Remove JSON manipulation from SwiftMetricsDash Fixes #185

[jonathan-spruce]

Removes the JSON used in the SwiftMetricsDash, which was causing a memory leak in Swift 4.1.2.

[seabaylea]

Rather than using using string templates, it would be much better (and safer!) to define Codable structs and then use the JSONEncoder from Foundation to create the payload, something like (not compiled!)

// Typesafe structs for CPU Data and wrapper object
struct CpuData: Codable {
    let process: Float
    let systemMean: Float
    let processMean: Float
    let time: Date
    let system: Float
}

struct Cpu: Codable {
    let topic = "cpu"
    let payload: Cpu
}

let cpu = Cpu(CpuData(.....))
let encoder = JSONEncoder()
let data = try encoder.encode(cpu)

[sjanuary]

@jonathan-spruce I actually did that work some time ago but it got taken out due to a clash with a more urgent piece of work. This might help you though: https://github.com/RuntimeTools/SwiftMetrics/pull/174/files

[jonathan-spruce]

There still seems to be a memory leak in the JSONEncoder, at least in the way I used it, so I have reverted back to the String implementation.

[codecov-io]

Codecov Report

Merging #188 into master will decrease coverage by 0.21%. The diff coverage is 31.35%.

@@            Coverage Diff             @@
##           master     #188      +/-   ##
==========================================
- Coverage   22.95%   22.73%   -0.22%     
==========================================
  Files           9        9              
  Lines        2100     2111      +11     
==========================================
- Hits          482      480       -2     
- Misses       1618     1631      +13

Flag	Coverage Δ
#SwiftBAMDC	0% <ø> (ø)	:arrow_up:
#SwiftMetrics	22.73% <31.35%> (-0.22%)	:arrow_down:
#SwiftMetricsBluemix	20.15% <97.36%> (-0.11%)	:arrow_down:
#SwiftMetricsDash	17.95% <31.35%> (-0.23%)	:arrow_down:
#SwiftMetricsKitura	19.56% <31.35%> (-0.23%)	:arrow_down:
#SwiftMetricsPrometheus	18.06% <31.35%> (-0.21%)	:arrow_down:
#SwiftMetricsREST	22.73% <31.35%> (-0.22%)	:arrow_down:

Impacted Files	Coverage Δ
Sources/SwiftMetricsDash/SwiftMetricsDash.swift	0% <0%> (ø)	:arrow_up:
Sources/SwiftMetrics/SwiftMonitor.swift	86.47% <97.36%> (+0.16%)	:arrow_up:
Sources/SwiftMetrics/SwiftMetrics.swift	62.9% <0%> (-0.54%)	:arrow_down:

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[sjanuary]

I would not normally merge a fix with a failing Travis build, but I can see that the master build started failing in the same way about 10 days ago and it's important that we get this memory leak fix in. I will open another issue to investigate the test failures.