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101 строка
3.4 KiB
Markdown
101 строка
3.4 KiB
Markdown
<!--
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Copyright (C) Daniel Stenberg, <daniel@haxx.se>, et al.
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SPDX-License-Identifier: curl
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-->
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# HTTPS RR
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[RFC 9460](https://www.rfc-editor.org/rfc/rfc9460.html) documents the HTTPS
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DNS Resource Record.
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curl features **experimental** support for HTTPS RR.
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- The ALPN list from the record is parsed and used
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- The ECH field is stored - and used if ECH is enabled in the build
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- The port number is not used (Firefox supports it, Chrome does not)
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- The target name is not used
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- The IP addresses (`Ipv6hints`, `Ipv4hints`) from the HTTPS RR are not used
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- It only supports a single HTTPS RR per hostname
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- Hostnames without A/AAAA records but *with* HTTPS RR fails
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- consider service profiles where the RR provides different addresses for TCP
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vs QUIC etc
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`HTTPSRR` is listed as a feature in the `curl -V` output if curl contains
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HTTPS RR support. If c-ares is not included in the build, the HTTPS RR support
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is limited to DoH.
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`asyn-rr` is listed as a feature in the `curl -V` output if c-ares is used for
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additional resolves in addition to a "normal" resolve done with the threaded
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resolver.
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The data extracted from the HTTPS RR is stored in the in-memory DNS cache to
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be reused on subsequent uses of the same hostnames.
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## limitations
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We have decided to work on the HTTPS RR support by following what seems to be
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(widely) used, and simply wait with implementing the details of the record
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that do not seem to be deployed. HTTPS RR is a DNS field with many odd corners
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and complexities and we might as well avoid them if no one seems to want them.
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## build
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./configure --enable-httpsrr
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or
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cmake -DUSE_HTTPSRR=ON
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## ALPN
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The list of ALPN IDs is parsed but may not be completely respected because of
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what the HTTP version preference is set to, which is a problem we are working
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on. Also, getting an `HTTP/1.1` ALPN in the HTTPS RR field for an HTTP://
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transfer should imply switching to HTTPS, HSTS style. Which curl currently
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does not.
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## DoH
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When HTTPS RR is enabled in the curl build, The DoH code asks for an HTTPS
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record in addition to the A and AAAA records, and if an HTTPS RR answer is
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returned, curl parses it and stores the retrieved information.
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## Non-DoH
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If DoH is not used for name resolving in an HTTPS RR enabled build, we must
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provide the ability using the regular resolver backends. We use the c-ares DNS
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library for the HTTPS RR lookup. Version 1.28.0 or later.
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### c-ares
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If curl is built to use the c-ares library for name resolves, an HTTPS RR
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enabled build makes a request for the HTTPS RR in addition to the regular
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lookup.
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### Threaded resolver
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When built to use the threaded resolver, which is the default, an HTTPS RR
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build still needs a c-ares installation provided so that a separate request
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for the HTTPS record can be done in parallel to the regular getaddrinfo()
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call.
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This is done by specifying both c-ares and threaded resolver to configure:
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./configure --enable-ares=... --enable-threaded-resolver
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or to cmake:
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cmake -DENABLE_ARES=ON -DENABLE_THREADED_RESOLVER=ON
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Because the HTTPS record is handled separately from the A/AAAA record
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retrieval, by a separate library, there is a small risk for discrepancies.
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When building curl using the threaded resolver with HTTPS RR support (using
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c-ares), the `curl -V` output looks exactly like a c-ares resolver build.
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## HTTPS RR Options
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Because curl is a low level transfer tool for which users sometimes want
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detailed control, we need to offer options to control HTTPS RR use.
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