如何ES6代理ArrayBuffer或Uint8Array？

Question

These work:

crypto.subtle.digest('SHA-512', new Uint8Array([0]))
crypto.subtle.digest('SHA-512', new Uint8Array([0]).buffer)

These don't:

crypto.subtle.digest('SHA-512', new Proxy(new Uint8Array([0]),{}))
crypto.subtle.digest('SHA-512', new Proxy(new Uint8Array([0]).buffer,{})

Error:

Failed to execute 'digest' on 'SubtleCrypto': The provided value is not of type '(ArrayBuffer or ArrayBufferView)'

instanceof Uint8Array and instanceof ArrayBuffer return true in both cases.

Answer 1

digest is specified by its IDL interface to only accept a BufferSource , which is either an ArrayBufferView or an ArrayBuffer . This IDL-level typing indicates that a correct implementation will categorically reject any inputs that doesn't have the correct internal type.

Any tricks you might want to use a Proxy for simply aren't going to work on digest . Instead, you could do proxy tricks to get the exact ArrayBuffer you want immediately before you pass in your data to digest .

For example, here's a proxy that fakes a buffer that differs from the buffer on its internal object. The buffer is genuine, so it can be passed into digest , but it was created by Proxy magic:

var proxy = new Proxy(new Uint8Array([0]), {
                          get:function(obj, prop) {
                              if(prop=="buffer"){ return new Uint8Array([42]).buffer }
                              else { return obj[prop]; }
                          }
            });
crypto.subtle.digest('SHA-512', proxy.buffer)

If it is impossible to produce the buffer (for example if it is too big to fit in RAM) you would currently have to rely on something other than SubtleCrypto.

This seems like a great point to raise with the W3C, eg, to support an update mechanism to iteratively collect input.