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dgram: skip dns.lookup() for literal IP addresses#64131
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Every unconnected send(), and the implicit bind on first send, resolved the destination through dns.lookup() even when it was already a literal IP. The address resolves to itself, so the call is redundant, and tools that instrument dns.lookup() record a lookup for every datagram sent to an IP. Skip the resolver for a literal IP of the socket's family and report it on the next tick, keeping dns.lookup()'s asynchronous contract. A custom lookup function is still consulted for every address. Refs: DataDog/dd-trace-js#2984 Signed-off-by: Ruben Bridgewater <ruben@bridgewater.de>
A user-supplied lookup function is no longer called when the destination is a literal IP of the socket's family; the address is used directly, matching net.connect(), which skips the lookup for a literal IP host before consulting options.lookup. This is a breaking change for a lookup that expected to be invoked for IP addresses. Refs: DataDog/dd-trace-js#2984 Signed-off-by: Ruben Bridgewater <ruben@bridgewater.de>
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Summary
dgramresolved the destination through the socket lookup (dns.lookup()bydefault) on every unconnected
send()and on the implicit first-send bind, evenwhen the destination was already a literal IP. The address resolves to itself,
so the call is redundant, and tools that instrument
dns.lookup()record alookup for every datagram sent to an IP.
Two commits, separated so the patch can land independently of the breaking part:
dns.lookup()for a literal IP of thesocket's family; a custom
lookupis still consulted.lookuptoo, for a literal IP of thesocket's family.
Why
net.connect()already skips resolution for a literal IP host before it evenreads
options.lookup;http/tlsinherit that.dgramwas the outlier,re-resolving per send. Aligning it removes the redundant work and the
per-datagram
dns.lookup()instrumentation noise. Commit 2 changes the contractfor a custom
lookupthat expected to be invoked for IP addresses, so it iskept separate.
Test plan
test/parallel/test-dgram-default-lookup-ip.js(new): an IPv4 send and a udp6bind to a literal IP do not call
dns.lookup(); a mismatched family (::1ona udp4 socket) still resolves through it.
test/parallel/test-dgram-custom-lookup.js: a customlookupis not calledfor a literal IP; host names still go through it.
Refs: DataDog/dd-trace-js#2984