3 files changed, 38 insertions, 6 deletions
diff --git a/services/forms/repo_form.go b/services/forms/repo_form.go
index afecc205f3..7a4a2123eb 100644
--- a/services/forms/repo_form.go
+++ b/services/forms/repo_form.go
@@ -17,7 +17,7 @@ import (
 	"code.gitea.io/gitea/modules/setting"
 	"code.gitea.io/gitea/modules/structs"
 	"code.gitea.io/gitea/modules/web/middleware"
-	"code.gitea.io/gitea/routers/utils"
+	"code.gitea.io/gitea/services/webhook"
 
 	"gitea.com/go-chi/binding"
 )
@@ -305,14 +305,16 @@ type NewSlackHookForm struct {
 // Validate validates the fields
 func (f *NewSlackHookForm) Validate(req *http.Request, errs binding.Errors) binding.Errors {
 	ctx := context.GetContext(req)
+	if !webhook.IsValidSlackChannel(strings.TrimSpace(f.Channel)) {
+		errs = append(errs, binding.Error{
+			FieldNames:     []string{"Channel"},
+			Classification: "",
+			Message:        ctx.Tr("repo.settings.add_webhook.invalid_channel_name"),
+		})
+	}
 	return middleware.Validate(errs, ctx.Data, f, ctx.Locale)
 }
 
-// HasInvalidChannel validates the channel name is in the right format
-func (f NewSlackHookForm) HasInvalidChannel() bool {
-	return !utils.IsValidSlackChannel(f.Channel)
-}
-
 // NewDiscordHookForm form for creating discord hook
 type NewDiscordHookForm struct {
 	PayloadURL string `binding:"Required;ValidUrl"`
diff --git a/services/webhook/slack.go b/services/webhook/slack.go
index 11e1d3c081..e3d0d406de 100644
--- a/services/webhook/slack.go
+++ b/services/webhook/slack.go
@@ -7,6 +7,7 @@ package webhook
 import (
 	"errors"
 	"fmt"
+	"regexp"
 	"strings"
 
 	webhook_model "code.gitea.io/gitea/models/webhook"
@@ -286,3 +287,13 @@ func GetSlackPayload(p api.Payloader, event webhook_model.HookEventType, meta st
 
 	return convertPayloader(s, p, event)
 }
+
+var slackChannel = regexp.MustCompile(`^#?[a-z0-9_-]{1,80}$`)
+
+// IsValidSlackChannel validates a channel name conforms to what slack expects:
+// https://api.slack.com/methods/conversations.rename#naming
+// Conversation names can only contain lowercase letters, numbers, hyphens, and underscores, and must be 80 characters or less.
+// Gitea accepts if it starts with a #.
+func IsValidSlackChannel(name string) bool {
+	return slackChannel.MatchString(name)
+}
diff --git a/services/webhook/slack_test.go b/services/webhook/slack_test.go
index 8278afb69a..0f08785d25 100644
--- a/services/webhook/slack_test.go
+++ b/services/webhook/slack_test.go
@@ -170,3 +170,22 @@ func TestSlackJSONPayload(t *testing.T) {
 	require.NoError(t, err)
 	assert.NotEmpty(t, json)
 }
+
+func TestIsValidSlackChannel(t *testing.T) {
+	tt := []struct {
+		channelName string
+		expected    bool
+	}{
+		{"gitea", true},
+		{"#gitea", true},
+		{"  ", false},
+		{"#", false},
+		{" #", false},
+		{"gitea   ", false},
+		{"  gitea", false},
+	}
+
+	for _, v := range tt {
+		assert.Equal(t, v.expected, IsValidSlackChannel(v.channelName))
+	}
+}