DAP4: Chunked encoding

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Background

One persistent (ahem) problem with DAP2 was the inability of client applications to recognize when a data transmission failed. If an error happened before the initial set of headers for the response were sent, then DAP2's error reporting scheme worked just fine. However, if the server encountered an error once the serialization of data started, for example, it was essentially impossible for a client to detect the error (essentially being the operative word; the Ocapi library did detect these errors, but it is the only client I know that did so).

This proposal suggests that DAP4 use a simple variation on the HTTP/1.1 chunked transmission scheme to serialize its response document so that errors are simple to detect. Furthermore, this scheme is independent of the form or content of the response, so the same scheme can be used with different response forms or dropped when/if DAP is used with protocols that support out-of-band error signaling.