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diff --git a/js/public/StreamConsumer.h b/js/public/StreamConsumer.h
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+++ b/js/public/StreamConsumer.h
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+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef js_StreamConsumer_h
+#define js_StreamConsumer_h
+
+#include "mozilla/Attributes.h"
+#include "mozilla/RefCountType.h"
+
+#include <stddef.h>
+#include <stdint.h>
+
+#include "jstypes.h"
+
+#include "js/AllocPolicy.h"
+#include "js/TypeDecls.h"
+#include "js/UniquePtr.h"
+#include "js/Vector.h"
+
+namespace JS {
+
+/**
+ * The ConsumeStreamCallback is called from an active JSContext, passing a
+ * StreamConsumer that wishes to consume the given host object as a stream of
+ * bytes with the given MIME type. On failure, the embedding must report the
+ * appropriate error on 'cx'. On success, the embedding must call
+ * consumer->consumeChunk() repeatedly on any thread until exactly one of:
+ *  - consumeChunk() returns false
+ *  - the embedding calls consumer->streamEnd()
+ *  - the embedding calls consumer->streamError()
+ * before JS_DestroyContext(cx) or JS::ShutdownAsyncTasks(cx) is called.
+ *
+ * Note: consumeChunk(), streamEnd() and streamError() may be called
+ * synchronously by ConsumeStreamCallback.
+ *
+ * When streamEnd() is called, the embedding may optionally pass an
+ * OptimizedEncodingListener*, indicating that there is a cache entry associated
+ * with this stream that can store an optimized encoding of the bytes that were
+ * just streamed at some point in the future by having SpiderMonkey call
+ * storeOptimizedEncoding(). Until the optimized encoding is ready, SpiderMonkey
+ * will hold an outstanding refcount to keep the listener alive.
+ *
+ * After storeOptimizedEncoding() is called, on cache hit, the embedding
+ * may call consumeOptimizedEncoding() instead of consumeChunk()/streamEnd().
+ * The embedding must ensure that the GetOptimizedEncodingBuildId() (see
+ * js/BuildId.h) at the time when an optimized encoding is created is the same
+ * as when it is later consumed.
+ */
+
+class OptimizedEncodingListener {
+ protected:
+  virtual ~OptimizedEncodingListener() = default;
+
+ public:
+  // SpiderMonkey will hold an outstanding reference count as long as it holds
+  // a pointer to OptimizedEncodingListener.
+  virtual MozExternalRefCountType MOZ_XPCOM_ABI AddRef() = 0;
+  virtual MozExternalRefCountType MOZ_XPCOM_ABI Release() = 0;
+
+  // SpiderMonkey may optionally call storeOptimizedEncoding() after it has
+  // finished processing a streamed resource.
+  virtual void storeOptimizedEncoding(const uint8_t* bytes, size_t length) = 0;
+};
+
+class JS_PUBLIC_API StreamConsumer {
+ protected:
+  // AsyncStreamConsumers are created and destroyed by SpiderMonkey.
+  StreamConsumer() = default;
+  virtual ~StreamConsumer() = default;
+
+ public:
+  // Called by the embedding as each chunk of bytes becomes available.
+  // If this function returns 'false', the stream must drop all pointers to
+  // this StreamConsumer.
+  virtual bool consumeChunk(const uint8_t* begin, size_t length) = 0;
+
+  // Called by the embedding when the stream reaches end-of-file, passing the
+  // listener described above.
+  virtual void streamEnd(OptimizedEncodingListener* listener = nullptr) = 0;
+
+  // Called by the embedding when there is an error during streaming. The
+  // given error code should be passed to the ReportStreamErrorCallback on the
+  // main thread to produce the semantically-correct rejection value.
+  virtual void streamError(size_t errorCode) = 0;
+
+  // Called by the embedding *instead of* consumeChunk()/streamEnd() if an
+  // optimized encoding is available from a previous streaming of the same
+  // contents with the same optimized build id.
+  virtual void consumeOptimizedEncoding(const uint8_t* begin,
+                                        size_t length) = 0;
+
+  // Provides optional stream attributes such as base or source mapping URLs.
+  // Necessarily called before consumeChunk(), streamEnd(), streamError() or
+  // consumeOptimizedEncoding(). The caller retains ownership of the strings.
+  virtual void noteResponseURLs(const char* maybeUrl,
+                                const char* maybeSourceMapUrl) = 0;
+};
+
+enum class MimeType { Wasm };
+
+using ConsumeStreamCallback = bool (*)(JSContext*, JS::HandleObject, MimeType,
+                                       StreamConsumer*);
+
+using ReportStreamErrorCallback = void (*)(JSContext*, size_t);
+
+extern JS_PUBLIC_API void InitConsumeStreamCallback(
+    JSContext* cx, ConsumeStreamCallback consume,
+    ReportStreamErrorCallback report);
+
+}  // namespace JS
+
+#endif  // js_StreamConsumer_h