Optimize memory usage when stream flush and save

[snowcrumble]

PR Details

Optimize memory usage when stream flush and save

Description

1. Record streams in File when new a stream
2. Do not close temp file when flush stream
3. use io.Copy to copy from stream buffer reader into zip writer.

Related Issue

#650

Motivation and Context

Avoid instantaneous memory usage.

How Has This Been Tested

I fix a OOM problem in k8s.

Types of changes

• Docs change / refactoring / dependency upgrade
• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.

[xuri]

Hi @snowcrumble, thanks for your PR. I've left some comments. Please make sure to pass the go test.

[codecov-commenter]

Codecov Report

Merging #659 into v2 will decrease coverage by 0.05%.
The diff coverage is 52.63%.

@@            Coverage Diff             @@
##               v2     #659      +/-   ##
==========================================
- Coverage   95.59%   95.53%   -0.06%     
==========================================
  Files          31       31              
  Lines        8442     8441       -1     
==========================================
- Hits         8070     8064       -6     
- Misses        225      229       +4     
- Partials      147      148       +1     

Impacted Files	Coverage Δ
excelize.go	95.85% <ø> (ø)
file.go	84.09% <35.71%> (-9.16%)	⬇️
stream.go	87.17% <100.00%> (+0.83%)	⬆️

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[Paxa]

this change will be very helpful for me

Can you give usage example please? (example in code worked)

I found few things not working in streaming API:

1. file.SetSheetName(file.GetSheetName(1), "TODO") - has no effect, file.NewStreamWriter will work only with Sheet1 and result will have Sheet1. As workaround I added new Sheet and made it active
2. using time in writer.SetRow(...) will print it as 44040,0976334606, as workaround I set custom style with date formatting

dateFormat := "[$-409]m/d/yy hh:mm;@"
dateStyle, err := file.NewStyle(&excelize.Style{CustomNumFmt: &dateFormat})

for ... {
  excelRow = append(excelRow, excelize.Cell{Value: val, StyleID: dateFormat})
}

3. file.SetColWidth has no effect (already reported by others)