This commit loosens the fwdpkg reference acking to be more tolerant
of prior deletions. Specifically, we won't fail if certain channels
are not found or fwdpkgs do not exist. This will make us more
tolerant to future changes where we:
- remove fwdpkgs on channel close
- defensively cleanup stray responses
In this commit, we add a new test to expose a lurking bug within the
graph database code. As is, when we go to delete a node from the
database, we don't also remove the entries within the update index. As a
result, if a user attempted to call NodeUpdatesInHorizon (or typically
as part of the p2p handshake), we would error out, as we would try to
read a node that no longer existed in the graph, as it was pruned.
In this commit we fix a minor logging artifact. After the switch to
EdgePoint, the FilteredChainView implementations will try to log the
struct directly, as prior they would have an outpoint object. We restore
this behavior by adding a String() method to EdgePoint which will simply
proxy through to the outpoint so we can log that directly.
In this commit, we add a new method to the ChannelEdgeInfo that will
allow the path finding logic to get the node opposite the pivot node
without first creating a new db transaction. The new method is able to
use an existing db transaction, or create a new one if needed.
The commit ensures that for every channel, there will always
be two entries in the edges bucket. If the policy from one or
both ends of the channel is unknown, it is marked as such.
This allows efficient lookup of incoming edges. This is
required for backwards payment path finding.
In this commit, we update the ChannelView method to be compatible with
the new set of interfaces that require the script to be passed in in
addition to the outpoint. In order to do this, we introduce a new
EdgePoint struct which packages together a channel point along with the
funding pkScript. Along the way, we've copied over a utility method from
the lnwallet package to avoid having to deal with an import cycle.
In this commit, we fix a slight race condition that can occur when we go
to add a shell node for a node announcement, but then right afterwards,
a new block arrives that causes us to prune an unconnected node. To
ensure this doesn't happen, we now add shell nodes within the same db
transaction as AddChannelEdge. This ensures that the state is fully
consistent and shell nodes will be added atomically along with the new
channel edge.
As a result of this change, we no longer need to add shell nodes within
the ChannelRouter, as the database will take care of this operation as
it should.
In this commit, we fix an existing bug in the pruneGraphNodes method.
Before this commit, if a node was involved in a channel, but only one of
the edges was advertised, then either it, or the other node would be
erroneously pruned from the graph. They shouldn't be pruned as there's
still an edge connecting the, although only 1/2 of the edge is actually
advertised.
In order to fix this, we'll now do two passes: the first pass will
populate a ref count map of all known nodes in the graph, the second
pass will increment the ref count each time a node is found in the
graph. With this two pass method, we ensure that nodes are only deleted
if there are absolutely no edges pointing to them within the graph.
In this commit, we extend the TestPruneGraphNodes test to also test the
case of when a node is involved in a channel, but only a single edge for
that channel has been advertised. In order to test this, we add an
additional node to the graph, and also a new channel. However, this
channel will only have a single edge advertised. As result, when we
prune the set of edges, the only node remaining should be the node that
didn't have any edges at all.
In this commit, we extend the server's functionality to prune link nodes
on startup. Since we currently only decide whether to prune a link node
from the database based on a channel close, it's possible that we have
link nodes lingering from before this functionality was added on.
In this commit, we fix an existing bug related to duplicate invoice
settle.s Before this commit, the second (and later) times an invoice was
settled we would return a nil pointer. This would result in the new
invoiceRegistry panicing as it would go to attempt to notify with a nil
invoice.
We fix this by returning the invoice on disk (unmodified) for each
settle after the initial one.
Fixes#1568.
In this commit, we add a new test to ensure that duplicate invoice
settles work as expected. At the present time, this test will fail as
the second to last assertion fails as we'll return a nil invoice the
second time around.
In this commit, we migrate the database away from a partially migrated
state. In a prior commit, we migrated the database in order to update
the Invoice struct with three new fields: add index, settle index, paid
amt. However, it was overlooked that the OutgoingPayment struct also
embedded an Invoice within it. As a result, nodes that upgraded to the
first migration found themselves unable to start up, or call
listpayments, as the internal invoice within the OutgoignPayment hadn't
yet been updated. This would result in an OOM typically as we went to
allocate a slice with a integer that should have been small, but may
have ended up actually being a set of random bytes, so a very large
number.
