Move parameter argument after stream argument so will be possible to accept
multiple variadic parameter arguments in the following commit.
Also reverse template parameter order for consistency.
fb5bfed26a cli: add transport protcol column to -netinfo (Martin Zumsande)
9eed22e870 net: attempt v2 transport for addrfetch connections if we support it (Martin Zumsande)
770c0311ef net: attempt v2 transport for manual connections if we support it (Martin Zumsande)
Pull request description:
Some preparations before enabling `-v2transport` as the default:
* Use v2 for `-connect`, `-addnode` config arg and `-seednode` if `-v2transport` is enabled.
Our peer may or may not support v2, but I don't think an extra option is necessary for any of these (we have that for the `addnode` rpc), because we have the reconnection mechanism that will try again with `v1` if our peer doesn't support `v2`.
* Add a column for the transport protocol to `-netinfo`. I added it next to the `net` column because I thought it looked nice there, but if people prefer it somewhere else I'm happy to move it.
ACKs for top commit:
sipa:
utACK fb5bfed26a
achow101:
ACK fb5bfed26a
stratospher:
tested ACK fb5bfed. addrfetch + manual connections aren't frequent and it would be useful to have this for transition to v2 one day.
theStack:
ACK fb5bfed26a
kristapsk:
ACK fb5bfed26a
Tree-SHA512: c4575ad11b99613870b342acae369fa08f877ac79e6e04eb62e94ad7a92d528e289183c0963c78aa779ba11cb91e2a6fad7c8b0d813126c46c3e5b54bd962c26
This affects manual connections made either with -connect, or with
-addnode provided as a bitcoind config arg (the addnode RPC has an
extra option for v2).
We don't necessarily know if our peer supports v2, but will reconnect
with v1 if they don't. In order to do that, improve the reconnection
behavior such that we will reconnect after a sleep of 500ms
(which usually should be enough for our peer to send us their
version message).
Making the `GenerateRandomKey` helper available to other modules via
key.{h.cpp} allows us to create random private keys directly at
instantiation of CKey, in contrast to the two-step process of creating
the instance and then having to call `MakeNewKey(...)`.
3ea54e5db7 net: Add continuous ASMap health check logging (Fabian Jahr)
28d7e55dff test: Add tests for unfiltered GetAddr usage (Fabian Jahr)
b8843d37ae fuzz: Let fuzzers use filter options in GetAddr/GetAddresses (Fabian Jahr)
e16f420547 net: Optionally include terrible addresses in GetAddr results (Fabian Jahr)
Pull request description:
There are certain statistics we can collect by running all our known clearnet addresses against the ASMap file. This could show issues with a maliciously manipulated file or with an old file that has decayed with time.
This is just a proof of concept for now. My idea currently is to run the analysis once per day and print the results to logs if an ASMap file is used.
ACKs for top commit:
achow101:
ACK 3ea54e5db7
mzumsande:
ACK 3ea54e5db7
brunoerg:
crACK 3ea54e5db7
Tree-SHA512: 777acbfac43cc43ce4a0a3612434e4ddbc65f59ae8ffc9e24f21de09011bccb297f0599cbaa82bcf40ef68e5af582c4e98556379db7ceff7d9f97574a1cf8e09
fa79a881ce refactor: P2P transport without serialize version and type (MarcoFalke)
fa9b5f4fe3 refactor: NetMsg::Make() without nVersion (MarcoFalke)
66669da4a5 Remove unused Make() overload in netmessagemaker.h (MarcoFalke)
fa0ed07941 refactor: VectorWriter without nVersion (MarcoFalke)
Pull request description:
Now that the serialize framework ignores the serialize version and serialize type, everything related to it can be removed from the code.
This is the first step, removing dead code from the P2P stack. A different pull will remove it from the wallet and other parts.
ACKs for top commit:
ajtowns:
reACK fa79a881ce
Tree-SHA512: 785b413580d980f51f0d4f70ea5e0a99ce14cd12cb065393de2f5254891be94a14f4266110c8b87bd2dbc37467676655bce13bdb295ab139749fcd8b61bd5110
to allocate our limited outbound slots correctly, and to ensure addnode
connections benefit from their intended protections.
