Allow zlib to be optional

[jmjatlanta]

permessage_deflate was added assuming zlib will always be available. This change allows compilation without zlib.

Part of bitshares/bitshares-core#1593

[pmconrad]

Looks reasonable. Can't test without zlib though.

[abitmore]

Should we initialize HAS_ZLIB in CMake file, or it's already done?

[jmjatlanta]

Should we initialize HAS_ZLIB in CMake file, or it's already done?

Already there. See

bitshares-fc/CMakeLists.txt

Line 365 in 063be69

add_definitions( -DHAS_ZLIB )

I am now questioning the negotiation between nodes with one enabled and another disabled. I will hold off on merging this until I feel a bit better about it.

[pmconrad]

Nodes do not interact via websocket.

Not quite true, delayed_node connects to its trusted_node via WS-RPC. It uses the same methods as cli_wallet though.

[pmconrad]

Tested server versions with {no,enabled} per_message_deflate against cli_wallet with {no,enabled,disabled} per_message_deflate.
Observed with wireshark that messages are compressed only when both are enabled, uncompressed in all other cases.