Convert invoices to PDF with WeasyPrint

Although it is possible to just print the invoice from the browser, many
people will not even try an assume that they can not create a PDF for
the invoice.

I thought of using Groff or TeX to create the PDF, but it would mean
maintaining two templates in two different systems (HTML and whatever i
would use), and would probably look very different, because i do not
know Groff or TeX that well.

I wish there was a way to tell the browser to print to PDF, and it can
be done, but only with the Chrome Protocol to a server-side running
Chrome instance.   This works, but i would need a Chrome running as a
daemon.

I also wrote a Qt application that uses QWebEngine to print the PDF,
much like wkhtmltopdf, but with support for more recent HTML and CSS
standards.  Unfortunately, Qt 6.4’s embedded Chromium does not follow
break-page-inside as well as WeasyPrint does.

To use WeasyPrint, at first i wanted to reach the same URL as the user,
passing the cookie to WeasyPrint so that i can access the same invoice
as the user, something that can be done with wkhtmltopdf, but WeasyPrint
does not have such option.  I did it with a custom Python script, but
then i need to package and install that script, that is not that much
work, but using the Debian-provided script is even less work, and less
likely to drift when WeasyPrint changes API.

Also, it is unnecessary to do a network round-trip from Go to Python
back to Go, because i can already write the invoice HTML as is to
WeasyPrint’s stdin.

debian/control

@@ -32,7 +32,7 @@ Depends:
   ${misc:Depends},
   golang-github-jackc-pgx-v4-dev
 Description: Simple invoicing and accounting web application
- A simple web application to keep invoice and accouting records, intended for
+ A simple web application to keep invoice and accounting records, intended for
  freelancers working in Spain.
  .
  This is the dev package.
@@ -41,7 +41,8 @@ Package: numerus
 Architecture: any
 Depends:
  ${shlibs:Depends},
- ${misc:Depends}
+ ${misc:Depends},
+ weasyprint
 Built-Using: ${misc:Built-Using}
 Description: Simple invoicing and accounting web application
  A simple web application to keep invoice and accouting records, intended for

pkg/invoices.go

@@ -1,13 +1,18 @@
 package pkg
 
 import (
+	"bytes"
 	"context"
 	"fmt"
 	"github.com/julienschmidt/httprouter"
 	"html/template"
+	"io"
+	"log"
 	"math"
 	"net/http"
+	"os/exec"
 	"strconv"
+	"strings"
 	"time"
 )
 
@@ -52,7 +57,7 @@ func mustCollectInvoiceEntries(ctx context.Context, conn *Conn, company *Company
 	return entries
 }
 
-func GetInvoiceForm(w http.ResponseWriter, r *http.Request, params httprouter.Params) {
+func ServeInvoice(w http.ResponseWriter, r *http.Request, params httprouter.Params) {
 	locale := getLocale(r)
 	conn := getConn(r)
 	company := mustGetCompany(r)
@@ -65,16 +70,52 @@ func GetInvoiceForm(w http.ResponseWriter, r *http.Request, params httprouter.Pa
 		return
 	}
 
+	pdf := false
+	if strings.HasSuffix(slug, ".pdf") {
+		pdf = true
+		slug = slug[:len(slug)-len(".pdf")]
+	}
 	invoice := mustGetInvoice(r.Context(), conn, company, slug)
 	if invoice == nil {
 		http.NotFound(w, r)
 		return
 	}
-	mustRenderAppTemplate(w, r, "invoices/view.gohtml", invoice)
+	if pdf {
+		cmd := exec.Command("weasyprint", "--stylesheet", "web/static/invoice.css", "-", "-")
+		var stderr bytes.Buffer
+		cmd.Stderr = &stderr
+		stdin, err := cmd.StdinPipe()
+		if err != nil {
+			panic(err)
+		}
+		stdout, err := cmd.StdoutPipe()
+		if err != nil {
+			panic(err)
+		}
+		defer stdout.Close()
+		if err = cmd.Start(); err != nil {
+			panic(err)
+		}
+		go func() {
+			defer stdin.Close()
+			mustRenderAppTemplate(stdin, r, "invoices/view.gohtml", invoice)
+		}()
+		w.Header().Set("Content-Type", "application/pdf")
+		if _, err = io.Copy(w, stdout); err != nil {
+			panic(err)
+		}
+		if err := cmd.Wait(); err != nil {
+			log.Printf("ERR - %v\n", stderr.String())
+			panic(err)
+		}
+	} else {
+		mustRenderAppTemplate(w, r, "invoices/view.gohtml", invoice)
+	}
 }
 
