Is there any alternative to string_view in embind?

[hzhangxyz]

Hello, I am using embind to export a buffer to js, and it works well, but I want to know how to do the inversed operator, how to pass a js uint8array to c++ part without copy?

em::val(em::typed_memory_view(size, reinterpret_cast<unsigned char*>(ptr)));

[hoodmane]

If the Uint8Array isn't already a view into WebAssembly memory, you'll need at least one copy if you want to have pointers into the buffer. All pointers are offsets into the WebAssembly memory. OTOH if you are okay with a read() style interface, it's possible to avoid a copy.

[hzhangxyz]

Thanks for your help :) Is there any docs about so called read() style interface?

[hoodmane]

Well, I was referring to https://www.man7.org/linux/man-pages/man2/read.2.html.
For instance if you use the JavaScript file system and the buffer is not going to change, you could mount it as a file with

FS.writeFile(`/some/path`, buf, { canOwn: true });

and then you can open /some/path and read bytes from it as you need them. This is zero copy. If the buffer will change, you might need to make a custom device.