Commit Graph

68 Commits

Author SHA1 Message Date
Derzsi Dániel
ebd83bfbae
wolfssl: support setting CA certificates as blob
Closes #11445
2023-07-16 23:37:14 +02:00
Derzsi Dániel
eccf896df8
wolfssl: detect when TLS 1.2 support is not built into wolfssl
Closes #11444
2023-07-16 23:28:57 +02:00
Viktor Szakats
3f8fc25720
cmake: add support for "unity" builds
Aka "jumbo" or "amalgamation" builds. It means to compile all sources
per target as a single C source. This is experimental.

You can enable it by passing `-DCMAKE_UNITY_BUILD=ON` to cmake.
It requires CMake 3.16 or newer.

It makes builds (much) faster, allows for better optimizations and tends
to promote less ambiguous code.

Also add a new AppVeyor CI job and convert an existing one to use
"unity" mode (one MSVC, one MinGW), and enable it for one macOS CI job.

Fix related issues:
- add missing include guard to `easy_lock.h`.
- rename static variables and functions (and a macro) with names reused
  across sources, or shadowed by local variables.
- add an `#undef` after use.
- add a missing `#undef` before use.
- move internal definitions from `ftp.h` to `ftp.c`.
- `curl_memory.h` fixes to make it work when included repeatedly.
- stop building/linking curlx bits twice for a static-mode curl tool.
  These caused doubly defined symbols in unity builds.
- silence missing extern declarations compiler warning for ` _CRT_glob`.
- fix extern declarations for `tool_freq` and `tool_isVistaOrGreater`.
- fix colliding static symbols in debug mode: `debugtime()` and
  `statename`.
- rename `ssl_backend_data` structure to unique names for each
  TLS-backend, along with the `ssl_connect_data` struct member
  referencing them. This required adding casts for each access.
- add workaround for missing `[P]UNICODE_STRING` types in certain Windows
  builds when compiling `lib/ldap.c`. To support "unity" builds, we had
  to enable `SCHANNEL_USE_BLACKLISTS` for Schannel (a Windows
  `schannel.h` option) _globally_. This caused an indirect inclusion of
  Windows `schannel.h` from `ldap.c` via `winldap.h` to have it enabled
  as well. This requires `[P]UNICODE_STRING` types, which is apperantly
  not defined automatically (as seen with both MSVS and mingw-w64).
  This patch includes `<subauth.h>` to fix it.
  Ref: https://github.com/curl/curl/runs/13987772013
  Ref: https://dev.azure.com/daniel0244/curl/_build/results?buildId=15827&view=logs&jobId=2c9f582d-e278-56b6-4354-f38a4d851906&j=2c9f582d-e278-56b6-4354-f38a4d851906&t=90509b00-34fa-5a81-35d7-5ed9569d331c
- tweak unity builds to compile `lib/memdebug.c` separately in memory
  trace builds to avoid PP confusion.
- force-disable unity for test programs.
- do not compile and link libcurl sources to libtests _twice_ when libcurl
  is built in static mode.

KNOWN ISSUES:
- running tests with unity builds may fail in cases.
- some build configurations/env may not compile in unity mode. E.g.:
  https://ci.appveyor.com/project/curlorg/curl/builds/47230972/job/51wfesgnfuauwl8q#L250

Ref: https://github.com/libssh2/libssh2/issues/1034
Ref: https://cmake.org/cmake/help/latest/prop_tgt/UNITY_BUILD.html
Ref: https://en.wikipedia.org/wiki/Unity_build

Closes #11095
2023-06-07 13:06:08 +00:00
Stefan Eissing
4ae2d9f24d
proxy: http2 proxy tunnel implementation
- currently only on debug build and when env variable
  CURL_PROXY_TUNNEL_H2 is present.
- will ALPN negotiate with the proxy server and switch
  tunnel filter based on the protocol negotiated.
- http/1.1 tunnel code moved into cf-h1-proxy.[ch]
- http/2 tunnel code implemented in cf-h2-proxy.[ch]
- tunnel start and ALPN set remains in http_proxy.c
- moving all haproxy related code into cf-haproxy.[ch]

VTLS changes
- SSL filters rely solely on the "alpn" specification they
  are created with and no longer check conn->bits.tls_enable_alpn.
- checks on which ALPN specification to use (or none at all) are
  done in vtls.c when creating the filter.