 type invoice struct {
 	Number   string
+	Slug     string
 	Date     time.Time
 	Invoicer taxDetails
 	Invoicee taxDetails
@@ -105,7 +146,9 @@ type invoiceProduct struct {
 }
 
 func mustGetInvoice(ctx context.Context, conn *Conn, company *Company, slug string) *invoice {
-	inv := &invoice{}
+	inv := &invoice{
+		Slug: slug,
+	}
 	var invoiceId int
 	var decimalDigits int
 	if notFoundErrorOrPanic(conn.QueryRow(ctx, "select invoice_id, decimal_digits, invoice_number, invoice_date, notes, business_name, vatin, phone, email, address, city, province, postal_code, to_price(subtotal, decimal_digits), to_price(total, decimal_digits) from invoice join contact using (contact_id) join invoice_amount using (invoice_id) join currency using (currency_code) where invoice.slug = $1", slug).Scan(&invoiceId, &decimalDigits, &inv.Number, &inv.Date, &inv.Notes, &inv.Invoicee.Name, &inv.Invoicee.VATIN, &inv.Invoicee.Phone, &inv.Invoicee.Email, &inv.Invoicee.Address, &inv.Invoicee.City, &inv.Invoicee.Province, &inv.Invoicee.PostalCode, &inv.Subtotal, &inv.Total)) {

pkg/router.go

@@ -24,7 +24,7 @@ func NewRouter(db *Db) http.Handler {
 	companyRouter.PUT("/products/:slug", HandleUpdateProduct)
 	companyRouter.GET("/invoices", IndexInvoices)
 	companyRouter.POST("/invoices", HandleAddInvoice)
-	companyRouter.GET("/invoices/:slug", GetInvoiceForm)
+	companyRouter.GET("/invoices/:slug", ServeInvoice)
 	companyRouter.POST("/invoices/new/products", HandleAddProductsToInvoice)
 	companyRouter.GET("/", func(w http.ResponseWriter, r *http.Request, _ httprouter.Params) {
 		mustRenderAppTemplate(w, r, "dashboard.gohtml", nil)

po/ca.po

@@ -8,7 +8,7 @@ msgid ""
 msgstr ""
 "Project-Id-Version: numerus\n"
 "Report-Msgid-Bugs-To: jordi@tandem.blog\n"
-"POT-Creation-Date: 2023-02-24 11:52+0100\n"
+"POT-Creation-Date: 2023-02-26 17:11+0100\n"
 "PO-Revision-Date: 2023-01-18 17:08+0100\n"
 "Last-Translator: jordi fita mas <jordi@tandem.blog>\n"
 "Language-Team: Catalan <ca@dodds.net>\n"
@@ -59,7 +59,7 @@ msgid "Name"
 msgstr "Nom"
 
 #: web/template/invoices/products.gohtml:43
-#: web/template/invoices/view.gohtml:42 web/template/products/index.gohtml:23
+#: web/template/invoices/view.gohtml:59 web/template/products/index.gohtml:23
 msgctxt "title"
 msgid "Price"
 msgstr "Preu"
@@ -74,13 +74,13 @@ msgctxt "action"
 msgid "Add products"
 msgstr "Afegeix productes"
 
-#: web/template/invoices/new.gohtml:41 web/template/invoices/view.gohtml:44
-#: web/template/invoices/view.gohtml:71
+#: web/template/invoices/new.gohtml:41 web/template/invoices/view.gohtml:61
+#: web/template/invoices/view.gohtml:87
 msgctxt "title"
 msgid "Subtotal"
 msgstr "Subtotal"
 
