Messenger/server/internal/api/respond.go

// Package api implements the HTTP handlers for the messenger REST API.
package api

import (
	"encoding/json"
	"errors"
	"net/http"

	"messenger/internal/store"
)

func writeJSON(w http.ResponseWriter, status int, body any) {
	w.Header().Set("Content-Type", "application/json")
	w.WriteHeader(status)
	if err := json.NewEncoder(w).Encode(body); err != nil {
		http.Error(w, `{"error":"failed to encode response"}`, http.StatusInternalServerError)
	}
}

func writeError(w http.ResponseWriter, status int, message string) {
	writeJSON(w, status, map[string]string{"error": message})
}

func writeStoreError(w http.ResponseWriter, err error) {
	switch {
	case errors.Is(err, store.ErrNotFound):
		writeError(w, http.StatusNotFound, "not found")
	case errors.Is(err, store.ErrDuplicate):
		writeError(w, http.StatusConflict, "already exists")
	default:
		writeError(w, http.StatusInternalServerError, "internal server error")
	}
}

// decodeJSON parses the request body into dst, rejecting oversized payloads.
func decodeJSON(w http.ResponseWriter, r *http.Request, dst any) bool {
	r.Body = http.MaxBytesReader(w, r.Body, 1<<20)
	if err := json.NewDecoder(r.Body).Decode(dst); err != nil {
		writeError(w, http.StatusBadRequest, "invalid json")
		return false
	}
	return true
}