Our addnode logic usually connects the addnode peers before the automatic
outbound logic does, but not always, as a connection race can occur. If an
addnode peer disconnects us and if it was the only one from its network, there
can be a race between reconnecting to it with the addnode thread, and it being
picked as automatic network-specific outbound peer. Or our internet connection
or router, or the addnode peer, could be temporarily offline, and then return
online during the automatic outbound thread. Or we could add a new manual peer
using the addnode RPC at that time.
The race can be more apparent when our node doesn't know many peers, or with
networks like cjdns that currently have few bitcoin peers.
When an addnode peer is connected as an automatic outbound peer and is the only
connection we have to a network, it can be protected by our new outbound
eviction logic and persist in the "wrong role".
Examples on mainnet using logging added in the same pull request:
2023-08-12T14:51:05.681743Z [opencon] [net.cpp:1949] [ThreadOpenConnections]
[net:debug] Not making automatic network-specific outbound-full-relay connection
to i2p peer selected for manual (addnode) connection: [geh...odq.b32.i2p]:0
2023-08-13T03:59:28.050853Z [opencon] [net.cpp:1949] [ThreadOpenConnections]
[net:debug] Not making automatic block-relay-only connection to onion peer
selected for manual (addnode) connection: kpg...aid.onion:8333
2023-08-13T16:21:26.979052Z [opencon] [net.cpp:1949] [ThreadOpenConnections]
[net:debug] Not making automatic network-specific outbound-full-relay connection
to cjdns peer selected for manual (addnode) connection: [fcc...8ce]:8333
2023-08-14T20:43:53.401271Z [opencon] [net.cpp:1949] [ThreadOpenConnections]
[net:debug] Not making automatic network-specific outbound-full-relay connection
to cjdns peer selected for manual (addnode) connection: [fc7...59e]:8333
2023-08-15T00:10:01.894147Z [opencon] [net.cpp:1949] [ThreadOpenConnections]
[net:debug] Not making automatic feeler connection to i2p peer selected for
manual (addnode) connection: geh...odq.b32.i2p:8333
Finally, there does not seem to be a reason to make block-relay or short-lived
feeler connections to addnode peers, as the addnode logic will ensure we connect
to them if they are up, within the addnode connection limit.
Fix these issues by checking if the address is an addnode peer in our automatic
outbound connection logic.
0420f99f42 Create net_peer_connection unit tests (Jon Atack)
4b834f6499 Allow unit tests to access additional CConnman members (Jon Atack)
34b9ef443b net/rpc: Makes CConnman::GetAddedNodeInfo able to return only non-connected address on request (Sergi Delgado Segura)
94e8882d82 rpc: Prevents adding the same ip more than once when formatted differently (Sergi Delgado Segura)
2574b7e177 net/rpc: Check all resolved addresses in ConnectNode rather than just one (Sergi Delgado Segura)
Pull request description:
## Rationale
Currently, `addnode` has a couple of corner cases that allow it to either connect to the same peer more than once, hence wasting outbound connection slots, or add redundant information to `m_added_nodes`, hence making Bitcoin iterate through useless data on a regular basis.
### Connecting to the same node more than once
In general, connecting to the same node more than once is something we should try to prevent. Currently, this is possible via `addnode` in two different ways:
1. Calling `addnode` more than once in a short time period, using two equivalent but distinct addresses
2. Calling `addnode add` using an IP, and `addnode onetry` after with an address that resolved to the same IP
For the former, the issue boils down to `CConnman::ThreadOpenAddedConnections` calling `CConnman::GetAddedNodeInfo` once, and iterating over the result to open connections (`CConman::OpenNetworkConnection`) on the same loop for all addresses.`CConnman::ConnectNode` only checks a single address, at random, when resolving from a hostname, and uses it to check whether we are already connected to it.
An example to test this would be calling:
```
bitcoin-cli addnode "127.0.0.1:port" add
bitcoin-cli addnode "localhost:port" add
```
And check how it allows us to perform both connections some times, and some times it fails.
The latter boils down to the same issue, but takes advantage of `onetry` bypassing the `CConnman::ThreadOpenAddedConnections` logic and calling `CConnman::OpenNetworkConnection` straightaway. A way to test this would be:
```
bitcoin-cli addnode "127.0.0.1:port" add
bitcoin-cli addnode "localhost:port" onetry
```
### Adding the same peer with two different, yet equivalent, addresses
The current implementation of `addnode` is pretty naive when checking what data is added to `m_added_nodes`. Given the collection stores strings, the checks at `CConnman::AddNode()` basically check wether the exact provided string is already in the collection. If so, the data is rejected, otherwise, it is accepted. However, ips can be formatted in several ways that would bypass those checks.
