Update Prometheus exporter name and unit processing

build/Common.props

@@ -1,6 +1,6 @@
 <Project>
   <PropertyGroup>
-    <LangVersion>10.0</LangVersion>
+    <LangVersion>latest</LangVersion>
     <SignAssembly>true</SignAssembly>
     <RepoRoot>$([System.IO.Directory]::GetParent($(MSBuildThisFileDirectory)).Parent.FullName)</RepoRoot>
     <AssemblyOriginatorKeyFile>$(MSBuildThisFileDirectory)debug.snk</AssemblyOriginatorKeyFile>

src/OpenTelemetry.Exporter.Prometheus.AspNetCore/OpenTelemetry.Exporter.Prometheus.AspNetCore.csproj

@@ -26,6 +26,8 @@
     <Compile Include="$(RepoRoot)\src\OpenTelemetry.Exporter.Prometheus.HttpListener\Internal\PrometheusExporterOptions.cs" Link="Includes/PrometheusExporterOptions.cs" />
     <Compile Include="$(RepoRoot)\src\OpenTelemetry.Exporter.Prometheus.HttpListener\Internal\PrometheusSerializer.cs" Link="Includes/PrometheusSerializer.cs" />
     <Compile Include="$(RepoRoot)\src\OpenTelemetry.Exporter.Prometheus.HttpListener\Internal\PrometheusSerializerExt.cs" Link="Includes/PrometheusSerializerExt.cs" />
+    <Compile Include="$(RepoRoot)\src\OpenTelemetry.Exporter.Prometheus.HttpListener\Internal\PrometheusType.cs" Link="Includes/PrometheusType.cs" />
+    <Compile Include="$(RepoRoot)\src\OpenTelemetry.Exporter.Prometheus.HttpListener\Internal\PrometheusMetric.cs" Link="Includes/PrometheusMetric.cs" />
     <Compile Include="$(RepoRoot)\src\Shared\ExceptionExtensions.cs" Link="Includes\ExceptionExtensions.cs" />
   </ItemGroup>
 

