func()

in sumdb/client.go [397:461]

• 51 lines of code
• 12 McCabe index (conditional complexity)

func (c *Client) mergeLatestMem(msg []byte) (when int, err error) {
	if len(msg) == 0 {
		// Accept empty msg as the unsigned, empty timeline.
		c.latestMu.Lock()
		latest := c.latest
		c.latestMu.Unlock()
		if latest.N == 0 {
			return msgNow, nil
		}
		return msgPast, nil
	}

	note, err := note.Open(msg, c.verifiers)
	if err != nil {
		return 0, fmt.Errorf("reading tree note: %v\nnote:\n%s", err, msg)
	}
	tree, err := tlog.ParseTree([]byte(note.Text))
	if err != nil {
		return 0, fmt.Errorf("reading tree: %v\ntree:\n%s", err, note.Text)
	}

	// Other lookups may be calling mergeLatest with other heads,
	// so c.latest is changing underfoot. We don't want to hold the
	// c.mu lock during tile fetches, so loop trying to update c.latest.
	c.latestMu.Lock()
	latest := c.latest
	latestMsg := c.latestMsg
	c.latestMu.Unlock()

	for {
		// If the tree head looks old, check that it is on our timeline.
		if tree.N <= latest.N {
			if err := c.checkTrees(tree, msg, latest, latestMsg); err != nil {
				return 0, err
			}
			if tree.N < latest.N {
				return msgPast, nil
			}
			return msgNow, nil
		}

		// The tree head looks new. Check that we are on its timeline and try to move our timeline forward.
		if err := c.checkTrees(latest, latestMsg, tree, msg); err != nil {
			return 0, err
		}

		// Install our msg if possible.
		// Otherwise we will go around again.
		c.latestMu.Lock()
		installed := false
		if c.latest == latest {
			installed = true
			c.latest = tree
			c.latestMsg = msg
		} else {
			latest = c.latest
			latestMsg = c.latestMsg
		}
		c.latestMu.Unlock()

		if installed {
			return msgFuture, nil
		}
	}
}