Testing
- added a nghttpx forward proxy to the pytest setup that
  speaks HTTP/2 and forwards all requests to the Apache httpd
  forward proxy server.
- extending test coverage in test_10 cases
- adding proxy tests for direct/tunnel h1/h2 use of basic auth.
- adding test for http/1.1 and h2 proxy tunneling to pytest

Closes #10780
2023-04-06 13:04:46 +02:00
Stefan Eissing
940b67803a
wolfSSL: ressurect the BIO io_result
In pytest'ing the situation occored that wolfSSL reported an
IO error when the underlying BIO operation was returning an
CURLE_AGAIN condition.

Readding the `io_result` filter context member to detect such
situations.

Also, making sure that the returned CURLcode is initialized
on all recv operations outcome.

Closes #10716
2023-03-10 08:06:17 +01:00
Anthony Hu
12e9186fc4
wolfssl: remove deprecated post-quantum algorithms
Closes #10440
2023-02-08 08:31:45 +01:00
Stefan Eissing
671158242d
connections: introduce http/3 happy eyeballs
New cfilter HTTP-CONNECT for h3/h2/http1.1 eyeballing.
- filter is installed when `--http3` in the tool is used (or
  the equivalent CURLOPT_ done in the library)
- starts a QUIC/HTTP/3 connect right away. Should that not
  succeed after 100ms (subject to change), a parallel attempt
  is started for HTTP/2 and HTTP/1.1 via TCP
- both attempts are subject to IPv6/IPv4 eyeballing, same
  as happens for other connections
- tie timeout to the ip-version HAPPY_EYEBALLS_TIMEOUT
- use a `soft` timeout at half the value. When the soft timeout
  expires, the HTTPS-CONNECT filter checks if the QUIC filter
  has received any data from the server. If not, it will start
  the HTTP/2 attempt.

HTTP/3(ngtcp2) improvements.
- setting call_data in all cfilter calls similar to http/2 and vtls filters
  for use in callback where no stream data is available.
- returning CURLE_PARTIAL_FILE for prematurely terminated transfers
- enabling pytest test_05 for h3
- shifting functionality to "connect" UDP sockets from ngtcp2
  implementation into the udp socket cfilter. Because unconnected
  UDP sockets are weird. For example they error when adding to a
  pollset.

HTTP/3(quiche) improvements.
- fixed upload bug in quiche implementation, now passes 251 and pytest
- error codes on stream RESET
- improved debug logs
- handling of DRAIN during connect
- limiting pending event queue

HTTP/2 cfilter improvements.
- use LOG_CF macros for dynamic logging in debug build
- fix CURLcode on RST streams to be CURLE_PARTIAL_FILE
- enable pytest test_05 for h2
- fix upload pytests and improve parallel transfer performance.

GOAWAY handling for ngtcp2/quiche
- during connect, when the remote server refuses to accept new connections
  and closes immediately (so the local conn goes into DRAIN phase), the
  connection is torn down and a another attempt is made after a short grace
  period.
  This is the behaviour observed with nghttpx when we tell it to  shut
  down gracefully. Tested in pytest test_03_02.

TLS improvements
- ALPN selection for SSL/SSL-PROXY filters in one vtls set of functions, replaces
  copy of logic in all tls backends.
- standardized the infof logging of offered ALPNs
- ALPN negotiated: have common function for all backends that sets alpn proprty
  and connection related things based on the negotiated protocol (or lack thereof).

- new tests/tests-httpd/scorecard.py for testing h3/h2 protocol implementation.
  Invoke:
    python3 tests/tests-httpd/scorecard.py --help
  for usage.

Improvements on gathering connect statistics and socket access.
- new CF_CTRL_CONN_REPORT_STATS cfilter control for having cfilters
  report connection statistics. This is triggered when the connection
  has completely connected.
- new void Curl_pgrsTimeWas(..) method to report a timer update with
  a timestamp of when it happend. This allows for updating timers
  "later", e.g. a connect statistic after full connectivity has been
  reached.
- in case of HTTP eyeballing, the previous changes will update
  statistics only from the filter chain that "won" the eyeballing.
- new cfilter query CF_QUERY_SOCKET for retrieving the socket used
  by a filter chain.
  Added methods Curl_conn_cf_get_socket() and Curl_conn_get_socket()
  for convenient use of this query.
- Change VTLS backend to query their sub-filters for the socket when
  checks during the handshake are made.