Two examples would be `127.0.0.1` being equal to `127.1` and `[::1]` being equal to `[0:0:0:0:0:0:0:1]`. Adding any pair of these will be allowed by the rpc command, and both will be reported as connected by `getaddednodeinfo`, given they map to the same `CService`.
This is less severe than the previous issue, since even tough both nodes are reported as connected by `getaddednodeinfo`, there is only a single connection to them (as properly reported by `getpeerinfo`). However, this adds redundant data to `m_added_nodes`, which is undesirable.
### Parametrize `CConnman::GetAddedNodeInfo`
Finally, this PR also parametrizes `CConnman::GetAddedNodeInfo` so it returns either all added nodes info, or only info about the nodes we are **not** connected to. This method is used both for `rpc`, in `getaddednodeinfo`, in which we are reporting all data to the user, so the former applies, and to check what nodes we are not connected to, in `CConnman::ThreadOpenAddedConnections`, in which we are currently returning more data than needed and then actively filtering using `CService.fConnected()`
ACKs for top commit:
jonatack:
re-ACK 0420f99f42
kashifs:
> > tACK [0420f9](0420f99f42)
sr-gi:
> > > tACK [0420f9](0420f99f42)
mzumsande:
Tested ACK 0420f99f42
Tree-SHA512: a3a10e748c12d98d439dfb193c75bc8d9486717cda5f41560f5c0ace1baef523d001d5e7eabac9fa466a9159a30bb925cc1327c2d6c4efb89dcaf54e176d1752
df69b22f2e doc: improve documentation around connection limit maximums (Amiti Uttarwar)
adc171edf4 scripted-diff: Rename connection limit variables (Amiti Uttarwar)
e9fd9c0225 net: add m_max_inbound to connman (Amiti Uttarwar)
c25e0e0555 net, refactor: move calculations for connection type limits into connman (Amiti Uttarwar)
Pull request description:
This is joint work with amitiuttarwar.
This has the first few commits of #28463. It is not strictly a prerequisite for that, but has changes that in our opinion make sense on their own.
It improves the handling of maximum numbers for different connection types (that are set during init and don’t change after) by:
* moving all calculations into one place, `CConnMan::Init()`. Before, they were dispersed between `Init`, `CConnman::Init` and other parts of `CConnman`, resulting in some duplicated test code.
* removing the possibility of having a negative maximum of inbound connections, which is hard to argue about
* renaming of variables and doc improvements
ACKs for top commit:
amitiuttarwar:
co-author review ACK df69b22f2e
naumenkogs:
ACK df69b22f2e
achow101:
ACK df69b22f2e
Tree-SHA512: 913d56136bc1df739978de50db67302f88bac2a9d34748ae96763288d97093e998fc0f94f9b6eff12867712d7e86225af6128f4170bf2b5b8ab76f024870a22c
af0fca530e netbase: use reliable send() during SOCKS5 handshake (Vasil Dimov)
1b19d1117c sock: change Sock::SendComplete() to take Span (Vasil Dimov)
Pull request description:
The `Socks5()` function which does the SOCKS5 handshake with the SOCKS5 proxy sends bytes to the socket without retrying partial writes.
`send(2)` may write only part of the provided data and return. In this case the caller is responsible for retrying the operation with the remaining data. Change `Socks5()` to do that. There is already a method `Sock::SendComplete()` which does exactly that, so use it in `Socks5()`.
A minor complication for this PR is that `Sock::SendComplete()` takes `std::string` argument whereas `Socks5()` has `std::vector<uint8_t>`. Thus the necessity for the first commit. It is possible to do also in other ways - convert the data in `Socks5()` to `std::string` or have just one `Sock::SendComplete()` that takes `void*` and change the callers to pass `str.data(), str.size()` or `vec.data(), vec.size()`.
This came up while testing https://github.com/bitcoin/bitcoin/pull/27375.
ACKs for top commit:
achow101:
ACK af0fca530e
jonatack:
ACK af0fca530e
pinheadmz:
ACK af0fca530e
Tree-SHA512: 1d4a53d0628f7607378038ac56dc3b8624ce9322b034c9547a0c3ce052eafb4b18213f258aa3b57bcb4d990a5e0548a37ec70af2bd55f6e8e6399936f1ce047a
`send(2)` can be interrupted or for another reason it may not fully
complete sending all the bytes. We should be ready to retry the send
with the remaining bytes. This is what `Sock::SendComplete()` does,
thus use it in `Socks5()`.
