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//! A [`metrics`][metrics]-compatible exporter that outputs metrics to clients over TCP.
//!
//! This exporter creates a TCP server, that when connected to, will stream individual metrics to
//! the client using a Protocol Buffers encoding.
//!
//! # Backpressure
//! The exporter has configurable buffering, which allows users to trade off how many metrics they
//! want to be queued up at any given time. This buffer limit applies both to incoming metrics, as
//! well as the individual buffers for each connected client.
//!
//! By default, the buffer limit is set at 1024 metrics. When the incoming buffer -- metrics being
//! fed to the exported -- is full, metrics will be dropped. If a client's buffer is full,
//! potentially due to slow network conditions or slow processing, then messages in the client's
//! buffer will be dropped in FIFO order in order to allow the exporter to continue fanning out
//! metrics to clients.
//!
//! If no buffer limit is set, then te exporter will ingest and enqueue as many metrics as possible,
//! potentially up until the point of memory exhaustion. A buffer limit is advised for this reason,
//! even if it is many multiples of the default.
//!
//! # Encoding
//! Metrics are encoded using Protocol Buffers. The protocol file can be found in the repository at
//! `proto/event.proto`.
//!
//! # Usage
//! The TCP exporter can be constructed by creating a [`TcpBuilder`], configuring it as needed, and
//! calling [`TcpBuilder::install`] to both spawn the TCP server as well as install the exporter
//! globally.
//!
//! If necessary, the recorder itself can be returned so that it can be composed separately, while
//! still installing the TCP server itself, by calling [`TcpBuilder::build`].
//!
//! ```
//! # use metrics_exporter_tcp::TcpBuilder;
//! # fn direct() {
//! // Install the exporter directly:
//! let builder = TcpBuilder::new();
//! builder.install().expect("failed to install TCP exporter");
//!
//! // Or install the TCP server and get the recorder:
//! let builder = TcpBuilder::new();
//! let recorder = builder.build().expect("failed to install TCP exporter");
//! # }
//! ```
//!
//! [metrics]: https://docs.rs/metrics
#![deny(missing_docs)]
#![cfg_attr(docsrs, feature(doc_cfg), deny(rustdoc::broken_intra_doc_links))]
use std::io::{self, Write};
use std::net::SocketAddr;
use std::sync::{
atomic::{AtomicBool, Ordering},
Arc,
};
use std::thread;
use std::time::SystemTime;
use std::{
collections::{BTreeMap, HashMap, VecDeque},
sync::atomic::AtomicUsize,
};
use bytes::Bytes;
use crossbeam_channel::{bounded, unbounded, Receiver, Sender};
use metrics::{
Counter, CounterFn, Gauge, GaugeFn, Histogram, HistogramFn, Key, KeyName, Metadata, Recorder,
SetRecorderError, SharedString, Unit,
};
use mio::{
net::{TcpListener, TcpStream},
Events, Interest, Poll, Token, Waker,
};
use prost::{EncodeError, Message};
use tracing::{error, trace, trace_span};
const WAKER: Token = Token(0);
const LISTENER: Token = Token(1);
const START_TOKEN: Token = Token(2);
const CLIENT_INTEREST: Interest = Interest::READABLE.add(Interest::WRITABLE);
mod proto {
include!(concat!(env!("OUT_DIR"), "/event.proto.rs"));
}
use self::proto::metadata::MetricType;
enum MetricOperation {
IncrementCounter(u64),
SetCounter(u64),
IncrementGauge(f64),
DecrementGauge(f64),
SetGauge(f64),
RecordHistogram(f64),
}
enum Event {
Metadata(KeyName, MetricType, Option<Unit>, SharedString),
Metric(Key, MetricOperation),
}
/// Errors that could occur while installing a TCP recorder/exporter.
#[derive(Debug)]
pub enum Error {
/// Creating the networking event loop did not succeed.
Io(io::Error),
/// Installing the recorder did not succeed.
