Avoid unnecessary async for no-op body decoding, and drop encoded data

We now drop encoded data entirely after it's been decoded, which ensures
we don't duplicate data storage here especially for large body cases.

Author: pimterry

src/model/events/bodies.ts

@@ -31,4 +31,12 @@ export function testEncodings(message: ExchangeMessage): EncodedBodySizes | unde
         // Will be undefined, but ensures we're subscribed to the observable
         return sizesObservable.get();
     }
+}
+
+export function decodingRequired(encodedBuffer: Buffer, encodings: string[]): boolean {
+    return !(
+        encodings.length === 0 || // No encoding
+        (encodings.length === 1 && encodings[0] === 'identity') || // No-op only encoding
+        encodedBuffer.length === 0 // Empty body (e.g. HEAD, 204, etc)
+    );
 }

src/model/http/http-body.ts

@@ -19,6 +19,7 @@ import {
 
 import { logError } from '../../errors';
 import { decodeBody } from '../../services/ui-worker-api';
+import { decodingRequired } from '../events/bodies';
 
 export class HttpBody implements MessageBody {
 
@@ -116,13 +117,17 @@ export class HttpBody implements MessageBody {
                 // One is always set - so if _decoded is not set, _encoded must be.
                 const encodedBuffer = this._encoded as Buffer;
 
-                // Temporarily change to a fake buffer, while the web worker takes the data to decode
+                // Change to a fake buffer, while the web worker takes the data to decode. If we
+                // decoded successfully, we never put this back (to avoid duplicting the data).
                 const encodedLength = encodedBuffer.byteLength;
                 this._encoded = fakeBuffer(encodedLength);
 
                 try {
-                    const { decoded, encoded } = await decodeBody(encodedBuffer, this._contentEncoding);
-                    this._encoded = encoded;
+                    // We short-circuit (to avoid the render+async+re-render) if we know that
+                    // decoding is not actually required here.
+                    const { decoded } = decodingRequired(encodedBuffer, this._contentEncoding)
+                        ? await decodeBody(encodedBuffer, this._contentEncoding)
+                        : { decoded: encodedBuffer };
 
                     runInAction(() => {
                         this._decoded = decoded;

src/services/ui-worker-api.ts

@@ -24,6 +24,7 @@ import type {
 import { Headers, Omit } from '../types';
 import type { ApiMetadata, ApiSpec } from '../model/api/api-interfaces';
 import { WorkerFormatterKey } from './ui-worker-formatters';
+import { decodingRequired } from '../model/events/bodies';
 
 const worker = new Worker(new URL('./ui-worker', import.meta.url));
 
@@ -68,11 +69,7 @@ function callApi<
  * original encoded data (transferred back) in a new buffer.
  */
 export async function decodeBody(encodedBuffer: Buffer, encodings: string[]) {
-    if (
-        encodings.length === 0 || // No encoding
-        (encodings.length === 1 && encodings[0] === 'identity') || // No-op only encoding
-        encodedBuffer.length === 0 // Empty body (e.g. HEAD, 204, etc)
-    ) {
+    if (!decodingRequired(encodedBuffer, encodings)) {
         // Shortcut to skip decoding when we know it's not required:
         return { encoded: encodedBuffer, decoded: encodedBuffer };
     }