golang/go

time: unchecked overflow in Add and AddDays

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#20,678 opened on Jun 14, 2017

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Description

I'm trying to define a mapping between time.Time and a C++ time library.

The library that I'm trying to map to supports distinct "infinite past" and "infinite future" times, which need to be mapped to distinct time.Time values. The logical choices would seem to be the maximum and minimum representable time.Time values.

One way to try to obtain those is to call (time.Time).AddDate with absurdly positive or absurdly negative values. AddDate does not return an error, and it cannot reasonably panic on overflow (because the package does not define a way for users to check for such an overflow ahead of time). That leaves one "obvious" behavior: saturation.

Sadly, the current implementation fails to provide that behavior, and instead silently overflows to nonsensical values (https://play.golang.org/p/UUC2JG7Xcj).

(Further evidence for https://github.com/golang/go/issues/19624?)

Contributor guide

Research direction
Inspect the `time.Time.AddDate` implementation to understand the unchecked overflow and propose saturation logic.
Tech stack
go
Domain
backend
Issue type
Bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
2
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-3 hours
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
Active
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
Clear
Prerequisites
Go
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
75