Since `Sock::SendComplete()` takes a `CThreadInterrupt` argument,
change also the recv part of `Socks5()` to use `CThreadInterrupt`
instead of a boolean.
Easier reviewed with `git show -b` (ignore white-space changes).
`CConnman::GetAddedNodeInfo` is used both to get a list of addresses to manually connect to
in `CConnman::ThreadOpenAddedConnections`, and to report about manually added connections in
`getaddednodeinfo`. In both cases, all addresses added to `m_added_nodes` are returned, however
the nodes we are already connected to are only relevant to the latter, in the former they are
actively discarded.
Parametrizes `CConnman::GetAddedNodeInfo` so we can ask for only addresses we are not connected to,
to avoid passing useless information around.
Currently it is possible to add the same node twice when formatting IPs in
different, yet equivalent, manner. This applies to both ipv4 and ipv6, e.g:
127.0.0.1 = 127.1 | [::1] = [0:0:0:0:0:0:0:1]
`addnode` will accept both and display both as connected (given they translate to
the same IP). This will not result in multiple connections to the same node, but
will report redundant info when querying `getaddednodeinfo` and populate `m_added_nodes`
with redundant data.
This can be avoided performing comparing the contents of `m_added_addr` and the address
to be added as `CServices` instead of as strings.
The current `addnode` rpc command has some edge cases in where it is possible to
connect to the same node twice by combining ip and address requests. This can happen under two situations:
The two commands are run one right after each other, in which case they will be processed
under the same loop in `CConnman::ThreadOpenAddedConnections` without refreshing `vInfo`, so both
will go trough. An example of this would be:
```
bitcoin-cli addnode "localhost:port" add
```
A node is added by IP using `addnode "add"` while the other is added by name using
`addnode "onetry"` with an address that resolves to multiple IPs. In this case, we currently
only check one of the resolved IPs (picked at random), instead of all the resolved ones, meaning
this will only probabilistically fail/succeed. An example of this would be:
```
bitcoin-cli addnode "127.0.0.1:port" add
[...]
bitcoin-cli addnode "localhost:port" onetry
```
Both cases can be fixed by iterating over all resolved addresses in `CConnman::ConnectNode` instead
of picking one at random
5c8e15c451 i2p: destroy the session if we get an unexpected error from the I2P router (Vasil Dimov)
762404a68c i2p: also sleep after errors in Accept() (Vasil Dimov)
Pull request description:
### Background
In the `i2p::sam::Session` class:
`Listen()` does:
* if the session is not created yet
* create the control socket and on it:
* `HELLO`
* `SESSION CREATE ID=sessid`
* leave the control socked opened
* create a new socket and on it:
* `HELLO`
* `STREAM ACCEPT ID=sessid`
* read reply (`STREAM STATUS`), `Listen()` only succeeds if it contains `RESULT=OK`
Then a wait starts, for a peer to connect. When connected,
`Accept()` does:
* on the socket from `STREAM ACCEPT` from `Listen()`: read the Base64 identification of the connecting peer
### Problem
The I2P router may be in such a state that this happens in a quick succession (many times per second, see https://github.com/bitcoin/bitcoin/issues/22759#issuecomment-1609907115): `Listen()`-succeeds, `Accept()`-fails.
`Accept()` fails because the I2P router sends something that is not Base64 on the socket: `STREAM STATUS RESULT=I2P_ERROR MESSAGE="Session was closed"`
We only sleep after failed `Listen()` because the assumption was that if `Accept()` fails then the next `Listen()` will also fail.
### Solution
Avoid filling the log with "Error accepting:" messages and sleep also after a failed `Accept()`.
### Extra changes
* Reset the error waiting time after one successful connection. Otherwise the timer will remain high due to problems that have been solved long time in the past.
* Increment the wait time less aggressively.
* Handle the unexpected "Session was closed" message more gracefully (don't log stupid messages like `Cannot decode Base64: "STREAM STATUS...`) and destroy the session right way.
