We should learn about new peers via address messages.
An inbound peer connecting to us tells us nothing about
its ability to accept incoming connections from us, so
we shouldn't assume that we can connect to it based on
this.
The vast majority of nodes on the network do not accept
incoming connections, adding them will only slow down
the process of making a successful connection in the
future.
Nodes which have configured themselves to not announce would prefer we
not violate their privacy by announcing them in GETADDR responses.
Tests if addresses are online or offline by briefly connecting to them. These short lived connections are referred to as feeler connections. Feeler connections are designed to increase the number of fresh online addresses in tried by selecting and connecting to addresses in new. One feeler connection is attempted on average once every two minutes.
This change was suggested as Countermeasure 4 in
Eclipse Attacks on Bitcoin’s Peer-to-Peer Network, Ethan Heilman,
Alison Kendler, Aviv Zohar, Sharon Goldberg. ePrint Archive Report
2015/263. March 2015.
9d4eb9a Do diskspace check before import thread is started (Pieter Wuille)
aa59f2e Add extra message to avoid a long 'Loading banlist' (Pieter Wuille)
0fd2a33 Use a signal to continue init after genesis activation (Pieter Wuille)
a5072a7 util: Remove zero-argument versions of LogPrint and error (Wladimir J. van der Laan)
695041e util: Update tinyformat (Wladimir J. van der Laan)
c59c434 qa: Add test for standardness of segwit v0 outputs (Suhas Daftuar)
1ffaff2 Make witness v0 outputs non-standard before segwit activation (Johnson Lau)
46c9620 Test that unnecessary witnesses can't be used for mempool DoS (Suhas Daftuar)
bb66a11 Fix DoS vulnerability in mempool acceptance (Suhas Daftuar)
When processing a headers message that looks like a block announcement,
send peer a getheaders if the headers message won't connect.
Apply DoS points after too many consecutive unconnecting headers messages.
Moves the IsStandard check to happen after the premature-witness check,
so that adding a witness to a transaction can't prevent mempool acceptance.
Note that this doesn't address the broader category of potential mempool DoS
issues that affect transactions after segwit activation.
Changes in tinyformat, recently imported from upstream have made the
zero-argument versions of formatting functions unnecessary. Remove them.
This is a slight semantic change: `%` characters in the zero-argument
call are now regarded and need to be escaped. As for as I know, the only
use of this is in `main.cpp`.
