Fix "WordPress\ByteStream\ByteStreamException: Cannot seek to a negative offset"

This errors seems to occur in some scenarios when the RequestReadStream reaches
the end of the data, without processing the FINISHED event within pull_until_event().
Originally, the remote_file_length was backfilled only while processing the FINISHED
event; now it's ensured also when the file length is actually read.

Author: JanJakes

.github/workflows/debugging-tests.yml

@@ -0,0 +1,24 @@
+name: CI
+on: [push]
+jobs:
+  build:
+    runs-on: macos-latest
+    steps:
+    - uses: actions/checkout@v2
+
+    - name: Set up PHP
+      uses: shivammathur/setup-php@v2
+      with:
+        php-version: '8.0'
+        tools: phpunit-polyfills
+        extensions: zip, sqlite3, pdo, pdo_sqlite
+
+    - name: Install Composer dependencies (using composer-ci-matrix-tests.json)
+      run: |
+        php -r "echo OPENSSL_VERSION_TEXT;"
+        rm composer.lock
+        cp composer-ci-matrix-tests.json composer.json
+        composer install --no-interaction --no-progress --optimize-autoloader
+
+    - name: Setup tmate session
+      uses: mxschmitt/action-tmate@v3

components/HttpClient/ByteStream/RequestReadStream.php

@@ -183,6 +183,14 @@ private function pull_until_event( $options = array() ) {
 	}
 
 	public function length(): ?int {
+		/*
+		 * If the server did not provide a Content-Length header and we've reached
+		 * the end of the data without processing the FINISHED event, we need to
+		 * ensure the file length is backfilled to the number of downloaded bytes.
+		 */
+		if ( null === $this->remote_file_length && $this->internal_reached_end_of_data() ) {
+			$this->remote_file_length = $this->bytes_already_forgotten + strlen( $this->buffer );
+		}
 		return $this->remote_file_length;
 	}