HTTP/3 documentation on how https eyeballing works.

TLS improvements
- ALPN selection for SSL/SSL-PROXY filters in one vtls set of functions, replaces
  copy of logic in all tls backends.
- standardized the infof logging of offered ALPNs
- ALPN negotiated: have common function for all backends that sets alpn proprty
  and connection related things based on the negotiated protocol (or lack thereof).

Scorecard with Caddy.
- configure can be run with `--with-test-caddy=path` to specify which caddy to use for testing
- tests/tests-httpd/scorecard.py now measures download speeds with caddy

pytest improvements
- adding Makfile to clean gen dir
- adding nghttpx rundir creation on start
- checking httpd version 2.4.55 for test_05 cases where it is needed. Skipping with message if too old.
- catch exception when checking for caddy existance on system.

Closes #10349
2023-02-02 09:57:34 +01:00
Stefan Eissing
9e93bd47c2 vtls: Manage current easy handle in nested cfilter calls
The previous implementation cleared `data` so the outer invocation lost
its data, which could lead to a crash.

Bug: https://github.com/curl/curl/issues/10336
Reported-by: Fujii Hironori

Closes https://github.com/curl/curl/pull/10340
2023-01-26 03:05:01 -05:00
Daniel Stenberg
2bc1d775f5
copyright: update all copyright lines and remove year ranges
- they are mostly pointless in all major jurisdictions
- many big corporations and projects already don't use them
- saves us from pointless churn
- git keeps history for us
- the year range is kept in COPYING

checksrc is updated to allow non-year using copyright statements

Closes #10205
2023-01-03 09:19:21 +01:00
Daniel Stenberg
df856cb5c9
vtls: use ALPN HTTP/1.0 when HTTP/1.0 is used
Previously libcurl would use the HTTP/1.1 ALPN id even when the
application specified HTTP/1.0.

Reported-by: William Tang
Ref: #10183
2022-12-31 16:53:21 +01:00
Stefan Eissing
2d3e20a2fc
wolfssl: remove special BIO return code handling
- rely solely on the retry flag in BIO, similar to OpenSSL vtls
  implementation.

Ref: https://github.com/curl/curl/pull/10021#issuecomment-1336147053

Closes #10033
2022-12-06 11:08:12 +01:00
Stefan Eissing
55807e6c05
tls: backends use connection filters for IO, enabling HTTPS-proxy
- OpenSSL (and compatible)
 - BearSSL
 - gnutls
 - mbedtls
 - rustls
 - schannel
 - secure-transport
 - wolfSSL (v5.0.0 and newer)

 This leaves only the following without HTTPS-proxy support:
 - gskit
 - nss
 - wolfSSL (versions earlier than v5.0.0)

Closes #9962
2022-11-28 13:56:23 +01:00
Stefan Eissing
af22c2a546
vtls: localization of state data in filters
- almost all backend calls pass the Curl_cfilter intance instead of
   connectdata+sockindex
 - ssl_connect_data is remove from struct connectdata and made internal
   to vtls
 - ssl_connect_data is allocated in the added filter, kept at cf->ctx

 - added function to let a ssl filter access its ssl_primary_config and
   ssl_config_data this selects the propert subfields in conn and data,
   for filters added as plain or proxy
 - adjusted all backends to use the changed api
 - adjusted all backends to access config data via the exposed
   functions, no longer using conn or data directly

cfilter renames for clear purpose:

 - methods `Curl_conn_*(data, conn, sockindex)` work on the complete
   filter chain at `sockindex` and connection `conn`.
 - methods `Curl_cf_*(cf, ...)` work on a specific Curl_cfilter
   instance.
 - methods `Curl_conn_cf()` work on/with filter instances at a
   connection.
 - rebased and resolved some naming conflicts
 - hostname validation (und session lookup) on SECONDARY use the same
   name as on FIRST (again).

new debug macros and removing connectdata from function signatures where not
needed.

adapting schannel for new Curl_read_plain paramter.