In this commit, we finish the DB migration by also migrating the
internal invoice within each OutgoingPayment.
Fixes#1538.
Fixes#1546.
In this commit, we fix an existing bu gin the invoice time series
migration code. Before this commit, the migration would fail as we would
try to migrate an empty invoice. We now detect this case and skip all
empty invoices.
We also add a bit more logging on both the info and trace logging level.
In this commit, we add two new methods: InvoicesAddedSince and
InvoicesSettledSince. These methods will be used by higher level
sub-systems that implement notifications to deliver any notifications
backlog based on the last add index, and last settle index that the
client knows of.
It's important to note that care has been taken to ensure that this new
API can be used in a backwards compatible manner. If a client specifies
and index of 0 for either of the methods, then no backlog will be sent.
This is due to the fact that current users of the API don't expect any
backlog notifications to be sent. Additionally, the index actually
starts at 1, instead of 0.
In this commit, we add two new indexes to the invoice database: the add
index, and the settle index. These to indexes essentially form a time
series index on top of the existing primary index bucket. Each time an
invoice is added, we'll advance the addIndex seqno, and then create a
mapping from seqNo -> invoiceNum. Each time an invoice is settled, we'll
do the same, but within the settle index.
This change is required in order to allow callers to effectively seek
into the current invoice database in order to obtain notifications for
any invoices they may have missed out on while they were disconnected.
This will allow us to implement robust streaming invoice notifications
within lnd to ensure that clients never miss an event.
In this commit, in order to allow the caller to specify the amount that
was ultimately accepted for an invoice, the SettleInvoice method has
gained a new parameter: amtPaid. SettleInvoice will now populate the
final amount paid in the database upon db commit.
In this commit, we move to explicitly storing a bit more information
within the invoice. Currently this information is already stored in the
payment request, but by storing it at this level, callers that may not
be in the state to fully decode a payment request can obtain this data.
We avoid a database migration by appending this data to the end of an
invoice. When decoding, we'll try to read out this extra information,
and simply return what we have if it isn't found.
This commit synchronizes the in-memory cache with the
on-disk state to ensure the waiting proof store is
externally consistent. Currently, there are scenarios
where the in-memory state is updated, and not reverted
if the write fails. The general fix is to wait to apply
modifications until the write succeeds, and use a
read/write lock to synchronize access with db operations.
In this commit, we fix an existing bug in the new graph query sync
feature. Before this commit, when a block is pruned, we would never
actually delete the update index entries. This is due to the fact that
we would attempt to delete the entries from the update index _after_ we
had already removed the edges from the update index.
We fix this by simply swapping the order: first we delete from the
update index, then we delete the edges themselves. A test ensuring that
the entires are cleared (which failed before this commit), has been
added.
In this commit, we go through the codebase looking for TCP address
assumptions and modifying them to include the recently introduced onion
addresses. This enables us to fully support onion addresses within the
daemon.
In this commit, we modify the waiting proof slightly to acept dupliacte
waiting proofs, rather than reject them. Otherwise, it's possible that
the remote node first sends us their half of the waiting proof (before
we do), we write that to disk, then upon restart, we'll try to add it
again, but be rejected by the system.
Fixes#1315.
In this commit, we ensure that all indexes for a particular channel have
any relevant keys deleted once a channel is removed from the database.
Before this commit, if we pruned a channel due to closing, then its
entry in the channel update index would ever be removed.
In this commit, we add a new database migration required to update old
database to the version of the database that tracks the update index for
the nodes and edge policies. The migration is straight forward, we
simply need to populate the new indexes for the all the nodes, and then
all the edges.
In this commit, we add a series of methods, and a new database index
that we'll use to implement the new discovery.ChannelGraphTimeSeries
interface interface. The primary change is that we now maintain two new
indexes tracking the last update time for each node, and the last update
time for each edge. These two indexes allow us to implement the
NodeUpdatesInHorizon and ChanUpdatesInHorizon methods. The remaining
methods added simply utilize the existing database indexes to allow us to
respond to any peer gossip range queries.
A set of new unit tests has been added to exercise the added logic.
The pending state definitin in ChannelCloseSummary was slightly changed
in such a way that channels that has had their commitment broadcasted
now is no longer considered "pending close". They now instead stay in
the open chan bucket with the ChanStatus "CommitmentBroadcasted" until
their commitment is confirmed. This commit updates the IsPending godoc
to reflect this.
