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| -rw-r--r-- | doc/internals/stconn-close.txt | 74 |
1 files changed, 74 insertions, 0 deletions
diff --git a/doc/internals/stconn-close.txt b/doc/internals/stconn-close.txt new file mode 100644 index 0000000..fe1ddca --- /dev/null +++ b/doc/internals/stconn-close.txt @@ -0,0 +1,74 @@ +2023-05-23 - closing states on the stream endpoint descriptor + +This document deals with the current flags on the SE desc: + + - SE_FL_ERR_PENDING: an error was met while sending, but some incoming data + might still be pending. This flag will be promoted to SE_FL_ERROR when the + SE_FL_EOI or SE_FL_EOS flags are set via the standard API (se_fl_set()). + + - SE_FL_ERROR ("ERR"): an error was met, last data were received if any, and no + more progress will happen. + + - SE_FL_EOI ("EOI"): the end of the input message was seen, without implying + an end of the connection nor the end of event reporting for this stream. For + example and end of HTTP request or response will set EOI, after which it's + still possible (in case of a request) to bring an abort or error. Said + differently, the expected end of the message was seen. + + - SE_FL_EOS ("EOS"): the definitive end of the input data was detected. It may + result from an error, an abort, a connection shutdown, and no more receive + events will be reported. + +The different muxes (H1,H2,H3) can face slightly different situations due to +the nature, properties, and limitations of their underlying protocols, and will +set these 3 flags to best translate the lower layer's situation and report it +to the upper layer: + + +-----------+----------------------------------------------------------------- + |ERR EOS EOI| Description per mux + +-----------+----------------------------------------------------------------- + | 0 0 0 | all: transfer still in progress + +-----------+----------------------------------------------------------------- + | 0 0 1 | H1: end of message reached. + | | H2: "ES" flag seen on a frame. + | | H3: not set + +-----------+----------------------------------------------------------------- + | 0 1 0 | H1: not set (*1) + | | H2: not set (*2) + | | H3: RST received before FIN (client stops uploading) + +-----------+----------------------------------------------------------------- + | 0 1 1 | H1: end of message + read0, such as close response or aborted + | | request + | | H2: not set (*2) + | | H3: end of message reached (any subsequent RSTs are ignored) + +-----------+----------------------------------------------------------------- + | 1 0 0 | all: could be used to report a protocol error (ex: invalid chunk + | | encoding, forbidden response header seen from a server). + +-----------+----------------------------------------------------------------- + | 1 0 1 | all: could be used to report an internal error or a downstream + | | protocol error, such as a forbidden header in an HTX block + | | coming from the stream layer or the impossibility to encode + | | a message. Seems unused right now. + +-----------+----------------------------------------------------------------- + | 1 1 0 | H1: truncated client input data before response, or truncated + | | response from the server + | | H2: RST or read0 received before end of input message + | | H3: RST + STOP_SENDING before FIN + +-----------+----------------------------------------------------------------- + | 1 1 1 | H1: error face while sending after end of input message + | | H2: RST or read0 received after end of input message + | | H3: STOP_SENDING received after a frame with FIN + +-----------+----------------------------------------------------------------- + +*1: EOS alone is currently not set by H1, however this situation could best + describe an H1 upload that was interrupted by the client while receiving + an early response, a reused persistent server connection that delivered a + read0 immediately after the request was sent, or a truncated server + response (or possibly one in close mode when no C-L was advertised). Right + now these situations are always accompanied with an ERR flag in addition to + the EOS one. + +*2: H2 doesn't set EOS without ERR because currently the only ways to close a + stream in H2 are by resetting the stream (which conveys an error) or + closing the connection (which renders it unusable in both directions and + prevents from sending as well). |