Sanitize Dropwizard metric names to comply with OpenTelemetry spec by Copilot · Pull Request #15954 · open-telemetry/opentelemetry-java-instrumentation

Copilot · 2026-01-20T23:02:01Z

Fix illegal characters when bridging from Dropwizard metrics

Based on issue #15931 and OpenTelemetry specification for instrument name syntax:

Plan:

Understand the OpenTelemetry spec requirements (alphanumeric, _, ., -, / only; must start with letter; max 255 chars)
Create a sanitization method to clean instrument names
Update DropwizardMetricsAdapter to sanitize names in all metric creation methods (gauge, counter, histogram, meter, timer)
Simplify tests: removed new test methods and updated existing tests to use metric names with special characters
Run tests to validate the fix (all tests passed)
Address code review feedback:
- Simplified sanitization to strip invalid characters instead of replacing
- Return null for invalid names and skip instrument creation (preventing exceptions from propagating to application code)
- Log warnings when sanitization fails to produce a valid name
- Log warnings when sanitization changes the metric name
- Log warnings when truncating metric names exceeding 255 characters
- Use precompiled regex Pattern for better performance
- Inlined sanitizedName variable in onGaugeAdded
- Simplified tests by updating existing ones instead of adding new ones
- Applied code formatting with spotlessApply
Review and finalize

Summary:

Fixed issue where Dropwizard metric names with illegal characters (like single quotes in jvm.memory.pools.CodeHeap-'non-profiled-nmethods'.used) were causing OpenTelemetry validation errors. The solution sanitizes metric names by stripping illegal characters using a precompiled regex Pattern. For invalid names (null, empty, no valid characters, or doesn't start with a letter), logs a warning and skips instrument creation entirely. Also logs warnings when sanitization changes a metric name or when metric names exceed 255 characters and are truncated, providing full visibility into which metrics are affected by the sanitization process.

Original prompt

fix #15931

by stripping illegal characters when briding from dropwizard metrics based on OpenTelemetry specification: https://github.com/open-telemetry/opentelemetry-specification/blob/main/specification/metrics/api.md#instrument-name-syntax

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Co-authored-by: trask <[email protected]>

trask · 2026-01-20T23:22:34Z

+  /**
+   * Sanitizes instrument names to comply with OpenTelemetry specification.
+   * Instrument names must consist of alphanumeric characters, '_', '.', '-', '/',
+   * and must start with a letter.
+   * Invalid characters are replaced with '_', and consecutive underscores are collapsed.
+   * If the name doesn't start with a letter, 'metric_' is prepended.
+   *
+   * @param name the original metric name from Dropwizard
+   * @return the sanitized instrument name
+   */


@copilot keep the logic simple, and just strip invalid characters. If there are no characters left, then throw exception.

Simplified the logic in c9ae12a:

Now strips invalid characters instead of replacing with _

Throws IllegalArgumentException if name is null, empty, contains no valid characters, or doesn't start with a letter after sanitization

Removed the logic for prepending metric_ and collapsing consecutive underscores

Returning empty string could be weird as probably then the sdk will log a warning that empty string is not a valid name. Perhaps when sanitization fails to come up with a name we should skip creating the instrument? Maybe we should log warning? Maybe we should log something when sanitization changes the name of the instrument?

@copilot

when sanitization fails to come up with a name (it's empty) log a warning and should skip creating the instrument

also log a warning any time that sanitization changes the name of the instrument

Done in 73747cf:

When sanitization fails (returns null), logs a warning and skips instrument creation

When sanitization changes the name, logs a warning with both original and sanitized names

All tests pass with visible warning logs for the sanitized metric names

…, throw exception for invalid names Co-authored-by: trask <[email protected]>

Co-authored-by: trask <[email protected]>

…l characters Co-authored-by: trask <[email protected]>

laurit · 2026-01-21T07:40:38Z

+   */
+  private static String sanitizeInstrumentName(String name) {
+    if (name == null || name.isEmpty()) {
+      throw new IllegalArgumentException("Metric name cannot be null or empty");


we shouldn't throw exceptions from here as they'll propagate into application code

good point, I checked SDK and it will handle this and return noop instrument

@copilot don't throw exceptions from this method, returning empty string is ok

i wonder if copilot is referencing this or not, or if we need to use different language

