wasm: Move streamFile() to qstdweb

This function is useful also outside of local file access,
for example when reading clipboard (file) content.

Change-Id: I132546deb6df2969467051c348c05d9331d2cfd2
Reviewed-by: David Skoland <david.skoland@qt.io>
Reviewed-by: Lorn Potter <lorn.potter@gmail.com>

src/corelib/platform/wasm/qstdweb.cpp

@@ -95,6 +95,51 @@ uint64_t File::size() const
     return uint64_t(m_file["size"].as<uint53_t>());
 }
 
+// Streams partial file content into the given buffer asynchronously. The completed
+// callback is called on completion.
+void File::stream(uint32_t offset, uint32_t length, char *buffer, const std::function<void ()> &completed) const
+{
+    // Read file in chunks in order to avoid holding two copies in memory at the same time
+    const uint32_t chunkSize = 256 * 1024;
+    const uint32_t end = offset + length;
+    // assert end < file.size
+    auto fileReader = std::make_shared<qstdweb::FileReader>();
+
+    // "this" is valid now, but may not be by the time the chunkCompleted callback
+    // below is made. Make a copy of the file handle.
+    const File fileHandle = *this;
+    auto chunkCompleted = std::make_shared<std::function<void (uint32_t, char *buffer)>>();
+    *chunkCompleted = [=](uint32_t chunkBegin, char *chunkBuffer) mutable {
+
+        // Copy current chunk from JS memory to Wasm memory
+        qstdweb::ArrayBuffer result = fileReader->result();
+        qstdweb::Uint8Array(result).copyTo(chunkBuffer);
+
+        // Read next chunk if not at buffer end
+        uint32_t nextChunkBegin = std::min(chunkBegin + result.byteLength(), end);
+        uint32_t nextChunkEnd = std::min(nextChunkBegin + chunkSize, end);
+        if (nextChunkBegin == end) {
+            completed();
+            chunkCompleted.reset();
+            return;
+        }
+        char *nextChunkBuffer = chunkBuffer + result.byteLength();
+        fileReader->onLoad([=]() { (*chunkCompleted)(nextChunkBegin, nextChunkBuffer); });
+        qstdweb::Blob blob = fileHandle.slice(nextChunkBegin, nextChunkEnd);
+        fileReader->readAsArrayBuffer(blob);
+    };
+
+    // Read first chunk. First iteration is a dummy iteration with no available data.
+    (*chunkCompleted)(offset, buffer);
+}
+
+// Streams file content into the given buffer asynchronously. The completed
+// callback is called on completion.
+void File::stream(char *buffer, const std::function<void ()> &completed) const
+{
+    stream(0, size(), buffer, completed);
+}
+
 FileList::FileList(const emscripten::val &fileList)
     :m_fileList(fileList)
 {

src/corelib/platform/wasm/qstdweb_p.h

@@ -99,6 +99,8 @@ namespace qstdweb {
         Blob slice(uint64_t begin, uint64_t end) const;
         std::string name() const;
         uint64_t size() const;
+        void stream(uint32_t offset, uint32_t length, char *buffer, const std::function<void ()> &completed) const;
+        void stream(char *buffer, const std::function<void ()> &completed) const;
 
     private:
         emscripten::val m_file = emscripten::val::undefined();

src/gui/platform/wasm/qwasmlocalfileaccess.cpp

@@ -48,44 +48,6 @@ QT_BEGIN_NAMESPACE
 
 namespace QWasmLocalFileAccess {
 
-void streamFile(const qstdweb::File &file, uint32_t offset, uint32_t length, char *buffer, const std::function<void ()> &completed)
-{
-    // Read file in chunks in order to avoid holding two copies in memory at the same time
-    const uint32_t chunkSize = 256 * 1024;
-    const uint32_t end = offset + length;
-    // assert end < file.size
-    auto fileReader = std::make_shared<qstdweb::FileReader>();
-
-    auto chunkCompleted = std::make_shared<std::function<void (uint32_t, char *buffer)>>();
-    *chunkCompleted = [=](uint32_t chunkBegin, char *chunkBuffer) mutable {
-
-        // Copy current chunk from JS memory to Wasm memory
-        qstdweb::ArrayBuffer result = fileReader->result();
-        qstdweb::Uint8Array(result).copyTo(chunkBuffer);
-
-        // Read next chunk if not at buffer end
-        uint32_t nextChunkBegin = std::min(chunkBegin + result.byteLength(), end);
-        uint32_t nextChunkEnd = std::min(nextChunkBegin + chunkSize, end);
-        if (nextChunkBegin == end) {
-            completed();
-            chunkCompleted.reset();
-            return;
-        }
-        char *nextChunkBuffer = chunkBuffer + result.byteLength();
-        fileReader->onLoad([=]() { (*chunkCompleted)(nextChunkBegin, nextChunkBuffer); });
-        qstdweb::Blob blob = file.slice(nextChunkBegin, nextChunkEnd);
-        fileReader->readAsArrayBuffer(blob);
-    };
-
-    // Read first chunk. First iteration is a dummy iteration with no available data.
-    (*chunkCompleted)(offset, buffer);
-}
-
-void streamFile(const qstdweb::File &file, char *buffer, const std::function<void ()> &completed)
-{
-    streamFile(file, 0, file.size(), buffer, completed);
-}
-
 void readFiles(const qstdweb::FileList &fileList,
     const std::function<char *(uint64_t size, const std::string name)> &acceptFile,
     const std::function<void ()> &fileDataReady)
@@ -109,7 +71,7 @@ void readFiles(const qstdweb::FileList &fileList,
         }
 
         // Read file data into caller-provided buffer
-        streamFile(file, buffer, [=]() {
+        file.stream(buffer, [=]() {
             fileDataReady();
             (*readFile)(fileIndex + 1);
         });