Add RFC for incremental delivery

rfcs/IncrementalDelivery.md

@@ -0,0 +1,45 @@
+# Incremental Delivery over HTTP
+
+This RFC proposes adding a specification of how "Incremental" GraphQL results should be delivered to clients, using HTTP chunked transfer encoding.
+
+## Incremental Results
+
+An Incremental result is a GraphQL result that is split up into multiple payloads, allowing clients quicker access to parts of the results. Currently this is supported by the proposed `@defer` and `@stream` directives ([RFC](https://github.com/graphql/graphql-spec/blob/master/rfcs/DeferStream.md)).
+
+## `transfer-encoding: chunked`
+
+The HTTP response for an incrementally delivered response should contain the `transfer-encoding: chunked` response header. Chunked transfer encoding allows the body of the response to be delivered as a series of chunks, allowing clients to read each chunk of the response as it is sent without waiting for the entire response.
+
+## `content-type: multipart/mixed`
+
+The HTTP response for an incrementally delivered response should contain the `content-type: multipart/mixed; boundary="-"` response header and conform to the [specification of multipart content defined by the W3 in rfc1341](https://www.w3.org/Protocols/rfc1341/7_2_Multipart.html). An example response body will look like:
+
+```
+---
+Content-Type: application/json; charset=utf-8
+Content-Length: 45
+
+{"data":{"hello":"Hello Rob"},"hasNext":true}
+
+---
+Content-Type: application/json; charset=utf-8
+Content-Length: 57
+
+{"data":{"test":"Hello World"},"path":[],"hasNext":false}
+
+-----
+```
+* The boundary used is `-` and is passed to the client in the http response's content-type header. 
+* Each part of the multipart response must start with `---` and a `CRLF`
+* Each part of the multipart response must contain a `Content-Type` header. Similar to the GraphQL specification this specification does not require a specific serialization format. For consistency and ease of notation, examples of the response are given in JSON throughout the spec.
+* Each part of the multipart response must contain a `Content-Length` header. This should be the number of bytes of the payload of the response. It does not include the size of the headers, boundaries, or `CRLF`s used to separate the content.
+* After all headers, an additional `CRLF` is sent.
+* The payload is sent, followed by two `CRLF`s.
+* After the last part of the multipart response is sent, the terminating boundary `-----` is sent, followed by a `CRLF`
+
+## Server Implementations
+* `express-graphql`: [pull request](https://github.com/graphql/express-graphql/pull/583)
+
+## Client Implementations
+* [fetch-multipart-graphql](https://github.com/relay-tools/fetch-multipart-graphql) - Browser support using `fetch` or `XMLHttpRequest`
+