Add thread_id support for discord service

docs/services/discord.md

@@ -14,6 +14,26 @@ The shoutrrr service URL should look like this:
 
 --8<-- "docs/services/discord/config.md"
 
+## Optional: Sending messages to a specific thread
+
+Discord supports sending messages via webhook to threads. You can target a specific thread by appending
+`?thread_id=<id>` to the end of the url.
+
+!!! info ""
+### Example
+
+```
+discord://<token>@<webhook_id>?thread_id=1234567890123456789
+```
+
+To get the thread ID:
+ - Open a Discord Thread
+ - Right click -> copy link
+ - OR Right click -> copy thread ID (Developer mode turned on in discord settings)
+
+!!! warning ""
+A valid thread_id must is 19 digits long. If extracting from a link don't confuse the channel ID and thread ID.
+
 ## Creating a webhook in Discord
 
 1. Open your channel settings by first clicking on the gear icon next to the name of the channel.

pkg/services/discord/discord.go

@@ -126,11 +126,19 @@ func (service *Service) Initialize(configURL *url.URL, logger types.StdLogger) e
 
 // CreateAPIURLFromConfig takes a discord config object and creates a post url
 func CreateAPIURLFromConfig(config *Config) string {
+	// Optional queryParams
+	queryParams := ""
+	if config.ThreadID != "" {
+		queryParams = "?thread_id=" + config.ThreadID
+	}
+
 	return fmt.Sprintf(
-		"%s/%s/%s",
+		"%s/%s/%s%s",
 		hookURL,
 		config.WebhookID,
-		config.Token)
+		config.Token,
+		queryParams,
+	)
 }
 
 func doSend(payload []byte, postURL string) error {

pkg/services/discord/discord_config.go

@@ -23,6 +23,7 @@ type Config struct {
 	ColorDebug uint   `key:"colorDebug" default:"0x7b00ab" desc:"The color of the left border for debug messages"   base:"16"`
 	SplitLines bool   `key:"splitLines" default:"Yes"      desc:"Whether to send each line as a separate embedded item"`
 	JSON       bool   `key:"json"       default:"No"       desc:"Whether to send the whole message as the JSON payload instead of using it as the 'content' field"`
+	ThreadID   string `key:"thread_id"  default:""         desc:"Optional thread ID for posting into a channel thread"`
 }
 
 // LevelColors returns an array of colors with a MessageLevel index