dgram: add support for UDP connected sockets

[santigimeno]

Added the dgram.connect() and dgram.disconnect() methods that
associate/disassociate a udp socket to/from a remote address.
It optimizes for cases where lots of packets are sent to the same
address.
Also added the dgram.remoteAddress() method to retrieve the associated
remote address.

Checklist

• make -j4 test (UNIX), or vcbuild test (Windows) passes
• tests and/or benchmarks are included
• documentation is changed or added
• commit message follows commit guidelines

Would like some feedback as I'm not sure about some decisions I made:

• Should a disconnect event be added?
• I'm throwing on the ENOTCONN and EISCONN errors. Should I be emitting an event instead?
• The send() is now more overloaded than ever.

Thanks

[nodejs-github-bot]

@santigimeno build started: https://ci.nodejs.org/blue/organizations/jenkins/node-test-pull-request-lite-pipeline/detail/node-test-pull-request-lite-pipeline/3016/pipeline

[santigimeno]

/cc @cjihrig

[reklatsmasters]

I think this API shouldn't be a part of nodejs core. There may be some misunderstandings. Some developers may expect messages only from a connected socket, like in tcp, but it's not. You may receive messages from anyone but may send only to an associated address. It's important.

Almost a year ago i solved this problem by creating unicast. This module provided real 1:1 association (for incoming and outgoing messages) and streaming interface.

[santigimeno]

@reklatsmasters I think that's actually how a connected UDP socket behaves (and tested locally in linux). From the linux connect(2) manual:

If the socket sockfd is of type SOCK_DGRAM, then addr is the address to which datagrams are sent by default, and the only address from which datagrams are received.

[reklatsmasters]

@santigimeno Thanks for the explanation! I researched only the libuv sources.

It would be great to implement a connected UDP socket like a duplex stream.

[santigimeno]

Updated to add the review comments. Thanks!

[nodejs-github-bot]

CI: https://ci.nodejs.org/job/node-test-pull-request/21958/

[vsemozhetbyt]

Some doc nits.

[santigimeno]

Updated addressing docs comments. Thanks

[targos]

this needs to be rebased.

/cc @nodejs/dgram

[santigimeno]

Rebased to current master.

[nodejs-github-bot]

CI: https://ci.nodejs.org/job/node-test-pull-request/22091/

[danbev]

Re-run of failing node-test-commit-linux

[mcollina]

LGTM

[danbev]

test/parallel/test-dgram-connect.js seems to be consistently failing on ubuntu.

test/osx failure looks unrelated

console output:

08:22:28 not ok 386 parallel/test-dgram-connect08:22:28 ---08:22:28 duration_ms: 0.7608:22:28 severity: fail08:22:28 exitcode: 108:22:28 stack: |-08:22:28 assert.js:8708:22:28 throw new AssertionError(obj);08:22:28 ^08:22:28 08:22:28 AssertionError [ERR_ASSERTION]: Expected values to be strictly equal:08:22:28 + actual - expected08:22:28 08:22:28 + 'EAI_AGAIN'08:22:28 - 'ENOTFOUND'08:22:28 at /home/iojs/build/workspace/node-test-commit-linux/nodes/ubuntu1804-64/test/parallel/test-dgram-connect.js:40:1208:22:28 at /home/iojs/build/workspace/node-test-commit-linux/nodes/ubuntu1804-64/test/common/index.js:369:1508:22:28 at dgram.js:408:908:22:28 at processTicksAndRejections (internal/process/task_queues.js:79:9)08:22:28 ...

[santigimeno]

Updated with a test fixup. Thanks!

[nodejs-github-bot]

CI: https://ci.nodejs.org/job/node-test-pull-request/22113/

[danbev]

Re-build of failing node-test-commit-linux (✔️)

[danbev]

Landed in 9e96017.