You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: upstreams.go
    path of file: ./repos/caddy/modules/caddyhttp/reverseproxy
    
    the code of the file until where you have to start completion: package reverseproxy

import (
	"context"
	"encoding/json"
	"fmt"
	weakrand "math/rand"
	"net"
	"net/http"
	"strconv"
	"sync"
	"time"

	"go.uber.org/zap"

	"github.com/caddyserver/caddy/v2"
)

func init() {
	caddy.Regi
    
func (mu MultiUpstreams) GetUpstreams(r *http.Request) ([]*Upstream, error) {
	var upstreams []*Upstream

	for i, src := range mu.sources {
		select {
		case <-r.Context().Done():
			return upstreams, context.Canceled
		default:
		}

		up, err := src.GetUpstreams(r)
		if err != nil {
			mu.logger.Error("upstream source returned error",
				zap.Int("source_idx", i),
				zap.Error(err))
		} else if len(up) == 0 {
			mu.logger.Warn("upstream source returned 0 upstreams", zap.Int("source_idx", i))
		} else {
			upstreams = append(upstreams, up...)
		}
	}

	return upstreams, nil
}