Recorder(SetRecorderError<TcpRecorder>),
}
impl From<io::Error> for Error {
fn from(e: io::Error) -> Self {
Error::Io(e)
}
}
impl From<SetRecorderError<TcpRecorder>> for Error {
fn from(e: SetRecorderError<TcpRecorder>) -> Self {
Error::Recorder(e)
}
}
impl std::fmt::Display for Error {
fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
match self {
Error::Io(e) => write!(f, "IO error: {}", e),
Error::Recorder(e) => write!(f, "recorder error: {}", e),
}
}
}
impl std::error::Error for Error {
fn source(&self) -> Option<&(dyn std::error::Error + 'static)> {
match self {
Error::Io(e) => Some(e),
Error::Recorder(e) => Some(e),
}
}
}
struct State {
client_count: AtomicUsize,
should_send: AtomicBool,
waker: Waker,
tx: Sender<Event>,
}
impl State {
pub fn new(waker: Waker, tx: Sender<Event>) -> State {
State { client_count: AtomicUsize::new(0), should_send: AtomicBool::new(false), waker, tx }
}
pub fn should_send(&self) -> bool {
self.should_send.load(Ordering::Acquire)
}
pub fn increment_clients(&self) {
self.client_count.fetch_add(1, Ordering::AcqRel);
self.should_send.store(true, Ordering::Release);
}
pub fn decrement_clients(&self) {
let count = self.client_count.fetch_sub(1, Ordering::AcqRel);
if count == 1 {
self.should_send.store(false, Ordering::Release);
}
}
fn register_metric(
&self,
key_name: KeyName,
metric_type: MetricType,
unit: Option<Unit>,
description: SharedString,
) {
let _ = self.tx.try_send(Event::Metadata(key_name, metric_type, unit, description));
self.wake();
}
fn push_metric(&self, key: &Key, op: MetricOperation) {
if self.should_send() {
let _ = self.tx.try_send(Event::Metric(key.clone(), op));
self.wake();
}
}
pub fn wake(&self) {
let _ = self.waker.wake();
}
}
struct Handle {
key: Key,
state: Arc<State>,
}
impl Handle {
fn new(key: Key, state: Arc<State>) -> Handle {
Handle { key, state }
}
}
impl CounterFn for Handle {
fn increment(&self, value: u64) {
self.state.push_metric(&self.key, MetricOperation::IncrementCounter(value))
}
fn absolute(&self, value: u64) {
self.state.push_metric(&self.key, MetricOperation::SetCounter(value))
}
}
impl GaugeFn for Handle {
fn increment(&self, value: f64) {
self.state.push_metric(&self.key, MetricOperation::IncrementGauge(value))
}
fn decrement(&self, value: f64) {
self.state.push_metric(&self.key, MetricOperation::DecrementGauge(value))
}
fn set(&self, value: f64) {
self.state.push_metric(&self.key, MetricOperation::SetGauge(value))
}
}
impl HistogramFn for Handle {
fn record(&self, value: f64) {
self.state.push_metric(&self.key, MetricOperation::RecordHistogram(value))
}
}
/// A TCP recorder.
pub struct TcpRecorder {
state: Arc<State>,
}
/// Builder for creating and installing a TCP recorder/exporter.
pub struct TcpBuilder {
listen_addr: SocketAddr,
buffer_size: Option<usize>,
}
impl TcpBuilder {
/// Creates a new `TcpBuilder`.
pub fn new() -> TcpBuilder {
TcpBuilder { listen_addr: ([0, 0, 0, 0], 5000).into(), buffer_size: Some(1024) }
}
/// Sets the listen address.
///
/// The exporter will accept connections on this address and immediately begin forwarding
/// metrics to the client.
///
/// Defaults to `0.0.0.0:5000`.
pub fn listen_address<A>(mut self, addr: A) -> TcpBuilder
where
A: Into<SocketAddr>,
{
self.listen_addr = addr.into();
self
}
/// Sets the buffer size for internal operations.
///
/// The buffer size controls two operational aspects: the number of metrics processed
/// per iteration of the event loop, and the number of buffered metrics each client
/// can hold.
