From c2697725ead29c3c108a8e5f7a9f6ab7519ed7c3 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Ren=C3=A9=20=27Necoro=27=20Neumann?= <necoro@necoro.eu>
Date: Sun, 4 Jun 2023 21:55:50 +0200
Subject: Add new config option to set max number of IMAP connections.

Default is 5 (as was the hard-coded value before).

Closes issue #98.
---
 config.yml.example      |  2 ++
 internal/imap/client.go | 30 ++++++++++++++----------------
 internal/imap/imap.go   |  6 +++---
 main.go                 |  2 +-
 pkg/config/config.go    |  6 ++++++
 5 files changed, 26 insertions(+), 20 deletions(-)

diff --git a/config.yml.example b/config.yml.example
index f235928..7102671 100644
--- a/config.yml.example
+++ b/config.yml.example
@@ -34,6 +34,8 @@ timeout: 30
 # Maximum number of failures allowed before they are reported in normal mode.
 # By default, failures are only visible in verbose mode. Most feeds tend to suffer from temporary failures.
 max-failures:  10
+# Maximum number of concurrent IMAP connections opened.
+max-imap-connections: 5
 # Parts to generate in the resulting emails.
 # Valid parts are "text" and "html"
 parts: ["text", "html"]
diff --git a/internal/imap/client.go b/internal/imap/client.go
index 83903fa..4a0a0d8 100644
--- a/internal/imap/client.go
+++ b/internal/imap/client.go
@@ -13,8 +13,6 @@ import (
 	"github.com/Necoro/feed2imap-go/pkg/log"
 )
 
-const numberConns = 5
-
 type connConf struct {
 	host      string
 	delimiter string
@@ -23,13 +21,13 @@ type connConf struct {
 
 type Client struct {
 	connConf
-	mailboxes    *mailboxes
-	commander    *commander
-	connections  [numberConns]*connection
-	idxCounter   int
-	connChannel  chan *connection
-	connLock     sync.Mutex
-	disconnected bool
+	mailboxes      *mailboxes
+	commander      *commander
+	connections    []*connection
+	maxConnections int
+	connChannel    chan *connection
+	connLock       sync.Mutex
+	disconnected   bool
 }
 
 var dialer imapClient.Dialer
@@ -107,9 +105,7 @@ func (cl *Client) Disconnect() {
 
 func (cl *Client) createConnection(c *imapClient.Client) *connection {
 
-	cl.idxCounter++
-
-	if cl.idxCounter >= len(cl.connections) {
+	if len(cl.connections) == cl.maxConnections {
 		panic("Too many connections")
 	}
 
@@ -121,13 +117,15 @@ func (cl *Client) createConnection(c *imapClient.Client) *connection {
 		c:         client,
 	}
 
-	cl.connections[cl.idxCounter] = conn
+	cl.connections = append(cl.connections, conn)
 	return conn
 }
 
-func newClient() *Client {
+func newClient(maxConnections int) *Client {
 	return &Client{
-		mailboxes:   NewMailboxes(),
-		connChannel: make(chan *connection, 0),
+		mailboxes:      NewMailboxes(),
+		connChannel:    make(chan *connection, 0),
+		connections:    make([]*connection, 0, maxConnections),
+		maxConnections: maxConnections,
 	}
 }
diff --git a/internal/imap/imap.go b/internal/imap/imap.go
index a44a513..80a37a1 100644
--- a/internal/imap/imap.go
+++ b/internal/imap/imap.go
@@ -7,10 +7,10 @@ import (
 	"github.com/Necoro/feed2imap-go/pkg/log"
 )
 
-func Connect(url config.Url) (*Client, error) {
+func Connect(url config.Url, maxConnections int) (*Client, error) {
 	var err error
 
-	client := newClient()
+	client := newClient(maxConnections)
 	client.host = url.Host
 	defer func() {
 		if err != nil {
@@ -41,7 +41,7 @@ func Connect(url config.Url) (*Client, error) {
 	}
 
 	// the other connections
-	for i := 1; i < len(client.connections); i++ {
+	for i := 1; i < client.maxConnections; i++ {
 		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)
diff --git a/main.go b/main.go
index e4593be..e535f36 100644
--- a/main.go
+++ b/main.go
@@ -134,7 +134,7 @@ func run() error {
 	if !dryRun && !buildCache {
 		go func() {
 			var err error
-			c, err = imap.Connect(cfg.Target)
+			c, err = imap.Connect(cfg.Target, cfg.MaxConns)
 			imapErr <- err
 		}()
 
diff --git a/pkg/config/config.go b/pkg/config/config.go
index 0d2c944..aaf6701 100644
--- a/pkg/config/config.go
+++ b/pkg/config/config.go
@@ -23,6 +23,7 @@ type GlobalOptions struct {
 	Target       Url      `yaml:"target"`
 	Parts        []string `yaml:"parts"`
 	MaxFailures  int      `yaml:"max-failures"`
+	MaxConns     int      `yaml:"max-imap-connections"`
 	AutoTarget   bool     `yaml:"auto-target"`
 	HtmlTemplate string   `yaml:"html-template"`
 	TextTemplate string   `yaml:"text-template"`
@@ -32,6 +33,7 @@ var DefaultGlobalOptions = GlobalOptions{
 	Cache:        "feed.cache",
 	Timeout:      30,
 	MaxFailures:  10,
+	MaxConns:     5,
 	DefaultEmail: username() + "@" + Hostname(),
 	Target:       Url{},
 	Parts:        []string{"text", "html"},
@@ -103,6 +105,10 @@ func (cfg *Config) Validate() error {
 		}
 	}
 
+	if cfg.MaxConns < 1 {
+		return fmt.Errorf("max-imap-connections is '%d', but must be at least 1.", cfg.MaxConns)
+	}
+
 	return nil
 }
 
-- 
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