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/messages.go

@@ -0,0 +1,203 @@
+package api
+
+import (
+	"encoding/json"
+	"errors"
+	"io"
+	"net/http"
+	"net/url"
+	"strconv"
+	"time"
+
+	"sneak.berlin/go/simplexcalc/internal/simplex"
+)
+
+const (
+	// defaultCount and maxCount bound how many of a chat's last items a
+	// request for its messages reads.
+	defaultCount = 20
+	maxCount     = 100
+)
+
+// message is how the API shows a message, wherever it shows one.
+type message struct {
+	ID        int64     `json:"id"`
+	Direction string    `json:"direction"`
+	Type      string    `json:"type"`
+	Text      string    `json:"text"`
+	Time      time.Time `json:"time"`
+}
+
+// newMessage returns the message a chat item holds, and false for an
+// item that holds none: the chat client also records events in a chat,
+// such as the contact connecting.
+func newMessage(item simplex.ChatItem) (message, bool) {
+	var direction string
+
+	switch item.Content.Type {
+	case "rcvMsgContent":
+		direction = "received"
+	case "sndMsgContent":
+		direction = "sent"
+	default:
+		return message{}, false
+	}
+
+	content := item.Content.MsgContent
+	if content == nil {
+		return message{}, false
+	}
+
+	return message{
+		ID:        item.Meta.ItemID,
+		Direction: direction,
+		Type:      content.Type,
+		Text:      content.Text,
+		Time:      item.Meta.ItemTs,
+	}, true
+}
+
+// handleMessages answers with the messages among a chat's last count
+// items, oldest first.
+func (h *handlers) handleMessages() http.HandlerFunc {
+	type response struct {
+		Messages []message `json:"messages"`
+	}
+
+	return func(w http.ResponseWriter, r *http.Request) {
+		contactID, ok := h.chatID(w, r)
+		if !ok {
+			return
+		}
+
+		// Not r.URL.Query, which drops a pair it cannot decode and so
+		// would turn count=1% into the default.
+		query, err := url.ParseQuery(r.URL.RawQuery)
+		if err != nil {
+			h.respondError(w, http.StatusBadRequest, "the query cannot be read")
+
+			return
+		}
+
+		count, ok := messageCount(query)
+		if !ok {
+			h.respondError(w, http.StatusBadRequest,
+				"count must be a whole number from 1 to "+strconv.Itoa(maxCount))
+
+			return
+		}
+
+		items, err := h.client.ChatItems(r.Context(), contactID, count)
+		if err != nil {
+			h.respondChatError(w, err, "reading a chat's messages",
+				"the messages could not be read")
+
+			return
+		}
+
+		messages := make([]message, 0, len(items))
+
+		for _, item := range items {
+			if m, ok := newMessage(item); ok {
+				messages = append(messages, m)
+			}
+		}
+
+		h.respond(w, http.StatusOK, response{Messages: messages})
+	}
+}
+
+// handleSend sends the text in the request's body to a chat, and answers
+// with the message sent.
+func (h *handlers) handleSend() http.HandlerFunc {
+	type request struct {
+		Text string `json:"text"`
+	}
+
+	type response struct {
+		Message message `json:"message"`
+	}
+
+	return func(w http.ResponseWriter, r *http.Request) {
+		contactID, ok := h.chatID(w, r)
+		if !ok {
+			return
+		}
+
+		body, err := io.ReadAll(r.Body)
+
+		var tooLarge *http.MaxBytesError
+		if errors.As(err, &tooLarge) {
+			h.respondError(w, http.StatusRequestEntityTooLarge, "the body is too large")
+
+			return
+		}
+
+		var req request
+
+		if err != nil || json.Unmarshal(body, &req) != nil {
+			h.respondError(w, http.StatusBadRequest,
+				`the body must be JSON such as {"text":"hello"}`)
+
+			return
+		}
+
+		if req.Text == "" {
+			h.respondError(w, http.StatusBadRequest, "text is empty")
+
+			return
+		}
+
+		item, err := h.client.SendMessage(r.Context(), contactID, req.Text)
+		if err != nil {
+			h.respondChatError(w, err, "sending a message",
+				"the message could not be sent")
+
+			return
+		}
+
+		sent, ok := newMessage(item)
+		if !ok {
+			h.log.Error("sending a message: the answer holds no message",
+				"content_type", item.Content.Type)
+			h.respondError(w, http.StatusInternalServerError,
+				"the chat client's answer could not be read")
+
+			return
+		}
+
+		h.respond(w, http.StatusCreated, response{Message: sent})
+	}
+}
+
+// respondChatError answers a request the chat client did not serve: 404
+// for a contact removed after chatID found it, 409 for one who cannot
+// receive messages, 413 for a text too long to send, and 500 with
+// sentence for anything else, which is logged as what.
+func (h *handlers) respondChatError(
+	w http.ResponseWriter, err error, what, sentence string,
+) {
+	switch {
+	case errors.Is(err, simplex.ErrNoContact):
+		h.respondError(w, http.StatusNotFound, noSuchChat)
+	case errors.Is(err, simplex.ErrContactNotReady):
+		h.respondError(w, http.StatusConflict, "the contact cannot receive messages")
+	case errors.Is(err, simplex.ErrMessageTooLarge):
+		h.respondError(w, http.StatusRequestEntityTooLarge, "the text is too long")
+	default:
+		h.log.Error(what, "error", err)
+		h.respondError(w, http.StatusInternalServerError, sentence)
+	}
+}
+
+// messageCount returns the query's count, defaultCount if it has none,
+// and false if it is anything but a whole number from 1 to maxCount.
+func messageCount(query url.Values) (int, bool) {
+	if !query.Has("count") {
+		return defaultCount, true
+	}
+
+	count, err := strconv.Atoi(query.Get("count"))
+
+	return count, err == nil && count >= 1 && count <= maxCount
+}