///
/// This setting allows trading off responsiveness for throughput, where a smaller buffer
/// size will ensure that metrics are pushed to clients sooner, versus a larger buffer
/// size that allows us to push more at a time.
///
/// As well, the larger the buffer, the more messages a client can temporarily hold.
/// Clients have a circular buffer implementation so if their buffers are full, metrics
/// will be dropped as necessary to avoid backpressure in the recorder.
pub fn buffer_size(mut self, size: Option<usize>) -> TcpBuilder {
self.buffer_size = size;
self
}
/// Installs the recorder and exporter.
///
/// An error will be returned if there's an issue with creating the TCP server or with
/// installing the recorder as the global recorder.
pub fn install(self) -> Result<(), Error> {
let recorder = self.build()?;
metrics::set_global_recorder(recorder).map_err(Into::into)
}
/// Builds and installs the exporter, but returns the recorder.
///
/// In most cases, users should prefer to use [`TcpBuilder::install`] to create and install
/// the recorder and exporter automatically for them. If a caller is combining recorders,
/// however, then this method allows the caller the flexibility to do so.
pub fn build(self) -> Result<TcpRecorder, Error> {
let buffer_size = self.buffer_size;
let (tx, rx) = match buffer_size {
None => unbounded(),
Some(size) => bounded(size),
};
let poll = Poll::new()?;
let waker = Waker::new(poll.registry(), WAKER)?;
let mut listener = TcpListener::bind(self.listen_addr)?;
poll.registry().register(&mut listener, LISTENER, Interest::READABLE)?;
let state = Arc::new(State::new(waker, tx));
let recorder = TcpRecorder { state: state.clone() };
thread::spawn(move || run_transport(poll, listener, rx, state, buffer_size));
Ok(recorder)
}
}
impl Default for TcpBuilder {
fn default() -> Self {
TcpBuilder::new()
}
}
impl Recorder for TcpRecorder {
fn describe_counter(&self, key_name: KeyName, unit: Option<Unit>, description: SharedString) {
self.state.register_metric(key_name, MetricType::Counter, unit, description);
}
fn describe_gauge(&self, key_name: KeyName, unit: Option<Unit>, description: SharedString) {
self.state.register_metric(key_name, MetricType::Gauge, unit, description);
}
fn describe_histogram(&self, key_name: KeyName, unit: Option<Unit>, description: SharedString) {
self.state.register_metric(key_name, MetricType::Histogram, unit, description);
}
fn register_counter(&self, key: &Key, _metadata: &Metadata<'_>) -> Counter {
Counter::from_arc(Arc::new(Handle::new(key.clone(), self.state.clone())))
}
fn register_gauge(&self, key: &Key, _metadata: &Metadata<'_>) -> Gauge {
Gauge::from_arc(Arc::new(Handle::new(key.clone(), self.state.clone())))
}
fn register_histogram(&self, key: &Key, _metadata: &Metadata<'_>) -> Histogram {
Histogram::from_arc(Arc::new(Handle::new(key.clone(), self.state.clone())))
}
}
#[allow(clippy::mutable_key_type)]
fn run_transport(
mut poll: Poll,
listener: TcpListener,
rx: Receiver<Event>,
state: Arc<State>,
buffer_size: Option<usize>,
) {
let buffer_limit = buffer_size.unwrap_or(std::usize::MAX);
let mut events = Events::with_capacity(1024);
let mut clients = HashMap::new();
let mut clients_to_remove = Vec::new();
let mut metadata = HashMap::new();
let mut next_token = START_TOKEN;
let mut buffered_pmsgs = VecDeque::with_capacity(buffer_limit);
loop {
let _span = trace_span!("transport");
// Poll until we get something. All events -- metrics wake-ups and network I/O -- flow
// through here so we can block without issue.
let _evspan = trace_span!("event loop");
if let Err(e) = poll.poll(&mut events, None) {
error!(error = %e, "error during poll");
continue;
}
drop(_evspan);
// Technically, this is an abuse of size_hint() but Mio will return the number of events
// for both parts of the tuple.
trace!(events = events.iter().size_hint().0, "return from poll");
let _pspan = trace_span!("process events");
for event in events.iter() {
match event.token() {
WAKER => {
// Read until we hit our buffer limit or there are no more messages.
let _mrxspan = trace_span!("metrics in");
loop {
if buffered_pmsgs.len() >= buffer_limit {
// We didn't drain ourselves here, so schedule a future wake so we
// continue to drain remaining metrics.
state.wake();
break;
}
let msg = match rx.try_recv() {
Ok(msg) => msg,
Err(e) if e.is_empty() => {
trace!("metric rx drained");
break;
}
// If our sender is dead, we can't do anything else, so just return.
