The dns_request code is very sensitive about calling the connected and
deadlocks when the timing is "right" in several places. Move the call
to the connected callback to the (udp|tcp)_connected() functions, so
they are called asynchronously instead of directly from
the (udp|tcp)_dispentry_cancel() functions.
The TCP dispatches are removed from the dispatchmgr->list in the
dispatch_destroy() and there's a brief period of time where
dns_dispatch_gettcp() can find a dispatch in connected state that's
being destroyed.
Set the dispatch state to DNS_DISPATCHSTATE_NONE in the TCP connection
callback if there are no responses waiting, and ignore TCP dispatches
with zero references in dns_dispatch_gettcp().
In tcp_connected() a typo has turned a DbC check into an assignment
breaking the state machine and making the dns_dispatch_gettcp() try to
attach to dispatch in process of destruction.
The TCP dispatches in DNS_DISPATCHSTATE_NONE could be either very
fresh or those could be dispatches that failed connecting to the
destination. Ignore them when trying to connect to an existing
TCP dispatch via dns_dispatch_gettcp().
This commit modifies the Stream DNS message so that it uses the
optimised code path (isc__nm_senddns()) for sending DNS messages over
the underlying transport. This way we avoid allocating any
intermediate memory buffers needed to render a DNS message with its
length pre-pended ahead of the contents (TCP DNS message format).
The new internal function works in the same way as isc_nm_send()
except that it sends a DNS message size ahead of the DNS message
data (the format used in DNS over TCP).
The intention is to provide a fast path for sending DNS messages over
streams protocols - that is, without allocating any intermediate
memory buffers.
This commit optimises TLS send request object allocation to enable
send request object reuse, somewhat reducing pressure on the memory
manager. It is especially helpful in the case when Stream DNS uses the
TLS implementation as the transport.
This commit unties generic TLS code (isc_nm_tlssocket) from DoH, so
that it will be available regardless of the fact if BIND was built
with DNS over HTTP support or not.
This commit ensures that Stream DNS code attempts to disable Nagle's
algorithm regardless of underlying stream transport (TCP or TLS), as
we are not interested in trading latency for throughout when dealing
with DNS messages.
This commit ensures that Nagle's algorithm is disabled by default for
TLS connections on best effort basis, just like other networking
software (e.g. NGINX) does, as, in the case of TLS, we are not
interested in trading latency for throughput, rather vice versa.
We attempt to disable it as early as we can, right after TCP
connections establishment, as an attempt to speed up handshake
handling.
This commit adds ability to turn the Nagle's algorithm on or off via
connections handle. It adds the isc_nmhandle_set_tcp_nodelay()
function as the public interface for this functionality.
This commit adds an initial implementation of isc_nm_streamdnssocket
transport: a unified transport for DNS over stream protocols messages,
which is capable of replacing both TCP DNS and TLS DNS
transports. Currently, the interface it provides is a unified set of
interfaces provided by both of the transports it attempts to replace.
The transport is built around "isc_dnsbuffer_t" and
"isc_dnsstream_assembler_t" objects and attempts to minimise both the
number of memory allocations during network transfers as well as
memory usage.
This commit adds the implementation for an "isc_dnsstream_assembler_t"
object. The object is built on top of "isc_dnsbuffer_t" and is
intended to encapsulate the state machine used for handling DNS
messages received in the format used for messages transmitted over
TCP.
The idea is that the object accepts the input data received from a
socket, tries to assemble DNS messages from the incoming data and
calls the callback which contains the status of the incoming data as
well as a pointer to the memory region referencing the data of the
assembled message. It is capable of assembling DNS messages no matter
how torn apart they are when sent over network.
The following statuses might be passed to the callback:
* ISC_R_SUCCESS - a message has been successfully assembled;
* ISC_R_NOMORE - not enough data has been processed to assemble a
message;
* ISC_R_RANGE - there was an attempt to process a zero-sized DNS
message (someone attempts to send us junk data).
One could say that the object replaces the implementation of
"isc__nm_*_processbuffer()" functions used by the old TCP DNS and TLS
DNS transports with a better defined state machine completely
decoupled from the networking code itself.
