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net: fix bytesWritten during writev #14236

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net: fix bytesWritten during writev #14236

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net: fix bytesWritten during writev
brendanashworth Jul 13, 2017
ab6917b
!fixup fix test nits, net.js collapse if/else
brendanashworth Jul 15, 2017
1979f7f
!fixup avoid instanceof with data.allBuffers
brendanashworth Jul 18, 2017
9aadbf3
!fixup replace instanceof with typeof !== 'string'
brendanashworth Jul 27, 2017
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19 changes: 14 additions & 5 deletions lib/net.js
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Original file line number Diff line number Diff line change
Expand Up @@ -825,11 +825,20 @@ protoGetter('bytesWritten', function bytesWritten() {
bytes += Buffer.byteLength(el.chunk, el.encoding);
});

if (data) {
if (data instanceof Buffer)
bytes += data.length;
else
bytes += Buffer.byteLength(data, encoding);
if (Array.isArray(data)) {
// was a writev, iterate over chunks to get total length
for (var i = 0; i < data.length; i++) {
const chunk = data[i];

if (chunk instanceof Buffer)
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@mscdex mscdex Jul 14, 2017 •
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We can avoid this check for each item in the array if data.allBuffers === true. writeGeneric() uses this optimization already.

I think this will have a non 0 performance impact as it uses istanceof for each chunk but I guess there is no way around that.

/cc @lpinca ^

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Is it worth optimizing? This is a pretty rarely-traveled code area, so I'd favor simplicity here, but I can change it if you'd like.

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@mscdex mscdex Jul 15, 2017 •
edited
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I don't know how much bytesWritten is used, but I mostly mentioned the optimization because of @lpinca's comment.

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I think @mscdex’s suggestion makes sense. Also, using process.binding('util').isUint8Array(chunk) should be a faster alternative to a full instanceof check, that should be okay here.

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I've added the data.allBuffers check, thanks.

@addaleax I'm not so sure that's faster — this benchmark says its a bit slower, probably because of going past the C++ boundary.

bytes += chunk.length;
else
bytes += Buffer.byteLength(chunk.chunk, chunk.encoding);
}
} else if (data instanceof Buffer) {
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These instanceof checks are going to be expensive on perf

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This specific check wasn't added in this PR, it was just down-indented (no perf change).

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I wonder if we could get away with using data != undefined && typeof data !== 'string' instead? If so, we could first branch on the first condition and then do a if (typeof data !== 'string') { ... } else { ... } to avoid duplicate if (data)-style checks.

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@mscdex Yes, .write() will error if it's neither a Buffer nor a string, so this works! I've updated it with the optimization.

bytes += data.length;
} else if (data) {
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@mscdex mscdex Jul 14, 2017 •
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Perhaps this can be simplified a bit by merging with the if/else below:

if (Array.isArray(data)) {
  // ...
} else if (data instanceof Buffer) {
  // ...
} else if (data) {
  // ...
}

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Good tip! I just collapsed the branches.

bytes += Buffer.byteLength(data, encoding);
}

return bytes;
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35 changes: 35 additions & 0 deletions test/parallel/test-net-socket-byteswritten.js
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Original file line number Diff line number Diff line change
@@ -0,0 +1,35 @@
'use strict';

const common = require('../common');
const assert = require('assert');
const net = require('net');

const server = net.createServer(function(socket) {
socket.end();
});

server.listen(0, common.mustCall(function() {
const socket = net.connect(server.address().port);

// Cork the socket, then write twice; this should cause a writev, which
// previously caused an err in the bytesWritten count.
socket.cork();

socket.write('one');
socket.write(new Buffer('twø', 'utf8'));

socket.uncork();

// one = 3 bytes, twø = 4 bytes
assert.strictEqual(socket.bytesWritten, 3 + 4);

socket.on('connect', common.mustCall(function() {
assert.strictEqual(socket.bytesWritten, 3 + 4);
}));

socket.on('end', common.mustCall(function() {
assert.strictEqual(socket.bytesWritten, 3 + 4);

server.close();
}));
}));