Err(_) => return,
};
match msg {
Event::Metadata(key, metric_type, unit, desc) => {
let entry = metadata
.entry(key)
.or_insert_with(|| (metric_type, None, None));
let (_, uentry, dentry) = entry;
*uentry = unit;
*dentry = Some(desc);
}
Event::Metric(key, value) => {
match convert_metric_to_protobuf_encoded(key, value) {
Ok(pmsg) => buffered_pmsgs.push_back(pmsg),
Err(e) => error!(error = ?e, "error encoding metric"),
}
}
}
}
drop(_mrxspan);
if buffered_pmsgs.is_empty() {
trace!("woken for metrics but no pmsgs buffered");
continue;
}
// Now fan out each of these items to each client.
for (token, (conn, wbuf, msgs)) in clients.iter_mut() {
// Before we potentially do any draining, try and drive the connection to
// make sure space is freed up as much as possible.
let done = drive_connection(conn, wbuf, msgs);
if done {
clients_to_remove.push(*token);
state.decrement_clients();
continue;
}
// With the encoded metrics, we push them into each client's internal
// list. We try to write as many of those buffers as possible to the
// client before being told to back off. If we encounter a partial write
// of a buffer, we store the remaining of that message in a special field
// so that we don't write incomplete metrics to the client.
//
// If there are more messages to hand off to a client than the client's
// internal list has room for, we remove as many as needed to do so. This
// means we prioritize sending newer metrics if connections are backed up.
let available =
if msgs.len() < buffer_limit { buffer_limit - msgs.len() } else { 0 };
let to_drain = buffered_pmsgs.len().saturating_sub(available);
let _ = msgs.drain(0..to_drain);
msgs.extend(buffered_pmsgs.iter().take(buffer_limit).cloned());
let done = drive_connection(conn, wbuf, msgs);
if done {
clients_to_remove.push(*token);
state.decrement_clients();
}
}
// We've pushed each metric into each client's internal list, so we can clear
// ourselves and continue on.
buffered_pmsgs.clear();
// Remove any clients that were done.
for token in clients_to_remove.drain(..) {
if let Some((conn, _, _)) = clients.get_mut(&token) {
trace!(?conn, ?token, "removing client");
clients.remove(&token);
state.decrement_clients();
}
}
}
LISTENER => {
// Accept as many new connections as we can.
loop {
match listener.accept() {
Ok((mut conn, _)) => {
// Get our client's token and register the connection.
let token = next(&mut next_token);
poll.registry()
.register(&mut conn, token, CLIENT_INTEREST)
.expect("failed to register interest for client connection");
state.increment_clients();
// Start tracking them, and enqueue all of the metadata.
let metadata = generate_metadata_messages(&metadata);
clients
.insert(token, (conn, None, metadata))
.ok_or(())
.expect_err("client mapped to existing token!");
}
Err(ref e) if would_block(e) => break,
Err(e) => {
error!("caught error while accepting client connections: {:?}", e);
return;
}
}
}
}
token => {
if event.is_writable() {
if let Some((conn, wbuf, msgs)) = clients.get_mut(&token) {
let done = drive_connection(conn, wbuf, msgs);
if done {
trace!(?conn, ?token, "removing client");
clients.remove(&token);
state.decrement_clients();
}
}
}
}
}
}
}
}
#[allow(clippy::mutable_key_type)]
fn generate_metadata_messages(
metadata: &HashMap<KeyName, (MetricType, Option<Unit>, Option<SharedString>)>,
) -> VecDeque<Bytes> {
let mut bufs = VecDeque::new();
for (key_name, (metric_type, unit, desc)) in metadata.iter() {
let msg =
convert_metadata_to_protobuf_encoded(key_name, *metric_type, *unit, desc.as_ref())
.expect("failed to encode metadata buffer");
bufs.push_back(msg);
}
bufs
}
#[tracing::instrument(skip(wbuf, msgs))]
fn drive_connection(
conn: &mut TcpStream,
wbuf: &mut Option<Bytes>,
msgs: &mut VecDeque<Bytes>,
) -> bool {
trace!(?conn, "driving client");
loop {
let mut buf = match wbuf.take() {
// Send the leftover buffer first, if we have one.