-#: web/template/invoices/new.gohtml:51 web/template/invoices/view.gohtml:81
+#: web/template/invoices/new.gohtml:51 web/template/invoices/view.gohtml:97
 msgctxt "title"
 msgid "Total"
 msgstr "Total"
@@ -100,7 +100,7 @@ msgctxt "invoice"
 msgid "All"
 msgstr "Totes"
 
-#: web/template/invoices/index.gohtml:22 web/template/invoices/view.gohtml:18
+#: web/template/invoices/index.gohtml:22 web/template/invoices/view.gohtml:25
 msgctxt "title"
 msgid "Date"
 msgstr "Data"
@@ -135,21 +135,26 @@ msgctxt "title"
 msgid "Download"
 msgstr "Descàrrega"
 
-#: web/template/invoices/index.gohtml:47
+#: web/template/invoices/index.gohtml:50
 msgid "No invoices added yet."
 msgstr "No hi ha cap factura."
 
-#: web/template/invoices/view.gohtml:2 web/template/invoices/view.gohtml:17
+#: web/template/invoices/view.gohtml:2 web/template/invoices/view.gohtml:24
 msgctxt "title"
 msgid "Invoice %s"
 msgstr "Factura %s"
 
-#: web/template/invoices/view.gohtml:41
+#: web/template/invoices/view.gohtml:16
+msgctxt "action"
+msgid "Download invoice"
+msgstr "Descarrega factura"
+
+#: web/template/invoices/view.gohtml:58
 msgctxt "title"
 msgid "Concept"
 msgstr "Concepte"
 
-#: web/template/invoices/view.gohtml:43
+#: web/template/invoices/view.gohtml:60
 msgctxt "title"
 msgid "Units"
 msgstr "Unitats"
@@ -364,40 +369,40 @@ msgstr "No podeu deixar la contrasenya en blanc."
 msgid "Invalid user or password."
 msgstr "Nom d’usuari o contrasenya incorrectes."
 
-#: pkg/products.go:165 pkg/invoices.go:392
+#: pkg/products.go:165 pkg/invoices.go:435
 msgctxt "input"
 msgid "Name"
 msgstr "Nom"
 
-#: pkg/products.go:171 pkg/invoices.go:397
+#: pkg/products.go:171 pkg/invoices.go:440
 msgctxt "input"
 msgid "Description"
 msgstr "Descripció"
 
-#: pkg/products.go:176 pkg/invoices.go:401
+#: pkg/products.go:176 pkg/invoices.go:444
 msgctxt "input"
 msgid "Price"
 msgstr "Preu"
 
-#: pkg/products.go:186 pkg/invoices.go:307 pkg/invoices.go:427
+#: pkg/products.go:186 pkg/invoices.go:350 pkg/invoices.go:470
 msgctxt "input"
 msgid "Taxes"
 msgstr "Imposts"
 
-#: pkg/products.go:206 pkg/profile.go:92 pkg/invoices.go:340
-#: pkg/invoices.go:463
+#: pkg/products.go:206 pkg/profile.go:92 pkg/invoices.go:383
+#: pkg/invoices.go:506
 msgid "Name can not be empty."
 msgstr "No podeu deixar el nom en blanc."
 
-#: pkg/products.go:207 pkg/invoices.go:464
+#: pkg/products.go:207 pkg/invoices.go:507
 msgid "Price can not be empty."
 msgstr "No podeu deixar el preu en blanc."
 
-#: pkg/products.go:208 pkg/invoices.go:465
+#: pkg/products.go:208 pkg/invoices.go:508
 msgid "Price must be a number greater than zero."
 msgstr "El preu ha de ser un número major a zero."
 
-#: pkg/products.go:210 pkg/invoices.go:344 pkg/invoices.go:473
+#: pkg/products.go:210 pkg/invoices.go:387 pkg/invoices.go:516
 msgid "Selected tax is not valid."
 msgstr "Heu seleccionat un impost que no és vàlid."
 
@@ -460,70 +465,70 @@ msgstr "La confirmació no és igual a la contrasenya."
 msgid "Selected language is not valid."
 msgstr "Heu seleccionat un idioma que no és vàlid."
 
