From 9ea597016a55e68a3c05cd0984a97df890232aca Mon Sep 17 00:00:00 2001
From: Shannon Booth <shannon.ml.booth@gmail.com>
Date: Sun, 18 Jun 2023 21:45:39 +1200
Subject: [PATCH] LibWeb: Implement Streams AO ExtractHighWaterMark(strategy,
 defaultHWM)

---
 .../LibWeb/Streams/AbstractOperations.cpp     | 19 +++++++++++++++++++
 .../LibWeb/Streams/AbstractOperations.h       |  2 ++
 2 files changed, 21 insertions(+)

diff --git a/Userland/Libraries/LibWeb/Streams/AbstractOperations.cpp b/Userland/Libraries/LibWeb/Streams/AbstractOperations.cpp
index e1a2957c07..f374e74118 100644
--- a/Userland/Libraries/LibWeb/Streams/AbstractOperations.cpp
+++ b/Userland/Libraries/LibWeb/Streams/AbstractOperations.cpp
@@ -12,6 +12,7 @@
 #include <LibWeb/Bindings/ExceptionOrUtils.h>
 #include <LibWeb/DOM/AbortSignal.h>
 #include <LibWeb/Streams/AbstractOperations.h>
+#include <LibWeb/Streams/QueuingStrategy.h>
 #include <LibWeb/Streams/ReadableByteStreamController.h>
 #include <LibWeb/Streams/ReadableStream.h>
 #include <LibWeb/Streams/ReadableStreamBYOBReader.h>
@@ -186,6 +187,24 @@ bool readable_stream_has_default_reader(ReadableStream const& stream)
     return false;
 }
 
+// https://streams.spec.whatwg.org/#validate-and-normalize-high-water-mark
+WebIDL::ExceptionOr<double> extract_high_water_mark(QueuingStrategy const& strategy, double default_hwm)
+{
+    // 1. If strategy["highWaterMark"] does not exist, return defaultHWM.
+    if (!strategy.high_water_mark.has_value())
+        return default_hwm;
+
+    // 2. Let highWaterMark be strategy["highWaterMark"].
+    auto high_water_mark = strategy.high_water_mark.value();
+
+    // 3. If highWaterMark is NaN or highWaterMark < 0, throw a RangeError exception.
+    if (isnan(high_water_mark) || high_water_mark < 0)
+        return WebIDL::SimpleException { WebIDL::SimpleExceptionType::RangeError, "Invalid value for high water mark"sv };
+
+    // 4. Return highWaterMark.
+    return high_water_mark;
+}
+
 // https://streams.spec.whatwg.org/#readable-stream-close
 void readable_stream_close(ReadableStream& stream)
 {
diff --git a/Userland/Libraries/LibWeb/Streams/AbstractOperations.h b/Userland/Libraries/LibWeb/Streams/AbstractOperations.h
index 6ff90c6e5c..f76502ff8a 100644
--- a/Userland/Libraries/LibWeb/Streams/AbstractOperations.h
+++ b/Userland/Libraries/LibWeb/Streams/AbstractOperations.h
@@ -28,6 +28,8 @@ using WriteAlgorithm = JS::SafeFunction<WebIDL::ExceptionOr<JS::NonnullGCPtr<Web
 WebIDL::ExceptionOr<JS::NonnullGCPtr<ReadableStreamDefaultReader>> acquire_readable_stream_default_reader(ReadableStream&);
 bool is_readable_stream_locked(ReadableStream const&);
 
+WebIDL::ExceptionOr<double> extract_high_water_mark(QueuingStrategy const&, double default_hwm);
+
 void readable_stream_close(ReadableStream&);
 void readable_stream_error(ReadableStream&, JS::Value error);
 void readable_stream_add_read_request(ReadableStream&, ReadRequest const&);