ACKs for top commit:
achow101:
ACK 5c8e15c451
jonatack:
re-ACK 5c8e15c451
Tree-SHA512: 1d47958c50eeae9eefcb668b8539fd092adead93328e4bf3355267819304b99ab41cbe1b5dbedbc3452c2bc389dc8330c0e27eb5ccb880e33dc46930a1592885
`vfLimited`, `IsReachable()`, `SetReachable()` need not be in the `net`
module. Move them to `netbase` because they will be needed in
`LookupSubNet()` to possibly flip the result to CJDNS (if that network
is reachable).
In the process, encapsulate them in a class.
`NET_UNROUTABLE` and `NET_INTERNAL` are no longer ignored when adding
or removing reachable networks. This was unnecessary.
Background:
`Listen()` does:
* if the session is not created yet
* create the control socket and on it:
* `HELLO`
* `SESSION CREATE ID=sessid`
* leave the control socked opened
* create a new socket and on it:
* `HELLO`
* `STREAM ACCEPT ID=sessid`
* read reply (`STREAM STATUS`)
Then a wait starts, for a peer to connect. When connected,
`Accept()` does:
* on the socket from `STREAM ACCEPT` from `Listen()`: read the
Base64 identification of the connecting peer
Problem:
The I2P router may be in such a state that this happens in a quick
succession (many times per second, see https://github.com/bitcoin/bitcoin/issues/22759#issuecomment-1609907115):
`Listen()`-succeeds, `Accept()`-fails.
`Accept()` fails because the I2P router sends something that is
not Base64 on the socket:
STREAM STATUS RESULT=I2P_ERROR MESSAGE="Session was closed"
We only sleep after failed `Listen()` because the assumption was that
if `Accept()` fails then the next `Listen()` will also fail.
Solution:
Avoid filling the log with "Error accepting:" messages and sleep also
after a failed `Accept()`.
Extra changes:
* Reset the error waiting time after one successful connection.
Otherwise the timer will remain high due to problems that have
vanished long time ago.
* Increment the wait time less aggressively.
A "version" message in the V1 protocol starts with a fixed 16 bytes:
* The 4-byte network magic
* The 12-byte zero-padded command "version" plus 5 0x00 bytes
The current code detects incoming V1 connections by just looking at the
first 12 bytes (matching an earlier version of BIP324), but 16 bytes is
more precise. This isn't an observable difference right now, as a 12 byte
prefix ought to be negligible already, but it may become observable with
future extensions to the protocol, so make the code match the
specification.
Extract the logic for calculating & maintaining inbound connection limits to be
a member within connman for consistency with other maximum connection limits.
Note that we now limit m_max_inbound to 0 and don't call
AttemptToEvictConnection() when we don't have any inbounds.
Previously, nMaxInbound could become negative if the user ran with a low
-maxconnections, which didn't break any logic but didn't make sense.
Co-authored-by: Martin Zumsande <mzumsande@gmail.com>
7df4508369 test: improve sock_tests/move_assignment (Vasil Dimov)
5086a99b84 net: remove Sock default constructor, it's not necessary (Vasil Dimov)
7829272f78 net: remove now unnecessary Sock::Get() (Vasil Dimov)
944b21b70a net: don't check if the socket is valid in ConnectSocketDirectly() (Vasil Dimov)
aeac68d036 net: don't check if the socket is valid in GetBindAddress() (Vasil Dimov)
5ac1a51ee5 i2p: avoid using Sock::Get() for checking for a valid socket (Vasil Dimov)
Pull request description:
_This is a piece of #21878, chopped off to ease review._
Peeking at the underlying socket file descriptor of `Sock` and checkig if it is `INVALID_SOCKET` is bad encapsulation and stands in the way of testing/mocking/fuzzing.
Instead use an empty `unique_ptr` to denote that there is no valid socket where appropriate or outright remove such checks where they are not necessary.
The default constructor `Sock::Sock()` is unnecessary now after recent changes, thus remove it.
ACKs for top commit:
ajtowns:
ACK 7df4508369
jonatack:
ACK 7df4508369
Tree-SHA512: 9742aeeeabe8690530bf74caa6ba296787028c52f4a3342afd193b05dbbb1f6645935c33ba0a5230199a09af01c666bd3c7fb16b48692a0d185356ea59a8ddbf
When an outbound v2 connection is disconnected without receiving anything, but at
least 24 bytes of our pubkey were sent out (enough to constitute an invalid v1
header), add them to a queue of reconnections to be tried.
