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feat: extensible OTEL span filtering and naming #81

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028aed0
feat: extensible OTEL span filtering and naming
thoriqzs25-gojek Apr 12, 2026
3ef1438
fix: address MR review feedback
thoriqzs25-gojek Apr 14, 2026
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12 changes: 12 additions & 0 deletions config/config.go
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Original file line number Diff line number Diff line change
Expand Up @@ -179,6 +179,14 @@ type Config struct {
// EnableOTELMetrics enables OpenTelemetry metrics export via OTLP alongside
// Prometheus. Does not replace Prometheus. Default false.
EnableOTELMetrics bool `envconfig:"ENABLE_OTEL_METRICS" default:"false"`

// OTELGRPCSpanNameFormat controls gRPC span naming.
// "short" extracts just the method name (e.g., "V0GetStats")
// "full" keeps the full path (e.g., "/pkg.Service/V0GetStats") - default
OTELGRPCSpanNameFormat string `envconfig:"OTEL_GRPC_SPAN_NAME_FORMAT" default:"full"`
// OTELFilterSpanNames is a comma-separated list of span names to filter out (exact match).
// Common use: "ServeHTTP" to filter HTTP transport spans.
OTELFilterSpanNames string `envconfig:"OTEL_FILTER_SPAN_NAMES" default:""`
Comment on lines +183 to +189
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@coderabbitai coderabbitai Bot Apr 13, 2026

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⚠️ Potential issue | 🟡 Minor

Warn on unsupported OTEL_GRPC_SPAN_NAME_FORMAT values.

Anything other than "short" currently falls back to full naming silently, so a typo just disables the feature. Adding a Validate() warning here would match how other enum-like config fields are handled in this file.

🤖 Prompt for AI Agents 
Verify each finding against the current code and only fix it if needed.

In `@config/config.go` around lines 183 - 189, Add validation for the
OTELGRPCSpanNameFormat config field inside the existing Validate() function so
values other than "short" or "full" produce a warning and the code falls back to
"full"; specifically, check the OTELGRPCSpanNameFormat string (from the struct
field named OTELGRPCSpanNameFormat) and if it is non-empty and not equal to
"short" or "full", emit a warning via the same logger used by other Validate()
checks and set/keep the value as "full" to preserve current behavior.

// OTELMetricsInterval controls the export interval in seconds for OTEL
// metrics. Default 60.
OTELMetricsInterval int `envconfig:"OTEL_METRICS_INTERVAL" default:"60"`
Expand Down Expand Up @@ -291,5 +299,9 @@ func (c Config) Validate() []string {
warnings = append(warnings, "RateLimitBurst should be positive when RateLimitPerSecond is set")
}

if c.OTELGRPCSpanNameFormat != "" && c.OTELGRPCSpanNameFormat != "short" && c.OTELGRPCSpanNameFormat != "full" {
warnings = append(warnings, "OTELGRPCSpanNameFormat must be 'short' or 'full', got '"+c.OTELGRPCSpanNameFormat+"'; defaulting to 'full'")
}

return warnings
}
30 changes: 30 additions & 0 deletions config/config_test.go
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Expand Up @@ -272,3 +272,33 @@ func TestValidateTimeoutExceedsShutdown(t *testing.T) {
t.Error("timeout exceeding shutdown duration should produce a warning")
}
}

func TestValidateOTELGRPCSpanNameFormat(t *testing.T) {
// Invalid format
c := Config{
GRPCPort: 9090,
HTTPPort: 9091,
OTELGRPCSpanNameFormat: "invalid",
}
warnings := c.Validate()
found := false
for _, w := range warnings {
if strings.Contains(w, "OTELGRPCSpanNameFormat") {
found = true
}
}
if !found {
t.Error("invalid OTELGRPCSpanNameFormat should produce a warning")
}

