package rest

import (

"net/http"

"strconv"

"strings"

)

// ParseSizeFromHeaders parses HTTP response headers to get the full file size.

// Returns -1 if the headers did not exist or were invalid.

func ParseSizeFromHeaders(headers http.Header) (size int64) {

size = -1

var contentLength = headers.Get("Content-Length")

if len(contentLength) != 0 {

var err error

if size, err = strconv.ParseInt(contentLength, 10, 64); err != nil {

return -1

}

}

var contentRange = headers.Get("Content-Range")

if len(contentRange) == 0 {

return size

}

if !strings.HasPrefix(contentRange, "bytes ") {

return -1

}

slash := strings.IndexRune(contentRange, '/')

if slash < 0 {

return -1

}

ret, err := strconv.ParseInt(contentRange[slash+1:], 10, 64)

if err != nil {

return -1

}

return ret

}