wasi slog

slog_wasi.go

package main

// logger := slog.New(DefaultOptions().NewHandler())
// a 'context' attribute will be promote to wasilog 'context' field
// logger = logger.With("context", "Get")
//
// logger.Info("Hello world")
// logger.Warn("Hello world 1", "key", "value")
// logger.Info("Hello world 2", slog.String("key", "value"))
// logger.Info("Hello world 3", slog.Any("key", 123), slog.String("context", "SomethingElse"))
//
// 2024-08-19T13:30:58.279639Z  INFO log: wasmcloud_host::wasmbus::handler: Hello world component_id="demo_image_processor-task_manager" level=Level::Info context="Get"
// 2024-08-19T13:30:58.279860Z  WARN log: wasmcloud_host::wasmbus::handler: key="value" Hello world 1 component_id="demo_image_processor-task_manager" level=Level::Warn context="Get"
// 2024-08-19T13:30:58.279950Z  INFO log: wasmcloud_host::wasmbus::handler: key="value" Hello world 2 component_id="demo_image_processor-task_manager" level=Level::Info context="Get"
// 2024-08-19T13:30:58.280050Z  INFO log: wasmcloud_host::wasmbus::handler: key="123" Hello world 3 component_id="demo_image_processor-task_manager" level=Level::Info context="SomethingElse"

import (
	"context"
	"fmt"
	"log/slog"
	"strings"

	slogcommon "github.com/samber/slog-common"

	// need compiled wit with wasi logging
	. "github.com/cosmonic-labs/wasmcloud.space/components/task-manager/gen"
)

type WasiLoggingOption struct {
	// log level (default: debug)
	Level slog.Leveler

	// optional: fetch attributes from context
	AttrFromContext []func(ctx context.Context) []slog.Attr

	ReplaceAttr func(groups []string, a slog.Attr) slog.Attr
}

type WebassemblyHandler struct {
	option WasiLoggingOption
	attrs  []slog.Attr
	groups []string
}

var _ slog.Handler = (*WebassemblyHandler)(nil)

func wasiLevel(level slog.Level) WasiLoggingLoggingLevel {
	switch level {
	case slog.LevelDebug:
		return WasiLoggingLoggingLevelDebug()
	case slog.LevelInfo:
		return WasiLoggingLoggingLevelInfo()
	case slog.LevelWarn:
		return WasiLoggingLoggingLevelWarn()
	case slog.LevelError:
		return WasiLoggingLoggingLevelError()
	default:
		return WasiLoggingLoggingLevelDebug()
	}
}

func wasiConverter(replaceAttr func(groups []string, a slog.Attr) slog.Attr, loggerAttr []slog.Attr, groups []string, record *slog.Record) (string, string) {
	attrs := slogcommon.AppendRecordAttrsToAttrs(loggerAttr, groups, record)

	attrs = slogcommon.ReplaceAttrs(replaceAttr, []string{}, attrs...)
	attrs = slogcommon.RemoveEmptyAttrs(attrs)

	extra := slogcommon.AttrsToString(attrs...)

	context, ok := extra["context"]
	if ok {
		delete(extra, "context")
	}

	var formattedAttrs []string
	for k, v := range extra {
		formattedAttrs = append(formattedAttrs, fmt.Sprintf("%s=%q", k, v))
	}
	formattedAttrs = append(formattedAttrs, record.Message)

	return strings.Join(formattedAttrs, " "), context
}

func DefaultOptions() WasiLoggingOption {
	return WasiLoggingOption{
		Level:           slog.LevelDebug,
		AttrFromContext: []func(ctx context.Context) []slog.Attr{},
	}
}

func (o WasiLoggingOption) NewHandler() slog.Handler {
	return &WebassemblyHandler{
		option: o,
	}
}

func (h *WebassemblyHandler) Enabled(_ context.Context, level slog.Level) bool {
	return level >= h.option.Level.Level()
}

func (h *WebassemblyHandler) Handle(ctx context.Context, record slog.Record) error {
	fromContext := slogcommon.ContextExtractor(ctx, h.option.AttrFromContext)
	message, logContext := wasiConverter(h.option.ReplaceAttr, append(h.attrs, fromContext...), h.groups, &record)

	WasiLoggingLoggingLog(wasiLevel(record.Level), logContext, message)

	return nil
}

func (h *WebassemblyHandler) WithAttrs(attrs []slog.Attr) slog.Handler {
	return &WebassemblyHandler{
		option: h.option,
		attrs:  slogcommon.AppendAttrsToGroup(h.groups, h.attrs, attrs...),
		groups: h.groups,
	}
}

func (h *WebassemblyHandler) WithGroup(name string) slog.Handler {
	// https://cs.opensource.google/go/x/exp/+/46b07846:slog/handler.go;l=247
	if name == "" {
		return h
	}

	return &WebassemblyHandler{
		option: h.option,
		attrs:  h.attrs,
		groups: append(h.groups, name),
	}
}