relay_utils/metrics/
float_json_value.rs

1// Copyright 2019-2020 Parity Technologies (UK) Ltd.
2// This file is part of Parity Bridges Common.
3
4// Parity Bridges Common is free software: you can redistribute it and/or modify
5// it under the terms of the GNU General Public License as published by
6// the Free Software Foundation, either version 3 of the License, or
7// (at your option) any later version.
8
9// Parity Bridges Common is distributed in the hope that it will be useful,
10// but WITHOUT ANY WARRANTY; without even the implied warranty of
11// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
12// GNU General Public License for more details.
13
14// You should have received a copy of the GNU General Public License
15// along with Parity Bridges Common.  If not, see <http://www.gnu.org/licenses/>.
16
17use crate::{
18	error::{self, Error},
19	metrics::{
20		metric_name, register, F64SharedRef, Gauge, Metric, PrometheusError, Registry,
21		StandaloneMetric, F64,
22	},
23};
24
25use async_std::sync::{Arc, RwLock};
26use async_trait::async_trait;
27use std::time::Duration;
28
29/// Value update interval.
30const UPDATE_INTERVAL: Duration = Duration::from_secs(300);
31
32/// Metric that represents float value received from HTTP service as float gauge.
33///
34/// The float value returned by the service is assumed to be normal (`f64::is_normal`
35/// should return `true`) and strictly positive.
36#[derive(Debug, Clone)]
37pub struct FloatJsonValueMetric {
38	url: String,
39	json_path: String,
40	metric: Gauge<F64>,
41	shared_value_ref: F64SharedRef,
42}
43
44impl FloatJsonValueMetric {
45	/// Create new metric instance with given name and help.
46	pub fn new(
47		url: String,
48		json_path: String,
49		name: String,
50		help: String,
51	) -> Result<Self, PrometheusError> {
52		let shared_value_ref = Arc::new(RwLock::new(None));
53		Ok(FloatJsonValueMetric {
54			url,
55			json_path,
56			metric: Gauge::new(metric_name(None, &name), help)?,
57			shared_value_ref,
58		})
59	}
60
61	/// Get shared reference to metric value.
62	pub fn shared_value_ref(&self) -> F64SharedRef {
63		self.shared_value_ref.clone()
64	}
65
66	/// Request value from HTTP service.
67	async fn request_value(&self) -> anyhow::Result<String> {
68		use isahc::{AsyncReadResponseExt, HttpClient, Request};
69
70		let request = Request::get(&self.url).header("Accept", "application/json").body(())?;
71		let raw_response = HttpClient::new()?.send_async(request).await?.text().await?;
72		Ok(raw_response)
73	}
74
75	/// Read value from HTTP service.
76	async fn read_value(&self) -> error::Result<f64> {
77		let raw_response = self.request_value().await.map_err(Error::FetchTokenPrice)?;
78		parse_service_response(&self.json_path, &raw_response)
79	}
80}
81
82impl Metric for FloatJsonValueMetric {
83	fn register(&self, registry: &Registry) -> Result<(), PrometheusError> {
84		register(self.metric.clone(), registry).map(drop)
85	}
86}
87
88#[async_trait]
89impl StandaloneMetric for FloatJsonValueMetric {
90	fn update_interval(&self) -> Duration {
91		UPDATE_INTERVAL
92	}
93
94	async fn update(&self) {
95		let value = self.read_value().await;
96		let maybe_ok = value.as_ref().ok().copied();
97		crate::metrics::set_gauge_value(&self.metric, value.map(Some));
98		*self.shared_value_ref.write().await = maybe_ok;
99	}
100}
101
102/// Parse HTTP service response.
103fn parse_service_response(json_path: &str, response: &str) -> error::Result<f64> {
104	let json =
105		serde_json::from_str(response).map_err(|err| Error::ParseHttp(err, response.to_owned()))?;
106
107	let mut selector = jsonpath_lib::selector(&json);
108	let maybe_selected_value =
109		selector(json_path).map_err(|err| Error::SelectResponseValue(err, response.to_owned()))?;
110	let selected_value = maybe_selected_value
111		.first()
112		.and_then(|v| v.as_f64())
113		.ok_or_else(|| Error::MissingResponseValue(response.to_owned()))?;
114	if !selected_value.is_normal() || selected_value < 0.0 {
115		return Err(Error::ParseFloat(selected_value))
116	}
117
118	Ok(selected_value)
119}
120
121#[cfg(test)]
122mod tests {
123	use super::*;
124
125	#[test]
126	fn parse_service_response_works() {
127		assert_eq!(
128			parse_service_response("$.kusama.usd", r#"{"kusama":{"usd":433.05}}"#).map_err(drop),
129			Ok(433.05),
130		);
131	}
132
133	#[test]
134	fn parse_service_response_rejects_negative_numbers() {
135		assert!(parse_service_response("$.kusama.usd", r#"{"kusama":{"usd":-433.05}}"#).is_err());
136	}
137
138	#[test]
139	fn parse_service_response_rejects_zero_numbers() {
140		assert!(parse_service_response("$.kusama.usd", r#"{"kusama":{"usd":0.0}}"#).is_err());
141	}
142
143	#[test]
144	fn parse_service_response_rejects_nan() {
145		assert!(parse_service_response("$.kusama.usd", r#"{"kusama":{"usd":NaN}}"#).is_err());
146	}
147}
relay_utils/metrics/float_json_value.rs

relay_utils/metrics/
float_json_value.rs
