Now that the `PeerConnector` handles both incoming and outgoing
handshakes, determining the next peer address is definitely out of scope
-- it takes a pre-existing tcp connection.
Failure uses a distinct Fail trait rather than the standard library's
Error trait, which causes a lot of interoperability problems with tower
and other Error-using crates. Since failure was created, the standard
library's Error trait was improved, and its conveniences are now
available without the custom Fail trait using `thiserror` (for easy
error derives) and `anyhow` (for a better boxed Error).
* Don't expose submodules of zebra_network::peer.
* PeerSet, PeerDiscover stubs.
Co-authored-by: Deirdre Connolly <deirdre@zfnd.org>
* Initial work on PeerSet.
This is adapted from the MIT-licensed tower-balance implementation.
* Use PeerSet in the connect stub.
This adds a type alias, BoxedStdError, for a boxed std::error::Error
trait object, and uses it in the where bounds for the generic service
code. In the future, we may want to standardize on using
std::error::Error exclusively, but we would then possibly lose out on
backtrace information.
* Fix authorship, license information.
I *thought* I had done a sed pass over the Cargo defaults when doing
repository initialization, but I guess I missed it or something.
Anyways, fixed now.
Add a tower-based peer implementation.
Tower provides middleware for request-response oriented protocols, while Bitcoin/Zcash just send messages which could be interpreted either as requests or responses, depending on context. To bridge this mismatch we define our own internal request/response protocol, and implement a per-peer event loop that scans incoming messages and interprets them either as requests from the remote peer to our node, or as responses to requests we made previously. This is performed by the `PeerService` task, and a corresponding `PeerClient: tower::Service` can send it requests. These tasks are themselves created by a `PeerConnector: tower::Service` which dials a remote peer and performs a handshake.
This field is called `services` in Bitcoin and Zcash, but because we use
that word internally for other purposes, calling it `PeerServices`
disambiguates the meaning to "the services advertised by the peer",
rather than, e.g., a `tower::Service`.
I don't feel super strongly about this change, so I'm happy to drop it,
but it makes the parsing match statements line up nicely and aligns
naming with the naming used in Bitcoin.
This removes the inventory vector structs from `zebra-chain` (as they
are really part of the network protocol) and refactors them into a
single `InventoryHash` type. This corresponds to Bitcoin's "inventory
vector" but with a different, better name (it's not a vector, it's just
a typed hash of some other item).
This provides a significantly cleaner API to consumers, because it
allows using adaptors that convert a TCP stream to a stream of messages,
and potentially allows more efficient message handling.
Because we want to be able to read messages from async sources (like a
tcp socket), we need to have at least async header parsing logic, so
that we can correctly determine how many bytes to await to parse each
message, so it makes sense for the entire message parsing functions
to be async.
Because we perform message serialization into async readers and writers
in the context of sending messages over the network, code using these
functions is more clear with these names.
When we perform a handshake with a remote peer, we need to encode the
version messages with a particular network version before we find out
what the remote peer's version preference is. So in addition to having
a CURRENT_VERSION constant (which represents our preference), we need to
have a MIN_VERSION during the handshake (and later to determine whether
we'll talk to the peer at all).
This adds convenience methods to `ReadZcashExt` that read 4 and 12 byte
fixed size arrays from the `Reader`, making the actual parsing code more
legible.
Closes#10.
* Replace Version MetaAddr by (Services, SocketAddr).
The version handshake message doesn't include last-seen timestamps for
the address fields, unlike other messages, so instead of modeling the
message data with a `MetaAddr` (which includes a timestamp), we should
just use a tuple.
* Simplify try_read_version implementation.
Because we no longer need to construct fake timestamps for the
`MetaAddr` fields, we don't need to use any of the parsed fields while
parsing later fields, and we can neatly wrap up the entire parsing logic
into a single expression.
* fmt
I didn't have the toolchain-specified `rustfmt` because I was mostly
offline and couldn't download it.
This has a test that the serialization implementation round trips
correctly, but is very much a work in progress. Issues with this code
include:
The deserialization logic for message headers is somewhat ugly because
of a lack of a convenient idiom for reading a few bytes at a time into a
fixed-size array. Perhaps this could be fixed with an extension trait,
or avoided altogether by using `u32`s instead of `[u8; 4]`, even when
the latter is the "morally correct type".
Deserialization does an extra allocation, copying the body into a
temporary buffer. This avoids two problems: 1) capping the number of
bytes that can be read by the `Read`er passed into the body parser and
2) allows making two passes over the body data, one to parse it and one
to compute the checksum.
We could avoid making two passes over the body by computing the checksum
simultaneously with the parsing. A convenient way to do this would be to
define a
```
struct ChecksumReader<R: Read> {
inner: R,
digest: Sha256,
}
impl<R: Read> Read for ChecksumReader<R> { /* ... */ }
```
and implement `Read` for `ChecksumReader` to forward reads from the
inner reader, copying data into the digest object as it does so. (It
could also have a maximum length to enforce that we do not read past the
nominal end of the body).
A similar `ChecksumWriter` could be used during serialization, although
because the checksum is at the beginning rather than the end of the
message it does not help avoid an allocation there. It could also be
generic over a `Digest` implementation, although because we need a
truncated double-SHA256 we would have to write a custom `Digest`
implementation, so this is probably not worthwhile unless we have other
checksum types.
Finally, this does very minimal testing -- just round-trip serialization
on a single message. It would be good to build in support for
property-based testing, probably using `proptest`; if we could define
generation and shrinking strategies for every component type of every
message, we could do strong randomized testing of the serialization.
The core serialization logic is now in zebra-chain and consists of two
pairs of traits:
These are analogues of the Serde `Serialize` and `Deserialize` traits,
but explicitly intended for consensus-critical serialization formats.
Thus some struct `Foo` may have derived `Serialize` and `Deserialize`
implementations for (internal) use with Serde, and explicitly-written
`ZcashSerialize` and `ZcashDeserialize` implementations for use in
consensus-critical contexts. The consensus-critical implementations
provide `zcash`-prefixed `zcash_serialize` and `zcash_deserialize`
methods to make it clear in client contexts that the serialization is
consensus-critical.
These are utility traits, analogous to the `ReadBytesExt` and
`WriteBytesExt` traits provided by `byteorder`. A generic
implementation is provided for any `io::Read` or `io::Write`, so that
bringing the traits into scope adds additional Zcash-specific traits to
generic readers and writers -- for instance, writing a `u64` in the
Bitcoin "CompactSize" format.
Currently these just have write_compactsize and read_compactsize methods which
allow reading and writing u64s to any `Read` or `Write` implementation using
the Bitcoin "CompactSize" variable integer encoding.
These methods read and write u64s rather than defining a new `CompactSize`
type, because the `CompactSize` is just an encoding detail, not a different
type with any distinct meaning.
The `NetworkAddress` type was a `(Services, SocketAddr)` pair as used in the
`version` handshake message, described as the `net_addr` struct in the Bitcoin
wiki protocol documentation. However, all of the other uses of the `net_addr`
struct are a `(Timestamp, Services, SocketAddr)` pair (where the timestamp is
the last-seen time of the peer), and the timestamp is omitted only during the
`version` messages, which are used only during the handshake, so it seems
better to include the timestamp field and omit it during serialization of
`version` packets.
Henry de Valence
Deirdre Connolly