1. 1. bug description

bson::DateTime from chrono::DateTime may failed to serialization

1. 1. step to reproduce

git clone https://github.com/pymongo/mongodb_bson_datetime_bug

cd mongodb_bson_datetime_bug && cargo b

1. 1. reason for bug

bson's DateTime use i64 timestamp in miliseconds like javascript, which means it can't contains microsecond or nanosecond

// now would failed to serialization
let now: mongodb::bson::DateTime = chrono::Utc::now().into();

must check chrono's DateTime whether contains microsecond or nanosecond in impl From<chrono> for bson

1. 1. suggestion

change From<chrono> to TryFrom<chrono>

all bson's DateTime is chrono's DateTime, but not all chrono's DateTime is bson's DateTime

must check chrono's DateTime whether a valid bson's DateTime in From<chrono>

or truncate microsecond and nanosecond on chrono's DateTime

I suggest to move these code to From<chrono>

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