Closes #9919
2022-11-22 14:25:50 +01:00
Stefan Eissing
dafdb20a26
lib: connection filters (cfilter) addition to curl:
- general construct/destroy in connectdata
 - default implementations of callback functions
 - connect: cfilters for connect and accept
 - socks: cfilter for socks proxying
 - http_proxy: cfilter for http proxy tunneling
 - vtls: cfilters for primary and proxy ssl
 - change in general handling of data/conn
 - Curl_cfilter_setup() sets up filter chain based on data settings,
   if none are installed by the protocol handler setup
 - Curl_cfilter_connect() boot straps filters into `connected` status,
   used by handlers and multi to reach further stages
 - Curl_cfilter_is_connected() to check if a conn is connected,
   e.g. all filters have done their work
 - Curl_cfilter_get_select_socks() gets the sockets and READ/WRITE
   indicators for multi select to work
 - Curl_cfilter_data_pending() asks filters if the have incoming
   data pending for recv
 - Curl_cfilter_recv()/Curl_cfilter_send are the general callbacks
   installed in conn->recv/conn->send for io handling
 - Curl_cfilter_attach_data()/Curl_cfilter_detach_data() inform filters
   and addition/removal of a `data` from their connection
 - adding vtl functions to prevent use of Curl_ssl globals directly
   in other parts of the code.

Reviewed-by: Daniel Stenberg
Closes #9855
2022-11-11 15:17:51 +01:00
Michael Drake
3c16697ebd
openssl: reduce CA certificate bundle reparsing by caching
Closes #9620
2022-11-08 10:06:12 +01:00
Hayden Roche
d797339202
wolfSSL: fix session management bug.
Prior to this commit, non-persistent pointers were being used to store
sessions.  When a WOLFSSL object was then freed, that freed the session
it owned, and thus invalidated the pointer held in curl's cache. This
commit makes it so we get a persistent (deep copied) session pointer
that we then add to the cache.  Accordingly, wolfssl_session_free, which
was previously a no-op, now needs to actually call SSL_SESSION_free.

This bug was discovered by a wolfSSL customer.

Closes #9492
2022-09-13 10:15:40 +02:00
Daniel Stenberg
472f1cbe7e
NPN: remove support for and use of
Next Protocol Negotiation is a TLS extension that was created and used
for agreeing to use the SPDY protocol (the precursor to HTTP/2) for
HTTPS. In the early days of HTTP/2, before the spec was finalized and
shipped, the protocol could be enabled using this extension with some
servers.

curl supports the NPN extension with some TLS backends since then, with
a command line option `--npn` and in libcurl with
`CURLOPT_SSL_ENABLE_NPN`.

HTTP/2 proper is made to use the ALPN (Application-Layer Protocol
Negotiation) extension and the NPN extension has no purposes
anymore. The HTTP/2 spec was published in May 2015.

Today, use of NPN in the wild should be extremely rare and most likely
totally extinct. Chrome removed NPN support in Chrome 51, shipped in
June 2016. Removed in Firefox 53, April 2017.

Closes #9307
2022-09-05 07:39:02 +02:00
max.mehl
ad9bc5976d
copyright: make repository REUSE compliant
Add licensing and copyright information for all files in this repository. This
either happens in the file itself as a comment header or in the file
`.reuse/dep5`.

This commit also adds a Github workflow to check pull requests and adapts
copyright.pl to the changes.

Closes #8869
2022-06-13 09:13:00 +02:00
Daniel Stenberg
a7a18d7589
wolfssl: correct the failf() message when a handle can't be made
Closes #8885
2022-05-19 19:05:17 +02:00
Daniel Stenberg
6968fb9d54
lib: remove exclamation marks
... from infof() and failf() calls. Make them less attention seeking.

Closes #8713
2022-04-16 11:55:05 +02:00
Daniel Stenberg
34ebf3f90d
vtls: use a generic "ALPN, server accepted" message
Closes #8657
2022-03-31 14:21:01 +02:00
Daniel Stenberg
55043b40c1
vtls: use a backend standard message for "ALPN: offers %s"
I call it VTLS_INFOF_ALPN_OFFER_1STR, the '1str' meaning that the
infof() call also needs a string argument: the ALPN ID.

Closes #8657
2022-03-31 14:20:56 +02:00
Daniel Stenberg
3bc5b32db5
vtls: provide a unified APLN-disagree string for all backends
Also rephrase to make it sound less dangerous:

 "ALPN: server did not agree on a protocol. Uses default."

