func tagHasPermission(tag string, uuidBytes uuid.UUID, uuidString string) bool {
var hasPerm bool
uuidarr := uuidBytes.Array()
permcacheLock.Lock()
taginfo, ok := permcache[tag]
if !ok {
/* Cache Miss: never seen this token */
taginfo = &TagInfo{name: tag, permissions: make(map[uuid.Array]bool)}
lruListLock.Lock()
taginfo.element = lruList.PushFront(taginfo)
lruListLock.Unlock()
permcache[tag] = taginfo
} else {
lruListLock.Lock()
lruList.MoveToFront(taginfo.element) // most recently used
lruListLock.Unlock()
hasPerm, ok = taginfo.permissions[uuidBytes.Array()]
if ok {
/* Cache Hit */
permcacheLock.Unlock()
return hasPerm
}
/* Cache Miss: never seen this UUID */
}
permcacheLock.Unlock()
/* Ask the metadata server for the metadata of the corresponding stream. */
query := fmt.Sprintf("select * where uuid = \"%s\";", uuidString)
mdReq, err := http.NewRequest("POST", fmt.Sprintf("%s?tags=%s", mdServer, tag), strings.NewReader(query))
if err != nil {
return false
}
mdReq.Header.Set("Content-Type", "text")
mdReq.Header.Set("Content-Length", fmt.Sprintf("%v", len(query)))
resp, err := http.DefaultClient.Do(mdReq)
if err != nil {
return false
}
/* If the response is [] we lack permission; if it's longer we have permission. */
buf := make([]byte, 3)
n, err := io.ReadFull(resp.Body, buf)
resp.Body.Close()
if n == 3 && buf[0] == '[' {
hasPerm = true
} else if n == 2 && err == io.ErrUnexpectedEOF && buf[0] == '[' && buf[1] == ']' {
hasPerm = false
} else {
/* Server error. */
fmt.Printf("Metadata server error: %v %c %c %c\n", n, buf[0], buf[1], buf[2])
return false
}
/* If we didn't return early due to some kind of error, cache the result and return it. */
permcacheLock.Lock()
if taginfo.element != nil { // If this has been evicted from the cache, don't bother
_, ok := taginfo.permissions[uuidarr]
taginfo.permissions[uuidarr] = hasPerm // still update cached value
if !ok { // If a different goroutine added it before we got here, then skip this part
totalCached += 1
if totalCached > MAX_CACHED {
// Make this access return quickly, so start pruning in a new goroutine
fmt.Println("Pruning cache")
go pruneCache()
}
}
}
permcacheLock.Unlock()
return hasPerm
}