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Server-Timing: Reuse the WordPress 6.9 template enhancement output buffer #2515

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Server-Timing: Reuse the WordPress 6.9 template enhancement output buffer #2515

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61 changes: 19 additions & 42 deletions plugins/performance-lab/includes/server-timing/class-perflab-server-timing.php
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Original file line number Diff line number Diff line change
Expand Up @@ -144,7 +144,10 @@ public function has_registered_metric( string $metric_slug ): bool {
/**
* Outputs the Server-Timing header.
*
* This method must be called before rendering the page.
* This must run before the response body is flushed. When output buffering is enabled it is called at the
* {@see 'wp_finalized_template_enhancement_output_buffer'} action, after the template has been captured and
* enhanced; otherwise it is called at the {@see 'wp_before_include_template'} action, right before the template
* is included. Any extra arguments passed by those hooks are ignored.
*
* @since 1.8.0
*/
Expand Down Expand Up @@ -236,56 +239,30 @@ public function use_output_buffer(): bool {
/**
* Adds hooks to send the Server-Timing header.
*
* When output buffering is enabled, buffer as early as possible so that any other plugins that also do output
* buffering will be able to register Server-Timing metrics. The first output buffer callback to be registered
* is the last one to be called, so by starting the Server-Timing output buffer as soon as possible we can be
* assured that other plugins' output buffer callbacks will run before the Server-Timing one that sends the
* Server-Timing header.
* Since WordPress 6.9, this relies on the template enhancement output buffer introduced in Core-43258 (see
* r60936) rather than starting its own output buffer.
*
* When output buffering is enabled, the header is sent at the {@see 'wp_finalized_template_enhancement_output_buffer'}
* action so that metrics measured while the template is rendering are included. Registering a callback on that
* action also opts in to starting the core output buffer (see {@see wp_should_output_buffer_template_for_enhancement()}),
* and core ensures the {@see 'wp_template_enhancement_output_buffer'} filter (used by other consumers such as
* Optimization Detective) runs before this action, so their metrics are captured before the header is sent.
*
* When output buffering is disabled, the header is sent at the {@see 'wp_before_include_template'} action, right
* before the template is included. Note this action only fires when the resolved template is a readable file,
* unlike the previously used `template_include` filter which fired unconditionally.
*
* @since 3.2.0
* @since n.e.x.t Relies on the WordPress 6.9 template enhancement output buffer instead of starting its own.
*/
public function add_hooks(): void {
if ( $this->use_output_buffer() ) {
add_action( 'template_redirect', array( $this, 'start_output_buffer' ), PHP_INT_MIN );
add_action( 'wp_finalized_template_enhancement_output_buffer', array( $this, 'send_header' ) );
} else {
add_filter( 'template_include', array( $this, 'on_template_include' ), PHP_INT_MAX );
add_action( 'wp_before_include_template', array( $this, 'send_header' ) );
}
}

/**
* Hook callback for the 'template_include' filter.
*
* This effectively initializes the class to send the Server-Timing header at the right point.
*
* This method is solely intended for internal use within WordPress.
*
* @since 1.8.0
*
* @param mixed $passthrough Optional. Filter value. Default null.
* @return mixed Unmodified value of $passthrough.
*/
public function on_template_include( $passthrough = null ) {
$this->send_header();
return $passthrough;
}

/**
* Starts output buffering to send the Server-Timing header right before returning the buffer.
*
* @since 3.2.0
*/
public function start_output_buffer(): void {
ob_start(
function ( string $output, ?int $phase ): string {
// Only send the header when the buffer is not being cleaned.
if ( ( $phase & PHP_OUTPUT_HANDLER_CLEAN ) === 0 ) {
$this->send_header();
}
return $output;
}
);
}

/**
* Formats the header segment for a single metric.
*
Expand Down
12 changes: 6 additions & 6 deletions plugins/performance-lab/tests/includes/server-timing/test-load.php
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Original file line number Diff line number Diff line change
Expand Up @@ -17,8 +17,8 @@ public function test_perflab_server_timing(): void {

$server_timing = perflab_server_timing();
$this->assertFalse( $server_timing->use_output_buffer() );
$this->assertSame( PHP_INT_MAX, has_filter( 'template_include', array( $server_timing, 'on_template_include' ) ), 'template_include filter not added' );
$this->assertFalse( has_action( 'template_redirect', array( $server_timing, 'start_output_buffer' ) ), 'template_redirect action added' );
$this->assertSame( 10, has_action( 'wp_before_include_template', array( $server_timing, 'send_header' ) ), 'wp_before_include_template action not added' );
$this->assertFalse( has_action( 'wp_finalized_template_enhancement_output_buffer', array( $server_timing, 'send_header' ) ), 'wp_finalized_template_enhancement_output_buffer action added' );

$server_timing2 = perflab_server_timing();
$this->assertSame( $server_timing, $server_timing2, 'Different instance returned' );
Expand All @@ -28,15 +28,15 @@ public function test_perflab_server_timing(): void {
* @covers Perflab_Server_Timing::add_hooks
*/
public function test_perflab_server_timing_with_output_buffering(): void {
remove_all_actions( 'template_redirect' );
remove_all_filters( 'template_include' );
remove_all_actions( 'wp_before_include_template' );
remove_all_actions( 'wp_finalized_template_enhancement_output_buffer' );

$server_timing = perflab_server_timing();
add_filter( 'perflab_server_timing_use_output_buffer', '__return_true' );
$this->assertTrue( $server_timing->use_output_buffer() );
$server_timing->add_hooks();
$this->assertFalse( has_filter( 'template_include', array( $server_timing, 'on_template_include' ) ), 'template_include filter added' );
$this->assertSame( PHP_INT_MIN, has_action( 'template_redirect', array( $server_timing, 'start_output_buffer' ) ), 'template_redirect action not added' );
$this->assertFalse( has_action( 'wp_before_include_template', array( $server_timing, 'send_header' ) ), 'wp_before_include_template action added' );
$this->assertSame( 10, has_action( 'wp_finalized_template_enhancement_output_buffer', array( $server_timing, 'send_header' ) ), 'wp_finalized_template_enhancement_output_buffer action not added' );
}

public function test_perflab_server_timing_register_metric(): void {
Expand Down
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