Add shared inbox support for ActivityPub delivery (#4755)

* feat(ap): add support for shared inboxes to reduce outbound load

* feat(db): refactor ap followers db into followers repository

* fix(ap): use the updated activity library to pull out the shared inbox endpoint

* chore(deps): point at updated build of owncast/activity

* fix(ap): typeless endpoints

* feat(test): update ActivityPub test to support shared inboxes

* chore(test): remove unused variable

* fix: feedback from review. Guard against SSRF/non-HTTPS/local and handle transaction errors

utils/utils.go

@@ -6,6 +6,7 @@ import (
 	"errors"
 	"fmt"
 	"io"
+	"math"
 	"math/rand"
 	"net/url"
 	"os"
@@ -422,6 +423,17 @@ func IntPercentage(x, total int) int {
 	return int(float64(x) / float64(total) * 100)
 }
 
+// SafeIntToInt32 safely converts an int to int32, clamping to int32 bounds.
+func SafeIntToInt32(n int) int32 {
+	if n > math.MaxInt32 {
+		return math.MaxInt32
+	}
+	if n < math.MinInt32 {
+		return math.MinInt32
+	}
+	return int32(n)
+}
+
 // DecodeBase64Image decodes a base64 image string into a byte array, returning the extension (including dot) for the content type.
 func DecodeBase64Image(url string) (bytes []byte, extension string, err error) {
 	s := strings.SplitN(url, ",", 2)