Golang: How to skip struct fields while reading from a buffer?

Question

http://play.golang.org/p/RQXB-hCq_M

type Header struct {
    ByteField1 uint32    // 4 bytes
    ByteField2 [32]uint8 // 32 bytes
    ByteField3 [32]uint8 // 32 bytes
    SkipField1 []SomethingElse
}

func main() {
    var header Header
    headerBytes := make([]byte, 68)  // 4 + 32 + 32 == 68
    headerBuf := bytes.NewBuffer(headerBytes)
    err := binary.Read(headerBuf, binary.LittleEndian, &header)
    if err != nil {
        fmt.Println(err)
    }
    fmt.Println(header)
}

I don't want to read from the buffer into the header struct in chunks. I want to read into the bytefield in one step but skip non byte fields. If you run the program in the given link (http://play.golang.org/p/RQXB-hCq_M) you will find that binary.Read to throw an error: binary.Read: invalid type []main.SomethingElse

Is there a way that I can skip this field?

Update: Based on dommage's answer, I decided to embed the fields inside the struct instead like this http://play.golang.org/p/i0xfmnPx4A

Unfortunately No. skipfield1 is a slice of struct of varying size — samol
– samol, Commented Jan 7, 2014 at 19:55
I think you could define a new struct consisting of pointers to the three fixed-length fields in your other struct, and binary.Read would read into that. (Haven't tested and short on time, so not sure enough to submit it as an answer.) — twotwotwo
– twotwotwo, Commented Jan 7, 2014 at 20:03

Dmitri Goldring · Accepted Answer · 2014-01-07 19:45:42Z

1

You can cause a field to be skipped by prefixing it's name with _ (underscore).

But: binary.Read() requires all fields to have a known size. If SkipField1 is of variable or unknown length then you have to leave it out of your struct.

You could then use io.Reader.Read() to manually skip over the skip field portion of your input and then call binary.Read() again.

answered Jan 7, 2014 at 19:45

Dmitri Goldring

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2 Comments

samol Over a year ago

Could you elaborate a little more on "io.Reader.Read() to manually skip over the skip field portion"

Dmitri Goldring Over a year ago

I was suggesting that if you just want to read the fixed header part, then skip the rest of the header, and then read the body, I would recommend using something like func (b *Buffer) Read(p []byte) or func (b *Buffer) ReadBytes(delim byte) to do so. (If you have an io.Reader as your data source then you will have to use Read. The Buffer methods though are more powerful.

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