-#: pkg/invoices.go:158
+#: pkg/invoices.go:201
 msgid "Select a customer to bill."
 msgstr "Escolliu un client a facturar."
 
-#: pkg/invoices.go:233
+#: pkg/invoices.go:276
 msgid "Invalid action"
 msgstr "Acció invàlida."
 
-#: pkg/invoices.go:284
+#: pkg/invoices.go:327
 msgctxt "input"
 msgid "Customer"
 msgstr "Client"
 
-#: pkg/invoices.go:290
+#: pkg/invoices.go:333
 msgctxt "input"
 msgid "Number"
 msgstr "Número"
 
-#: pkg/invoices.go:296
+#: pkg/invoices.go:339
 msgctxt "input"
 msgid "Invoice Date"
 msgstr "Data de factura"
 
-#: pkg/invoices.go:302
+#: pkg/invoices.go:345
 msgctxt "input"
 msgid "Notes"
 msgstr "Notes"
 
-#: pkg/invoices.go:341
+#: pkg/invoices.go:384
 msgid "Invoice date can not be empty."
 msgstr "No podeu deixar la data de la factura en blanc."
 
-#: pkg/invoices.go:342
+#: pkg/invoices.go:385
 msgid "Invoice date must be a valid date."
 msgstr "La data de facturació ha de ser vàlida."
 
-#: pkg/invoices.go:387
+#: pkg/invoices.go:430
 msgctxt "input"
 msgid "Id"
 msgstr "Identificador"
 
-#: pkg/invoices.go:410
+#: pkg/invoices.go:453
 msgctxt "input"
 msgid "Quantity"
 msgstr "Quantitat"
 
-#: pkg/invoices.go:418
+#: pkg/invoices.go:461
 msgctxt "input"
 msgid "Discount (%)"
 msgstr "Descompte (%)"
 
-#: pkg/invoices.go:467
+#: pkg/invoices.go:510
 msgid "Quantity can not be empty."
 msgstr "No podeu deixar la quantitat en blanc."
 
-#: pkg/invoices.go:468
+#: pkg/invoices.go:511
 msgid "Quantity must be a number greater than zero."
 msgstr "La quantitat ha de ser un número major a zero."
 
-#: pkg/invoices.go:470
+#: pkg/invoices.go:513
 msgid "Discount can not be empty."
 msgstr "No podeu deixar el descompte en blanc."
 
-#: pkg/invoices.go:471
+#: pkg/invoices.go:514
 msgid "Discount must be a percentage between 0 and 100."
 msgstr "El descompte ha de ser un percentatge entre 0 i 100."
 

po/es.po

@@ -7,7 +7,7 @@ msgid ""
 msgstr ""
 "Project-Id-Version: numerus\n"
 "Report-Msgid-Bugs-To: jordi@tandem.blog\n"
-"POT-Creation-Date: 2023-02-24 11:52+0100\n"
+"POT-Creation-Date: 2023-02-26 17:11+0100\n"
 "PO-Revision-Date: 2023-01-18 17:45+0100\n"
 "Last-Translator: jordi fita mas <jordi@tandem.blog>\n"
 "Language-Team: Spanish <es@tp.org.es>\n"
@@ -59,7 +59,7 @@ msgid "Name"
 msgstr "Nombre"
 
 #: web/template/invoices/products.gohtml:43
-#: web/template/invoices/view.gohtml:42 web/template/products/index.gohtml:23
+#: web/template/invoices/view.gohtml:59 web/template/products/index.gohtml:23
 msgctxt "title"
 msgid "Price"
 msgstr "Precio"
@@ -74,13 +74,13 @@ msgctxt "action"
 msgid "Add products"
 msgstr "Añadir productos"
 
-#: web/template/invoices/new.gohtml:41 web/template/invoices/view.gohtml:44
-#: web/template/invoices/view.gohtml:71
+#: web/template/invoices/new.gohtml:41 web/template/invoices/view.gohtml:61
+#: web/template/invoices/view.gohtml:87
 msgctxt "title"
 msgid "Subtotal"
 msgstr "Subtotal"
 
