From 4f112c16dfac61deb128b48e9d516f78ab55fc95 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Ren=C3=A9=20=27Necoro=27=20Neumann?= <necoro@necoro.eu>
Date: Sun, 28 Feb 2021 13:22:17 +0100
Subject: Start IMAP connections in the background and use them on the go

---
 internal/imap/client.go   | 24 ++++++++++++++++--------
 internal/imap/commando.go |  6 +++---
 internal/imap/imap.go     | 12 +++++++-----
 3 files changed, 26 insertions(+), 16 deletions(-)

diff --git a/internal/imap/client.go b/internal/imap/client.go
index 783acf6..c916a64 100644
--- a/internal/imap/client.go
+++ b/internal/imap/client.go
@@ -1,6 +1,8 @@
 package imap
 
 import (
+	"sync/atomic"
+
 	uidplus "github.com/emersion/go-imap-uidplus"
 	imapClient "github.com/emersion/go-imap/client"
 
@@ -17,15 +19,17 @@ type connConf struct {
 
 type Client struct {
 	connConf
-	mailboxes     *mailboxes
-	commander     *commander
-	connections   [numberConns]*connection
-	nextFreeIndex int
+	mailboxes   *mailboxes
+	commander   *commander
+	connections [numberConns]*connection
+	idxCounter  int32
+	connChannel chan *connection
 }
 
 func (cl *Client) Disconnect() {
 	if cl != nil {
 		cl.stopCommander()
+		close(cl.connChannel)
 
 		connected := false
 		for _, conn := range cl.connections {
@@ -39,7 +43,9 @@ func (cl *Client) Disconnect() {
 }
 
 func (cl *Client) createConnection(c *imapClient.Client) *connection {
-	if cl.nextFreeIndex >= len(cl.connections) {
+	nextIndex := int(atomic.AddInt32(&cl.idxCounter, 1)) - 1
+
+	if nextIndex >= len(cl.connections) {
 		panic("Too many connections")
 	}
 
@@ -51,12 +57,14 @@ func (cl *Client) createConnection(c *imapClient.Client) *connection {
 		c:         client,
 	}
 
-	cl.connections[cl.nextFreeIndex] = conn
-	cl.nextFreeIndex++
+	cl.connections[nextIndex] = conn
 
 	return conn
 }
 
 func NewClient() *Client {
-	return &Client{mailboxes: NewMailboxes()}
+	return &Client{
+		mailboxes:   NewMailboxes(),
+		connChannel: make(chan *connection, 0),
+	}
 }
diff --git a/internal/imap/commando.go b/internal/imap/commando.go
index 1ba4ed3..2edbc58 100644
--- a/internal/imap/commando.go
+++ b/internal/imap/commando.go
@@ -50,11 +50,11 @@ func (cl *Client) startCommander() {
 
 	cl.commander = &commander{cl, pipe, done}
 
-	for _, conn := range cl.connections {
-		if conn != nil {
+	go func() {
+		for conn := range cl.connChannel {
 			go executioner(conn, pipe, done)
 		}
-	}
+	}()
 }
 
 func (cl *Client) stopCommander() {
diff --git a/internal/imap/imap.go b/internal/imap/imap.go
index 369d4b4..20713a4 100644
--- a/internal/imap/imap.go
+++ b/internal/imap/imap.go
@@ -48,6 +48,7 @@ func (cl *Client) connect(url config.Url) (*connection, error) {
 		return nil, fmt.Errorf("login to %s: %w", url.Host, err)
 	}
 
+	cl.connChannel <- conn
 	return conn, nil
 }
 
@@ -61,6 +62,7 @@ func Connect(url config.Url) (*Client, error) {
 			client.Disconnect()
 		}
 	}()
+	client.startCommander()
 
 	var conn *connection // the main connection
 	if conn, err = client.connect(url); err != nil {
@@ -87,12 +89,12 @@ func Connect(url config.Url) (*Client, error) {
 
 	// the other connections
 	for i := 1; i < len(client.connections); i++ {
-		if _, err := client.connect(url); err != nil { // explicitly new var 'err', b/c these are now harmless
-			log.Warnf("connecting #%d: %s", i, err)
-		}
+		go func(id int) {
+			if _, err := client.connect(url); err != nil { // explicitly new var 'err', b/c these are now harmless
+				log.Warnf("connecting #%d: %s", id, err)
+			}
+		}(i)
 	}
 
-	client.startCommander()
-
 	return client, nil
 }
-- 
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