The reconnections are in a queue rather than performed immediately, because we should
not block the socket handler thread with connection creation (a blocking operation
that can take multiple seconds).
fac29a0ab1 Remove SER_GETHASH, hard-code client version in CKeyPool serialize (MarcoFalke)
fa72f09d6f Remove CHashWriter type (MarcoFalke)
fa4a9c0f43 Remove unused GetType() from OverrideStream, CVectorWriter, SpanReader (MarcoFalke)
Pull request description:
Removes a bunch of redundant, dead or duplicate code.
Uses the idea from and finishes the idea https://github.com/bitcoin/bitcoin/pull/28428 by theuni
ACKs for top commit:
ajtowns:
ACK fac29a0ab1
kevkevinpal:
added one nit but otherwise ACK [fac29a0](fac29a0ab1)
Tree-SHA512: cc805e2f38e73869a6691fdb5da09fa48524506b87fc93f05d32c336ad3033425a2d7608e317decd3141fde3f084403b8de280396c0c39132336fe0f7510af9e
See also https://github.com/bitcoin/bips/pull/1498
The benefit is a simpler implementation:
- The protocol state machine does not need separate states for garbage
authentication and version phases.
- The special case of "ignoring the ignore bit" is removed.
- The freedom to choose the contents of the garbage authentication
packet is removed. This simplifies testing.
3fcd7fc7ff Do not use std::vector = {} to release memory (Pieter Wuille)
Pull request description:
It appears that invoking `v = {};` for an `std::vector<...> v` is equivalent to `v.clear()`, which does not release its allocated memory. There are a number of places in the codebase where it appears to be used for that purpose however (mostly written by me). Replace those with `std::vector<...>{}.swap(v);` (using a helper function `ClearShrink` in util/vector.h).
To explain what is going on: `v = {...};` is equivalent in general to `v.operator=({...});`. For many types, the `{}` is converted to the type of `v`, and then assigned to `v` - which for `std::vector` would ordinarily have the effect of clearing its memory (constructing a new empty vector, and then move-assigning it to `v`). However, since `std::vector<T>` has an `operator=(std::initializer_list<T>)` defined, it has precedence (since no implicit conversion is needed), and with an empty list, that is equivalent to `clear()`.
I did consider using `v = std::vector<T>{};` as replacement for `v = {};` instances where memory releasing is desired, but it appears that it does not actually work universally either. `V{}.swap(v);` does.
ACKs for top commit:
ajtowns:
utACK 3fcd7fc7ff
stickies-v:
ACK 3fcd7fc7ff
theStack:
Code-review ACK 3fcd7fc7ff
Tree-SHA512: 6148558126ec3c8cfd6daee167ec1c67b360cf1dff2cbc132bd71768337cf9bc4dda3e5a9cf7da4f7457d2123288eeba77dd78f3a17fa2cfd9c6758262950cc5
Move functions requiring the netaddress.h include out of
libbitcoinkernel source files.
The netaddress.h file contains many non-consensus related definitions
and should thus not be part of the libbitcoinkernel. This commit makes
netaddress.h no longer a required include for users of the
libbitcoinkernel.
This commit is part of the libbitcoinkernel project, namely its stage 1
step 3: Decouple most non-consensus headers from libbitcoinkernel.
The protocol.h file contains many non-consensus related definitions and
should thus not be part of the libbitcoinkernel. This commit makes
protocol.h no longer a required include for users of the
libbitcoinkernel.
This commit is part of the libbitcoinkernel project, namely its stage 1
step 3: Decouple most non-consensus headers from libbitcoinkernel.
Co-Authored-By: Cory Fields <cory-nospam-@coryfields.com>
Before this commit the V2Transport::m_send_buffer is used to store the
garbage:
* During MAYBE_V1 state, it's there despite not being sent.
* During AWAITING_KEY state, while it is being sent.
* At the end of the AWAITING_KEY state it cannot be wiped as it's still
needed to compute the garbage authentication packet.
Change this by introducing a separate m_send_garbage field, taking over
the first and last role listed above. This means the garbage is only in
the send buffer when it's actually being sent, removing a few special
cases related to this.
This removes the ability for BIP324Cipher to generate its own key, moving that
responsibility to the caller (mostly, V2Transport). This allows us to write
the random-key V2Transport constructor by delegating to the explicit-key one.
