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[SR-9279] JSONEncoder with dateEncodingStrategy of millisecondsSince1970 produces Float type in resulting JSON #3587

swift-ci opened this issue Nov 16, 2018 · 1 comment


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@swift-ci swift-ci commented Nov 16, 2018

Previous ID SR-9279
Radar None
Original Reporter rkhalili (JIRA User)
Type Bug
Additional Detail from JIRA
Votes 0
Component/s Foundation
Labels Bug, Codable
Assignee None
Priority Medium

md5: 26375280f8cb81c834f177bb618146aa

Issue Description:

When JSON-encoding a dictionary with a Date object, and specifying millisecondsSince1970 for the date encoding strategy, the resulting encoded value for the Date object is a floating point number with some amount of decimal places, instead of an integer representing milliseconds. This doesn't seem correct, I feel like this can cause incompatibility with systems or APIs that don't expect floats for millisecond values (which was the case for my company's Java back-end API).

To reproduce:

let test = ["key": Date()]
let encoder = JSONEncoder()
encoder.dateEncodingStrategy = .millisecondsSince1970
if let result = try? encoder.encode(test) {
    if let backToString = String(data: result, encoding: .utf8) {
        print("JSON: " + backToString)

Expected output:

JSON: {"key":1542355551611}

Actual output:

JSON: {"key":1542355551611.2129}

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Contributor Author

@swift-ci swift-ci commented Feb 15, 2019

Comment by Charles Maria Tor (JIRA)

I don't think this is a bug, truncating the fractional bits would mean that a round-trip through JSON would be lossy in precision.

If you need this behaviour, customise your Date encoding by manually implementing the encode function and encoding

Int(date.timeIntervalSince1970 * 1000)

@swift-ci swift-ci transferred this issue from apple/swift-issues Apr 25, 2022
@shahmishal shahmishal transferred this issue from apple/swift May 5, 2022
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