-#: web/template/invoices/new.gohtml:51 web/template/invoices/view.gohtml:81
+#: web/template/invoices/new.gohtml:51 web/template/invoices/view.gohtml:97
 msgctxt "title"
 msgid "Total"
 msgstr "Total"
@@ -100,7 +100,7 @@ msgctxt "invoice"
 msgid "All"
 msgstr "Todas"
 
-#: web/template/invoices/index.gohtml:22 web/template/invoices/view.gohtml:18
+#: web/template/invoices/index.gohtml:22 web/template/invoices/view.gohtml:25
 msgctxt "title"
 msgid "Date"
 msgstr "Fecha"
@@ -135,21 +135,26 @@ msgctxt "title"
 msgid "Download"
 msgstr "Descargar"
 
-#: web/template/invoices/index.gohtml:47
+#: web/template/invoices/index.gohtml:50
 msgid "No invoices added yet."
 msgstr "No hay facturas."
 
-#: web/template/invoices/view.gohtml:2 web/template/invoices/view.gohtml:17
+#: web/template/invoices/view.gohtml:2 web/template/invoices/view.gohtml:24
 msgctxt "title"
 msgid "Invoice %s"
 msgstr "Factura %s"
 
-#: web/template/invoices/view.gohtml:41
+#: web/template/invoices/view.gohtml:16
+msgctxt "action"
+msgid "Download invoice"
+msgstr "Descargar factura"
+
+#: web/template/invoices/view.gohtml:58
 msgctxt "title"
 msgid "Concept"
 msgstr "Concepto"
 
-#: web/template/invoices/view.gohtml:43
+#: web/template/invoices/view.gohtml:60
 msgctxt "title"
 msgid "Units"
 msgstr "Unidades"
@@ -364,40 +369,40 @@ msgstr "No podéis dejar la contraseña en blanco."
 msgid "Invalid user or password."
 msgstr "Nombre de usuario o contraseña inválido."
 
-#: pkg/products.go:165 pkg/invoices.go:392
+#: pkg/products.go:165 pkg/invoices.go:435
 msgctxt "input"
 msgid "Name"
 msgstr "Nombre"
 
-#: pkg/products.go:171 pkg/invoices.go:397
+#: pkg/products.go:171 pkg/invoices.go:440
 msgctxt "input"
 msgid "Description"
 msgstr "Descripción"
 
-#: pkg/products.go:176 pkg/invoices.go:401
+#: pkg/products.go:176 pkg/invoices.go:444
 msgctxt "input"
 msgid "Price"
 msgstr "Precio"
 
-#: pkg/products.go:186 pkg/invoices.go:307 pkg/invoices.go:427
+#: pkg/products.go:186 pkg/invoices.go:350 pkg/invoices.go:470
 msgctxt "input"
 msgid "Taxes"
 msgstr "Impuestos"
 
-#: pkg/products.go:206 pkg/profile.go:92 pkg/invoices.go:340
-#: pkg/invoices.go:463
+#: pkg/products.go:206 pkg/profile.go:92 pkg/invoices.go:383
+#: pkg/invoices.go:506
 msgid "Name can not be empty."
 msgstr "No podéis dejar el nombre en blanco."
 
-#: pkg/products.go:207 pkg/invoices.go:464
+#: pkg/products.go:207 pkg/invoices.go:507
 msgid "Price can not be empty."
 msgstr "No podéis dejar el precio en blanco."
 
-#: pkg/products.go:208 pkg/invoices.go:465
+#: pkg/products.go:208 pkg/invoices.go:508
 msgid "Price must be a number greater than zero."
 msgstr "El precio tiene que ser un número mayor a cero."
 
-#: pkg/products.go:210 pkg/invoices.go:344 pkg/invoices.go:473
+#: pkg/products.go:210 pkg/invoices.go:387 pkg/invoices.go:516
 msgid "Selected tax is not valid."
 msgstr "Habéis escogido un impuesto que no es válido."
 
@@ -460,70 +465,70 @@ msgstr "La confirmación no corresponde con la contraseña."
 msgid "Selected language is not valid."
 msgstr "Habéis escogido un idioma que no es válido."
 
-#: pkg/invoices.go:158
+#: pkg/invoices.go:201
 msgid "Select a customer to bill."
 msgstr "Escoged un cliente a facturar."
 
