mochi/frontend/http/writer.go

package http

import (
	"errors"
	"net/http"
	"time"

	"github.com/anacrolix/torrent/bencode"

	"github.com/sot-tech/mochi/bittorrent"
	"github.com/sot-tech/mochi/pkg/log"
)

// WriteError communicates an error to a BitTorrent client over HTTP.
func WriteError(w http.ResponseWriter, err error) {
	message := "internal server error"
	var clientErr bittorrent.ClientError
	if errors.As(err, &clientErr) {
		message = clientErr.Error()
	} else {
		log.Error("http: internal error", log.Err(err))
	}

	w.WriteHeader(http.StatusOK)
	if err = bencode.NewEncoder(w).Encode(map[string]any{
		"failure reason": message,
	}); err != nil {
		log.Error("unable to encode string", log.Err(err))
	}
}

// WriteAnnounceResponse communicates the results of an Announce to a
// BitTorrent client over HTTP.
func WriteAnnounceResponse(w http.ResponseWriter, resp *bittorrent.AnnounceResponse) error {
	if resp.Interval > 0 {
		resp.Interval /= time.Second
	}

	if resp.Interval > 0 {
		resp.MinInterval /= time.Second
	}

	bdict := map[string]any{
		"complete":     resp.Complete,
		"incomplete":   resp.Incomplete,
		"interval":     resp.Interval,
		"min interval": resp.MinInterval,
	}

	// Add the peers to the dictionary in the compact format.
	if resp.Compact {
		var IPv4CompactDict, IPv6CompactDict []byte

		// Add the IPv4 peers to the dictionary.
		for _, peer := range resp.IPv4Peers {
			IPv4CompactDict = append(IPv4CompactDict, compact4(peer)...)
		}
		if len(IPv4CompactDict) > 0 {
			bdict["peers"] = IPv4CompactDict
		}

		// Add the IPv6 peers to the dictionary.
		for _, peer := range resp.IPv6Peers {
			IPv6CompactDict = append(IPv6CompactDict, compact6(peer)...)
		}
		if len(IPv6CompactDict) > 0 {
			bdict["peers6"] = IPv6CompactDict
		}
	} else {
		// Add the peers to the dictionary.
		peers := make([]map[string]any, 0, len(resp.IPv4Peers)+len(resp.IPv6Peers))
		for _, peer := range resp.IPv4Peers {
			peers = append(peers, dict(peer))
		}
		for _, peer := range resp.IPv6Peers {
			peers = append(peers, dict(peer))
		}
		bdict["peers"] = peers
	}

	return bencode.NewEncoder(w).Encode(bdict)
}

// WriteScrapeResponse communicates the results of a Scrape to a BitTorrent
// client over HTTP.
func WriteScrapeResponse(w http.ResponseWriter, resp *bittorrent.ScrapeResponse) error {
	filesDict := make(map[string]any, len(resp.Files))
	for _, scrape := range resp.Files {
		filesDict[string(scrape.InfoHash[:])] = map[string]any{
			"complete":   scrape.Complete,
			"incomplete": scrape.Incomplete,
		}
	}

	return bencode.NewEncoder(w).Encode(map[string]any{
		"files": filesDict,
	})
}

func compact4(peer bittorrent.Peer) (buf []byte) {
	if ip := peer.IP.To4(); ip == nil {
		panic("non-IPv4 IP for Peer in IPv4Peers")
	} else {
		buf = ip
	}
	buf = append(buf, byte(peer.Port>>8), byte(peer.Port))
	return
}

func compact6(peer bittorrent.Peer) (buf []byte) {
	if ip := peer.IP.To16(); ip == nil {
		panic("non-IPv6 IP for Peer in IPv6Peers")
	} else {
		buf = ip
	}
	buf = append(buf, byte(peer.Port>>8), byte(peer.Port))
	return
}

func dict(peer bittorrent.Peer) map[string]any {
	return map[string]any{
		"peer id": string(peer.ID[:]),
		"ip":      peer.IP.String(),
		"port":    peer.Port,
	}
}