
* filter tests
* use only secure random IDs
* attach arbitrary protocols to network
* basic integration of whisper into Parity
* eagerly prune low PoW entries
* broadcast messages with salted topics
* node info RPC
* fix import
* fix leading zeros calculation
* address minor grumbles
