Skip to content

Escape delimiters in metric event tags #132262

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Open
hoyosjs wants to merge 1 commit into
base: main
Choose a base branch
from
+185 −10
Open

Escape delimiters in metric event tags #132262

Show file tree
Hide file tree
Changes from all commits
Commits
Show all changes
1 commit
Select commit
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
36 changes: 34 additions & 2 deletions src/libraries/System.Diagnostics.DiagnosticSource/src/System/Diagnostics/Helpers.cs
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -10,6 +10,13 @@ namespace System.Diagnostics
{
internal static class Helpers
{
// Tag lists are flattened into a single "key=value,key=value" string. Because tag keys
// and values are arbitrary strings that may themselves contain the ',' pair separator or
// the '=' key/value separator, each key and value is escaped so the string can be decoded
// without ambiguity. The escaping rules are:
// '\' => "\\" ',' => "\," '=' => "\="

@noahfalk noahfalk Aug 13, 2026

Copy link
Copy Markdown
Member

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Escaping '\' as "\\" would be a breaking change on something that I assume currently works? I'd prefer we pick an escaping strategy that doesn't introduce new failures on existing tools. For example:

',' -> ",," 
'=' -> "=="

Admitedly its a little weird but I don't imagine there are going to be that many parsers for this event data in the world.

@hoyosjs hoyosjs Aug 13, 2026

Copy link
Copy Markdown
Member Author

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

agreed that since this scheme is not enough and this is close to platform complete - we'll park this until .NET 12.

// The ',' between pairs and the '=' between a key and its value are emitted literally
// (unescaped) as delimiters.
internal static string FormatTags(IEnumerable<KeyValuePair<string, object?>>? tags)
{
if (tags is null)
Expand All @@ -30,7 +37,9 @@ internal static string FormatTags(IEnumerable<KeyValuePair<string, object?>>? ta
sb.Append(',');
}

sb.Append(tag.Key).Append('=').Append(tag.Value);
AppendEscaped(sb, tag.Key);
sb.Append('=');
AppendEscaped(sb, tag.Value?.ToString());
}
return sb.ToString();
}
Expand All @@ -45,7 +54,9 @@ internal static string FormatTags(KeyValuePair<string, string>[] labels)
StringBuilder sb = new StringBuilder();
for (int i = 0; i < labels.Length; i++)
{
sb.Append(labels[i].Key).Append('=').Append(labels[i].Value);
AppendEscaped(sb, labels[i].Key);
sb.Append('=');
AppendEscaped(sb, labels[i].Value);
if (i != labels.Length - 1)
{
sb.Append(',');
Expand All @@ -54,6 +65,27 @@ internal static string FormatTags(KeyValuePair<string, string>[] labels)
return sb.ToString();
}

// Escapes the '\', ',' and '=' characters in a tag key or value so the flattened
// "key=value,key=value" representation produced by FormatTags can be decoded without
// ambiguity. See the comment on FormatTags for the encoding details.
private static void AppendEscaped(StringBuilder sb, string? value)
{
if (string.IsNullOrEmpty(value))
{
return;
}

foreach (char c in value)
{
if (c is '\\' or ',' or '=')
{
sb.Append('\\');
}

sb.Append(c);
}
}

internal static string FormatObjectHash(object? obj) =>
obj is null ? string.Empty : RuntimeHelpers.GetHashCode(obj).ToString(CultureInfo.InvariantCulture);
}
Expand Down
24 changes: 16 additions & 8 deletions .../System.Diagnostics.DiagnosticSource/src/System/Diagnostics/Metrics/MetricsEventSource.cs
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -125,7 +125,8 @@ public void CollectionStop(string sessionId, DateTime intervalStartTime, DateTim
WriteEvent(3, sessionId, intervalStartTime, intervalEndTime);
}

