chore: work around serde issue with f32 NaNs

Serde serializes f32s of value NaN to `null`, but doesn't serialize them
back from `null` to NaN. For that we need a custom deserialize.

Also see: <serde-rs/json#202>

src/metrics.rs

@@ -10,9 +10,11 @@
 
 mod common;
 mod delta;
+mod nullable;
 
 pub(crate) use common::{load_baseline_file, ReportData};
 pub(crate) use delta::*;
+pub(crate) use nullable::NullableFloat;
 
 use crate::config::GooseDefaults;
 use crate::goose::{get_base_url, GooseMethod, Scenario};

src/metrics/common.rs

@@ -2,11 +2,10 @@ use super::{
     delta::*, merge_times, per_second_calculations, prepare_status_codes, update_max_time,
     update_min_time, GooseMetrics,
 };
-use crate::report::ErrorMetric;
 use crate::{
     report::{
-        get_response_metric, CORequestMetric, RequestMetric, ResponseMetric, ScenarioMetric,
-        StatusCodeMetric, TransactionMetric,
+        get_response_metric, CORequestMetric, ErrorMetric, RequestMetric, ResponseMetric,
+        ScenarioMetric, StatusCodeMetric, TransactionMetric,
     },
     util, GooseError,
 };

src/metrics/delta.rs

@@ -1,3 +1,4 @@
+use crate::metrics::NullableFloat;
 use num_format::{Format, ToFormattedString};
 use std::fmt::{Debug, Display, Formatter, Write};
 
@@ -68,6 +69,12 @@ impl<T: DeltaValue> From<T> for Value<T> {
     }
 }
 
+impl From<f32> for Value<NullableFloat> {
+    fn from(value: f32) -> Self {
+        Self::Plain(NullableFloat(value))
+    }
+}
+
 impl<T: DeltaValue> Value<T> {
     pub fn diff(&mut self, other: T) {
         match self {

src/metrics/nullable.rs

@@ -0,0 +1,58 @@
+use crate::metrics::DeltaValue;
+use serde::Deserializer;
+use std::fmt::{Display, Formatter};
+use std::ops::{Deref, DerefMut};
+
+/// An `f32` which can deserialize from `null` as `NaN`.
+///
+/// Also see: <https://github.com/serde-rs/json/issues/202>
+#[derive(Clone, Copy, Debug, PartialEq, PartialOrd, serde::Serialize)]
+pub struct NullableFloat(pub f32);
+
+impl Deref for NullableFloat {
+    type Target = f32;
+
+    fn deref(&self) -> &Self::Target {
+        &self.0
+    }
+}
+
+impl DerefMut for NullableFloat {
+    fn deref_mut(&mut self) -> &mut Self::Target {
+        &mut self.0
+    }
+}
+
+impl From<f32> for NullableFloat {
+    fn from(value: f32) -> Self {
+        Self(value)
+    }
+}
+
+impl<'de> serde::Deserialize<'de> for NullableFloat {
+    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
+    where
+        D: Deserializer<'de>,
+    {
+        let value = Option::<f32>::deserialize(deserializer)?;
+        Ok(Self(value.unwrap_or(f32::NAN)))
+    }
+}
+
+impl Display for NullableFloat {
+    fn fmt(&self, f: &mut Formatter<'_>) -> std::fmt::Result {
+        self.0.fmt(f)
+    }
+}
+
+impl DeltaValue for NullableFloat {
+    type Delta = NullableFloat;
+
+    fn delta(self, value: Self) -> Self::Delta {
+        NullableFloat(self.0.delta(value.0))
+    }
+
+    fn is_delta_positive(value: Self::Delta) -> bool {
+        f32::is_delta_positive(value.0)
+    }
+}

src/report.rs

@@ -6,7 +6,7 @@ pub(crate) use markdown::write_markdown_report;
 
 use crate::{
     goose::GooseMethod,
-    metrics::{self, format_value, DeltaEval, DeltaTo, Value},
+    metrics::{self, format_value, DeltaEval, DeltaTo, NullableFloat, Value},
     report::common::OrEmpty,
 };
 use serde::{Deserialize, Serialize};
@@ -35,11 +35,11 @@ pub(crate) struct RequestMetric {
     pub name: String,
     pub number_of_requests: Value<usize>,
     pub number_of_failures: Value<usize>,
-    pub response_time_average: Value<f32>,
+    pub response_time_average: Value<NullableFloat>,
     pub response_time_minimum: Value<usize>,
     pub response_time_maximum: Value<usize>,
-    pub requests_per_second: Value<f32>,
-    pub failures_per_second: Value<f32>,
+    pub requests_per_second: Value<NullableFloat>,
+    pub failures_per_second: Value<NullableFloat>,
 }
 
 impl DeltaTo for RequestMetric {
@@ -59,8 +59,8 @@ impl DeltaTo for RequestMetric {
 pub(crate) struct CORequestMetric {
     pub method: String,
     pub name: String,
-    pub response_time_average: Value<f32>,
-    pub response_time_standard_deviation: Value<f32>,
+    pub response_time_average: Value<NullableFloat>,
+    pub response_time_standard_deviation: Value<NullableFloat>,
     pub response_time_maximum: Value<usize>,
 }
 
@@ -109,11 +109,11 @@ pub(crate) struct TransactionMetric {
     pub name: String,
     pub number_of_requests: Value<usize>,
     pub number_of_failures: Value<usize>,
-    pub response_time_average: Option<Value<f32>>,
+    pub response_time_average: Option<Value<NullableFloat>>,
     pub response_time_minimum: Value<usize>,
     pub response_time_maximum: Value<usize>,
-    pub requests_per_second: Option<Value<f32>>,
-    pub failures_per_second: Option<Value<f32>>,
+    pub requests_per_second: Option<Value<NullableFloat>>,
+    pub failures_per_second: Option<Value<NullableFloat>>,
 }
 
 impl DeltaTo for TransactionMetric {
@@ -134,11 +134,11 @@ pub(crate) struct ScenarioMetric {
     pub name: String,
     pub users: Value<usize>,
     pub count: Value<usize>,
-    pub response_time_average: Value<f32>,
+    pub response_time_average: Value<NullableFloat>,
     pub response_time_minimum: Value<usize>,
     pub response_time_maximum: Value<usize>,
-    pub count_per_second: Value<f32>,
-    pub iterations: Value<f32>,
+    pub count_per_second: Value<NullableFloat>,
+    pub iterations: Value<NullableFloat>,
 }
 
 impl DeltaTo for ScenarioMetric {