-#: pkg/invoices.go:233
+#: pkg/invoices.go:276
 msgid "Invalid action"
 msgstr "Acción inválida."
 
-#: pkg/invoices.go:284
+#: pkg/invoices.go:327
 msgctxt "input"
 msgid "Customer"
 msgstr "Cliente"
 
-#: pkg/invoices.go:290
+#: pkg/invoices.go:333
 msgctxt "input"
 msgid "Number"
 msgstr "Número"
 
-#: pkg/invoices.go:296
+#: pkg/invoices.go:339
 msgctxt "input"
 msgid "Invoice Date"
 msgstr "Fecha de factura"
 
-#: pkg/invoices.go:302
+#: pkg/invoices.go:345
 msgctxt "input"
 msgid "Notes"
 msgstr "Notas"
 
-#: pkg/invoices.go:341
+#: pkg/invoices.go:384
 msgid "Invoice date can not be empty."
 msgstr "No podéis dejar la fecha de la factura en blanco."
 
-#: pkg/invoices.go:342
+#: pkg/invoices.go:385
 msgid "Invoice date must be a valid date."
 msgstr "La fecha de factura debe ser válida."
 
-#: pkg/invoices.go:387
+#: pkg/invoices.go:430
 msgctxt "input"
 msgid "Id"
 msgstr "Identificador"
 
-#: pkg/invoices.go:410
+#: pkg/invoices.go:453
 msgctxt "input"
 msgid "Quantity"
 msgstr "Cantidad"
 
-#: pkg/invoices.go:418
+#: pkg/invoices.go:461
 msgctxt "input"
 msgid "Discount (%)"
 msgstr "Descuento (%)"
 
-#: pkg/invoices.go:467
+#: pkg/invoices.go:510
 msgid "Quantity can not be empty."
 msgstr "No podéis dejar la cantidad en blanco."
 
-#: pkg/invoices.go:468
+#: pkg/invoices.go:511
 msgid "Quantity must be a number greater than zero."
 msgstr "La cantidad tiene que ser un número mayor a cero."
 
-#: pkg/invoices.go:470
+#: pkg/invoices.go:513
 msgid "Discount can not be empty."
 msgstr "No podéis dejar el descuento en blanco."
 
-#: pkg/invoices.go:471
+#: pkg/invoices.go:514
 msgid "Discount must be a percentage between 0 and 100."
 msgstr "El descuento tiene que ser un percentage entre 0 y 100."
 

web/static/numerus.css

@@ -508,6 +508,15 @@ main > nav {
     text-align: right;
 }
 
+.invoice-download {
+    text-align: center;
+}
+
+.invoice-download a {
+    color: inherit;
+    text-decoration: none;
+}
+
 /* Remix Icon */
 
 @font-face {

web/template/invoices/index.gohtml

@@ -39,7 +39,10 @@
                     <td class="invoice-status-{{ .Status }}">{{ .StatusLabel }}</td>
                     <td></td>
                     <td class="numeric">{{ .Total|formatPrice }}</td>
-                    <td></td>
+                    <td class="invoice-download"><a href="{{ companyURI "/invoices/"}}{{ .Slug }}.pdf" download="{{ .Number}}.pdf"
+                           title="{{( pgettext "Download invoice" "action" )}}"
+                           aria-label="{{( pgettext "Download invoice %s" "action" )}}"><i
+                                    class="ri-download-line"></i></a></td>
                 </tr>
             {{- end }}
         {{ else }}

web/template/invoices/view.gohtml

@@ -10,7 +10,13 @@
             <a href="{{ companyURI "/invoices"}}">{{( pgettext "Invoices" "title" )}}</a> /
             <a>{{ .Number }}</a>
         </p>
+        <p>
+            <a class="primary button"
+               href="{{ companyURI "/invoices/" }}{{ .Slug }}.pdf"
+               download="{{ .Number}}.pdf">{{( pgettext "Download invoice" "action" )}}</a>
+        </p>
     </nav>
+
     <link rel="stylesheet" type="text/css" href="/static/invoice.css">
     <article class="invoice">
         <header>