[Event(4, Keywords = Keywords.TimeSeriesValues, Version = 2)]
// Version 3 escapes '\', ',' and '=' in the flattened 'tags' string (see Helpers.FormatTags).
[Event(4, Keywords = Keywords.TimeSeriesValues, Version = 3)]
#if !NET
[UnconditionalSuppressMessage("ReflectionAnalysis", "IL2026:RequiresUnreferencedCode",
Justification = "This calls WriteEvent with all primitive arguments which is safe. Primitives are always serialized properly.")]
Expand All @@ -135,7 +136,8 @@ public void CounterRateValuePublished(string sessionId, string meterName, string
WriteEvent(4, sessionId, meterName, meterVersion ?? "", instrumentName, unit ?? "", tags, rate, value, instrumentId);
}

[Event(5, Keywords = Keywords.TimeSeriesValues, Version = 2)]
// Version 3 escapes '\', ',' and '=' in the flattened 'tags' string (see Helpers.FormatTags).
[Event(5, Keywords = Keywords.TimeSeriesValues, Version = 3)]
#if !NET
[UnconditionalSuppressMessage("ReflectionAnalysis", "IL2026:RequiresUnreferencedCode",
Justification = "This calls WriteEvent with all primitive arguments which is safe. Primitives are always serialized properly.")]
Expand All @@ -145,7 +147,8 @@ public void GaugeValuePublished(string sessionId, string meterName, string? mete
WriteEvent(5, sessionId, meterName, meterVersion ?? "", instrumentName, unit ?? "", tags, lastValue, instrumentId);
}

[Event(6, Keywords = Keywords.TimeSeriesValues, Version = 2)]
// Version 3 escapes '\', ',' and '=' in the flattened 'tags' string (see Helpers.FormatTags).
[Event(6, Keywords = Keywords.TimeSeriesValues, Version = 3)]
#if !NET
[UnconditionalSuppressMessage("ReflectionAnalysis", "IL2026:RequiresUnreferencedCode",
Justification = "This calls WriteEvent with all primitive arguments which is safe. Primitives are always serialized properly.")]
Expand All @@ -158,7 +161,8 @@ public void HistogramValuePublished(string sessionId, string meterName, string?
// Sent when we begin to monitor the value of a instrument, either because new session filter arguments changed subscriptions
// or because an instrument matching the pre-existing filter has just been created. This event precedes all *MetricPublished events
// for the same named instrument.
[Event(7, Keywords = Keywords.TimeSeriesValues, Version = 3)]
// Version 4 escapes '\', ',' and '=' in the flattened instrumentTags/meterTags strings (see Helpers.FormatTags).
[Event(7, Keywords = Keywords.TimeSeriesValues, Version = 4)]
#if !NET
[UnconditionalSuppressMessage("ReflectionAnalysis", "IL2026:RequiresUnreferencedCode",
Justification = "This calls WriteEvent with all primitive arguments which is safe. Primitives are always serialized properly.")]
Expand All @@ -183,7 +187,8 @@ public void BeginInstrumentReporting(

// Sent when we stop monitoring the value of a instrument, either because new session filter arguments changed subscriptions
// or because the Meter has been disposed.
[Event(8, Keywords = Keywords.TimeSeriesValues, Version = 3)]
// Version 4 escapes '\', ',' and '=' in the flattened instrumentTags/meterTags strings (see Helpers.FormatTags).
[Event(8, Keywords = Keywords.TimeSeriesValues, Version = 4)]
#if !NET
[UnconditionalSuppressMessage("ReflectionAnalysis", "IL2026:RequiresUnreferencedCode",
Justification = "This calls WriteEvent with all primitive arguments which is safe. Primitives are always serialized properly.")]
Expand Down Expand Up @@ -218,7 +223,8 @@ public void InitialInstrumentEnumerationComplete(string sessionId)
WriteEvent(10, sessionId);
}

[Event(11, Keywords = Keywords.InstrumentPublishing, Version = 3)]
// Version 4 escapes '\', ',' and '=' in the flattened instrumentTags/meterTags strings (see Helpers.FormatTags).
[Event(11, Keywords = Keywords.InstrumentPublishing, Version = 4)]
#if !NET
[UnconditionalSuppressMessage("ReflectionAnalysis", "IL2026:RequiresUnreferencedCode",
Justification = "This calls WriteEvent with all primitive arguments which is safe. Primitives are always serialized properly.")]
Expand Down Expand Up @@ -265,7 +271,8 @@ public void MultipleSessionsNotSupportedError(string runningSessionId)
WriteEvent(15, runningSessionId);
}