src/OpenTelemetry.Exporter.Prometheus.HttpListener/Internal/PrometheusMetric.cs

@@ -0,0 +1,266 @@
+// <copyright file="PrometheusMetric.cs" company="OpenTelemetry Authors">
+// Copyright The OpenTelemetry Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+// </copyright>
+
+using System.Text;
+
+namespace OpenTelemetry.Exporter.Prometheus;
+
+internal sealed class PrometheusMetric
+{
+    public PrometheusMetric(string name, string unit, PrometheusType type)
+    {
+        // The metric name is
+        // required to match the regex: `[a-zA-Z_:]([a-zA-Z0-9_:])*`. Invalid characters
+        // in the metric name MUST be replaced with the `_` character. Multiple
+        // consecutive `_` characters MUST be replaced with a single `_` character.
+        // https://github.com/open-telemetry/opentelemetry-specification/blob/b2f923fb1650dde1f061507908b834035506a796/specification/compatibility/prometheus_and_openmetrics.md#L230-L233
+        var sanitizedName = SanitizeMetricName(name);
+
+        string sanitizedUnit = null;
+        if (!string.IsNullOrEmpty(unit))
+        {
+            sanitizedUnit = GetUnit(unit);
+
+            // The resulting unit SHOULD be added to the metric as
+            // [OpenMetrics UNIT metadata](https://github.com/OpenObservability/OpenMetrics/blob/main/specification/OpenMetrics.md#metricfamily)
+            // and as a suffix to the metric name unless the metric name already contains the
+            // unit, or the unit MUST be omitted. The unit suffix comes before any
+            // type-specific suffixes.
+            // https://github.com/open-telemetry/opentelemetry-specification/blob/b2f923fb1650dde1f061507908b834035506a796/specification/compatibility/prometheus_and_openmetrics.md#L242-L246
+            if (!sanitizedName.Contains(sanitizedUnit))
+            {
+                sanitizedName = sanitizedName + "_" + sanitizedUnit;
+            }
+        }
+
+        // If the metric name for monotonic Sum metric points does not end in a suffix of `_total` a suffix of `_total` MUST be added by default, otherwise the name MUST remain unchanged.
+        // Exporters SHOULD provide a configuration option to disable the addition of `_total` suffixes.
+        // https://github.com/open-telemetry/opentelemetry-specification/blob/b2f923fb1650dde1f061507908b834035506a796/specification/compatibility/prometheus_and_openmetrics.md#L286
+        if (type == PrometheusType.Counter && !sanitizedName.Contains("total"))
+        {
+            sanitizedName += "_total";
+        }
+
+        // Special case: Converting "1" to "ratio".
+        // https://github.com/open-telemetry/opentelemetry-specification/blob/b2f923fb1650dde1f061507908b834035506a796/specification/compatibility/prometheus_and_openmetrics.md#L239
+        if (type == PrometheusType.Gauge && unit == "1" && !sanitizedName.Contains("ratio"))
+        {
+            sanitizedName += "_ratio";
+        }
+
+        this.Name = sanitizedName;
+        this.Unit = sanitizedUnit;
+        this.Type = type;
+    }
+
+    public string Name { get; }
+
+    public string Unit { get; }
+
+    public PrometheusType Type { get; }
+
+    internal static string SanitizeMetricName(string metricName)
+    {
+        StringBuilder sb = null;
+        var lastCharUnderscore = false;
+
+        for (var i = 0; i < metricName.Length; i++)
+        {
+            var c = metricName[i];
+
+            if (i == 0 && char.IsNumber(c))
+            {
+                sb ??= CreateStringBuilder(metricName);
+                sb.Append('_');
+                lastCharUnderscore = true;
+                continue;
+            }
+
+            if (!char.IsLetterOrDigit(c) && c != ':')
+            {
+                if (!lastCharUnderscore)
+                {
+                    lastCharUnderscore = true;
+                    sb ??= CreateStringBuilder(metricName);
+                    sb.Append('_');
+                }
+            }
+            else
+            {
+                sb ??= CreateStringBuilder(metricName);
+                sb.Append(c);
+                lastCharUnderscore = false;
+            }
+        }
+
+        return sb?.ToString() ?? metricName;
+
+        static StringBuilder CreateStringBuilder(string name) => new StringBuilder(name.Length);
+    }
+
+    internal static string RemoveAnnotations(string unit)
+    {
+        StringBuilder sb = null;
+
+        var hasOpenBrace = false;
+        var startOpenBraceIndex = 0;
+        var lastWriteIndex = 0;
+
+        for (var i = 0; i < unit.Length; i++)
+        {
+            var c = unit[i];
+            if (c == '{')
+            {
+                if (!hasOpenBrace)
+                {
+                    hasOpenBrace = true;
+                    startOpenBraceIndex = i;
+                }
+            }
