Seed from go-template-repo, renamed to simplexcalc

The template's files at a77fd30, without its history or LICENSE, after
script/rename simplexcalc.

Model: opus-5-5

internal/handlers/index.go

@@ -0,0 +1,114 @@
+package handlers
+
+import (
+	"net/http"
+	"strings"
+
+	"github.com/dustin/go-humanize"
+	"sneak.berlin/go/simplexcalc/internal/render"
+)
+
+// widgetListLimit bounds the index query. An unbounded SELECT is fine
+// on the day it is written and is the outage two years later.
+const widgetListLimit = 50
+
+// maxWidgetNameLen matches the maxlength on the form input. The form is
+// a courtesy; this is the rule.
+const maxWidgetNameLen = 200
+
+// Index renders the front page from the embedded template, listing the
+// most recent widgets.
+func (h *Handlers) Index() http.HandlerFunc {
+	return func(w http.ResponseWriter, r *http.Request) {
+		ctx := r.Context()
+
+		widgets, err := h.params.Database.ListWidgets(ctx, widgetListLimit)
+		if err != nil {
+			h.fail(w, r, http.StatusInternalServerError, "Could not load widgets.", err)
+
+			return
+		}
+
+		count, err := h.params.Database.CountWidgets(ctx)
+		if err != nil {
+			h.fail(w, r, http.StatusInternalServerError, "Could not count widgets.", err)
+
+			return
+		}
+
+		data := render.IndexPage{
+			Page:        h.page(r),
+			WidgetCount: count,
+			Widgets:     widgets,
+		}
+
+		err = h.params.Renderer.HTML(w, http.StatusOK, "index.html", data)
+		if err != nil {
+			h.fail(w, r, http.StatusInternalServerError, "Could not render the page.", err)
+		}
+	}
+}
+
+// CreateWidget handles the form POST. State-changing, so it is behind
+// CSRF; see internal/server/routes.go for where that is applied.
+func (h *Handlers) CreateWidget() http.HandlerFunc {
+	return func(w http.ResponseWriter, r *http.Request) {
+		// ParseForm reads the body, which BodyLimit has already capped:
+		// an oversized submission fails here rather than being buffered
+		// in full first.
+		err := r.ParseForm()
+		if err != nil {
+			h.fail(w, r, http.StatusBadRequest, "Could not read the form.", err)
+
+			return
+		}
+
+		name := strings.TrimSpace(r.PostFormValue("name"))
+		if name == "" || len(name) > maxWidgetNameLen {
+			h.fail(w, r, http.StatusBadRequest,
+				"A widget needs a name of 1 to 200 characters.", errBadWidgetName)
+
+			return
+		}
+
+		size, err := parseSize(r.PostFormValue("size"))
+		if err != nil {
+			h.fail(w, r, http.StatusBadRequest,
+				"Size must be a byte count, like 4096 or 4KiB.", err)
+
+			return
+		}
+
+		_, err = h.params.Database.CreateWidget(r.Context(), name, size)
+		if err != nil {
+			h.fail(w, r, http.StatusInternalServerError, "Could not save the widget.", err)
+
+			return
+		}
+
+		// POST/redirect/GET: a reload must not repeat the write.
+		http.Redirect(w, r, "/", http.StatusSeeOther)
+	}
+}
+
+// parseSize accepts an empty value as zero and anything else as a
+// human-readable byte size.
+func parseSize(s string) (int64, error) {
+	s = strings.TrimSpace(s)
+	if s == "" {
+		return 0, nil
+	}
+
+	n, err := humanize.ParseBytes(s)
+	if err != nil {
+		return 0, errBadWidgetSize
+	}
+
+	// A size beyond this is not a widget, it is a typo with a suffix.
+	const maxWidgetSize = uint64(1) << 50
+	if n > maxWidgetSize {
+		return 0, errBadWidgetSize
+	}
+
+	return int64(n), nil
+}