[Event(16, Keywords = Keywords.TimeSeriesValues, Version = 2)]
// Version 3 escapes '\', ',' and '=' in the flattened 'tags' string (see Helpers.FormatTags).
[Event(16, Keywords = Keywords.TimeSeriesValues, Version = 3)]
#if !NET
[UnconditionalSuppressMessage("ReflectionAnalysis", "IL2026:RequiresUnreferencedCode",
Justification = "This calls WriteEvent with all primitive arguments which is safe. Primitives are always serialized properly.")]
Expand Down Expand Up @@ -297,7 +304,8 @@ public void Version(int Major, int Minor, int Patch)
/// <summary>
/// Used to send the value of a base 2 exponential histogram.
/// </summary>
[Event(19, Keywords = Keywords.TimeSeriesValues, Version = 1)]
// Version 2 escapes '\', ',' and '=' in the flattened 'tags' string (see Helpers.FormatTags).
[Event(19, Keywords = Keywords.TimeSeriesValues, Version = 2)]
#if !NET
[UnconditionalSuppressMessage("ReflectionAnalysis", "IL2026:RequiresUnreferencedCode",
Justification = "This calls WriteEvent with all primitive arguments which is safe. Primitives are always serialized properly.")]
Expand Down
135 changes: 135 additions & 0 deletions .../System.Diagnostics.DiagnosticSource/tests/MetricOuterLoopTests/MetricEventSourceTests.cs
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -36,6 +36,141 @@ public void GetInstanceMethodIsReflectable()
Assert.True(o is EventSource, "Expected object returned from MetricsEventSource.GetInstance() to be assignable to EventSource");
}

// The flattened "key=value,key=value" tag string escapes '\', ',' and '=' in each key and
// value so the pairs can be decoded without ambiguity. See Helpers.FormatTags.
[Theory]
// No special characters => unchanged.
[InlineData("plain", "simple", "plain=simple")]
// Comma in the value must be escaped so it isn't mistaken for a pair separator.
[InlineData("comma", "a,b,c", "comma=a\\,b\\,c")]
// Equals sign in the value must be escaped so it isn't mistaken for the key/value separator.
[InlineData("equals", "x=1", "equals=x\\=1")]
// Backslash must be escaped so it isn't mistaken for an escape sequence on decode.
[InlineData("path", "C:\\temp", "path=C:\\\\temp")]
// Special characters in the key are escaped too.
[InlineData("a,b=c", "v", "a\\,b\\=c=v")]
// Realistic URL value combining commas and equals signs.
[InlineData("url", "/api/items?filter=red,blue&sort=name", "url=/api/items?filter\\=red\\,blue&sort\\=name")]
public void FormatTags_EscapesDelimiters(string key, string value, string expected)
{
KeyValuePair<string, object?>[] objectTags = new[] { new KeyValuePair<string, object?>(key, value) };
Assert.Equal(expected, Helpers.FormatTags(objectTags));

KeyValuePair<string, string>[] stringTags = new[] { new KeyValuePair<string, string>(key, value) };
Assert.Equal(expected, Helpers.FormatTags(stringTags));
}

[Fact]
public void FormatTags_MultiplePairs_AreCommaSeparated()
{
KeyValuePair<string, object?>[] tags = new[]
{
new KeyValuePair<string, object?>("comma", "a,b,c"),
new KeyValuePair<string, object?>("equals", "x=1"),
new KeyValuePair<string, object?>("plain", "simple"),
};

// Escaped delimiters within values, literal ',' between pairs and literal '=' between key and value.
Assert.Equal("comma=a\\,b\\,c,equals=x\\=1,plain=simple", Helpers.FormatTags(tags));
}

[Theory]
[InlineData("plain", "simple")]
[InlineData("comma", "a,b,c")]
[InlineData("equals", "x=1")]
[InlineData("path", "C:\\temp")]
[InlineData("mixed=key,name", "=leading,and,trailing=")]
[InlineData("url", "/api/items?filter=red,blue&sort=name")]
public void FormatTags_RoundTripsThroughReferenceDecoder(string key, string value)
{
// Validates that the escaping produced by FormatTags can be decoded back to the original
// key/value pairs without ambiguity.
string encoded = Helpers.FormatTags(new[] { new KeyValuePair<string, object?>(key, value) });