+            else if (c == '}')
+            {
+                if (hasOpenBrace)
+                {
+                    sb ??= new StringBuilder();
+                    sb.Append(unit, lastWriteIndex, startOpenBraceIndex - lastWriteIndex);
+                    hasOpenBrace = false;
+                    lastWriteIndex = i + 1;
+                }
+            }
+        }
+
+        if (lastWriteIndex == 0)
+        {
+            return unit;
+        }
+
+        sb.Append(unit, lastWriteIndex, unit.Length - lastWriteIndex);
+        return sb.ToString();
+    }
+
+    private static string GetUnit(string unit)
+    {
+        // Dropping the portions of the Unit within brackets (e.g. {packet}). Brackets MUST NOT be included in the resulting unit. A "count of foo" is considered unitless in Prometheus.
+        // https://github.com/open-telemetry/opentelemetry-specification/blob/b2f923fb1650dde1f061507908b834035506a796/specification/compatibility/prometheus_and_openmetrics.md#L238
+        var updatedUnit = RemoveAnnotations(unit);
+
+        // Converting "foo/bar" to "foo_per_bar".
+        // https://github.com/open-telemetry/opentelemetry-specification/blob/b2f923fb1650dde1f061507908b834035506a796/specification/compatibility/prometheus_and_openmetrics.md#L240C3-L240C41
+        if (TryProcessRateUnits(updatedUnit, out var updatedPerUnit))
+        {
+            updatedUnit = updatedPerUnit;
+        }
+        else
+        {
+            // Converting from abbreviations to full words (e.g. "ms" to "milliseconds").
+            // https://github.com/open-telemetry/opentelemetry-specification/blob/b2f923fb1650dde1f061507908b834035506a796/specification/compatibility/prometheus_and_openmetrics.md#L237
+            updatedUnit = MapUnit(updatedUnit.AsSpan());
+        }
+
+        return updatedUnit;
+    }
+
+    private static bool TryProcessRateUnits(string updatedUnit, out string updatedPerUnit)
+    {
+        updatedPerUnit = null;
+
+        for (int i = 0; i < updatedUnit.Length; i++)
+        {
+            if (updatedUnit[i] == '/')
+            {
+                // Only convert rate expressed units if it's a valid expression.
+                if (i == updatedUnit.Length - 1)
+                {
+                    return false;
+                }
+
+                updatedPerUnit = MapUnit(updatedUnit.AsSpan(0, i)) + "_per_" + MapPerUnit(updatedUnit.AsSpan(i + 1, updatedUnit.Length - i - 1));
+                return true;
+            }
+        }
+
+        return false;
+    }
+
+    // The map to translate OTLP units to Prometheus units
+    // OTLP metrics use the c/s notation as specified at https://ucum.org/ucum.html
+    // (See also https://github.com/open-telemetry/opentelemetry-specification/blob/main/specification/metrics/semantic_conventions/README.md#instrument-units)
+    // Prometheus best practices for units: https://prometheus.io/docs/practices/naming/#base-units
+    // OpenMetrics specification for units: https://github.com/OpenObservability/OpenMetrics/blob/main/specification/OpenMetrics.md#units-and-base-units
+    private static string MapUnit(ReadOnlySpan<char> unit)
+    {
+        return unit switch
+        {
+            // Time
+            "d" => "days",
+            "h" => "hours",
+            "min" => "minutes",
+            "s" => "seconds",
+            "ms" => "milliseconds",
+            "us" => "microseconds",
+            "ns" => "nanoseconds",
+
+            // Bytes
+            "By" => "bytes",
+            "KiBy" => "kibibytes",
+            "MiBy" => "mebibytes",
+            "GiBy" => "gibibytes",
+            "TiBy" => "tibibytes",
+            "KBy" => "kilobytes",
+            "MBy" => "megabytes",
+            "GBy" => "gigabytes",
+            "TBy" => "terabytes",
+            "B" => "bytes",
+            "KB" => "kilobytes",
+            "MB" => "megabytes",
+            "GB" => "gigabytes",
+            "TB" => "terabytes",
+
+            // SI
+            "m" => "meters",
+            "V" => "volts",
+            "A" => "amperes",
+            "J" => "joules",
+            "W" => "watts",
+            "g" => "grams",
+
+            // Misc
+            "Cel" => "celsius",
+            "Hz" => "hertz",
+            "1" => string.Empty,
+            "%" => "percent",
+            "$" => "dollars",
+            _ => unit.ToString(),
+        };
+    }
+
+    // The map that translates the "per" unit
+    // Example: s => per second (singular)
+    private static string MapPerUnit(ReadOnlySpan<char> perUnit)
+    {
+        return perUnit switch
+        {
+            "s" => "second",
+            "m" => "minute",
+            "h" => "hour",
+            "d" => "day",
+            "w" => "week",
+            "mo" => "month",
+            "y" => "year",
+            _ => perUnit.ToString(),
+        };
+    }
+}