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Happy eyeballs #1

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bfb4af9
rfc2553_connect_to(): Implement Happy Eyeballs (RFC 8305)
rustyx Aug 28, 2026
1a5e16d
p-config.sgml: Document the connect-attempt-delay directive
rustyx Aug 28, 2026
4fde513
config: Add the connect-attempt-delay directive
rustyx Aug 28, 2026
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61 changes: 61 additions & 0 deletions config
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Original file line number Diff line number Diff line change
Expand Up @@ -2444,6 +2444,67 @@ socket-timeout 300
# receive-buffer-size 32768
#
#
# 6.20. connect-attempt-delay
# ============================
#
# Specifies:
#
# Number of milliseconds to wait before starting a connection
# attempt to the next address of a host while previous attempts
# are still pending.
#
# Type of value:
#
# Time in milliseconds.
#
# Default value:
#
# 250
#
# Effect if unset:
#
# A default value of 250 milliseconds is used.
#
# Notes:
#
# If a host resolves to multiple addresses, Privoxy tries to
# connect to them following the "Happy Eyeballs" algorithm
# described in RFC 8305: the addresses are sorted so that
# address families alternate, the first connection attempt is
# started right away and additional attempts are started in
# parallel whenever a previous attempt fails or the
# connect-attempt-delay expires. The first attempt to succeed
# wins, the other ones are aborted.
#
# This limits the delay caused by unreachable addresses, for
# example when a host has an IPv6 address but the system only
# has working IPv4 connectivity, to the configured value instead
# of the connection timeout.
#
# RFC 8305 recommends a value between 100 and 2000 milliseconds.
# Setting the value to 0 disables parallel connection attempts,
# so that the addresses are tried one after the other with the
# next attempt only being started after the previous one failed.
#
# Note that the addresses are resolved with a single synchronous
# lookup, the "Resolution Delay" described in RFC 8305 doesn't
# apply. The first attempt is made to the first address
# returned by the resolver, whichever family it belongs to,
# followed by an address of the other family.
#
# This directive has no effect if Privoxy has been compiled
# without getaddrinfo() support. On platforms where the
# connection attempts can't be made non-blocking the addresses
# are tried one after the other regardless of this setting.
#
# Example:
#
# # Give the first address a full second before trying the next one
# connect-attempt-delay 1000
#
connect-attempt-delay 250
#
#
# 7. HTTPS INSPECTION
# ====================
#
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1 change: 1 addition & 0 deletions configure.in
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Expand Up @@ -782,6 +782,7 @@ AC_CHECK_FUNCS([ \
gethostbyaddr_r \
gethostbyname \
gethostbyname_r \
clock_gettime \
gettimeofday \
inet_ntoa \
memchr \
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86 changes: 86 additions & 0 deletions doc/source/p-config.sgml
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Expand Up @@ -3910,6 +3910,92 @@ compression-level 0
</variablelist>
</sect3>

<sect3 renderas="sect4" id="connect-attempt-delay"><title>connect-attempt-delay</title>
<variablelist>
<varlistentry>
<term>Specifies:</term>
<listitem>
<para>
Number of milliseconds to wait before starting a connection attempt
to the next address of a host while previous attempts are still
pending.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>Type of value:</term>
<listitem>
<para>
<replaceable>Time in milliseconds.</replaceable>
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>Default value:</term>
<listitem>
<para>250</para>
</listitem>
</varlistentry>
<varlistentry>
<term>Effect if unset:</term>
<listitem>
<para>
A default value of 250 milliseconds is used.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>Notes:</term>
<listitem>
<para>
If a host resolves to multiple addresses, <application>Privoxy</application>
tries to connect to them following the <quote>Happy Eyeballs</quote>
algorithm described in RFC 8305: the addresses are sorted so that
address families alternate, the first connection attempt is started
right away and additional attempts are started in parallel whenever
a previous attempt fails or the <literal>connect-attempt-delay</literal>
expires. The first attempt to succeed wins, the other ones are aborted.
</para>
<para>
This limits the delay caused by unreachable addresses, for example
when a host has an IPv6 address but the system only has working
IPv4 connectivity, to the configured value instead of the connection
timeout.
</para>
<para>
RFC 8305 recommends a value between 100 and 2000 milliseconds.
Setting the value to 0 disables parallel connection attempts, so that
the addresses are tried one after the other with the next attempt
only being started after the previous one failed.
</para>
<para>
Note that the addresses are resolved with a single synchronous
lookup, the <quote>Resolution Delay</quote> described in RFC 8305
doesn't apply. The first attempt is made to the first address
returned by the resolver, whichever family it belongs to, followed
by an address of the other family.
</para>
<para>
This directive has no effect if <application>Privoxy</application>
has been compiled without getaddrinfo() support. On platforms where
the connection attempts can't be made non-blocking the addresses are
tried one after the other regardless of this setting.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>Example:</term>
<listitem>
<screen>
# Give the first address a full second before trying the next one
connect-attempt-delay 1000
</screen>
</listitem>
</varlistentry>
</variablelist>
<![%config-file;[<literallayout>@@connect-attempt-delay 250</literallayout>]]>
</sect3>

<!-- ~ End section ~ -->

</sect2>
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