/
cacher.go
51 lines (44 loc) · 1.33 KB
/
cacher.go
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
package sapphire
import (
"bytes"
"errors"
"io"
"io/ioutil"
"log"
"net/http"
"reflect"
)
// GetFile downloads a file from the specified URL and caches it, or loads the cached version.
func GetFile(filename string, url string) (io.Reader, error) {
fileBuf, err1 := ioutil.ReadFile(filename)
res, err2 := http.Get(url)
if err2 != nil {
log.Println("Could not access internet resource, falling back to cached resource.")
if err1 != nil {
return bytes.NewReader(fileBuf), nil
}
return nil, errors.New("getfile: no cached resource available")
}
defer res.Body.Close()
// Convert the io.Reader to a bytes.Buffer, so we can then read the bytes.Buffer into the []byte we created earlier
intermediaryBuf := &bytes.Buffer{}
nRead, err3 := io.Copy(intermediaryBuf, res.Body)
if err3 != nil {
return nil, err3
}
// Read the bytes.Buffer into the []byte
internetBuf := make([]byte, nRead)
_, err4 := intermediaryBuf.Read(internetBuf)
if err4 != nil {
return nil, err4
}
if err1 != nil || !reflect.DeepEqual(fileBuf, internetBuf) {
// If the file doesn't exist or the downloaded stuff is different, just write out the downloaded stuff and return
err5 := ioutil.WriteFile(filename, internetBuf, 0644)
if err5 != nil {
return nil, err5
}
return bytes.NewReader(internetBuf), nil
}
return bytes.NewReader(fileBuf), nil
}