[feature] Allow delivery to sharedInboxes where possible (#847)

* update Activity

* add instance-deliver-to-shared-inboxes setting

* update activity version again

* add SharedInboxURI field to accounts

* serdes for endpoints/sharedInbox

* deliver to sharedInbox if one is available

* update tests

* only assign shared inbox if shared domain

* look for shared inbox if currently nil

* go fmt

* finger to get params.RemoteAccountID if necessary

* make comments clearer

* compare dns more consistently

4 files changed, 32 insertions, 4 deletions

diff --git a/internal/config/config.go b/internal/config/config.go
index 7c0bf99a7..ff77bd367 100644
--- a/internal/config/config.go
+++ b/internal/config/config.go
@@ -67,8 +67,9 @@ type Configuration struct {
 	WebTemplateBaseDir string `name:"web-template-base-dir" usage:"Basedir for html templating files for rendering pages and composing emails."`
 	WebAssetBaseDir    string `name:"web-asset-base-dir" usage:"Directory to serve static assets from, accessible at example.org/assets/"`
 
-	InstanceExposePeers     bool `name:"instance-expose-peers" usage:"Allow unauthenticated users to query /api/v1/instance/peers?filter=open"`
-	InstanceExposeSuspended bool `name:"instance-expose-suspended" usage:"Expose suspended instances via web UI, and allow unauthenticated users to query /api/v1/instance/peers?filter=suspended"`
+	InstanceExposePeers            bool `name:"instance-expose-peers" usage:"Allow unauthenticated users to query /api/v1/instance/peers?filter=open"`
+	InstanceExposeSuspended        bool `name:"instance-expose-suspended" usage:"Expose suspended instances via web UI, and allow unauthenticated users to query /api/v1/instance/peers?filter=suspended"`
+	InstanceDeliverToSharedInboxes bool `name:"instance-deliver-to-shared-inboxes" usage:"Deliver federated messages to shared inboxes, if they're available."`
 
 	AccountsRegistrationOpen bool `name:"accounts-registration-open" usage:"Allow anyone to submit an account signup request. If false, server will be invite-only."`
 	AccountsApprovalRequired bool `name:"accounts-approval-required" usage:"Do account signups require approval by an admin or moderator before user can log in? If false, new registrations will be automatically approved."`
diff --git a/internal/config/defaults.go b/internal/config/defaults.go
index a0d409c5f..5eb87ce68 100644
--- a/internal/config/defaults.go
+++ b/internal/config/defaults.go
@@ -46,8 +46,9 @@ var Defaults = Configuration{
 	WebTemplateBaseDir: "./web/template/",
 	WebAssetBaseDir:    "./web/assets/",
 
-	InstanceExposePeers:     false,
-	InstanceExposeSuspended: false,
+	InstanceExposePeers:            false,
+	InstanceExposeSuspended:        false,
+	InstanceDeliverToSharedInboxes: true,
 
 	AccountsRegistrationOpen: true,
 	AccountsApprovalRequired: true,
diff --git a/internal/config/flags.go b/internal/config/flags.go
index 183ed3762..f37a50c9e 100644
--- a/internal/config/flags.go
+++ b/internal/config/flags.go
@@ -63,6 +63,7 @@ func AddServerFlags(cmd *cobra.Command) {
 		// Instance
 		cmd.Flags().Bool(InstanceExposePeersFlag(), cfg.InstanceExposePeers, fieldtag("InstanceExposePeers", "usage"))
 		cmd.Flags().Bool(InstanceExposeSuspendedFlag(), cfg.InstanceExposeSuspended, fieldtag("InstanceExposeSuspended", "usage"))
+		cmd.Flags().Bool(InstanceDeliverToSharedInboxesFlag(), cfg.InstanceDeliverToSharedInboxes, fieldtag("InstanceDeliverToSharedInboxes", "usage"))
 
 		// Accounts
 		cmd.Flags().Bool(AccountsRegistrationOpenFlag(), cfg.AccountsRegistrationOpen, fieldtag("AccountsRegistrationOpen", "usage"))
diff --git a/internal/config/helpers.gen.go b/internal/config/helpers.gen.go
index c8fd4f621..adc020aba 100644
--- a/internal/config/helpers.gen.go
+++ b/internal/config/helpers.gen.go
@@ -593,6 +593,31 @@ func GetInstanceExposeSuspended() bool { return global.GetInstanceExposeSuspende
 // SetInstanceExposeSuspended safely sets the value for global configuration 'InstanceExposeSuspended' field
 func SetInstanceExposeSuspended(v bool) { global.SetInstanceExposeSuspended(v) }
 
+// GetInstanceDeliverToSharedInboxes safely fetches the Configuration value for state's 'InstanceDeliverToSharedInboxes' field
+func (st *ConfigState) GetInstanceDeliverToSharedInboxes() (v bool) {
+	st.mutex.Lock()
+	v = st.config.InstanceDeliverToSharedInboxes
+	st.mutex.Unlock()
+	return
+}
+
+// SetInstanceDeliverToSharedInboxes safely sets the Configuration value for state's 'InstanceDeliverToSharedInboxes' field
+func (st *ConfigState) SetInstanceDeliverToSharedInboxes(v bool) {
+	st.mutex.Lock()
+	defer st.mutex.Unlock()
+	st.config.InstanceDeliverToSharedInboxes = v
+	st.reloadToViper()
+}
+
+// InstanceDeliverToSharedInboxesFlag returns the flag name for the 'InstanceDeliverToSharedInboxes' field
+func InstanceDeliverToSharedInboxesFlag() string { return "instance-deliver-to-shared-inboxes" }
+
+// GetInstanceDeliverToSharedInboxes safely fetches the value for global configuration 'InstanceDeliverToSharedInboxes' field
+func GetInstanceDeliverToSharedInboxes() bool { return global.GetInstanceDeliverToSharedInboxes() }
+
+// SetInstanceDeliverToSharedInboxes safely sets the value for global configuration 'InstanceDeliverToSharedInboxes' field
+func SetInstanceDeliverToSharedInboxes(v bool) { global.SetInstanceDeliverToSharedInboxes(v) }
+
 // GetAccountsRegistrationOpen safely fetches the Configuration value for state's 'AccountsRegistrationOpen' field
 func (st *ConfigState) GetAccountsRegistrationOpen() (v bool) {
 	st.mutex.Lock()