[GStreamer][WebCodecs] Harness dumping for easier debugging

https://bugs.webkit.org/show_bug.cgi?id=262177

Reviewed by Xabier Rodriguez-Calvar.

Dump the harness graph to disk when the first encoded or decoded payload has been notified. This can
be useful for debugging purposes. Also driving-by in the Harness, add space characters at link
boundaries to prevent ambiguous links, especially for pads or element names starting with 'o'.

* Source/WebCore/platform/audio/gstreamer/AudioDecoderGStreamer.cpp:
(WebCore::GStreamerInternalAudioDecoder::GStreamerInternalAudioDecoder):
* Source/WebCore/platform/audio/gstreamer/AudioEncoderGStreamer.cpp:
(WebCore::GStreamerInternalAudioEncoder::GStreamerInternalAudioEncoder):
* Source/WebCore/platform/graphics/gstreamer/VideoDecoderGStreamer.cpp:
(WebCore::GStreamerInternalVideoDecoder::GStreamerInternalVideoDecoder):
* Source/WebCore/platform/graphics/gstreamer/VideoEncoderGStreamer.cpp:
(WebCore::GStreamerInternalVideoEncoder::GStreamerInternalVideoEncoder):
* Source/WebCore/platform/gstreamer/GStreamerElementHarness.cpp:
(WebCore::MermaidBuilder::process):
(WebCore::MermaidBuilder::dumpElement):

Canonical link: https://commits.webkit.org/268583@main

Source/WebCore/platform/audio/gstreamer/AudioDecoderGStreamer.cpp

@@ -260,6 +260,11 @@ GStreamerInternalAudioDecoder::GStreamerInternalAudioDecoder(const String& codec
         if (!gst_buffer_n_memory(outputBuffer.get()))
             return;
 
+        static std::once_flag onceFlag;
+        std::call_once(onceFlag, [this] {
+            m_harness->dumpGraph("audio-decoder");
+        });
+
         GST_TRACE_OBJECT(m_harness->element(), "Got frame with PTS: %" GST_TIME_FORMAT, GST_TIME_ARGS(GST_BUFFER_PTS(outputBuffer.get())));
 
         const GstSegment* segment = nullptr;

Source/WebCore/platform/audio/gstreamer/AudioEncoderGStreamer.cpp

@@ -256,6 +256,11 @@ GStreamerInternalAudioEncoder::GStreamerInternalAudioEncoder(const String& codec
             return;
         }
 
+        static std::once_flag onceFlag;
+        std::call_once(onceFlag, [this] {
+            m_harness->dumpGraph("audio-encoder");
+        });
+
         bool isKeyFrame = !GST_BUFFER_FLAG_IS_SET(outputBuffer.get(), GST_BUFFER_FLAG_DELTA_UNIT);
         GST_TRACE_OBJECT(m_harness->element(), "Notifying encoded%s frame", isKeyFrame ? " key" : "");
         GstMappedBuffer mappedBuffer(outputBuffer.get(), GST_MAP_READ);

Source/WebCore/platform/graphics/gstreamer/VideoDecoderGStreamer.cpp

@@ -241,6 +241,11 @@ GStreamerInternalVideoDecoder::GStreamerInternalVideoDecoder(const String& codec
         if (m_isClosed)
             return;
 
+        static std::once_flag onceFlag;
+        std::call_once(onceFlag, [this] {
+            m_harness->dumpGraph("video-decoder");
+        });
+
         GST_TRACE_OBJECT(m_harness->element(), "Got frame with PTS: %" GST_TIME_FORMAT, GST_TIME_ARGS(GST_BUFFER_PTS(outputBuffer.get())));
 
         if (m_presentationSize.isEmpty())

Source/WebCore/platform/graphics/gstreamer/VideoEncoderGStreamer.cpp

@@ -221,6 +221,11 @@ GStreamerInternalVideoEncoder::GStreamerInternalVideoEncoder(const String& codec
         if (m_isClosed)
             return;
 
+        static std::once_flag onceFlag;
+        std::call_once(onceFlag, [this] {
+            m_harness->dumpGraph("video-encoder");
+        });
+
         bool isKeyFrame = !GST_BUFFER_FLAG_IS_SET(outputBuffer.get(), GST_BUFFER_FLAG_DELTA_UNIT);
         GST_TRACE_OBJECT(m_harness->element(), "Notifying encoded%s frame", isKeyFrame ? " key" : "");
         GstMappedBuffer encodedImage(outputBuffer.get(), GST_MAP_READ);

Source/WebCore/platform/gstreamer/GStreamerElementHarness.cpp

@@ -488,7 +488,7 @@ void MermaidBuilder::process(GStreamerElementHarness& harness, bool generateFoot
         if (!downstreamHarness)
             continue;
         process(*downstreamHarness, false);
-        m_stringBuilder.append(padId, "--->"_s, generatePadId(*downstreamHarness, downstreamHarness->inputPad()), '\n');
+        m_stringBuilder.append(padId, " ---> "_s, generatePadId(*downstreamHarness, downstreamHarness->inputPad()), '\n');
     }
 
     if (!generateFooter)
@@ -497,12 +497,12 @@ void MermaidBuilder::process(GStreamerElementHarness& harness, bool generateFoot
     for (auto& [padHarness, srcPad, sinkPad] : m_padLinks) {
         m_stringBuilder.append(generatePadId(padHarness, srcPad.get()), ":::"_s, getPadClass(srcPad));
         if (GST_IS_PROXY_PAD(srcPad.get()))
-            m_stringBuilder.append("--->"_s);
+            m_stringBuilder.append(" ---> "_s);
         else if (auto srcCaps = adoptGRef(gst_pad_get_current_caps(srcPad.get()))) {
             auto capsString = describeCaps(srcCaps.get());
-            m_stringBuilder.append("--\""_s, capsString, "\"-->"_s);
+            m_stringBuilder.append(" --\""_s, capsString, "\"--> "_s);
         } else
-            m_stringBuilder.append("--->"_s);
+            m_stringBuilder.append(" ---> "_s);
         m_stringBuilder.append(generatePadId(padHarness, sinkPad.get()), ":::"_s, getPadClass(sinkPad), '\n');
     }
 
@@ -572,7 +572,7 @@ void MermaidBuilder::dumpElement(GStreamerElementHarness& harness, GstElement* e
     // There is no clean way to maintain subgraph ordering, so draw invisible links between pads.
     // Upstream bug report: https://github.com/mermaid-js/mermaid/issues/815
     if (firstSinkPad && firstSrcPad) {
-        m_stringBuilder.append(generatePadId(harness, firstSinkPad.get()), "---"_s, generatePadId(harness, firstSrcPad.get()), '\n');
+        m_stringBuilder.append(generatePadId(harness, firstSinkPad.get()), " --- "_s, generatePadId(harness, firstSrcPad.get()), '\n');
         m_stringBuilder.append("linkStyle "_s, m_invisibleLinesCounter, " stroke-width:0px\n"_s);
         m_invisibleLinesCounter++;
     }