maintner: make godata.Get use locally cached data when network is unavailable
This is "Airplane mode". I had cached the latest maintner data before
a flight, but using godata.Get in flight failed when it tried to
update it.
Instead, detect the lack of network and just use whatever's available
instead.
Change-Id: Ieea29f844353377b3c36a531642a716f91f34436
Reviewed-on: https://go-review.googlesource.com/44813
Reviewed-by: Kevin Burke <kev@inburke.com>
diff --git a/maintner/netsource.go b/maintner/netsource.go
index df91149..5c4d28f 100644
--- a/maintner/netsource.go
+++ b/maintner/netsource.go
@@ -13,10 +13,12 @@
"io"
"io/ioutil"
"log"
+ "net"
"net/http"
"net/url"
"os"
"path/filepath"
+ "strconv"
"strings"
"time"
@@ -69,6 +71,87 @@
return ch
}
+// isNoInternetError reports whether the provided error is because there's no
+// network connectivity.
+func isNoInternetError(err error) bool {
+ switch err := err.(type) {
+ case *url.Error:
+ return isNoInternetError(err.Err)
+ case *net.OpError:
+ return isNoInternetError(err.Err)
+ case *net.DNSError:
+ // Trashy:
+ return err.Err == "no such host"
+ default:
+ log.Printf("Unknown error type %T: %#v", err, err)
+ return false
+ }
+}
+
+func (ns *netMutSource) locallyCachedSegments() (segs []fileSeg, err error) {
+ defer func() {
+ if err != nil {
+ log.Printf("No network connection and failed to use local cache: %v", err)
+ } else {
+ log.Printf("No network connection; using %d locally cached segments.", len(segs))
+ }
+ }()
+ fis, err := ioutil.ReadDir(ns.cacheDir)
+ if err != nil {
+ return nil, err
+ }
+ fiMap := map[string]os.FileInfo{}
+ segHex := map[int]string{}
+ segGrowing := map[int]bool{}
+ for _, fi := range fis {
+ name := fi.Name()
+ if !strings.HasSuffix(name, ".mutlog") {
+ continue
+ }
+ fiMap[name] = fi
+
+ if len(name) == len("0000.6897fab4d3afcda332424b2a2a1a4469021074282bc7be5606aaa221.mutlog") {
+ num, err := strconv.Atoi(name[:4])
+ if err != nil {
+ continue
+ }
+ segHex[num] = strings.TrimSuffix(name[5:], ".mutlog")
+ } else if strings.HasSuffix(name, ".growing.mutlog") {
+ num, err := strconv.Atoi(name[:4])
+ if err != nil {
+ continue
+ }
+ segGrowing[num] = true
+ }
+ }
+ for num := 0; ; num++ {
+ if hex, ok := segHex[num]; ok {
+ name := fmt.Sprintf("%04d.%s.mutlog", num, hex)
+ segs = append(segs, fileSeg{
+ seg: num,
+ file: filepath.Join(ns.cacheDir, name),
+ size: fiMap[name].Size(),
+ sha224: hex,
+ })
+ continue
+ }
+ if segGrowing[num] {
+ name := fmt.Sprintf("%04d.growing.mutlog", num)
+ slurp, err := ioutil.ReadFile(filepath.Join(ns.cacheDir, name))
+ if err != nil {
+ return nil, err
+ }
+ segs = append(segs, fileSeg{
+ seg: num,
+ file: filepath.Join(ns.cacheDir, name),
+ size: int64(len(slurp)),
+ sha224: fmt.Sprintf("%x", sha256.Sum224(slurp)),
+ })
+ }
+ return segs, nil
+ }
+}
+
// waitSizeNot optionally specifies that the request should long-poll waiting for the server
// to have a sum of log segment sizes different than the value specified.
func (ns *netMutSource) getServerSegments(ctx context.Context, waitSizeNot int64) ([]LogSegmentJSON, error) {
@@ -117,6 +200,18 @@
sumLast := sumSegSize(ns.last)
segs, err := ns.getServerSegments(ctx, sumLast)
+ if isNoInternetError(err) {
+ if sumLast == 0 {
+ return ns.locallyCachedSegments()
+ }
+ log.Printf("No internet; blocking.")
+ select {
+ case <-ctx.Done():
+ return nil, ctx.Err()
+ case <-time.After(15 * time.Second):
+ continue
+ }
+ }
if err != nil {
return nil, err
}
