fix: use CRC32 to shorten app subdomain (#9645)

coderd/httpapi/url.go

@@ -2,6 +2,7 @@ package httpapi
 
 import (
 	"fmt"
+	"hash/crc32"
 	"net"
 	"regexp"
 	"strings"
@@ -18,6 +19,8 @@ var (
 		nameRegex))
 
 	validHostnameLabelRegex = regexp.MustCompile(`^[a-z0-9]([-a-z0-9]*[a-z0-9])?$`)
+
+	crcTable = crc32.MakeTable(crc32.IEEE)
 )
 
 // ApplicationURL is a parsed application URL hostname.
@@ -39,7 +42,12 @@ func (a ApplicationURL) String() string {
 	_, _ = appURL.WriteString(a.WorkspaceName)
 	_, _ = appURL.WriteString("--")
 	_, _ = appURL.WriteString(a.Username)
-	return appURL.String()
+	hostname := appURL.String()
+
+	if len(hostname) < 64 { // max length for the subdomain level
+		return hostname
+	}
+	return fmt.Sprintf("app-%08x", crc32.Checksum([]byte(hostname), crcTable))
 }
 
 // ParseSubdomainAppURL parses an ApplicationURL from the given subdomain. If