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[Exporter.Prometheus] Fix untyped for OpenMetrics#7219

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martincostello merged 3 commits into
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martincostello:fix-type-metadata
May 4, 2026
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[Exporter.Prometheus] Fix untyped for OpenMetrics#7219
martincostello merged 3 commits into
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martincostello:fix-type-metadata

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Changes

Fix incorrect serialized value for PrometheusType.Untyped when using OpenMetrics.

Merge requirement checklist

  • CONTRIBUTING guidelines followed (license requirements, nullable enabled, static analysis, etc.)
  • Unit tests added/updated
  • Appropriate CHANGELOG.md files updated for non-trivial changes
  • Changes in public API reviewed (if applicable)

Fix incorrect serialized value for `PrometheusType.Untyped` when using OpenMetrics.
@github-actions github-actions Bot added pkg:OpenTelemetry.Exporter.Prometheus.AspNetCore Issues related to OpenTelemetry.Exporter.Prometheus.AspNetCore NuGet package pkg:OpenTelemetry.Exporter.Prometheus.HttpListener Issues related to OpenTelemetry.Exporter.Prometheus.HttpListener NuGet package labels Apr 29, 2026
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Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 89.80%. Comparing base (195497e) to head (d9327a9).
⚠️ Report is 1 commits behind head on main.
✅ All tests successful. No failed tests found.

Additional details and impacted files

Impacted file tree graph

@@            Coverage Diff             @@
##             main    #7219      +/-   ##
==========================================
+ Coverage   89.79%   89.80%   +0.01%     
==========================================
  Files         272      272              
  Lines       13433    13437       +4     
==========================================
+ Hits        12062    12067       +5     
+ Misses       1371     1370       -1     
Flag Coverage Δ
unittests-Project-Experimental 89.61% <100.00%> (-0.08%) ⬇️
unittests-Project-Stable 89.74% <100.00%> (+0.03%) ⬆️
unittests-UnstableCoreLibraries-Experimental 44.66% <100.00%> (+0.02%) ⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines Coverage Δ
...heus.HttpListener/Internal/PrometheusSerializer.cs 98.64% <100.00%> (+0.47%) ⬆️

... and 3 files with indirect coverage changes

@martincostello martincostello marked this pull request as ready for review April 29, 2026 19:46
@martincostello martincostello requested a review from a team as a code owner April 29, 2026 19:46
Copilot AI review requested due to automatic review settings April 29, 2026 19:46

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Pull request overview

Fixes Prometheus exporter serialization so PrometheusType.Untyped is emitted as unknown when the OpenMetrics format is requested, aligning with the OpenMetrics 1.0 specification while preserving Prometheus text format behavior.

Changes:

  • Update type mapping to emit unknown (OpenMetrics) vs untyped (Prometheus text format) for PrometheusType.Untyped.
  • Add unit tests covering both OpenMetrics and Prometheus text format outputs for untyped metrics.
  • Document the fix in both Prometheus HttpListener and AspNetCore exporter changelogs.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File Description
test/OpenTelemetry.Exporter.Prometheus.HttpListener.Tests/PrometheusSerializerTests.cs Adds regression tests verifying unknown vs untyped # TYPE output depending on OpenMetrics flag.
src/OpenTelemetry.Exporter.Prometheus.HttpListener/Internal/PrometheusSerializer.cs Adjusts type mapping to follow OpenMetrics unknown semantics for untyped metrics.
src/OpenTelemetry.Exporter.Prometheus.HttpListener/CHANGELOG.md Notes the OpenMetrics untyped handling fix.
src/OpenTelemetry.Exporter.Prometheus.AspNetCore/CHANGELOG.md Notes the same fix for the AspNetCore package (which shares serialization logic).

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This was referenced Jun 12, 2026
intellitect-bot pushed a commit to IntelliTect/EssentialCSharp.Web that referenced this pull request Jun 12, 2026
….0 (#1201)

Updated
[OpenTelemetry.Exporter.OpenTelemetryProtocol](https://github.com/open-telemetry/opentelemetry-dotnet)
from 1.15.3 to 1.16.0.

<details>
<summary>Release notes</summary>

_Sourced from [OpenTelemetry.Exporter.OpenTelemetryProtocol's
releases](https://github.com/open-telemetry/opentelemetry-dotnet/releases)._

## 1.16.0

For highlights and announcements pertaining to this release see:
[Release Notes >
1.16.0](https://github.com/open-telemetry/opentelemetry-dotnet/blob/main/RELEASENOTES.md#​1160).

