sonic

work-in-progress - expect breaking changes until v1.0.0

Sonic

Sonic is a Go library for network and I/O programming that provides developers with a consistent asynchronous model, with a focus on achieving the lowest possible latency and jitter in Go. Sonic aims to make it easy to write network protocols (websocket, http2, custom exchange binary) on a series of bytestreams and then make use of those bytestreams through multiple connections running in a single-thread and goroutine.

Sonic is an alternative to the net package. It removes the need to use multiple goroutines to handle multiple connections and reads/writes in the same process. By doing that, a single goroutine and thread is used to read/write from multiple connections which brings several benefits:

• No need to use synchronization primitives (channels, mutexes, etc.) as multiple connections can be handled in the same goroutine.
• It removes the need for the Go scheduler to do any work which could slow down the program.
• It allows latency-sensitive programs to run in a hot-loop pinned to a thread on an isolated core in order to achieve low latency and jitter.

Sonic currently supports only Unix-based systems (BSD, macOS, Linux).

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Getting Started

See examples/. A good starting point is examples/timer. All examples can be built by calling make in the root path of sonic. The builds will be put in bin/.

UDP Multicast

sonic offers a full-featured UDP Multicast peer for both IPv4 and IPv6. See multicast/peer.go. This peer can read and write data to a multicast group, join a group with source-IP and network interface filtering, and control its group membership by blocking/unblocking source-IPs at runtime.

Moreover, this peer, unlike the websocket client, does not allocate and copy any data in any of its functions. Additionally, the peer gives the programmer the option to change its read buffer after scheduling a read on it i.e.

var (
    b1, b2 []byte
)
peer.AsyncRead(b1, func(...) { ... }) // schedule an asynchronous read in b1
// ... some other code here
peer.SetAsyncReadBuffer(b2) // make the previously scheduled asynchronous read use b2 instead of b1

This is very useful when multiple UDP peers share the same read buffer. For example:

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Zero-copy FIFO buffers

We provide two types of FIFO buffers with zero-copy semantics. Regardless of the type, a FIFO buffer is essential when writing protocol encoders/decoders over UDP or TCP with Linux's socket API to minimize syscalls. For example, say we have a simple protocol where each message has a fixed-size header and a variable-sized payload - the length of the payload is in the header. Say we read data through TCP. We then have two options:

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option 1 is not efficient as n messages need n * 2 syscalls. option 2 is efficient as the number if syscalls is minimized - in the limit, we need just 1 syscall to read n messages. option 2 however is missing something:

• what if the last read message was incomplete i.e. we read the header with its size, say 255, but only had space to read 100 of those bytes into b as we're near the end of b.
• to read the rest of the 255 - 100 = 155 bytes of the payload, we need to move the read 100 bytes to the beginning of b, overwriting the already processed payloads.
• in other words, we need FIFO semantics over b.

The naive way of offering FIFO semantics over b would be to simply copy the 100 bytes to the beginning of the slice. But that's a memcpy that will take a lot of time if the message is relatively big, say over 1KB. That's not acceptable even though that's how we do things for websocket (see byte_buffer.go and codec/websocket/codec.go). In those cases we offer two types of FIFO semantics over a byte slice, both offering the same API:

• Claim(n) []byte - claim at most n bytes from the underlying []byte slice. Callers can now read into the returned slice.
• Commit(n) int - commit at most n previously claimed bytes i.e. queue at most n bytes
• Consume(n) int - consume at most n previously committed/queued bytes

Mirrored Buffer

This is a zero-copy FIFO buffer that works for both TCP and UDP protocols. It offers contiguous byte slices in a FIFO manner without care for wrapping. See bytes/mirrored_buffer.go. The only limitations are that the buffer size must be a multiple of the system's page size and the system must expose a shared memory filesystem like /dev/shm. In short, the mirrored buffer provides zero-copy FIFO semantics over a byte slice in the following way:

• it creates the underlying byte slice of size n (where n is a multiple of page size) and maps it twice, contiguously, in the process' virtual address space with mmap.
• there are n physical bytes backing up the underlying byte slice and n * 2 virtual bytes
• the buffer is mirrored in a sense that reading/writing to the sequence b[n], b[n+1], ..., b[2*n-1] is permitted and in fact, touches the bytes at b[0], b[1], ..., b[n-1]

Bip Buffer

This is a zero-copy FIFO buffer meant solely for writing packet-based (UDP) protocols. Refer to the creator's post for an explanation of how it works.

What is next

The two buffers above are not yet standardized across sonic. TCP codecs, including websocket, still use the memcpy based byte buffer abstraction byte_buffer.go which is not that performant for large messages. The plan is to port websocket to use the mirrored buffer by v1.0.0.

The Bip Buffer is actively used in Talos UDP-based gateways.

Peculiarities

Async preemption

If, for some reason, you have a single goroutine that ends up waiting for more than 10ms for something to happen, sonic will crash on Linux due to epoll_wait being interrupted by the signal SIGURG. This happens because, by default, the Go runtime non-cooperatively preempts goroutines that are idle for more than 10ms. To turn off this behavior, set GODEBUG=asyncpreemptoff=1 before running your binary.

This issue has been addressed in this commit.

Credits

• boost.asio - the main inspiration for the sonic API
• boost.beast
• mio
• tungstenite-rs