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Document how :max_header_list_size limits are enforced #532

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Document how :max_header_list_size limits are enforced #532

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21 changes: 12 additions & 9 deletions lib/mint/http2.ex
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Expand Up @@ -309,15 +309,18 @@ defmodule Mint.HTTP2 do
* `:max_frame_size` - corresponds to `SETTINGS_MAX_FRAME_SIZE`. Tells what is the
maximum size of an HTTP/2 frame for the peer that sends this setting.

* `:max_header_list_size` - corresponds to `SETTINGS_MAX_HEADER_LIST_SIZE`. For the
client, this also bounds the size of an inbound header block (a HEADERS frame plus
its trailing CONTINUATION frames): the connection is closed with a connection error
if a server streams a header block larger than this value, which prevents a server
from exhausting client memory with an unbounded chain of CONTINUATION frames. A
decoded header list larger than this value fails the request with a
`{:max_header_list_size_exceeded, size, max_size}` error, and a server push whose
promised request headers are larger than this value is refused. Defaults to
`256 KB` for the client.
* `:max_header_list_size` - corresponds to `SETTINGS_MAX_HEADER_LIST_SIZE`. The
server setting is `:infinity` until the server sends it. The client setting must be
an integer and defaults to `256 KB`. It limits the decoded size (names, values and
32 bytes per field) of header lists received from the server. Response headers,
informational response headers and trailers over the limit reset the request with
`PROTOCOL_ERROR` and fail it with a `{:max_header_list_size_exceeded, size, max_size}`
error. Promised request headers over the limit reset the promised stream with
`REFUSED_STREAM`. The connection stays open in both cases. Header block fragments
buffered while waiting for `END_HEADERS` close the connection with `PROTOCOL_ERROR`
if they exceed `max_header_list_size * 30 / 8 + 12` bytes, an upper bound on the
encoded size of a header list within the limit (assuming minimal integer
representations and at most two dynamic table size updates).

* `:enable_connect_protocol` - corresponds to `SETTINGS_ENABLE_CONNECT_PROTOCOL`.
Sets whether the client may invoke the extended connect protocol which is used to
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