Done in 54b96e5 - now returns empty string instead of throwing exceptions, which allows the SDK to handle invalid names and return noop instruments

Done in 54b96e5 - now returns empty string instead of throwing exceptions

i wonder if copilot is referencing this or not, or if we need to use different language

the problem is me #15954 (comment)

…eptions Co-authored-by: trask <[email protected]>

Co-authored-by: trask <[email protected]>

…r invalid names Co-authored-by: trask <[email protected]>

Co-authored-by: trask <[email protected]>

Initial plan

8f2fcf1

Copilot AI assigned Copilot and trask Jan 20, 2026

Copilot started work on behalf of trask January 20, 2026 23:02 View session

Copilot AI and others added 2 commits January 20, 2026 23:12

Add sanitization for illegal characters in Dropwizard metric names

6d1e65f

Co-authored-by: trask <[email protected]>

Add clarifying comment for 255 character limit

7ee3b6f

Co-authored-by: trask <[email protected]>

Copilot AI changed the title ~~[WIP] Fix illegal characters when bridging from Dropwizard metrics~~ Sanitize Dropwizard metric names to comply with OpenTelemetry spec Jan 20, 2026

Copilot AI requested a review from trask January 20, 2026 23:15

Copilot finished work on behalf of trask January 20, 2026 23:15

trask reviewed Jan 20, 2026

View reviewed changes

Copilot started work on behalf of trask January 20, 2026 23:23 View session

Copilot AI and others added 2 commits January 20, 2026 23:30

Simplify sanitization logic: strip invalid chars instead of replacing…

c9ae12a

…, throw exception for invalid names Co-authored-by: trask <[email protected]>

Improve error message to show invalid starting character

ec8e90c

Co-authored-by: trask <[email protected]>

Copilot AI requested a review from trask January 20, 2026 23:33

Copilot finished work on behalf of trask January 20, 2026 23:33

trask reviewed Jan 21, 2026

View reviewed changes

Comment thread ...java/io/opentelemetry/javaagent/instrumentation/dropwizardmetrics/DropwizardMetricsTest.java

Copilot started work on behalf of trask January 21, 2026 02:03 View session

Simplify tests: remove new tests and update existing ones with specia…

e5f7b7d

…l characters Co-authored-by: trask <[email protected]>

Copilot AI requested a review from trask January 21, 2026 02:11

Copilot finished work on behalf of trask January 21, 2026 02:11

trask approved these changes Jan 21, 2026

View reviewed changes

trask marked this pull request as ready for review January 21, 2026 03:53

trask requested a review from a team as a code owner January 21, 2026 03:53

laurit reviewed Jan 21, 2026

View reviewed changes

Comment thread ...a/io/opentelemetry/javaagent/instrumentation/dropwizardmetrics/DropwizardMetricsAdapter.java Outdated

Copilot started work on behalf of trask January 21, 2026 16:44 View session

Copilot AI and others added 2 commits January 21, 2026 16:52

Use precompiled regex and return empty string instead of throwing exc…

54b96e5

…eptions Co-authored-by: trask <[email protected]>

Improve javadoc to clarify noop instrument behavior

fe590bf

Co-authored-by: trask <[email protected]>

Copilot AI requested a review from trask January 21, 2026 16:56

Copilot finished work on behalf of trask January 21, 2026 16:56

Copilot started work on behalf of trask January 21, 2026 18:59 View session

Add logging for sanitization warnings and skip instrument creation fo…

73747cf

…r invalid names Co-authored-by: trask <[email protected]>

Copilot finished work on behalf of trask January 21, 2026 19:12

Copilot started work on behalf of trask January 21, 2026 19:28 View session

Add warning log when truncating metric names exceeding 255 characters

e26ef80

Co-authored-by: trask <[email protected]>

Copilot finished work on behalf of trask January 21, 2026 19:35

trask approved these changes Jan 21, 2026

View reviewed changes

laurit approved these changes Jan 22, 2026

View reviewed changes

laurit merged commit 6a2393f into main Jan 22, 2026
86 checks passed

laurit deleted the copilot/fix-illegal-characters-dropwizard branch January 22, 2026 08:21

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Fix illegal characters when bridging from Dropwizard metrics

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Summary:

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Copilot AI commented Jan 20, 2026 •

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