In this commit, we modify the existing updateChanBucket function to no
longer auto-create buckets if they don't exist. We do this in order to
fix a class of bug that could arise wherein after a channel has actually
be closed (and the parent buckets removed) a method that mutates the
channel state is called, which then re-creates the relevant set of
buckets. As a result, subsequent calls to any RPCs which need to read
all the channels will fail as most of the fields won't actually be
populated.
After this commit, the fullSync method is the only one that's able to
create the full bucket hierarchy.
In this commit, we extend the CloseChannelSummary by also storing: the
current unrevoked revocation for the remote party, the next pending
unused revocation, and also the local channel config. We move to store
these as the provide an extra level of defense against bugs as we'll
always store information required to derive keys for any current and
prior states.
This commit adds a new method FetchWaitingCloseChannels to the database,
used for fetching OpenChannels that have a ChanStatus != Default. These
are channels that are borked, or have had a commitment broadcasted, and
is now waiting for it to confirm.
The fetchChannels method is rewritten to return channels exclusively
based on wheter they are pending or waitingClose.
This commit changes the bool `IsBorked` in OpenChannel to a `ChanStatus`
struct, of type ChannelStatus. This is used to indicated that a channel
that is technically still open, is either borked, or has had a
commitment broadcasted, but is not confirmed on-chain yet.
The ChannelStatus type has the value 1 for the status Borked, meaning it
is backwards compatible with the old database format.
Modifies TestFetchPendingChannels to verify that calls to
MarkAsOpen also modify the in-memory state. Previously we
only tested the persistent state loaded immediately after.
Modifies the MarkAsOpen operation to also update the
ShortChanID and IsPending fields in-memory. Before,
only the on-disk representation was updated, which
may have lead to stale data channel states being
passed in-memory.
In this commit, we remove references to raw keys from the main
ChannelConfig struct and instead replace it with usage of
keychain.KeyDescriptor. We do this, as the ChannelConfig as it stands
is a near complete static description of a channel. In the future, it
will be possible to export these static descriptions as backups. We
prefer the KeyDescriptor of a plain PublicKey, as the KeyLocator
portion of the struct allows a stateless signer to re-derive the keys
as needed when signing.
In this commit, we add a new storage namespace to channeldb: the
ForwardingLog. This log will be used by higher level sub-systems to log
each successfully completed HTLC. Each payment circuit will be
summarized as a “ForwardingEvent”. A series of events can then be
queried via a time slice query. In a time slice query, the caller
specifies a time range, a number of events to skip, and the max number
of events to return. Each query will return the index of the final
item. As we have a max number of events we’ll return in a response,
callers may need to use this last offset index to seek further by
skipping that number of entries. Combining these fields, callers are
able to query the time series, skipping an arbitrary amount of events,
and capping the max number of returned events.
In this commit, we made a series of modification to the way we handle
reading edges and vertexes from disk, in order to reduce the amount of
garbage generated:
1. Properly use PubKeyBytes are required rather than PubKey()
2. Return direct structs rather than pointers, and leave it to the
runtime to perform escape analysis.
3. In-line the former readSig() method when reading sigs from disk.
This commit changes the definition of the
constraints in the ChannelConstraints struct
to specify that these are all constraints the
*owner* of the set of constraints must *never
violate*.
This is done to make it easier to check that
a particular node is not violating any
constraint for a gien update, as before it
could violate constraints found both in its
local and the remote contraints.
In this commit, we make an API change that’s meant to reduce the amount
of garbage we generate when doing pathfinding or syncing nodes with our
latest graph state. Before this commit, we would always have to fully
decode the public key and signatures when reading a edge or vertex
struct. For the edges, we may need several EC operations to fully
decode all the pubkeys. This has been seen to generate a ton of
garbage, as well as slow down path finding a good bit.
To remedy this, we’ll now only ever read the *raw* bytes from disk. In
the event that we actually need to verify a signature (or w/e), only
*then* will we fully decode everything.
This commit adds Tor support. Users can set the --TorSocks flag
to specify which port Tor's SOCKS5 proxy is listening on so that
lnd can connect to it. When this flag is set, ALL traffic gets
routed over Tor including DNS traffic. Special functions for
DNS lookups were added, and since Tor doesn't natively support
SRV requests, the proxySRV function routes connects us to
a DNS server via Tor and SRV requests can be issued directly
to the DNS server.
