From 3dbf9048fa4f26a09e1b8bf2029ef5abcdacce0d Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Ferdinand=20M=C3=BCtsch?= <ferdinand@muetsch.io>
Date: Mon, 18 Dec 2023 09:29:56 +0100
Subject: [PATCH] chore: option to truncate messages to maximum length (resolve
 #66)

---
 README.md           |  2 ++
 config/config.go    |  3 +++
 handlers/message.go | 13 +++++++++----
 util/string.go      | 14 ++++++++++++++
 4 files changed, 28 insertions(+), 4 deletions(-)
 create mode 100644 util/string.go

diff --git a/README.md b/README.md
index b1775ee..0835da5 100644
--- a/README.md
+++ b/README.md
@@ -118,9 +118,11 @@ For self-signed certificates, you'll need to pass your public key to Telegram's
 * `-certPath` (`string`) – Path of your SSL certificate when using webhook mode with `useHttp`. Default to none.
 * `-keyPath` (`string`) – Path of your private SSL key when using webhook mode with `useHttp`. Default to none.
 * `-dataDir` (`string`) – File system location where to store persistent data. Defaults to `.`.
+* `-inlets` (`string`) – Path to folder containing config-based inlet definitions in YAML format. Defaults to `./inlets.d`.
 * `-blacklist` (`string`) – Path to a line-separated blacklist file containing user IDs (send `/help` to get your id). Defaults to `blacklist.txt`.
 * `-whitelist` (`string`) – Path to a line-separated whitelist file containing user IDs (send `/help` to get your id). Defaults to `whitelist.txt`.
 * `-rateLimit` (`int`) – Maximum number of messages to be delivered to each recipient per hour. Defaults to `100`.
+* `-truncateMsgs` (`bool`) – Truncate too long messages to 4096 characters instead of rejecting them. Defaults to `false`.
 * `-metrics` (`bool`) – Whether to expose [Prometheus](https://prometheus.io) metrics under `/metrics`. Defaults
   to `false`.
 
diff --git a/config/config.go b/config/config.go
index ba394d7..c9e9901 100644
--- a/config/config.go
+++ b/config/config.go
@@ -68,6 +68,7 @@ type BotConfig struct {
 	UrlSecret    string
 	ReqRateLimit int
 	CmdRateLimit int
+	TruncateMsgs bool
 	Address      string
 	Address6     string
 	Disable6     bool
@@ -131,6 +132,7 @@ func Get() *BotConfig {
 		urlSecretPtr := flag.String("urlSecret", "", "Secret suffix to append to Telegram updates endpoint")
 		reqRateLimitPtr := flag.Int("rateLimit", 100, "Max number of requests per recipient per hour")
 		cmdRateLimitPtr := flag.Int("cmdRateLimit", 10, "Max number of chat commands to execute per hour")
+		truncateMsgsPtr := flag.Bool("truncateMsgs", false, "Truncate too long messages to 4096 characters instead of rejecting them")
 		addrPtr := flag.String("address", "127.0.0.1", "IPv4 address to bind the webserver to")
 		addr6Ptr := flag.String("address6", "::1", "IPv6 address to bind the webserver to")
 		disable6Ptr := flag.Bool("disableIPv6", false, "Set if your device doesn't support IPv6. address6 will be ignored if this is set.")
@@ -173,6 +175,7 @@ func Get() *BotConfig {
 			UrlSecret:    *urlSecretPtr,
 			ReqRateLimit: *reqRateLimitPtr,
 			CmdRateLimit: *cmdRateLimitPtr,
+			TruncateMsgs: *truncateMsgsPtr,
 			Address:      *addrPtr,
 			Address6:     *addr6Ptr,
 			Disable6:     *disable6Ptr,
diff --git a/handlers/message.go b/handlers/message.go
index 366cf8e..b7bb724 100644
--- a/handlers/message.go
+++ b/handlers/message.go
@@ -6,11 +6,13 @@ import (
 	"github.com/muety/telepush/model"
 	"github.com/muety/telepush/resolvers"
 	"github.com/muety/telepush/services"
+	"github.com/muety/telepush/util"
 	"log"
 	"net/http"
 	"regexp"
 	"strconv"
 	"strings"
+	"unicode/utf8"
 )
 
 var telegramApiErrorRegexp *regexp.Regexp
@@ -39,10 +41,13 @@ func (h *MessageHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
-	if len(m.Text) > 4096 {
-		w.WriteHeader(http.StatusBadRequest)
-		w.Write([]byte("message too long (max is 4096 characters)"))
-		return
+	if utf8.RuneCountInString(m.Text) > 4096 {
+		if !config.Get().TruncateMsgs {
+			w.WriteHeader(http.StatusBadRequest)
+			w.Write([]byte("message too long (max is 4096 characters)"))
+			return
+		}
+		m.Text = util.TruncateInRunes(m.Text, 4096)
 	}
 
 	if params := r.Context().Value(config.KeyParams); params != nil {
diff --git a/util/string.go b/util/string.go
new file mode 100644
index 0000000..0df83b8
--- /dev/null
+++ b/util/string.go
@@ -0,0 +1,14 @@
+package util
+
+// TruncateInRunes truncates a string to fit the given size in Runes.
+// https://github.com/prometheus/alertmanager/blob/dc1466487a537ea7cfce366b69429ac79a04a221/notify/util.go#L89
+func TruncateInRunes(s string, n int) string {
+	r := []rune(s)
+	if len(r) <= n {
+		return s
+	}
+	if n <= 3 {
+		return string(r[:n])
+	}
+	return string(r[:n-1]) + "..."
+}