HTTP API: a chat's recent messages, and sending a message (closes #5)

`GET /api/v1/chats/{id}/messages?count=N` returns a chat's recent messages, oldest first (`count` 1 to 100, default 20), and `POST` to the same path sends a text message and returns it once the chat client has taken it. Both answer `404` for any id the chats list does not show, looked up in the same contact list. The message record is defined once, for the webhooks to reuse.

Disclosures: items are read five at a time, because one item can be many times its text and 100 at once could pass the 16 MiB read limit; text too long gets `413`, a contact who deleted the chat `409` (unverified for one still connecting); a query the server cannot read gets its own `400`.

Model: opus-5-5

internal/api/chats.go

@@ -2,26 +2,55 @@ package api
 
 import (
 	"cmp"
+	"context"
 	"net/http"
 	"slices"
+	"strconv"
+
+	"github.com/go-chi/chi/v5"
 )
 
-// handleChats lists the bot's chats, ordered by id. The bot talks to
-// people only one to one, so its chats are its contacts, and a chat's
-// id is its contact's.
-func (h *handlers) handleChats() http.HandlerFunc {
-	type chat struct {
-		ID             int64  `json:"id"`
-		DisplayName    string `json:"display_name"`
-		ContactDeleted bool   `json:"contact_deleted"`
+// noSuchChat answers a request naming a chat the bot does not have.
+const noSuchChat = "no such chat"
+
+// chat is how the API shows a chat. The bot talks to people only one to
+// one, so its chats are its contacts, and a chat's id is its contact's.
+type chat struct {
+	ID             int64  `json:"id"`
+	DisplayName    string `json:"display_name"`
+	ContactDeleted bool   `json:"contact_deleted"`
+}
+
+// chats returns the bot's chats, ordered by id. GET /api/v1/chats
+// answers with this list, and chatID accepts only an id in it.
+func (h *handlers) chats(ctx context.Context) ([]chat, error) {
+	contacts, err := h.client.Contacts(ctx, h.userID)
+	if err != nil {
+		return nil, err
 	}
 
+	chats := make([]chat, 0, len(contacts))
+	for _, c := range contacts {
+		chats = append(chats, chat{
+			ID:             c.ContactID,
+			DisplayName:    c.Profile.DisplayName,
+			ContactDeleted: c.Deleted(),
+		})
+	}
+
+	slices.SortFunc(chats, func(a, b chat) int { return cmp.Compare(a.ID, b.ID) })
+
+	return chats, nil
+}
+
+// handleChats lists the bot's chats.
+func (h *handlers) handleChats() http.HandlerFunc {
 	type response struct {
 		Chats []chat `json:"chats"`
 	}
 
 	return func(w http.ResponseWriter, r *http.Request) {
-		contacts, err := h.client.Contacts(r.Context(), h.userID)
+		chats, err := h.chats(r.Context())
 		if err != nil {
 			h.log.Error("listing the chats", "error", err)
 			h.respondError(w, http.StatusInternalServerError,
@@ -30,17 +59,39 @@ func (h *handlers) handleChats() http.HandlerFunc {
 			return
 		}
 
-		chats := make([]chat, 0, len(contacts))
-		for _, c := range contacts {
-			chats = append(chats, chat{
-				ID:             c.ContactID,
-				DisplayName:    c.Profile.DisplayName,
-				ContactDeleted: c.Deleted(),
-			})
-		}
-
-		slices.SortFunc(chats, func(a, b chat) int { return cmp.Compare(a.ID, b.ID) })
-
 		h.respond(w, http.StatusOK, response{Chats: chats})
 	}
 }
+
+// chatID returns the chat id in the request's path, if it is one of the
+// bot's chats. Otherwise it answers the request itself, 404, or 500 if
+// the chats could not be read, and returns false.
+//
+// The id is looked up rather than passed to the chat client, which also
+// keeps contact records that are not chats, such as the bot's own
+// profile, and would read or send in them.
+func (h *handlers) chatID(w http.ResponseWriter, r *http.Request) (int64, bool) {
+	id, err := strconv.ParseInt(chi.URLParam(r, "id"), 10, 64)
+	if err != nil {
+		h.respondError(w, http.StatusNotFound, noSuchChat)
+
+		return 0, false
+	}
+
+	chats, err := h.chats(r.Context())
+	if err != nil {
+		h.log.Error("looking up a chat", "error", err)
+		h.respondError(w, http.StatusInternalServerError,
+			"the chats could not be read")
+
+		return 0, false
+	}
+
+	if !slices.ContainsFunc(chats, func(c chat) bool { return c.ID == id }) {
+		h.respondError(w, http.StatusNotFound, noSuchChat)
+
+		return 0, false
+	}
+
+	return id, true
+}