Co-authored-by: MeshCollider <dobsonsa68@gmail.com>
Before this commit, we’d unnecessarily use a write transaction within
the FetchChannelEdgesByOutpoint. This is wasteful as the function only
actually reads items from the database, and doesn’t attempt any
mutations at all.
Fixes#481.
Prior to this commit, payments stored in the channel DB only kept a
record of the payment hash. This is a problem as the preimage is what
serves as proof of payment and a user should be able to look up this
value in the future (not just immediately after payment).
Instead of storing both the payment hash and the preimage, we store the
preimage only since the hash can be derrived from this using a SHA256.
In the RPC listpayments command, we now give the preimage in addition to
the payment hash.
This commit adds a FetchClosedChannel method to the
channeldb, which allows querying based on a known
channel point. This will be used in the nursery to
load channel close summaries, which can be used to
provide more accurate height hints when recovering
from failures.
In this commit, we add the WitnessCache sub-storage system of the
greater database. The WitnessCache is a persistent cache of all
witnesses we’ve encountered on the network. We’ll use this cache to
share any on-chain discoveries between active channels. Eventually
we’ll also use this to enforce the variant that a preimage is only to
be used ONCE on the network.
This commit adds the ChannelFlags field, of type
lnwire.FundingFlags, to the OpenChannel struct,
including serialization for database storage.
This is done to preserve the flags that were
sent during channel opening, currently used
to determine whether a channel should be made
public or not after opening.
In this commit, we fix an existing bug that arose due to incorrectly
crafting the key we use to store channel commitments. Before this
commit, we tried to copy to a slice that hadn’t been allocated yet. As
a result, the key would only have the 0x00 or 0x01 as its value. We fix
this by properly crafting the key using the built-in append function.
In this commit, we fix an existing bug wherein if we closed two
channels, then we were unable to read the channel state afterwards as
we deleted the enclosing bucket.
In this commit, we fix an existing bug wherein we failed to update the
channels state once we accepted a new commitment. As a result, after a
state transition, if the channel state was read from disk, values like
TotalMSatSent wouldn’t be properly updated.
In this commit we’ve extended the TestChannelStateTransition method to
exercise the new state transition related messages. This includes
ensuring that when we add a new dangling commitment, and then the
remote party revokes it, then the on-disk state is update accordingly.
In this commit, we update the CloseChannel method to respect the new
on-disk bucket based structure. Additionally, we now ensure that we
delete the new chainBucket.
In this commit, in addition to the renaming we’ve modified the behavior
of AdvanceCommitChainTail as follows: this method now will simply
atomically advance the commitment tail, set the new commitment to the
prior dangling commitment, and update the on-disk revocation log.
The macho expects the new revocation state to already be stored within
the channel. This method is to be called once the remote party revokes
their current commitment state.
In this commit, we add a new method: RemoteCommitChainTip. This method
allows callers to poll the database state to check if we have an
un-acked commitment for the remote party. If so, then it should be
retransmitted once a communication channel has been re-established with
the channel peer. This method will return ErrNoPendingCommit if we
don’t currently have a dangling commitment.
In this commit, we add a new method AppendRemoteCommitChain. This
method is meant to be used once we extend a new state to the remote
party, but before we actually transmit the CommitSig message. With this
method, we store a fully valid CommitDiff on disk which can be used in
the case that we need to retransmit the state to the party as they
didn’t fully receive it.
In this commit we finalized the structure of the CommitDiff struct by
adding a set of LogUpdates, and also a valid CommitSig message.
The LogUpdate struct houses a messages that were transmitted and
locked-in with the new commitment state. We include the LogIndex along
with the wire messages itself in order to be able to properly
reconstruct the update log upon restart.
The CommitSig message included should be transmitted after the set of
LogUpdates, and fully covers the new commitment state and any new (or
already present) HTLC’s that were included as part of the state.
In this commit, we modify the UpdateCommitment method to accept a full
ChannelCommitment rather than a new transaction, the sig, and a
ChannelDelta. This new structure of this method also takes advantage of
the new bucket structure of the storage schema. Additionally, this
method will now atomically swap in the new passed commitment to point
to the LocalCommitment value within the struct.
In this commit we add a new MarkAsOpen method to the OpenChannel
struct. This method replaces the existing MarkChannelAsOpen method
which targeted the database struct itself.
