agent/cache: Make the return values of getEntryLocked more obvious

Use named returned so that the caller has a better idea of what these
bools mean.

Return early to reduce the scope, and make it more obvious what values
are returned in which cases. Also reduces the number of conditional
expressions in each case.

agent/cache/cache.go

@@ -227,42 +227,43 @@ func (c *Cache) Get(t string, r Request) (interface{}, ResultMeta, error) {
 // getEntryLocked retrieves a cache entry and checks if it is ready to be
 // returned given the other parameters. It reads from entries and the caller
 // has to issue a read lock if necessary.
-func (c *Cache) getEntryLocked(tEntry typeEntry, key string, maxAge time.Duration, revalidate bool, minIndex uint64) (bool, bool, cacheEntry) {
+func (c *Cache) getEntryLocked(
+	tEntry typeEntry,
+	key string,
+	maxAge time.Duration,
+	revalidate bool,
+	minIndex uint64,
+) (entryExists bool, entryValid bool, entry cacheEntry) {
 	entry, ok := c.entries[key]
-	cacheHit := false
-
-	if !ok {
-		return ok, cacheHit, entry
+	if !entry.Valid {
+		return ok, false, entry
 	}
 
-	// Check if we have a hit
-	cacheHit = ok && entry.Valid
-
-	supportsBlocking := tEntry.Type.SupportsBlocking()
-
 	// Check index is not specified or lower than value, or the type doesn't
 	// support blocking.
-	if cacheHit && supportsBlocking &&
-		minIndex > 0 && minIndex >= entry.Index {
+	if tEntry.Type.SupportsBlocking() && minIndex > 0 && minIndex >= entry.Index {
 		// MinIndex was given and matches or is higher than current value so we
 		// ignore the cache and fallthrough to blocking on a new value below.
-		cacheHit = false
+		return true, false, entry
 	}
 
 	// Check MaxAge is not exceeded if this is not a background refreshing type
 	// and MaxAge was specified.
-	if cacheHit && !tEntry.Opts.Refresh && maxAge > 0 &&
-		!entry.FetchedAt.IsZero() && maxAge < time.Since(entry.FetchedAt) {
-		cacheHit = false
+	if !tEntry.Opts.Refresh && maxAge > 0 && entryExceedsMaxAge(maxAge, entry) {
+		return true, false, entry
 	}
 
-	// Check if we are requested to revalidate. If so the first time round the
+	// Check if re-validate is requested. If so the first time round the
 	// loop is not a hit but subsequent ones should be treated normally.
-	if cacheHit && !tEntry.Opts.Refresh && revalidate {
-		cacheHit = false
+	if !tEntry.Opts.Refresh && revalidate {
+		return true, false, entry
 	}
 
-	return ok, cacheHit, entry
+	return true, true, entry
+}
+
+func entryExceedsMaxAge(maxAge time.Duration, entry cacheEntry) bool {
+	return !entry.FetchedAt.IsZero() && maxAge < time.Since(entry.FetchedAt)
 }
 
 // getWithIndex implements the main Get functionality but allows internal
@@ -289,10 +290,10 @@ func (c *Cache) getWithIndex(tEntry typeEntry, r Request, minIndex uint64) (inte
 RETRY_GET:
 	// Get the current value
 	c.entriesLock.RLock()
-	_, cacheHit, entry := c.getEntryLocked(tEntry, key, info.MaxAge, info.MustRevalidate && first, minIndex)
+	_, entryValid, entry := c.getEntryLocked(tEntry, key, info.MaxAge, info.MustRevalidate && first, minIndex)
 	c.entriesLock.RUnlock()
 
-	if cacheHit {
+	if entryValid {
 		meta := ResultMeta{Index: entry.Index}
 		if first {
 			metrics.IncrCounter([]string{"consul", "cache", tEntry.Name, "hit"}, 1)
@@ -401,11 +402,11 @@ func (c *Cache) fetch(tEntry typeEntry, key string, r Request, allowNew bool, at
 	// We acquire a write lock because we may have to set Fetching to true.
 	c.entriesLock.Lock()
 	defer c.entriesLock.Unlock()
-	ok, cacheHit, entry := c.getEntryLocked(tEntry, key, info.MaxAge, info.MustRevalidate && !ignoreRevalidation, minIndex)
+	ok, entryValid, entry := c.getEntryLocked(tEntry, key, info.MaxAge, info.MustRevalidate && !ignoreRevalidation, minIndex)
 
 	// This handles the case where a fetch succeeded after checking for its existence in
 	// getWithIndex. This ensures that we don't miss updates.
-	if ok && cacheHit && !ignoreExisting {
+	if ok && entryValid && !ignoreExisting {
 		ch := make(chan struct{})
 		close(ch)
 		return ch, nil