[feature] add worker task serialization logic (#2989)

* improved server shutdown with more precise shutdown of modules + deferring of ALL of it

* move delivery and workers into separate files

* add worker task model and Serialize() / Deserialize() methods for message types

* start adding message serialize / deserialize tests

* start adding test cases

* update body rewinding to rely on standard library mechanism of r.GetBody()

* remove request rewinding (http.Client{} should already handle this)

* standard library already handles rewinding

* improved code comment

* move the newPOST() function contents to prepare(), fits better with current API

* add Serialize() / Deserialize() implementations for Delivery{} type

* finish writing FromClientAPI sserialize / deserialize tests

* start adding FromFediAPI{} serialize / deserialize test cases

* fix FromFediAPI{} tests

* add tests for delivery message type

* fix repeat code

* missing license header

* use testrig status and accounts for marshal / unmarshaling tests

* add a specific test for checking account RSA keys are preserved

internal/transport/deliver.go

@@ -18,12 +18,12 @@
 package transport
 
 import (
+	"bytes"
 	"context"
 	"encoding/json"
 	"net/http"
 	"net/url"
 
-	"codeberg.org/gruf/go-byteutil"
 	apiutil "github.com/superseriousbusiness/gotosocial/internal/api/util"
 	"github.com/superseriousbusiness/gotosocial/internal/config"
 	"github.com/superseriousbusiness/gotosocial/internal/gtscontext"
@@ -130,25 +130,28 @@ func (t *transport) prepare(
 	*delivery.Delivery,
 	error,
 ) {
-	url := to.String()
-
-	// Use rewindable reader for body.
-	var body byteutil.ReadNopCloser
-	body.Reset(data)
-
 	// Prepare POST signer.
 	sign := t.signPOST(data)
 
+	// Use *bytes.Reader for request body,
+	// as NewRequest() automatically will
+	// set .GetBody and content-length.
+	// (this handles necessary rewinding).
+	body := bytes.NewReader(data)
+
 	// Update to-be-used request context with signing details.
 	ctx = gtscontext.SetOutgoingPublicKeyID(ctx, t.pubKeyID)
 	ctx = gtscontext.SetHTTPClientSignFunc(ctx, sign)
 
 	// Prepare a new request with data body directed at URL.
-	r, err := http.NewRequestWithContext(ctx, "POST", url, &body)
+	r, err := http.NewRequestWithContext(ctx, "POST", to.String(), body)
 	if err != nil {
 		return nil, gtserror.Newf("error preparing request: %w", err)
 	}
 
+	// Set our predefined controller user-agent.
+	r.Header.Set("User-Agent", t.controller.userAgent)
+
 	// Set the standard ActivityPub content-type + charset headers.
 	r.Header.Add("Content-Type", string(apiutil.AppActivityLDJSON))
 	r.Header.Add("Accept-Charset", "utf-8")