In this commit we comptely overhaul the existing storage of the
OpenChannel struct to use the new common serialization defined within
the codec.go file. Additionally, we’ve modified the structure of the
channel database on disk. Rather then use the existing prefix based
segmentation, everything is now bucket based. This has resulted in much
simpler and easier to follow code. The bucket progression is:
openChannelBucket -> nodeBucket -> chainBucket -> channelBucket. We add
a chainBucket as it’s possible that in the future we may have several
channels on distinct chains with a given node.
With the above changes, we’re able to delete much of the existing code
within the file, drastically reducing its size.
By adding these two fields, it is now possible to fully reconstruct the
channel’s update log from the set of HTLC’s stored on disk, as we now
properly note both the log index and HTLC index. Prior to this commit
we would simply start the new log index based on the amount of HTLC’s
that were present in the prior state.
In this commit, we restructure the OpenChannel struct to used two
distinct ChannelCommitments: one for the remote party, and one for the
local party. With this, we now partition the local state and the remote
state. Previously, we weren’t properly tracking the state of the remote
party. As a result, there were certain classes of failures we were
unable to properly recover from. With this separation, we can now
handle them, and the OpenChannel struct is slimmer and more
understandable.
In this commit we’ve added a new struct to the package:
ChannelCommitment. This sturct houses all the common data the comprises
a particular commitment state. This will soon replace the open fielded
commitmetn fields within the OpenChannel struct.
In this commit, we add a new files to the channeldb package: codec.go.
This file is similar to the way that serialization is done within the
lnwire package. The goal of this file is to reduce all the duplication
within the common serialization methods across the package.
In this commit htlc channeldb representation have been augmented
with onion blob field, and (de)serialisaion functions have been changed
to make the onion blob persistant.
This commit adds the method DisconnectBlockAtHeight to the channel
graph database, making it possible to "rewind" the database in case
a block is disconnected from the main chain. To accomplish this,
a prune log is introduced, making it possible to keep track of the
point in time where the database was pruned. This is necessary for
the case where lnd might wake up on a stale branch, and must "walk
backwards" on this branch after it finds a common block fro the
graph database and the new main chain.
This commit modifies the recently modified logic for self-channel
retransmission to exclude pruning *our* channels which haven’t been
updated since the broadcastInterval. Instead, we only re-broadcast
channels of ours that haven’t been updated in 24 hours.
Use binary.Read/Write in functions to serialize and deserialize
channel close summary and HTLC boolean data, as well as in
methods to put and fetch channel funding info. Remove lnd
implementations of readBool and writeBool as they are no
longer needed. Also fix a few minor typos.
This modifies the tests that deal serializing the Invoice type to limit
the creation date to seconds since Go1.9 added the concept of a
monotonic component to times which does not round trip through
MarshalBinary and UnmarshalBinary and therefore causes the tests to fail.
In particular, it modifies the creation dates in the randInvoice,
makeFakePayment, makeRandomFakePayment, and TestInvoiceWorkflow
functions.
This results in allowing TestOutgoingPaymentSerialization,
TestOutgoingPaymentWorkflow, and TestInvoiceWorkflow to pass.
This commit modifies the node.ForEachChannel to *also* return the
incoming edge as well as the outgoing edge. We make this modification
as when we’re doing path finding, we need to return the incoming edge
as well, since we need to use the to properly compute the time lock and
fees for transit on that edge.
Persists the state of a channel opening process after funding
transaction is confirmed. This tracks the messages sent to
the peer such that the process can be continued in case of a
restart. Also introduces that the receiver side forgets about
channel if funding transaction is not confirmed in 48hrs.
Adds a HaveNodeAnnouncement field to the LightningNode
struct, which is used to indicate if we have gotten
all the necessary information to fill the remaining
fields in the struct. If we haven't gotten a node
announcement for this specific node, then we only
know the pubkey, and can only fill that field in
the struct. Still, we should be able to add it to the
channel graph and use it for routes, as long as we
know about channels to this node.
This commit removes the RevocationDelay field from the HTLC struct as
with the latest commitment transaction scheme, it is no longer needed.
This is due to the fact the the delay is now observed when an on-chain
HTLC claim is attempted, rather than from Shane the HTLC itself has
been broadcast.
