Switch between gzip and csv reader dynamically

Question

i am using the following code snippet to unpack a zipped csv file and split it into even parts.

  func split(feed MerchantFeed, db *gorm.DB) {
    var merchant Merchant
    db.First(&merchant, feed.MerchantID)
    merchant.Title = strings.Replace(merchant.Title, ".", "_", -1)
    fileID := merchant.Title + "__" + fmt.Sprint(feed.MerchantID) + "__" + uniuri.NewLen(20)
    out, _ := os.Create("/tmp/feeds/" + fileID)

    resp, err := http.Get(feed.Url)
    if err != nil {
        fmt.Println("Feed download error!")
    }
    defer resp.Body.Close()

    // Calling Copy method with its parameters
    bytes, err := io.Copy(out, resp.Body)

    if err != nil {
        fmt.Println("Could not create feed csv")
    }

    defer out.Close()

    in, _ := os.Open("/tmp/feeds/" + fileID)

    reader, err := gzip.NewReader(in)

    if err != nil {
        fmt.Println("Could not unzip feed " + fmt.Sprint(feed.MerchantID))
        err.Error()
        return
    }

    defer in.Close()

    // Empty byte slice.
    csvString := make([]byte, 100)

    // Read in data.
    _, errRead := reader.Read(csvString)
    if errRead != nil {
        fmt.Println(err)
    }
    path := "/tmp/split/feed__" + fileID + "__.csv"
    csvfile, err := os.Create(path)

    io.Copy(csvfile, reader)

    if fileID != "" {
        _, errx := splitter.Split(path, splitDir)

        if errx != nil {
            fmt.Println(errx)
        }

        defer csvfile.Close()
        //fmt.Println(result)

        result := os.Remove(path)
        if result != nil {
            fmt.Println(result)
        }
    }

    fmt.Printf("Size in MB (Feed %d): %d\n", feed.MerchantID, bytes)
    if bytes == 64 {
        fmt.Println("could not download feed from " + fmt.Sprint(feed.MerchantID))
        e := os.Remove("/tmp/feeds/" + fileID + ".gz")
        if e != nil {
            log.Fatal(e)
        }
        return
    }

}

So far so good. It's all working. But some Merchants pack their csv as zip, and others don't. So my idea is to dynamically switch between gzip.NewReader() and csv.NewReader() but i don't know the proper way to do that. I want to repeat as few code as possible. So i tried to say

    var zipNetworks []int
    zipNetworks = append(zipNetworks, 2)
    
    if slices.Contains(zipMerchants,merchant.Network_ID) {
        reader := zip.NewReader(in)
    } else {
        reader := csv.NewReader(in)
    }

but then I have problems with the scope.

Is there any smart solution around that I don't know?

score 1 · Answer 1 · answered Jan 23 '23 at 19:09

1

You can use the common io.Reader interface.

var reader io.Reader
if slices.Contains(zipMerchants, merchant.Network_ID) {
    reader = zip.NewReader(in)
} else {
    reader = csv.NewReader(in)
}

answered Jan 23 '23 at 19:09

Gavin

4,365
1
18
27

Hi Gavin, with your code i receive ./main.go:694:17: cannot use zip.NewReader(in) (value of type *zip.Reader) as type io.Reader in assignment: *zip.Reader does not implement io.Reader (missing Read method) ./main.go:694:31: not enough arguments in call to zip.NewReader have (*os.File) want (io.ReaderAt, int64) ./main.go:696:12: cannot use csv.NewReader(in) (value of type *csv.Reader) as type io.Reader in assignment: *csv.Reader does not implement io.Reader (wrong type for Read method) have Read() (record []string, err error) want Read(p []byte) (n int, err error) – DudiDude Jan 24 '23 at 08:30

score 0 · Answer 2 · answered Jan 23 '23 at 20:26

Set the reader to the file. If gzipping, then replace reader with gzip reader around the file:

var reader io.Reader = in
if shouldUseGzip {
   reader, err = gzip.NewReader(reader)
   if err != nil {
       fmt.Println("Could not unzip feed " + fmt.Sprint(feed.MerchantID), err)
       return
}

Switch between gzip and csv reader dynamically

2 Answers2