[Exporter.Prometheus] Improve performance

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

@@ -259,7 +259,7 @@ private ExportResult OnCollect(in Batch<Metric> metrics)
 
                         break;
                     }
-                    catch (IndexOutOfRangeException)
+                    catch (Exception ex) when (ex is IndexOutOfRangeException or ArgumentException)
                     {
                         if (!IncreaseBufferSize(ref buffer))
                         {
@@ -276,7 +276,7 @@ private ExportResult OnCollect(in Batch<Metric> metrics)
                     cursor = PrometheusSerializer.WriteEof(buffer, cursor);
                     break;
                 }
-                catch (IndexOutOfRangeException)
+                catch (Exception ex) when (ex is IndexOutOfRangeException or ArgumentException)
                 {
                     if (!IncreaseBufferSize(ref buffer))
                     {
@@ -328,7 +328,7 @@ private int WriteTargetInfo(ref byte[] buffer)
                     targetInfoBufferLength = PrometheusSerializer.WriteTargetInfo(buffer, 0, this.exporter.Resource, this.exporter.OpenMetricsRequested);
                     break;
                 }
-                catch (IndexOutOfRangeException)
+                catch (Exception ex) when (ex is IndexOutOfRangeException or ArgumentException)
                 {
                     if (!IncreaseBufferSize(ref buffer))
                     {

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

@@ -64,6 +64,23 @@ public PrometheusMetric(string name, string unit, PrometheusType type, bool disa
         this.OpenMetricsMetadataName = openMetricsMetadataName;
         this.Unit = sanitizedUnit;
         this.Type = type;
+        this.NameBytes = ConvertToAsciiBytes(sanitizedName);
+        this.OpenMetricsNameBytes = ConvertToAsciiBytes(openMetricsName);
+        this.OpenMetricsMetadataNameBytes = ConvertToAsciiBytes(openMetricsMetadataName);
+        this.UnitBytes = sanitizedUnit == null ? null : ConvertToAsciiBytes(sanitizedUnit);
+
+        static byte[] ConvertToAsciiBytes(string value)
+        {
+            // Metric names and units are sanitized before conversion, so every character here is ASCII
+            var bytes = new byte[value.Length];
+
+            for (var i = 0; i < value.Length; i++)
+            {
+                bytes[i] = unchecked((byte)value[i]);
+            }
+
+            return bytes;
+        }
     }
 
     public string Name { get; }
@@ -76,6 +93,14 @@ public PrometheusMetric(string name, string unit, PrometheusType type, bool disa
 
     public PrometheusType Type { get; }
 
+    internal byte[] NameBytes { get; }
+
+    internal byte[] OpenMetricsNameBytes { get; }
+
+    internal byte[] OpenMetricsMetadataNameBytes { get; }
+
+    internal byte[]? UnitBytes { get; }
+
     public static PrometheusMetric Create(Metric metric, bool disableTotalNameSuffixForCounters)
         => new(metric.Name, metric.Unit, GetPrometheusType(metric.MetricType), disableTotalNameSuffixForCounters);