Once upon time I had a need to read the GRIB2 file in golang. I used Google search and found the following libraries:

• https://github.com/analogic/grib - obsolete
• https://github.com/brockwood/gogrib2 - empty
• https://github.com/nilsmagnus/grib

Library nilsmagnus/grib looked reassuringly. I downloaded gfs.t00z.pgrb2.0p25.f001 file from nomads.ncep.noaa.gov, ran grib export and got error format is not supported (((.

I decided to develop GRIB2 library by myself. I looked at nilsmagnus/grib and libraries for Java and Python. All libraries are attempts to understand how GRIB2 is arranged inside and to develop GRIB2 engine using appropriated programming language.

There was the reference GRIB2 implementation - wgrib2 tool. Look at wgrib2 source code. It's a lot of "crazy" C language code ))). As for me it's very difficult to understand how it works in details. There was the way to call wgrib2 from golang application. But I rejected that due to the following reasons:

• wgrib2 is not thread-safe. There are a lot of global read/write variables inside code.

• I prefer pure golang libraries

I saw the only one way - to port wgrib2 to golang. I did not want to repeat approach of another libraries. I was not going to rewrite wgrib2 to golang. I decided to port wgrib2 engine C code to golang with minimal correction and develop simple wrapper. I used results of wgrib2 export to CSV as the reference for testing. That approach allows:

• safe time (porting spent few days only)
• easy apply new features and patches from original wgrib2 development stream

I used grib2-v2.0.6c version. Here is the result of my work. The work is on final stage.

go get -u github.com/amsokol/go-grib2

It contains only one function that reads GRIB2 file:

func Read(data []byte) ([]GRIB2, error)

where GRIB2 is the structure with parsed data:

// GRIB2 is simplified GRIB2 file structure
type GRIB2 struct {
    RefTime     time.Time
    VerfTime    time.Time
    Name        string
    Description string
    Unit        string
    Level       string
    Values      []Value
}

// Value is data item of GRIB2 file
type Value struct {
    Longitude float64
    Latitude  float64
    Value     float32
}

Unlike wgrib2 It's thread-safe.

See the following usage examples:

• file-grib2csv - export GRIB2 file to CSV
• http-grib2csv - export nomads.ncep.noaa.gov HTTP response to CSV

Major work is finished. go-grib2 is ready to use. I have a little bit to port:

• parse longitude and latitude are stored as gauss, space_view, irr_grid
• parse data are stored using complex and run_length algorithms

go-grib2 does not support jpeg, png and aec data package formats. The reason is wgrib2 uses external C libraries to read these formats. If you have an idea how to easy port jpeg, png and aec please let me know.

I need help is testing. Please test go-grib2 with several GRIB2 files from several providers. Use wgrib2 CSV export to validate results. Please create issues here.

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