Such a design makes it trivial to write unit tests for it, leading to
better verification of its correctness.
Another important difference is directly related to the fact that it
is built on top of "isc_dnsbuffer_t", which tries to manage memory in
a smart way. In particular:
* It tries to use a static buffer for smaller messages, reducing
pressure on the memory manager (hot path);
* When allocating dynamic memory for larger messages, it tries to
allocate memory conservatively (generic path).
These characteristics is a significant upgrade over the older logic
where a 64KB(+2 bytes) buffer was allocated from dynamic memory
regardless of the fact if we need a buffer this large or not. That is,
lesser memory usage is expected in a generic case for DNS transports
built on top of "isc_dnsstream_assembler_t."
This commit adds "isc_dnsbuffer_t" object implementation, a thin
wrapper on top of "isc_buffer_t" which has the following
characteristics:
* provides interface specifically atuned for handling/generating DNS
messages, especially in the format used for DNS messages over TCP;
* avoids allocating dynamic memory when handling small DNS messages,
while transparently switching to using dynamic memory when handling
larger messages. This approach significantly reduces pressure on the
memory allocator, as most of the DNS messages are small.
The added function provides the interface for getting an ALPN tag
negotiated during TLS connection establishment.
The new function can be used by higher level transports.
This commit adds manual read timer control mode, similarly to TCP.
This way the read timer can be controlled manually using:
* isc__nmsocket_timer_start();
* isc__nmsocket_timer_stop();
* isc__nmsocket_timer_restart().
The change is required to make it possible to implement more
sophisticated read timer control policies in DNS transports, built on
top of TLS.
This commit adds a manual read timer control mode to the TCP
code (adding isc__nmhandle_set_manual_timer() as the interface to it).
Manual read timer control mode suppresses read timer restarting the
read timer when receiving any amount of data. This way the read timer
can be controlled manually using:
* isc__nmsocket_timer_start();
* isc__nmsocket_timer_stop();
* isc__nmsocket_timer_restart().
The change is required to make it possible to implement more
sophisticated read timer control policies in DNS transports, built on
top of TCP.
This commit adds implementation of isc__nmsocket_timer_restart() and
isc__nmsocket_timer_stop() for generic TLS code in order to make its
interface more compatible with that of TCP.
This commit adds implementations of isc_nm_bad_request() and
isc__nmsocket_reset() to the generic TLS stream code in order to make
it more compatible with TCP code.
The purpose of this commit is to aid compiler in generating better
code when working with `isc_buffer_t` objects by using restricted
pointers (and, to a lesser extent, 'const' modifier for read-only
arguments).
This way we, basically, instruct the compiler that the members of
structured passed by pointers into the functions can be treated as
local variables in the scope of a function. That should reduce the
number of load/store operations emitted by compilers when accessing
objects (e.g. 'isc_buffer_t') via pointers.
Add two extra functions needed by StreamDNS:
1. isc_buffer_setmctx() sets the buffer internal memory context, so we
can use isc_buffer_reserve() on the buffer. For this, we also need
to track whether the .base was dynamically allocated or not. This
needs to be called after isc_buffer_init() and before first
isc_buffer_reserve() call.
2. isc_buffer_clearmctx() clears the buffer internal memory context, and
frees any dynamically allocated buffer. This needs to be called
after the last isc_buffer_reserve() call and before calling the
isc_buffer_invalidate()
When the buffer is allocated via isc_buffer_allocate() and the size is
smaller or equal ISC_BUFFER_STATIC_SIZE (currently 512 bytes), the
buffer will be allocated as a flexible array member in the buffer
structure itself instead of allocating it on the heap. This should help
when the buffer is used on the hot-path with small allocations.
When isc_buffer_t buffer is created with isc_buffer_allocate() assume
that we want it to always auto-reallocate instead of having an extra
call to enable auto-reallocation.
The isc_buffer_putdecint() could be easily replaced with
isc_buffer_printf() with just a small overhead of calling vsnprintf()
twice instead once. This is not on a hot-path (dns_catz unit), so we
can ignore the overhead and instead have less single-use code in favor
of using reusable more generic function.
