net/http: flaky "connection reset by peer" on macOS Sierra

[rsc]

all.bash on Sierra at master:

--- FAIL: TestTransportDiscardsUnneededConns (0.14s)
    clientserver_test.go:979: Get: Get https://127.0.0.1:59047: read tcp 127.0.0.1:59050->127.0.0.1:59047: read: connection reset by peer
FAIL
FAIL    net/http    10.072s

I saw this on the Go 1.6 branch too. Haven't dug into it to find out what it means, whether it's Sierra or a race in the test. Just happens once in a while.

/cc @bradfitz

[bradfitz]

I at least can't reproduce it on Linux with a high -count value and/or -race (which randomizes goroutine scheduling a bit and often exposes timing issues).

Will try on Mac.

[rsc]

Another from all.bash:

--- FAIL: TestTransportConcurrency (0.00s)
    transport_test.go:1323: error on req request-3: Get http://127.0.0.1:60940/?echo=request-3: read tcp 127.0.0.1:60941->127.0.0.1:60940: read: connection reset by peer
FAIL
FAIL    net/http    9.874s

[bradfitz]

My corp laptop is still 10.11 so I'll need to setup Sierra builders before I can work on this.

[bradfitz]

I've been running go test -short net/http in a loop for the past hour on my home Sierra desktop and haven't gotten a single error. I also tried go test -short -run=TransportConcurrency -count=500 and go test -short -run=TestTransportDiscardsUnneededConns -count=500.

I suspect I might've accidentally fixed this during my recent test parallelization and de-flaking spree:

cd670a6
276c29f
f9d406e
27a3d30
2f2b578

I'm going to close for now, but please reopen if you see it happen again or have ideas on how I can make it fail.