Reading the first two bytes from a file efficiently - Golang

Question

I'm trying to find a good way of reading the first two bytes from a file using Go.

I have some .zip files in my current directory, mixed in with other files.

I would like to loop through all the files in the directory and check if the first two bytes contain the right .zip identifier, namely 50 4B.

What would be a good way to accomplish this using the standard library without having to read the entire file?

Going through the available functions in the io package I managed to find:

func LimitReader(r Reader, n int64) Reader

Which seems to fit my description, it reads from Reader (How do I get a Reader?) but stops after n bytes. Since I'm rather new to Go, I'm not sure how to go about it.

os.File which you obtain with os.Open("path") IS a Reader

Uvelichitel
– Uvelichitel

2017-02-12 20:13:57 +00:00
Commented Feb 12, 2017 at 20:13 — Uvelichitel
– Uvelichitel, Commented Feb 12, 2017 at 20:13

jimt · Accepted Answer · 2017-02-12 20:19:39Z

8

You get the initial reader by opening the file. For 2 bytes, I wouldn't use the LimitReader though. Just reading 2 bytes with io.ReadFull is easier.

r, err := os.Open(file)
if err != nil {
    return err
}

defer r.Close()

var header [2]byte
n, err := io.ReadFull(r, header[:])
if err != nil {
    return err
}

answered Feb 12, 2017 at 20:19

jimt

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