The Stream DNS implementation needs a peek methods that read the value
from the buffer, but it doesn't advance the current position. Add
isc_buffer_peekuintX methods, refactor the isc_buffer_{get,put}uintN
methods to modern integer types, and move the isc_buffer_getuintN to the
header as static inline functions.
Move the U8TO{32,64}_LE and U{32,64}TO8_LE macros to endian.h and extend
the macros for 16-bit and Big-Endian variants.
Use the macros both in isc_siphash (LE) and isc_buffer (BE) units.
The isc_buffer_reserve() would be passed a reference to the buffer
pointer, which was unnecessary as the pointer would never be changed
in the current implementation. Remove the extra dereference.
The dispatches are not thread-bound, and used freely between various
threads (see the dns_resolver and dns_request units for details).
This refactoring make sure that all non-const dns_dispatch_t and
dns_dispentry_t members are accessed under a lock, and both object now
track their internal state (NONE, CONNECTING, CONNECTED, CANCELED)
instead of guessing the state from the state of various struct members.
During the refactoring, the artificial limit DNS_DISPATCH_SOCKSQUOTA on
UDP sockets per dispatch was removed as the limiting needs to happen and
happens on in dns_resolver and limiting the number of UDP sockets
artificially in dispatch could lead to unpredictable behaviour in case
one dispatch has the limit exhausted by others are idle.
The TCP artificial limit of DNS_DISPATCH_MAXREQUESTS makes even less
sense as the TCP connections are only reused in the dns_request API
that's not a heavy user of the outgoing connections.
As a side note, the fact that UDP and TCP dispatch pretends to be same
thing, but in fact the connected UDP is handled from dns_dispentry_t and
dns_dispatch_t acts as a broker, but connected TCP is handled from
dns_dispatch_t and dns_dispatchmgr_t acts as a broker doesn't really
help the clarity of this unit.
This refactoring kept to API almost same - only dns_dispatch_cancel()
and dns_dispatch_done() were merged into dns_dispatch_done() as we need
to cancel active netmgr handles in any case to not leave dangling
connections around. The functions handling UDP and TCP have been mostly
split to their matching counterparts and the dns_dispatch_<function>
functions are now thing wrappers that call <udp|tcp>_dispatch_<function>
based on the socket type.
More debugging-level logging was added to the unit to accomodate for
this fact.
When get_attached_entry() encounters entry that would be expired, it
needs to get reference to the entry before calling maybe_expire_entry(),
so the ADB entry doesn't get destroyed inside the its own lock.
This creeped into the code base again during review, so I am adding
an extra comment to prevent this.
The overmem cleaning in ADB could become overzealous and clean fresh ADB
names and entries. Add a safety check to not clean any ADB names and
entries that are below ADB_CACHE_MINIMUM threshold.
The ADB overmem accounting would include the memory used by hashtables
thus vastly reducing the space that can be used for ADB names and
entries when the hashtables would grow. Create own memory context for
the ADB names and entries hash tables.
There was a datarace that could expire a freshly created ADB names and
entries between the return from get_attached_{name,entry} and locking it
again. Lock the ADB name and ADB entry inside the hash table lock, so
they won't get expired until the full initialization has been complete.
The dns_catz_update_from_db() function prints serial number as a signed
number (with "%d" in the format string), but the `vers` variable's type
is 'uint32_t'. This breaks serials bigger than 2^31.
Use PRIu32 instead of "d" in the format string.
The dns_adb_getcookie() doesn't use the 'adb' parameter, remove it.
Refactor the dns_adb_getcookie() function to just return the size of
the cookie when the caller passes 'NULL' as the 'cookie' argument.
Add internal logging functions isc__netmgr_log, isc__nmsocket_log(), and
isc__nmhandle_log() that can be used to add logging messages to the
netmgr, and change all direct use of isc_log_write() to use those
logging functions to properly prefix them with netmgr, nmsocket and
nmsocket+nmhandle.