The following changes are from the previous release
[1.16.0-rc.1](https://github.com/open-telemetry/opentelemetry-dotnet/releases/tag/core-1.16.0-rc.1).

* NuGet: [OpenTelemetry
v1.16.0](https://www.nuget.org/packages/OpenTelemetry/1.16.0)

  No notable changes.

See
[CHANGELOG](https://github.com/open-telemetry/opentelemetry-dotnet/blob/core-1.16.0/src/OpenTelemetry/CHANGELOG.md)
for details.

* NuGet: [OpenTelemetry.Api
v1.16.0](https://www.nuget.org/packages/OpenTelemetry.Api/1.16.0)

  No notable changes.

See
[CHANGELOG](https://github.com/open-telemetry/opentelemetry-dotnet/blob/core-1.16.0/src/OpenTelemetry.Api/CHANGELOG.md)
for details.

* NuGet: [OpenTelemetry.Api.ProviderBuilderExtensions
v1.16.0](https://www.nuget.org/packages/OpenTelemetry.Api.ProviderBuilderExtensions/1.16.0)

  No notable changes.

See
[CHANGELOG](https://github.com/open-telemetry/opentelemetry-dotnet/blob/core-1.16.0/src/OpenTelemetry.Api.ProviderBuilderExtensions/CHANGELOG.md)
for details.

* NuGet: [OpenTelemetry.Exporter.Console
v1.16.0](https://www.nuget.org/packages/OpenTelemetry.Exporter.Console/1.16.0)

  No notable changes.

See
[CHANGELOG](https://github.com/open-telemetry/opentelemetry-dotnet/blob/core-1.16.0/src/OpenTelemetry.Exporter.Console/CHANGELOG.md)
for details.

* NuGet: [OpenTelemetry.Exporter.InMemory
v1.16.0](https://www.nuget.org/packages/OpenTelemetry.Exporter.InMemory/1.16.0)

  No notable changes.

See
[CHANGELOG](https://github.com/open-telemetry/opentelemetry-dotnet/blob/core-1.16.0/src/OpenTelemetry.Exporter.InMemory/CHANGELOG.md)
for details.

* NuGet: [OpenTelemetry.Exporter.OpenTelemetryProtocol
v1.16.0](https://www.nuget.org/packages/OpenTelemetry.Exporter.OpenTelemetryProtocol/1.16.0)

  No notable changes.

See
[CHANGELOG](https://github.com/open-telemetry/opentelemetry-dotnet/blob/core-1.16.0/src/OpenTelemetry.Exporter.OpenTelemetryProtocol/CHANGELOG.md)
for details.

* NuGet: [OpenTelemetry.Exporter.Zipkin
v1.16.0](https://www.nuget.org/packages/OpenTelemetry.Exporter.Zipkin/1.16.0)

  No notable changes.

See
[CHANGELOG](https://github.com/open-telemetry/opentelemetry-dotnet/blob/core-1.16.0/src/OpenTelemetry.Exporter.Zipkin/CHANGELOG.md)
for details.

* NuGet: [OpenTelemetry.Extensions.Hosting
v1.16.0](https://www.nuget.org/packages/OpenTelemetry.Extensions.Hosting/1.16.0)

  No notable changes.

 ... (truncated)

## 1.16.0-rc.1

The following changes are from the previous release
[1.15.3](https://github.com/open-telemetry/opentelemetry-dotnet/releases/tag/core-1.15.3).

* NuGet: [OpenTelemetry
v1.16.0-rc.1](https://www.nuget.org/packages/OpenTelemetry/1.16.0-rc.1)

* Stop validating View-provided metric stream `Name` against the
instrument
    name syntax, per
[spec
clarification](open-telemetry/opentelemetry-specification#5094).

([#​7300](open-telemetry/opentelemetry-dotnet#7300))
  
* Fix incorrect validation of `OTEL_BSP_*` and `OTEL_BLRP_*` environment
    variables.

([#​7187](open-telemetry/opentelemetry-dotnet#7187))
  
* Fix observable instrument callbacks running once per reader instead of
    once per collection cycle.

([#​7188](open-telemetry/opentelemetry-dotnet#7188))
  
* Added exception safety for user-supplied `ExemplarReservoir`
implementations.
Exceptions thrown from `Offer` are now caught and logged rather than
propagating
    out of `Counter.Add`/`Histogram.Record`.

([#​7277](open-telemetry/opentelemetry-dotnet#7277))
  
* Update `OpenTelemetrySdkEventSource` to support the W3C randomness
flag.

