chore: ignore logs for context.Canceled errors (#9945)

cmd/zap.go

@@ -1,6 +1,10 @@
 package cmd
 
 import (
+	"context"
+	"time"
+
+	"github.com/SigNoz/signoz/pkg/errors"
 	"go.uber.org/zap"         //nolint:depguard
 	"go.uber.org/zap/zapcore" //nolint:depguard
 )
@@ -10,6 +14,97 @@ func newZapLogger() *zap.Logger {
 	config := zap.NewProductionConfig()
 	config.EncoderConfig.TimeKey = "timestamp"
 	config.EncoderConfig.EncodeTime = zapcore.ISO8601TimeEncoder
+
+	// Extract sampling config before building the logger.
+	// We need to disable sampling in the config and apply it manually later
+	// to ensure correct core ordering. See filteringCore documentation for details.
+	samplerConfig := config.Sampling
+	config.Sampling = nil
+
 	logger, _ := config.Build()
-	return logger
+
+	// Wrap with custom core wrapping to filter certain log entries.
+	// The order of wrapping is important:
+	//   1. First wrap with filteringCore
+	//   2. Then wrap with sampler
+	//
+	// This creates the call chain: sampler -> filteringCore -> ioCore
+	//
+	// During logging:
+	//   - sampler.Check decides whether to sample the log entry
+	//   - If sampled, filteringCore.Check is called
+	//   - filteringCore adds itself to CheckedEntry.cores
+	//   - All cores in CheckedEntry.cores have their Write method called
+	//   - filteringCore.Write can now filter the entry before passing to ioCore
+	//
+	// If we didn't disable the sampler above, filteringCore would have wrapped
+	// sampler. By calling sampler.Check we would have allowed it to call
+	// ioCore.Check that adds itself to CheckedEntry.cores. Then ioCore.Write
+	// would have bypassed our checks, making filtering impossible.
+	return logger.WithOptions(zap.WrapCore(func(core zapcore.Core) zapcore.Core {
+		core = &filteringCore{core}
+		if samplerConfig != nil {
+			core = zapcore.NewSamplerWithOptions(
+				core,
+				time.Second,
+				samplerConfig.Initial,
+				samplerConfig.Thereafter,
+			)
+		}
+		return core
+	}))
+}
+
+// filteringCore wraps a zapcore.Core to filter out log entries based on a
+// custom logic.
+//
+// Note: This core must be positioned before the sampler in the core chain
+// to ensure Write is called. See newZapLogger for ordering details.
+type filteringCore struct {
+	zapcore.Core
+}
+
+// filter determines whether a log entry should be written based on its fields.
+// Returns false if the entry should be suppressed, true otherwise.
+//
+// Current filters:
+//   - context.Canceled: These are expected errors from cancelled operations,
+//     and create noise in logs.
+func (c *filteringCore) filter(fields []zapcore.Field) bool {
+	for _, field := range fields {
+		if field.Type == zapcore.ErrorType {
+			if loggedErr, ok := field.Interface.(error); ok {
+				// Suppress logs containing context.Canceled errors
+				if errors.Is(loggedErr, context.Canceled) {
+					return false
+				}
+			}
+		}
+	}
+	return true
+}
+
+// With implements zapcore.Core.With
+// It returns a new copy with the added context.
+func (c *filteringCore) With(fields []zapcore.Field) zapcore.Core {
+	return &filteringCore{c.Core.With(fields)}
+}
+
+// Check implements zapcore.Core.Check.
+// It adds this core to the CheckedEntry if the log level is enabled,
+// ensuring that Write will be called for this entry.
+func (c *filteringCore) Check(ent zapcore.Entry, ce *zapcore.CheckedEntry) *zapcore.CheckedEntry {
+	if c.Enabled(ent.Level) {
+		return ce.AddCore(ent, c)
+	}
+	return ce
+}
+
+// Write implements zapcore.Core.Write.
+// It filters log entries based on their fields before delegating to the wrapped core.
+func (c *filteringCore) Write(ent zapcore.Entry, fields []zapcore.Field) error {
+	if !c.filter(fields) {
+		return nil
+	}
+	return c.Core.Write(ent, fields)
 }