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02cedc48d3
Fix typos found in the design-thoughts, internals and lua-api subsections of the documentation.
197 lines
8.1 KiB
Plaintext
197 lines
8.1 KiB
Plaintext
2010/01/16 - Connection header adjustments depending on the transaction mode.
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HTTP transactions supports 5 possible modes :
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WANT_TUN : default, nothing changed
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WANT_TUN + httpclose : headers set for close in both dirs
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WANT_KAL : keep-alive desired in both dirs
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WANT_SCL : want close with the server and KA with the client
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WANT_CLO : want close on both sides.
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When only WANT_TUN is set, nothing is changed nor analysed, so for commodity
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below, we'll refer to WANT_TUN+httpclose as WANT_TUN.
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The mode is adjusted in 3 steps :
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- configuration sets initial mode
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- request headers set required request mode
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- response headers set the final mode
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1) Adjusting the initial mode via the configuration
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option httpclose => TUN
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option http-keep-alive => KAL
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option http-server-close => SCL
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option forceclose => CLO
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Note that option httpclose combined with any other option is equivalent to
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forceclose.
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2) Adjusting the request mode once the request is parsed
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If we cannot determine the body length from the headers, we set the mode to CLO
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but later we'll switch to tunnel mode once forwarding the body. That way, all
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parties are informed of the correct mode.
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Depending on the request version and request Connection header, we may have to
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adjust the current transaction mode and to update the connection header.
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mode req_ver req_hdr new_mode hdr_change
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TUN 1.0 - TUN -
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TUN 1.0 ka TUN del_ka
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TUN 1.0 close TUN del_close
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TUN 1.0 both TUN del_ka, del_close
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TUN 1.1 - TUN add_close
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TUN 1.1 ka TUN del_ka, add_close
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TUN 1.1 close TUN -
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TUN 1.1 both TUN del_ka
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KAL 1.0 - CLO -
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KAL 1.0 ka KAL -
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KAL 1.0 close CLO del_close
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KAL 1.0 both CLO del_ka, del_close
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KAL 1.1 - KAL -
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KAL 1.1 ka KAL del_ka
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KAL 1.1 close CLO -
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KAL 1.1 both CLO del_ka
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SCL 1.0 - CLO -
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SCL 1.0 ka SCL del_ka
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SCL 1.0 close CLO del_close
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SCL 1.0 both CLO del_ka, del_close
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SCL 1.1 - SCL add_close
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SCL 1.1 ka SCL del_ka, add_close
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SCL 1.1 close CLO -
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SCL 1.1 both CLO del_ka
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CLO 1.0 - CLO -
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CLO 1.0 ka CLO del_ka
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CLO 1.0 close CLO del_close
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CLO 1.0 both CLO del_ka, del_close
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CLO 1.1 - CLO add_close
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CLO 1.1 ka CLO del_ka, add_close
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CLO 1.1 close CLO -
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CLO 1.1 both CLO del_ka
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=> Summary:
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- KAL and SCL are only possible with the same requests :
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- 1.0 + ka
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- 1.1 + ka or nothing
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- CLO is assumed for any non-TUN request which contains at least a close
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header, as well as for any 1.0 request without a keep-alive header.
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- del_ka is set whenever we want a CLO or SCL or TUN and req contains a KA,
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or when the req is 1.1 and contains a KA.
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- del_close is set whenever a 1.0 request contains a close.
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- add_close is set whenever a 1.1 request must be switched to TUN, SCL, CLO
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and did not have a close hdr.
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Note that the request processing is performed in two passes, one with the
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frontend's config and a second one with the backend's config. It is only
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possible to "raise" the mode between them, so during the second pass, we have
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no reason to re-add a header that we previously removed. As an exception, the
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TUN mode is converted to CLO once combined because in fact it's an httpclose
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option set on a TUN mode connection :
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BE (2)
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| TUN KAL SCL CLO
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----+----+----+----+----
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TUN | TUN CLO CLO CLO
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+
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KAL | CLO KAL SCL CLO
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FE +
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(1) SCL | CLO SCL SCL CLO
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+
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CLO | CLO CLO CLO CLO
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3) Adjusting the final mode once the response is parsed
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This part becomes trickier. It is possible that the server responds with a
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version that the client does not necessarily understand. Obviously, 1.1 clients
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are asusmed to understand 1.0 responses. The problematic case is a 1.0 client
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receiving a 1.1 response without any Connection header. Some 1.0 clients might
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know that in 1.1 this means "keep-alive" while others might ignore the version
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and assume a "close". Since we know the version on both sides, we may have to
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adjust some responses to remove any ambiguous case. That's the reason why the
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following table considers both the request and the response version. If the
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response length cannot be determined, we switch to CLO mode.
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mode res_ver res_hdr req_ver new_mode hdr_change
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TUN 1.0 - any TUN -
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TUN 1.0 ka any TUN del_ka
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TUN 1.0 close any TUN del_close
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TUN 1.0 both any TUN del_ka, del_close
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TUN 1.1 - any TUN add_close
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TUN 1.1 ka any TUN del_ka, add_close
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TUN 1.1 close any TUN -
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TUN 1.1 both any TUN del_ka
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KAL 1.0 - any SCL add_ka
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KAL 1.0 ka any KAL -
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KAL 1.0 close any SCL del_close, add_ka
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KAL 1.0 both any SCL del_close
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KAL 1.1 - 1.0 KAL add_ka
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KAL 1.1 - 1.1 KAL -
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KAL 1.1 ka 1.0 KAL -
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KAL 1.1 ka 1.1 KAL del_ka
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KAL 1.1 close 1.0 SCL del_close, add_ka
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KAL 1.1 close 1.1 SCL del_close
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KAL 1.1 both 1.0 SCL del_close
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KAL 1.1 both 1.1 SCL del_ka, del_close
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SCL 1.0 - any SCL add_ka
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SCL 1.0 ka any SCL -
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SCL 1.0 close any SCL del_close, add_ka
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SCL 1.0 both any SCL del_close
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SCL 1.1 - 1.0 SCL add_ka
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SCL 1.1 - 1.1 SCL -
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SCL 1.1 ka 1.0 SCL -
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SCL 1.1 ka 1.1 SCL del_ka
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SCL 1.1 close 1.0 SCL del_close, add_ka
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SCL 1.1 close 1.1 SCL del_close
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SCL 1.1 both 1.0 SCL del_close
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SCL 1.1 both 1.1 SCL del_ka, del_close
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CLO 1.0 - any CLO -
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CLO 1.0 ka any CLO del_ka
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CLO 1.0 close any CLO del_close
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CLO 1.0 both any CLO del_ka, del_close
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CLO 1.1 - any CLO add_close
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CLO 1.1 ka any CLO del_ka, add_close
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CLO 1.1 close any CLO -
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CLO 1.1 both any CLO del_ka
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=> in summary :
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- the header operations do not depend on the initial mode, they only depend
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on versions and current connection header(s).
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- both CLO and TUN modes work similarly, they need to set a close mode on the
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response. A 1.1 response will exclusively need the close header, while a 1.0
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response will have it removed. Any keep-alive header is always removed when
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found.
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- a KAL request where the server wants to close turns into an SCL response so
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that we release the server but still maintain the connection to the client.
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- the KAL and SCL modes work the same way as we need to set keep-alive on the
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response. So a 1.0 response will only have the keep-alive header with any
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close header removed. A 1.1 response will have the keep-alive header added
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for 1.0 requests and the close header removed for all requests.
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Note that the SCL and CLO modes will automatically cause the server connection
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to be closed at the end of the data transfer.
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