([#​7301](open-telemetry/opentelemetry-dotnet#7301))
  
  * Added `ObservedTimestamp` property to `LogRecord`.

([#​6979](open-telemetry/opentelemetry-dotnet#6979))
  
* **Breaking Change** Explicit histogram boundaries no longer allow more
than
    10 million values.

([#​7165](open-telemetry/opentelemetry-dotnet#7165))
  
* Fixed a circular reference which could cause a `LoggerProvider` to
fail to
resolve when one of its dependencies depends on `ILogger` or
`ILoggerFactory`.
As part of this fix the `LoggerProvider` resolved from dependency
injection
is now created lazily when the first logger is created rather than when
`ILoggerProvider` or `ILoggerFactory` is resolved. A consequence is that
any
invalid configuration now surfaces when the first log record is written
instead
    of when the logging services are resolved.

([#​7308](open-telemetry/opentelemetry-dotnet#7308))

See
[CHANGELOG](https://github.com/open-telemetry/opentelemetry-dotnet/blob/core-1.16.0-rc.1/src/OpenTelemetry/CHANGELOG.md)
for details.

* NuGet: [OpenTelemetry.Api
v1.16.0-rc.1](https://www.nuget.org/packages/OpenTelemetry.Api/1.16.0-rc.1)

  * **Experimental (pre-release builds only):**
Add support for using environment variables as context propagation
carriers.

([#​7174](open-telemetry/opentelemetry-dotnet#7174))
  
* Fix `BaggagePropagator` to correctly follow Key and Value Encoding
rules as per
 ... (truncated)

## 1.16.0-beta.1

The following changes are from the previous release
[1.15.3-beta.1](https://github.com/open-telemetry/opentelemetry-dotnet/releases/tag/coreunstable-1.15.3-beta.1).

* NuGet: [OpenTelemetry.Exporter.Prometheus.AspNetCore
v1.16.0-beta.1](https://www.nuget.org/packages/OpenTelemetry.Exporter.Prometheus.AspNetCore/1.16.0-beta.1)

* Fixed scrape response cache freshness using monotonic time so it is
not
    affected by NTP system clock adjustments.

([#​7253](open-telemetry/opentelemetry-dotnet#7253))
  
  * **Breaking Change** Removed `DisableTimestamp` property from
    `PrometheusAspNetCoreOptions`.

([#​7176](open-telemetry/opentelemetry-dotnet#7176))
  
* Fixed the serialization of `NaN`, `PositiveInfinity`, and
`NegativeInfinity`
    values in Prometheus metrics to be compliant with the specification.

([#​7179](open-telemetry/opentelemetry-dotnet#7179))
  
* Fixed loss of precision when serializing `double` and `float` values
in
Prometheus metrics to be compliant with the specification by using 17
    significant digits to represent such values.

([#​7179](open-telemetry/opentelemetry-dotnet#7179))
  
* Fix non-ASCII characters in metric names and unit strings not being
sanitized
    correctly during Prometheus serialization.

([#​7184](open-telemetry/opentelemetry-dotnet#7184))
  
* Fix case where reader tracking could be reset while readers were still
active.

([#​7190](open-telemetry/opentelemetry-dotnet#7190))
  
* Improve `Accept` header handling for format negotiation so OpenMetrics
is
    selected correctly by considering whitespace and `q` weights.

([#​7208](open-telemetry/opentelemetry-dotnet#7208))
  
  * Emit OpenMetrics exemplars for counters and histogram buckets.

([#​7222](open-telemetry/opentelemetry-dotnet#7222))
  
* Fix incorrect handling of untyped metrics when using OpenMetrics
format.

([#​7219](open-telemetry/opentelemetry-dotnet#7219))
  
* Fix Prometheus/OpenMetrics serialization to emit metric and label
names
containing `_` instead of dropping them and prefixing leading digits.
    Invalid characters are replaced with `_` instead of being dropped.

([#​7209](open-telemetry/opentelemetry-dotnet#7209))
  
* Add `escaping=underscores` to the `Accept` header handling for content
    negotiation so OpenMetrics are handled correctly.

([#​7209](open-telemetry/opentelemetry-dotnet#7209))
  
* Omit histogram `_sum` and `_count` in OpenMetrics when negative bucket
    thresholds are present.

([#​7221](open-telemetry/opentelemetry-dotnet#7221))
 ... (truncated)

Commits viewable in [compare
view](open-telemetry/opentelemetry-dotnet@core-1.15.3...core-1.16.0).
</details>

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alter it yourself. You can also trigger a rebase manually by commenting
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</details>

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