List<KeyValuePair<string, string>> decoded = DecodeTags(encoded);

KeyValuePair<string, string> single = Assert.Single(decoded);
Assert.Equal(key, single.Key);
Assert.Equal(value, single.Value);
}

// Reference decoder for the escaped "key=value,key=value" format produced by Helpers.FormatTags.
// '\' escapes the following character; an unescaped '=' separates the first key from its value;
// an unescaped ',' separates pairs.
private static List<KeyValuePair<string, string>> DecodeTags(string encoded)
{
List<KeyValuePair<string, string>> result = new();
if (string.IsNullOrEmpty(encoded))
{
return result;
}

StringBuilder key = new();
StringBuilder value = new();
bool inValue = false;
for (int i = 0; i < encoded.Length; i++)
{
char c = encoded[i];
if (c == '\\' && i + 1 < encoded.Length)
{
(inValue ? value : key).Append(encoded[++i]);
}
else if (c == '=' && !inValue)
{
inValue = true;
}
else if (c == ',')
{
result.Add(new KeyValuePair<string, string>(key.ToString(), value.ToString()));
key.Clear();
value.Clear();
inValue = false;
}
else
{
(inValue ? value : key).Append(c);
}
}

result.Add(new KeyValuePair<string, string>(key.ToString(), value.ToString()));
return result;
}

// End-to-end validation that tag keys/values containing the ',' pair separator, the '='
// key/value separator, or the '\' escape character are escaped in the flattened tag string
// that MetricsEventSource publishes, so they can be decoded without ambiguity.
[Fact]
[OuterLoop("Slow and has lots of console spew")]
public async Task EventSourcePublishesTimeSeriesWithTagsContainingDelimiters()
{
using Meter meter = new Meter("TestMeterDelimiters");
Counter<int> c = meter.CreateCounter<int>("counter1");

EventWrittenEventArgs[] events;
using (MetricsEventListener listener = new MetricsEventListener(_output, MetricsEventListener.TimeSeriesValues, IntervalSecs, "TestMeterDelimiters"))
{
await listener.WaitForCollectionStop(s_waitForEventTimeout, 1);

c.Add(5, new KeyValuePair<string, object?>("url", "/api/items?filter=red,blue&sort=name"));
c.Add(6, new KeyValuePair<string, object?>("comma", "a,b,c"), new KeyValuePair<string, object?>("equals", "x=1"));
c.Add(7, new KeyValuePair<string, object?>("path", @"C:\temp"));
await listener.WaitForCollectionStop(s_waitForEventTimeout, 2);

c.Add(12, new KeyValuePair<string, object?>("url", "/api/items?filter=red,blue&sort=name"));
c.Add(13, new KeyValuePair<string, object?>("comma", "a,b,c"), new KeyValuePair<string, object?>("equals", "x=1"));
c.Add(14, new KeyValuePair<string, object?>("path", @"C:\temp"));
await listener.WaitForCollectionStop(s_waitForEventTimeout, 3);
events = listener.Events.ToArray();
}

// Expected escaped tag strings: '\' => "\\", ',' => "\,", '=' => "\="; the ',' between
// pairs and the '=' between a key and its value remain literal delimiters.
AssertCounterEventsPresent(events, meter.Name, c.Name, @"url=/api/items?filter\=red\,blue&sort\=name", "", ("5", "5"), ("12", "17"));
AssertCounterEventsPresent(events, meter.Name, c.Name, @"comma=a\,b\,c,equals=x\=1", "", ("6", "6"), ("13", "19"));
AssertCounterEventsPresent(events, meter.Name, c.Name, @"path=C:\\temp", "", ("7", "7"), ("14", "21"));
AssertCollectStartStopEventsPresent(events, IntervalSecs, 3);
}

// Tests that version event from MetricsEventSource is fired.
[ConditionalFact(typeof(RemoteExecutor), nameof(RemoteExecutor.IsSupported))]
public void TestVersion()
Expand Down
Loading