// Valid formats should not warn
for _, format := range []string{"short", "full", ""} {
c.OTELGRPCSpanNameFormat = format
warnings = c.Validate()
for _, w := range warnings {
if strings.Contains(w, "OTELGRPCSpanNameFormat") {
t.Errorf("format %q should not produce a warning, got: %s", format, w)
}
}
}
}
49 changes: 22 additions & 27 deletions core.go
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Expand Up @@ -180,38 +180,33 @@ func (c *cb) processConfig() {
if c.config.OTLPEndpoint != "" {
headers := parseHeaders(c.config.OTLPHeaders)
otlpConfig = OTLPConfig{
Endpoint: c.config.OTLPEndpoint,
Headers: headers,
ServiceName: c.config.AppName,
ServiceVersion: c.config.ReleaseName,
SamplingRatio: c.config.OTLPSamplingRatio,
Compression: c.config.OTLPCompression,
Insecure: c.config.OTLPInsecure,
Endpoint: c.config.OTLPEndpoint,
Headers: headers,
ServiceName: c.config.AppName,
ServiceVersion: c.config.ReleaseName,
SamplingRatio: c.config.OTLPSamplingRatio,
Compression: c.config.OTLPCompression,
Insecure: c.config.OTLPInsecure,
GRPCSpanNameFormat: c.config.OTELGRPCSpanNameFormat,
FilterSpanNames: c.config.OTELFilterSpanNames,
}
if err := SetupOpenTelemetry(otlpConfig); err != nil {
log.Error(context.Background(), "msg", "Failed to setup custom OTLP", "err", err)
}
} else if c.config.NewRelicOpentelemetry {
err := SetupNROpenTelemetry(
nrName,
c.config.NewRelicLicenseKey,
c.config.ReleaseName,
c.config.NewRelicOpentelemetrySample,
)
if err != nil {
log.Error(context.Background(), "msg", "Failed to setup New Relic OpenTelemetry", "err", err)
} else if c.config.NewRelicOpentelemetry && strings.TrimSpace(c.config.NewRelicLicenseKey) != "" {
// Build full config for NR path to include filter/transformer settings.
otlpConfig = OTLPConfig{
Endpoint: nrOTLPEndpoint,
Headers: map[string]string{"api-key": c.config.NewRelicLicenseKey},
ServiceName: nrName,
ServiceVersion: c.config.ReleaseName,
SamplingRatio: c.config.NewRelicOpentelemetrySample,
Compression: "gzip",
GRPCSpanNameFormat: c.config.OTELGRPCSpanNameFormat,
FilterSpanNames: c.config.OTELFilterSpanNames,
}
// Build otlpConfig for NR path so OTEL metrics can reuse the endpoint.
// Only populate when the license key is non-empty (SetupNROpenTelemetry
// no-ops without it, so metrics would just get auth failures).
if strings.TrimSpace(c.config.NewRelicLicenseKey) != "" {
otlpConfig = OTLPConfig{
Endpoint: nrOTLPEndpoint,
Headers: map[string]string{"api-key": c.config.NewRelicLicenseKey},
ServiceName: nrName,
ServiceVersion: c.config.ReleaseName,
Compression: "gzip",
}
if err := SetupOpenTelemetry(otlpConfig); err != nil {
log.Error(context.Background(), "msg", "Failed to setup New Relic OpenTelemetry", "err", err)
}
}

Expand Down
51 changes: 49 additions & 2 deletions initializers.go
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Expand Up @@ -13,6 +13,7 @@ import (
"time"

