dchain/node/api_channels.go

// Package node — channel endpoints.
//
// `/api/channels/:id/members` returns every Ed25519 pubkey registered as a
// channel member together with their current X25519 pubkey (from the
// identity registry). Clients sealing a message to a channel iterate this
// list and call relay.Seal once per recipient — that's the "fan-out"
// group-messaging model (R1 in the roadmap).
//
// Why enrich with X25519 here rather than making the client do it?
//   - One HTTP round trip vs N. At 10+ members the latency difference is
//     significant over mobile networks.
//   - The server already holds the identity state; no extra DB hops.
//   - Clients get a stable, already-joined view — if a member hasn't
//     published an X25519 key yet, we return them with `x25519_pub_key=""`
//     so the caller knows to skip or retry later.
package node

import (
	"fmt"
	"net/http"
	"strings"

	"go-blockchain/blockchain"
	"go-blockchain/wallet"
)

func registerChannelAPI(mux *http.ServeMux, q ExplorerQuery) {
	// GET /api/channels/{id}              → channel metadata
	// GET /api/channels/{id}/members      → enriched member list
	//
	// One HandleFunc deals with both by sniffing the path suffix.
	mux.HandleFunc("/api/channels/", func(w http.ResponseWriter, r *http.Request) {
		if r.Method != http.MethodGet {
			jsonErr(w, fmt.Errorf("method not allowed"), 405)
			return
		}
		path := strings.TrimPrefix(r.URL.Path, "/api/channels/")
		path = strings.Trim(path, "/")
		if path == "" {
			jsonErr(w, fmt.Errorf("channel id required"), 400)
			return
		}
		switch {
		case strings.HasSuffix(path, "/members"):
			id := strings.TrimSuffix(path, "/members")
			handleChannelMembers(w, q, id)
		default:
			handleChannelInfo(w, q, path)
		}
	})
}

func handleChannelInfo(w http.ResponseWriter, q ExplorerQuery, channelID string) {
	if q.GetChannel == nil {
		jsonErr(w, fmt.Errorf("channel queries not configured"), 503)
		return
	}
	ch, err := q.GetChannel(channelID)
	if err != nil {
		jsonErr(w, err, 500)
		return
	}
	if ch == nil {
		jsonErr(w, fmt.Errorf("channel %s not found", channelID), 404)
		return
	}
	jsonOK(w, ch)
}

func handleChannelMembers(w http.ResponseWriter, q ExplorerQuery, channelID string) {
	if q.GetChannelMembers == nil {
		jsonErr(w, fmt.Errorf("channel queries not configured"), 503)
		return
	}
	pubs, err := q.GetChannelMembers(channelID)
	if err != nil {
		jsonErr(w, err, 500)
		return
	}
	out := make([]blockchain.ChannelMember, 0, len(pubs))
	for _, pub := range pubs {
		member := blockchain.ChannelMember{
			PubKey:  pub,
			Address: wallet.PubKeyToAddress(pub),
		}
		// Best-effort X25519 lookup — skip silently on miss so a member
		// who hasn't published their identity yet doesn't prevent the
		// whole list from returning. The sender will just skip them on
		// fan-out and retry later (after that member does register).
		if q.IdentityInfo != nil {
			if info, err := q.IdentityInfo(pub); err == nil && info != nil {
				member.X25519PubKey = info.X25519Pub
			}
		}
		out = append(out, member)
	}
	jsonOK(w, map[string]any{
		"channel_id": channelID,
		"count":      len(out),
		"members":    out,
	})
}