Some(buf) => buf,
None => match msgs.pop_front() {
Some(msg) => msg,
None => {
trace!("client write queue drained");
return false;
}
},
};
match conn.write(&buf) {
// Zero write = client closed their connection, so remove 'em.
Ok(0) => {
trace!(?conn, "zero write, closing client");
return true;
}
Ok(n) if n < buf.len() => {
// We sent part of the buffer, but not everything. Keep track of the remaining
// chunk of the buffer. TODO: do we need to reregister ourselves to track writable
// status??
let remaining = buf.split_off(n);
trace!(?conn, written = n, remaining = remaining.len(), "partial write");
wbuf.replace(remaining);
return false;
}
Ok(_) => continue,
Err(ref e) if would_block(e) => return false,
Err(ref e) if interrupted(e) => return drive_connection(conn, wbuf, msgs),
Err(e) => {
error!(?conn, error = %e, "write failed");
return true;
}
}
}
}
fn convert_metadata_to_protobuf_encoded(
key_name: &KeyName,
metric_type: MetricType,
unit: Option<Unit>,
desc: Option<&SharedString>,
) -> Result<Bytes, EncodeError> {
let name = key_name.as_str().to_string();
let metadata = proto::Metadata {
name,
metric_type: metric_type.into(),
unit: unit.map(|u| proto::metadata::Unit::UnitValue(u.as_str().to_owned())),
description: desc.map(|d| proto::metadata::Description::DescriptionValue(d.to_string())),
};
let event = proto::Event { event: Some(proto::event::Event::Metadata(metadata)) };
let mut buf = Vec::new();
event.encode_length_delimited(&mut buf)?;
Ok(Bytes::from(buf))
}
fn convert_metric_to_protobuf_encoded(
key: Key,
operation: MetricOperation,
) -> Result<Bytes, EncodeError> {
let name = key.name().to_string();
let labels = key
.labels()
.map(|label| (label.key().to_owned(), label.value().to_owned()))
.collect::<BTreeMap<_, _>>();
let operation = match operation {
MetricOperation::IncrementCounter(v) => proto::metric::Operation::IncrementCounter(v),
MetricOperation::SetCounter(v) => proto::metric::Operation::SetCounter(v),
MetricOperation::IncrementGauge(v) => proto::metric::Operation::IncrementGauge(v),
MetricOperation::DecrementGauge(v) => proto::metric::Operation::DecrementGauge(v),
MetricOperation::SetGauge(v) => proto::metric::Operation::SetGauge(v),
MetricOperation::RecordHistogram(v) => proto::metric::Operation::RecordHistogram(v),
};
let now: prost_types::Timestamp = SystemTime::now().into();
let metric = proto::Metric { name, labels, timestamp: Some(now), operation: Some(operation) };
let event = proto::Event { event: Some(proto::event::Event::Metric(metric)) };
let mut buf = Vec::new();
event.encode_length_delimited(&mut buf)?;
Ok(Bytes::from(buf))
}
fn next(current: &mut Token) -> Token {
let next = current.0;
current.0 += 1;
Token(next)
}
fn would_block(err: &io::Error) -> bool {
err.kind() == io::ErrorKind::WouldBlock
}
fn interrupted(err: &io::Error) -> bool {
err.kind() == io::ErrorKind::Interrupted
}