Reported-by: Nick Coghlan
Fixes #8643
Closes #8651
2022-03-31 09:20:16 +02:00
Daniel Stenberg
471d5f44c5
wolfssl: fix compiler error without IPv6
Reported-by: Joseph Chen
Fixes #8550
Closes #8552
2022-03-07 09:47:26 +01:00
MAntoniak
ccc2752ce8
ssl: reduce allocated space for ssl backend when FTP is disabled
Add assert() for the backend pointer in many places

Closes #8471
2022-02-21 08:39:55 +01:00
Daniel Stenberg
e1667a61ea
wolfssl: return CURLE_AGAIN for the SSL_ERROR_NONE case
Closes #8431
2022-02-11 12:36:52 +01:00
Daniel Stenberg
327ef30530
wolfssl: when SSL_read() returns zero, check the error
Returning zero indicates end of connection, so if there's no data read
but the connection is alive, it needs to return -1 with CURLE_AGAIN.

Closes #8431
2022-02-11 10:48:52 +01:00
Daniel Stenberg
2218c3a57e
vtls: pass on the right SNI name
The TLS backends convert the host name to SNI name and need to use that.
This involves cutting off any trailing dot and lowercasing.

Co-authored-by: Jay Satiro
Closes #8320
2022-01-27 08:36:10 +01:00
Daniel Stenberg
54aa9c48b2
tls: remove newline from three infof() calls
Follow-up to e7416cf

Reported-by: billionai on github
Fixes #7879
Closes #7880
2021-10-19 23:03:57 +02:00
Anthony Hu
d10a0af2f3
wolfssl: allow setting of groups/curves
In particular, the quantum safe KEM and hybrid curves if wolfSSL is
built to support them.

Closes #7728
2021-09-30 17:28:56 +02:00
Michael Kaufmann
60738f398c vtls: Fix a memory leak if an SSL session cannot be added to the cache
On connection shutdown, a new TLS session ticket may arrive after the
SSL session cache has already been destructed. In this case, the new
SSL session cannot be added to the SSL session cache.

The callers of Curl_ssl_addsessionid() need to know whether the SSL
session has been added to the cache. If it has not been added, the
reference counter of the SSL session must not be incremented, or memory
used by the SSL session must be freed. This is now possible with the new
output parameter "added" of Curl_ssl_addsessionid().

Fixes #7683
Closes #7752
2021-09-24 13:23:42 +02:00
Ehren Bendler
797bacf9c5
wolfssl: clean up wolfcrypt error queue
If wolfSSL is built in certain ways (OPENSSL_EXTRA or Debug), the error
queue gets added on to for each session and never freed. Fix it by
calling ERR_clear_error() like in vtls/openssl when needed. This func is
a no-op in wolfcrypt if the error queue is not enabled.

Closes #7594
2021-08-21 17:05:14 +02:00
Daniel Stenberg
e7416cfd2b
infof: remove newline from format strings, always append it
- the data needs to be "line-based" anyway since it's also passed to the
  debug callback/application

- it makes infof() work like failf() and consistency is good

- there's an assert that triggers on newlines in the format string

- Also removes a few instances of "..."

- Removes the code that would append "..." to the end of the data *iff*
  it was truncated in infof()

Closes #7357
2021-07-07 22:54:01 +02:00
Daniel Stenberg
1e488d38c9
wolfssl: failing to set a session id is not reason to error out
... as it is *probably* just timed out.

Reported-by: Francisco Munoz

Closes #7358
2021-07-07 10:19:28 +02:00
Michael Kaufmann
b249592d29 ssl: read pending close notify alert before closing the connection
This avoids a TCP reset (RST) if the server initiates a connection
shutdown by sending an SSL close notify alert and then closes the TCP
connection.

For SSL connections, usually the server announces that it will close the
connection with an SSL close notify alert. curl should read this alert.
If curl does not read this alert and just closes the connection, some
operating systems close the TCP connection with an RST flag.

See RFC 1122, section 4.2.2.13

If curl reads the close notify alert, the TCP connection is closed
normally with a FIN flag.

The new code is similar to existing code in the "SSL shutdown" function:
try to read an alert (non-blocking), and ignore any read errors.

Closes #7095
2021-06-01 09:40:40 +02:00
Harry Sintonen
7f4a9a9b2a
openssl: associate/detach the transfer from connection
CVE-2021-22901

Bug: https://curl.se/docs/CVE-2021-22901.html
2021-05-24 13:15:10 +02:00
Daniel Stenberg
7b6d771a19
wolfssl: remove SSLv3 support leftovers
Closes #7088
2021-05-18 16:23:17 +02:00
Jacob Hoffman-Andrews
a3268eca79
tls: add USE_HTTP2 define
This abstracts across the two HTTP/2 backends: nghttp2 and Hyper.