metricCollector "github.com/afex/hystrix-go/hystrix/metric_collector"
cbotel "github.com/go-coldbrew/core/otel"
"github.com/go-coldbrew/errors/notifier"
"github.com/go-coldbrew/hystrixprometheus" //nolint:staticcheck // deprecated but still in use
"github.com/go-coldbrew/interceptors"
Expand All @@ -26,9 +27,9 @@ import (
"go.opentelemetry.io/otel/attribute"
"go.opentelemetry.io/otel/exporters/otlp/otlpmetric/otlpmetricgrpc"
"go.opentelemetry.io/otel/exporters/otlp/otlptrace"
"go.opentelemetry.io/otel/propagation"
"go.opentelemetry.io/otel/exporters/otlp/otlptrace/otlptracegrpc"
otelmetric "go.opentelemetry.io/otel/metric"
"go.opentelemetry.io/otel/propagation"
"go.opentelemetry.io/otel/sdk/resource"
sdkmetric "go.opentelemetry.io/otel/sdk/metric"
sdktrace "go.opentelemetry.io/otel/sdk/trace"
Expand Down Expand Up @@ -145,6 +146,15 @@ type OTLPConfig struct {
// Insecure disables TLS verification for the connection
// Only use this for local development or testing
Insecure bool

// GRPCSpanNameFormat controls gRPC span naming.
// "short" extracts just the method name (e.g., "V0GetStats")
// "full" keeps the full path (e.g., "/pkg.Service/V0GetStats") - default
GRPCSpanNameFormat string

// FilterSpanNames is a comma-separated string of span names to filter out.
// Common use: "ServeHTTP" to filter HTTP transport spans.
FilterSpanNames string
}

// nrOTLPEndpoint is the New Relic OTLP gRPC endpoint.
Expand All @@ -157,6 +167,9 @@ var otelResource *resource.Resource
// otelTracerProvider stores the concrete TracerProvider for shutdown.
var otelTracerProvider *sdktrace.TracerProvider

// otelSpanProcessor stores the custom span processor for runtime filter/transformer additions.
var otelSpanProcessor *cbotel.SpanProcessor

// buildOTELResource builds a resource with service name, version, build info,
// and VCS metadata. The result is cached in otelResource for reuse.
func buildOTELResource(serviceName, serviceVersion string) (*resource.Resource, error) {
Expand Down Expand Up @@ -268,9 +281,25 @@ func SetupOpenTelemetry(config OTLPConfig) error {
ratio = 0.2
}

// Wrap the batcher with custom SpanProcessor for filtering/transformation.
batcher := sdktrace.NewBatchSpanProcessor(otlpExporter)
var filterNames []string
if config.FilterSpanNames != "" {
for _, name := range strings.Split(config.FilterSpanNames, ",") {
if trimmed := strings.TrimSpace(name); trimmed != "" {
filterNames = append(filterNames, trimmed)
}
}
}
processor := cbotel.NewSpanProcessor(batcher, cbotel.SpanProcessorConfig{
GRPCSpanNameFormat: config.GRPCSpanNameFormat,
FilterSpanNames: filterNames,
})
otelSpanProcessor = processor

tracerProvider := sdktrace.NewTracerProvider(
sdktrace.WithSampler(sdktrace.ParentBased(sdktrace.TraceIDRatioBased(ratio))),
sdktrace.WithBatcher(otlpExporter),
sdktrace.WithSpanProcessor(processor),
sdktrace.WithResource(r),
)
otelTracerProvider = tracerProvider
Expand Down Expand Up @@ -506,3 +535,21 @@ func (vtprotoCodec) Name() string {
// name registered for the proto compressor
return "proto"
}

// AddOTELSpanFilter adds a custom span filter at runtime.
// Filters are checked for each span; if any filter returns true, the span is dropped.
// Must be called after SetupOpenTelemetry; no-op if OTEL is not initialized.
func AddOTELSpanFilter(f cbotel.SpanFilter) {
if otelSpanProcessor != nil {
otelSpanProcessor.AddFilter(f)
}
}

// AddOTELSpanTransformer adds a custom span transformer at runtime.
// Transformers are applied in order; first non-empty result wins.
// Must be called after SetupOpenTelemetry; no-op if OTEL is not initialized.
func AddOTELSpanTransformer(t cbotel.SpanTransformer) {
if otelSpanProcessor != nil {
otelSpanProcessor.AddTransformer(t)
}
}
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