Add support for Windows specific metrics in Stats

[cstavro]

Docker for Windows has some new metrics that are currently ignored.

This adds support for reading those values from the docker response with no attempt to decode their meaning as that is an exercise left to the application.

Some details about the Windows specific implementations are here:

• Windows: Add support for docker stats moby/moby#25737

An example JSON blob returned from <windows_dockerd>/containers/{id}/stats :

{
    "read": "2017-07-25T14:29:14.9514732Z",
    "preread": "2017-07-25T14:29:13.9532443Z",
    "pids_stats": {},
    "blkio_stats": {
        "io_service_bytes_recursive": null,
        "io_serviced_recursive": null,
        "io_queue_recursive": null,
        "io_service_time_recursive": null,
        "io_wait_time_recursive": null,
        "io_merged_recursive": null,
        "io_time_recursive": null,
        "sectors_recursive": null
    },
    "num_procs": 8,
    "storage_stats": {
        "read_count_normalized": 5829,
        "read_size_bytes": 42184192,
        "write_count_normalized": 3474,
        "write_size_bytes": 23913472
    },
    "cpu_stats": {
        "cpu_usage": {
            "total_usage": 92803750,
            "usage_in_kernelmode": 0,
            "usage_in_usermode": 0
        },
        "throttling_data": {
            "periods": 0,
            "throttled_periods": 0,
            "throttled_time": 0
        }
    },
    "precpu_stats": {
        "cpu_usage": {
            "total_usage": 92795260,
            "usage_in_kernelmode": 0,
            "usage_in_usermode": 0
        },
        "throttling_data": {
            "periods": 0,
            "throttled_periods": 0,
            "throttled_time": 0
        }
    },
    "memory_stats": {
        "commitbytes": 1157246976,
        "commitpeakbytes": 1157246976,
        "privateworkingset": 145084416
    },
    "name": "/clever_cori",
    "id": "b8b0cb1c55f1285ae02bafcc2fc3f265b714716de5740c080909265cc98cc129",
    "networks": {
        "9983bec3-54d1-4152-96c0-3cc7ab3176d4": {
            "rx_bytes": 53086,
            "rx_packets": 259,
            "rx_errors": 0,
            "rx_dropped": 1,
            "tx_bytes": 46044,
            "tx_packets": 128,
            "tx_errors": 0,
            "tx_dropped": 0
        }
    }
}

[cstavro]

I presume the test failure here is because the tests are running on a Linux system that doesn't have these extra fields in the Docker stats output. Does it make sense to have platform specific tests here? Or can we loosen up these failing tests so that they allow for this change?

[fsouza]

@cstavro appveyor runs windows, travis runs linux and macos. If this is a test that would work only on windows (or linux/macos), I'd recommend making it platform specific.

I haven't look at the source or the test failure yet (sorry about that), but I wanted to answer your question. I'll take a better look at the PR later today.

Thanks for contributing!

[cstavro]

So it turns out the test failure was because I wasn't initializing the PreRead time.Time value in the test which seems to behave differently in 1.7.5 vs 1.8.x.

[fsouza]

lgtm, thanks!