Add our own define for the "h2" ALPN protocol, so TLS backends can use
it without depending on a specific HTTP backend.

Closes #6959
2021-04-29 15:04:39 +02:00
Daniel Stenberg
9fc284427c
wolfssl: handle SSL_write() returns 0 for error
Reported-by: Timo Lange

Closes #6967
2021-04-26 14:27:45 +02:00
Michał Antoniak
e4ba999646
vtls: deduplicate some DISABLE_PROXY ifdefs
continue from #5735

- using SSL_HOST_NAME, SSL_HOST_DISPNAME, SSL_PINNED_PUB_KEY for other
  tls backend

- create SSL_HOST_PORT

Closes #6660
2021-04-22 22:50:56 +02:00
Daniel Stenberg
eff614fb02
vtls: refuse setting any SSL version
... previously they were supported if a TLS library would (unexpectedly)
still support them, but from this change they will be refused already in
curl_easy_setopt(). SSLv2 and SSLv3 have been known to be insecure for
many years now.

Closes #6773
2021-04-19 08:16:02 +02:00
Daniel Stenberg
f573998c22
TLS: fix HTTP/2 selection
for GnuTLS, BearSSL, mbedTLS, NSS, SChannnel, Secure Transport and
wolfSSL...

Regression since 88dd1a8a11 (shipped in 7.76.0)
Reported-by: Kenneth Davidson
Reported-by: romamik om github
Fixes #6825
Closes #6827
2021-04-02 22:53:17 +02:00
Daniel Stenberg
b09c8ee157
vtls: add 'isproxy' argument to Curl_ssl_get/addsessionid()
To make sure we set and extract the correct session.

Reported-by: Mingtao Yang
Bug: https://curl.se/docs/CVE-2021-22890.html

CVE-2021-22890
2021-03-28 23:19:56 +02:00
Daniel Stenberg
70472a44de
urldata: remove the _ORIG suffix from string names
It doesn't provide any useful info but only makes the names longer.

Closes #6624
2021-02-19 08:07:19 +01:00
Daniel Stenberg
bc928be02c
wolfssl: don't store a NULL sessionid
This caused a memory leak as the session id cache entry was still
erroneously stored with a NULL sessionid and that would later be treated
as not needed to get freed.

Reported-by: Gisle Vanem
Fixes #6616
Closes #6617
2021-02-17 22:55:45 +01:00
Daniel Stenberg
88dd1a8a11
urldata: don't touch data->set.httpversion at run-time
Rename it to 'httpwant' and make a cloned field in the state struct as
well for run-time updates.

Also: refuse non-supported HTTP versions. Verified with test 129.

Closes #6585
2021-02-12 08:13:37 +01:00
Jacob Hoffman-Andrews
c30bf22f1c
vtls: factor out Curl_ssl_getsock to field of Curl_ssl
Closes #6558
2021-02-08 14:10:55 +01:00
Daniel Stenberg
2c4b338f7e
vtls: remove md5sum
As it is not used anymore.

Reported-by: Jacob Hoffman-Andrews
Bug: https://curl.se/mail/lib-2021-02/0000.html

Closes #6557
2021-02-02 08:13:09 +01:00
Patrick Monnerat
bbe3aa9f88
vtls: reduce conn->data use
Closes #6474
2021-01-19 09:14:40 +01:00
Daniel Stenberg
215db086e0
lib: pass in 'struct Curl_easy *' to most functions
... in most cases instead of 'struct connectdata *' but in some cases in
addition to.

- We mostly operate on transfers and not connections.

- We need the transfer handle to log, store data and more. Everything in
  libcurl is driven by a transfer (the CURL * in the public API).

- This work clarifies and separates the transfers from the connections
  better.

- We should avoid "conn->data". Since individual connections can be used
  by many transfers when multiplexing, making sure that conn->data
  points to the current and correct transfer at all times is difficult
  and has been notoriously error-prone over the years. The goal is to
  ultimately remove the conn->data pointer for this reason.

Closes #6425
2021-01-17 23:56:09 +01:00