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Add defensive validation to tag parsing in dotnet-counters #5685

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Add defensive validation to tag parsing in dotnet-counters #5685

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a6ed77d
Fix: Handle multiple tags in dotnet-counters display
steveisok Jan 21, 2026
b8686c0
Add test demonstrating defensive fix prevents crash on malformed tags
steveisok Jan 22, 2026
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28 changes: 22 additions & 6 deletions src/Tools/dotnet-counters/Exporters/ConsoleWriter.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -192,17 +192,33 @@ private bool RenderTagSetsInColumnMode(ref int row, ObservedCounter counter)
for (int i = 0; i < tags.Length; i++)
{
string tag = tags[i];
string[] keyValue = tag.Split("=");
int posTag = observedTags.FindIndex (tag => tag.header == keyValue[0]);
string[] keyValue = tag.Split(new char[] { '=' }, 2); // Split into at most 2 parts to handle values with '='

// Skip malformed tags that don't have both key and value
if (keyValue.Length != 2)
{
continue;
}

string key = keyValue[0].Trim();
string value = keyValue[1];
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Copilot AI Jan 21, 2026

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Consider trimming the value as well to handle potential whitespace around the '=' delimiter, similar to how the key is trimmed. For example, if a tag is formatted as "key = value" with spaces around the equals sign, the value would currently preserve the leading space.

Suggested change
string value = keyValue[1];
string value = keyValue[1].Trim();

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// Skip empty keys
if (string.IsNullOrEmpty(key))
{
continue;
}

int posTag = observedTags.FindIndex (tag => tag.header == key);
if (posTag == -1)
{
observedTags.Add((keyValue[0], new string[counter.TagSets.Count]));
columnHeaderLen.Add(keyValue[0].Length);
observedTags.Add((key, new string[counter.TagSets.Count]));
columnHeaderLen.Add(key.Length);
maxValueColumnLen.Add(default(int));
posTag = observedTags.Count - 1;
}
observedTags[posTag].values[tagsCount] = keyValue[1];
maxValueColumnLen[posTag] = Math.Max(keyValue[1].Length, maxValueColumnLen[posTag]);
observedTags[posTag].values[tagsCount] = value;
maxValueColumnLen[posTag] = Math.Max(value.Length, maxValueColumnLen[posTag]);
}
tagsCount++;
}
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24 changes: 24 additions & 0 deletions src/tests/dotnet-counters/ConsoleExporterTests.cs
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Expand Up @@ -300,6 +300,30 @@ public void CountersAreTruncatedBeyondScreenHeight()
" color");
}

[Fact]
public void MalformedTagsDoNotCrash()
{
// Defensive test: verifies that malformed tags are handled gracefully
// WITHOUT the defensive fix, this test throws IndexOutOfRangeException
// WITH the defensive fix, malformed tags are skipped and no crash occurs
MockConsole console = new MockConsole(60, 40);
ConsoleWriter exporter = new ConsoleWriter(console);
exporter.Initialize();

// These would crash the old code by trying to access keyValue[1] when keyValue.Length == 1
// Tag with no '=' - would cause IndexOutOfRangeException in old code
exporter.CounterPayloadReceived(CreateMeterCounterPreNet8("Provider1", "Counter1", "{widget}", "BadTagNoEquals", 10), false);

// Tag with only whitespace
exporter.CounterPayloadReceived(CreateMeterCounterPreNet8("Provider1", "Counter2", "{widget}", " ", 20), false);

// Mix of valid and invalid tags - only valid one should be processed
exporter.CounterPayloadReceived(CreateMeterCounterPreNet8("Provider1", "Counter3", "{widget}", "InvalidTag,color=blue", 30), false);

// If we got here without throwing IndexOutOfRangeException, the defensive code worked!
// The test passes simply by completing successfully
}

[Fact]
public void ErrorStatusIsDisplayed()
{
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