vendor/github.com/Microsoft/hcsshim/internal/log/hook.go

package log

import (
	"bytes"
	"reflect"
	"time"

	"github.com/Microsoft/hcsshim/internal/logfields"
	"github.com/sirupsen/logrus"
	"go.opencensus.io/trace"
)

const nullString = "null"

// Hook intercepts and formats a [logrus.Entry] before it logged.
//
// The shim either outputs the logs through an ETW hook, discarding the (formatted) output
// or logs output to a pipe for logging binaries to consume.
// The Linux GCS outputs logrus entries over stdout, which is then consumed and re-output
// by the shim.
type Hook struct {
	// EncodeAsJSON formats structs, maps, arrays, slices, and [bytes.Buffer] as JSON.
	// Variables of [bytes.Buffer] will be converted to []byte.
	//
	// Default is false.
	EncodeAsJSON bool

	// FormatTime specifies the format for [time.Time] variables.
	// An empty string disables formatting.
	// When disabled, the fall back will the JSON encoding, if enabled.
	//
	// Default is [TimeFormat].
	TimeFormat string

	// Duration format converts a [time.Duration] fields to an appropriate encoding.
	// nil disables formatting.
	// When disabled, the fall back will the JSON encoding, if enabled.
	//
	// Default is [DurationFormatString], which appends a duration unit after the value.
	DurationFormat DurationFormat

	// AddSpanContext adds [logfields.TraceID] and [logfields.SpanID] fields to
	// the entry from the span context stored in [logrus.Entry.Context], if it exists.
	AddSpanContext bool
}

var _ logrus.Hook = &Hook{}

func NewHook() *Hook {
	return &Hook{
		TimeFormat:     TimeFormat,
		DurationFormat: DurationFormatString,
		AddSpanContext: true,
	}
}

func (h *Hook) Levels() []logrus.Level {
	return logrus.AllLevels
}

func (h *Hook) Fire(e *logrus.Entry) (err error) {
	// JSON encode, if necessary, then add span information
	h.encode(e)
	h.addSpanContext(e)

	return nil
}

// encode loops through all the fields in the [logrus.Entry] and encodes them according to
// the settings in [Hook].
// If [Hook.TimeFormat] is non-empty, it will be passed to [time.Time.Format] for
// fields of type [time.Time].
//
// If [Hook.EncodeAsJSON] is true, then fields that are not numeric, boolean, strings, or
// errors will be encoded via a [json.Marshal] (with HTML escaping disabled).
// Chanel- and function-typed fields, as well as unsafe pointers are left alone and not encoded.
//
// If [Hook.TimeFormat] and [Hook.DurationFormat] are empty and [Hook.EncodeAsJSON] is false,
// then this is a no-op.
func (h *Hook) encode(e *logrus.Entry) {
	d := e.Data

	formatTime := h.TimeFormat != ""
	formatDuration := h.DurationFormat != nil
	if !h.EncodeAsJSON && !formatTime && !formatDuration {
		return
	}

	for k, v := range d {
		// encode types with dedicated formatting options first

		if vv, ok := v.(time.Time); formatTime && ok {
			d[k] = vv.Format(h.TimeFormat)
			continue
		}

		if vv, ok := v.(time.Duration); formatDuration && ok {
			d[k] = h.DurationFormat(vv)
			continue
		}

		// general case JSON encoding

		if !h.EncodeAsJSON {
			continue
		}

		switch vv := v.(type) {
		// built in types
		// "json" marshals errors as "{}", so leave alone here
		case bool, string, error, uintptr,
			int8, int16, int32, int64, int,
			uint8, uint32, uint64, uint,
			float32, float64:
			continue

		// Rather than setting d[k] = vv.String(), JSON encode []byte value, since it
		// may be a binary payload and not representable as a string.
		// `case bytes.Buffer,*bytes.Buffer:` resolves `vv` to `interface{}`,
		// so cannot use `vv.Bytes`.
		// Could move to below the `reflect.Indirect()` call below, but
		// that would require additional typematching and dereferencing.
		// Easier to keep these duplicate branches here.
		case bytes.Buffer:
			v = vv.Bytes()
		case *bytes.Buffer:
			v = vv.Bytes()
		}

		// dereference pointer or interface variables
		rv := reflect.Indirect(reflect.ValueOf(v))
		// check if `v` is a null pointer
		if !rv.IsValid() {
			d[k] = nullString
			continue
		}

		switch rv.Kind() {
		case reflect.Map, reflect.Struct, reflect.Array, reflect.Slice:
		default:
			// Bool, [U]?Int*, Float*, Complex*, Uintptr, String: encoded as normal
			// Chan, Func: not supported by json
			// Interface, Pointer: dereferenced above
			// UnsafePointer: not supported by json, not safe to de-reference; leave alone
			continue
		}

		b, err := encode(v)
		if err != nil {
			// Errors are written to stderr (ie, to `panic.log`) and stops the remaining
			// hooks (ie, exporting to ETW) from firing. So add encoding errors to
			// the entry data to be written out, but keep on processing.
			d[k+"-"+logrus.ErrorKey] = err.Error()
			// keep the original `v` as the value,
			continue
		}
		d[k] = string(b)
	}
}

func (h *Hook) addSpanContext(e *logrus.Entry) {
	ctx := e.Context
	if !h.AddSpanContext || ctx == nil {
		return
	}
	span := trace.FromContext(ctx)
	if span == nil {
		return
	}
	sctx := span.SpanContext()
	e.Data[logfields.TraceID] = sctx.TraceID.String()
	e.Data[logfields.SpanID] = sctx.SpanID.String()
}