wasm: Move Blob creation code to qstdweb

Add Uint8Array::copyFrom() and Blob::copyFrom(), which
constructs JS data containers with content copied from
the C heap.

These should not be confused with e.g. the Uint8Array(buffer, size)
constructor, which creates a Uint8Array which references
content on the heap, without making a copy.

Change-Id: Id7d25d8044ee3914d74698e5a15c93226568eaf3
Reviewed-by: David Skoland <david.skoland@qt.io>
Reviewed-by: Lorn Potter <lorn.potter@gmail.com>

2 files changed, 51 insertions, 2 deletions

diff --git a/src/corelib/platform/wasm/qstdweb.cpp b/src/corelib/platform/wasm/qstdweb.cpp
index 789ceda6ab..fc2bf9cf96 100644
--- a/src/corelib/platform/wasm/qstdweb.cpp
+++ b/src/corelib/platform/wasm/qstdweb.cpp
@@ -49,6 +49,11 @@ namespace qstdweb {
 
 typedef double uint53_t; // see Number.MAX_SAFE_INTEGER
 
+ArrayBuffer::ArrayBuffer(uint32_t size)
+{
+    m_arrayBuffer = emscripten::val::global("ArrayBuffer").new_(size);
+}
+
 ArrayBuffer::ArrayBuffer(const emscripten::val &arrayBuffer)
     :m_arrayBuffer(arrayBuffer)
 {
@@ -74,6 +79,23 @@ uint32_t Blob::size() const
     return m_blob["size"].as<uint32_t>();
 }
 
+// Copies content from the given buffer into a Blob object
+Blob Blob::copyFrom(const char *buffer, uint32_t size)
+{
+    Uint8Array contentCopy = Uint8Array::copyFrom(buffer, size);
+
+    emscripten::val contentArray = emscripten::val::array();
+    contentArray.call<void>("push", contentCopy.m_uint8Array);
+    emscripten::val type = emscripten::val::object();
+    type.set("type","application/octet-stream");
+    return Blob(emscripten::val::global("Blob").new_(contentArray, type));
+}
+
+emscripten::val Blob::val()
+{
+    return m_blob;
+}
+
 File::File(const emscripten::val &file)
 :m_file(file)
 {
@@ -191,30 +213,41 @@ Uint8Array Uint8Array::heap()
     return Uint8Array(heap_());
 }
 
+// Constructs a Uint8Array which references the given emscripten::val, which must contain a JS Unit8Array
 Uint8Array::Uint8Array(const emscripten::val &uint8Array)
 : m_uint8Array(uint8Array)
 {
 
 }
 
+// Constructs a Uint8Array which references an ArrayBuffer
 Uint8Array::Uint8Array(const ArrayBuffer &buffer)
 : m_uint8Array(Uint8Array::constructor_().new_(buffer.m_arrayBuffer))
 {
 
 }
 
+// Constructs a Uint8Array which references a view into an ArrayBuffer
 Uint8Array::Uint8Array(const ArrayBuffer &buffer, uint32_t offset, uint32_t length)
 : m_uint8Array(Uint8Array::constructor_().new_(buffer.m_arrayBuffer, offset, length))
 {
 
 }
 
-Uint8Array::Uint8Array(char *buffer, uint32_t size)
+// Constructs a Uint8Array which references an area on the heap.
+Uint8Array::Uint8Array(const char *buffer, uint32_t size)
 :m_uint8Array(Uint8Array::constructor_().new_(Uint8Array::heap().buffer().m_arrayBuffer, uint32_t(buffer), size))
 {
 
 }
 
+// Constructs a Uint8Array which allocates and references a new ArrayBuffer with the given size.
+Uint8Array::Uint8Array(uint32_t size)
+: m_uint8Array(Uint8Array::constructor_().new_(size))
+{
+
+}
+
 ArrayBuffer Uint8Array::buffer() const
 {
     return ArrayBuffer(m_uint8Array["buffer"]);
@@ -230,16 +263,26 @@ void Uint8Array::set(const Uint8Array &source)
     m_uint8Array.call<void>("set", source.m_uint8Array); // copies source content
 }
 
+// Copies the Uint8Array conent to a destination on the heap
 void Uint8Array::copyTo(char *destination) const
 {
     Uint8Array(destination, length()).set(*this);
 }
 
+// Copies the Uint8Array conent to a destination on the heap
 void Uint8Array::copy(char *destination, const Uint8Array &source)
 {
     Uint8Array(destination, source.length()).set(source);
 }
 
+// Copies content from a source on the heap to a new Uint8Array object
+Uint8Array Uint8Array::copyFrom(const char *buffer, uint32_t size)
+{
+    Uint8Array contentCopy(size);
+    contentCopy.set(Uint8Array(buffer, size));
+    return contentCopy;
+}
+
 emscripten::val Uint8Array::heap_()
 {
     return emscripten::val::module_property("HEAPU8");
diff --git a/src/corelib/platform/wasm/qstdweb_p.h b/src/corelib/platform/wasm/qstdweb_p.h
index ff83c73dd5..fc52dc1a71 100644
--- a/src/corelib/platform/wasm/qstdweb_p.h
+++ b/src/corelib/platform/wasm/qstdweb_p.h
@@ -73,6 +73,7 @@ namespace qstdweb {
 
     class ArrayBuffer {
     public:
+        explicit ArrayBuffer(uint32_t size);
         explicit ArrayBuffer(const emscripten::val &arrayBuffer);
         uint32_t byteLength() const;
 
@@ -85,6 +86,8 @@ namespace qstdweb {
     public:
         explicit Blob(const emscripten::val &blob);
         uint32_t size() const;
+        static Blob copyFrom(const char *buffer, uint32_t size);
+        emscripten::val val();
 
     private:
         friend class FileReader;
@@ -140,8 +143,9 @@ namespace qstdweb {
         static Uint8Array heap();
         explicit Uint8Array(const emscripten::val &uint8Array);
         explicit Uint8Array(const ArrayBuffer &buffer);
+        explicit Uint8Array(uint32_t size);
         Uint8Array(const ArrayBuffer &buffer, uint32_t offset, uint32_t length);
-        Uint8Array(char *buffer, uint32_t size);
+        Uint8Array(const char *buffer, uint32_t size);
 
         ArrayBuffer buffer() const;
         uint32_t length() const;
@@ -149,7 +153,9 @@ namespace qstdweb {
 
         void copyTo(char *destination) const;
         static void copy(char *destination, const Uint8Array &source);
+        static Uint8Array copyFrom(const char *buffer, uint32_t size);
     private:
+        friend class Blob;
         static emscripten::val heap_();
         static emscripten::val constructor_();
         emscripten::val m_uint8Array = emscripten::val::undefined();