This commit adds a new method to the OpenChannel struct:
InsertNextRevocation. This functionality is required in order to
properly implement the new funding workflow and commitment transaction
state machine.
In the prior state machine, we utilized the “initial revocation window”
which would provide both sides with the necessary revocation keys that
they needed to create new commitment states. The version of the
commitment state machine within the specification has been simplified a
bit, and instead essentially incorporates a revocation window of 1. The
window is initially filled at the _opening_ of the commitment
transaction, then never extended, only “slid down” from there on.
This commit modifies the HTLC struct within the channeldb struct in
order to accommodate the additional storage that’s now required as a
result of the change to 2-of-2 HTLC covenant transactions within the
commitment transaction.
This commit is the next phase in a rather major overhaul of the
OpenChannel struct. With this commit we remove the old ours vs theirs
semantics with channel related state variables, and instead encapsulate
all local vs remote state into a ChannelConfig structure for each party
within the channel.
This commit introduces two new structs to the channeled package:
ChannelConfig and ChannelConstraints.
The ChannelConfig struct will eliminate many of the fields on the
OpenChannel struct (ours vs theirs), in favor of having a single config
for both sides (local and remote).
The ChannelConstraints struct will house the channel flow control and
HTLC policies for both sides. The fields of this struct will be used to
control the flow of HTLC’s within the channel. In the occasion that any
of these constraints are violated, either the connection, or the
channel entirely is to be failed.
This commit removes a database migration that was added to fix a bug
introduced within the first alpha release. This migration is no longer
needed as the underlying database scheme has changed since then.
This commit adds the possibility for the initiator of a
channel to send the update_fee message, as specified
in BOLT#2. After the message is sent and both parties
have committed to the updated fee, all new commitment
messages in the channel will use the specified fee.
The btclog package has been changed to defining its own logging
interface (rather than seelog's) and provides a default implementation
for callers to use.
There are two primary advantages to the new logger implementation.
First, all log messages are created before the call returns. Compared
to seelog, this prevents data races when mutable variables are logged.
Second, the new logger does not implement any kind of artifical rate
limiting (what seelog refers to as "adaptive logging"). Log messages
are outputted as soon as possible and the application will appear to
perform much better when watching standard output.
Because log rotation is not a feature of the btclog logging
implementation, it is handled by the main package by importing a file
rotation package that provides an io.Reader interface for creating
output to a rotating file output. The rotator has been configured
with the same defaults that btcd previously used in the seelog config
(10MB file limits with maximum of 3 rolls) but now compresses newly
created roll files. Due to the high compressibility of log text, the
compressed files typically reduce to around 15-30% of the original
10MB file.
This commit modifies the OpenChannel struct to include the full short
channel ID rather than simply the opening height. This new field will
be needed by an upcoming change to uniformly switch to using short
channel ID’s when forwarding HTLC’s due to the change in per-hop
payloads.
This commit expands the field within the OpenChannel struct in order to
start tracking the height that the funding transaction was initially
broadcast. Other sub-systems within lnd can now use this data to give a
more accurate height hint to the ChainNotifier, or to use during the
funding workflow to decide if a channel should be forgotten after it
fails to confirm for N blocks.
This commit modifies the name of a field in the OpenChannel struct to
better reflect its actual usage within this protocol. The FeePerKw
represents the amount of satoshi to be paid as fees per kilo-weight.
This field is set at the opening of a transaction and will be able to
be updated properly via the usage of the update_fee method.
In order to cleanly handle shutdowns and restarts during state machine operation, the fee for the current
commitment transaction must be persisted. This allows the fee to be
reapplied when the current state is reloaded.
This commit adds the total time locked balance of a closed channel at
closure time to the CloseChannelSummary struct. With this information,
we now provide sub-systems within the daemon further knowledge which
can aide them in properly handling querying for the state of pending
close transactions, or if they should watch a channel for closure or
not.
This commit modifies the OpenChannel structure on-disk to also track
that opening height of a channel. This change is being made in order to
make and more light client friendly. A follow up commit will modify
several areas of the codebase to use this new functionality.
This commit introduces a new method to the ChannelGraph struct:
ChannelView. This struct returns all the outpoints that represent the
set of active channels within the network. The set of items returned by
this new method will possibly shrink with each call to `PruneGraph`,
and possibly be expanded by each call to `AddChannelEdge`.
The graph pruning tests have been updated to ensure the description
above holds true.
