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Overview

The go-siat SDK uses a fluent builder pattern to construct invoices safely and efficiently. The builder pattern ensures:
  • Type safety with opaque interfaces
  • Prevention of direct manipulation of internal structures
  • Clear, readable invoice construction code
  • Compile-time validation of required fields

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Invoice Structure

A complete invoice consists of three main components:
  1. Factura - The root invoice container
  2. Cabecera - The header with issuer, customer, and transaction details
  3. Detalle - Individual line items (products/services)
FacturaCompraVenta (Invoice)
├── Cabecera (Header)
│   ├── Issuer information
│   ├── Customer information
│   └── Transaction totals
└── Detalle[] (Line Items)
    ├── Product/service details
    ├── Quantities and prices
    └── Subtotals

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Building an Invoice

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1. Create Cabecera (Header)

The header contains issuer, customer, and transaction information: 
cabecera := models.CompraVenta.NewCabecera().
    // Issuer information
    WithNitEmisor(123456789).
    WithRazonSocialEmisor("Mi Empresa S.A.").
    WithMunicipio("La Paz").
    WithDireccion("Av. Principal 123").
    WithTelefono("+591 2 1234567").
    
    // Invoice identification
    WithNumeroFactura(1).
    WithCuf("GENERATED_CUF").
    WithCufd("DAILY_CUFD").
    WithCodigoSucursal(0).
    WithCodigoPuntoVenta(0).
    WithFechaEmision("2024-01-15T14:30:00.000").
    
    // Customer information
    WithNombreRazonSocial("JUAN PEREZ").
    WithCodigoTipoDocumentoIdentidad(1).
    WithNumeroDocumento("5544332").
    WithComplemento("1A").
    WithCodigoCliente("CLI-001").
    
    // Payment information
    WithCodigoMetodoPago(1).
    WithMontoTotal(100.0).
    WithMontoTotalSujetoIva(100.0).
    WithCodigoMoneda(1).
    WithTipoCambio(1.0).
    WithMontoTotalMoneda(100.0).
    
    // Additional fields
    WithLeyenda("Ley N° 453: El proveedor deberá suministrar el servicio...").
    WithUsuario("admin").
    WithCodigoDocumentoSector(1).
    Build()

​
2. Create Detalle (Line Items)

Add one or more line items describing the products or services: 
detalle1 := models.CompraVenta.NewDetalle().
    WithActividadEconomica("461000").
    WithCodigoProductoSin("12345").
    WithCodigoProducto("PROD-001").
    WithDescripcion("Producto de prueba").
    WithCantidad(2.0).
    WithUnidadMedida(57).
    WithPrecioUnitario(50.0).
    WithSubTotal(100.0).
    Build()

detalle2 := models.CompraVenta.NewDetalle().
    WithActividadEconomica("461000").
    WithCodigoProductoSin("67890").
    WithCodigoProducto("PROD-002").
    WithDescripcion("Servicio adicional").
    WithCantidad(1.0).
    WithUnidadMedida(62).
    WithPrecioUnitario(25.0).
    WithMontoDescuento(5.0).
    WithSubTotal(20.0).
    Build()

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3. Assemble the Invoice

Combine the header and line items into a complete invoice: 
factura := models.CompraVenta.NewFactura().
    WithCabecera(cabecera).
    AddDetalle(detalle1).
    AddDetalle(detalle2).
    Build()

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Cabecera Builder Methods

Complete reference for all CabeceraBuilder methods:

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Issuer Information

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WithNitEmisor
func(int64)
required
Tax identification number (NIT) of the issuing company
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WithRazonSocialEmisor
func(string)
required
Legal name of the issuing company
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WithMunicipio
func(string)
required
Municipality where the issuer is located (e.g., “La Paz”, “Santa Cruz”)
​
WithDireccion
func(string)
required
Physical address of the issuer
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WithTelefono
func(string)
Contact phone number (optional)

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Invoice Identification

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WithNumeroFactura
func(int64)
required
Sequential invoice number
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WithCuf
func(string)
required
CUF (Código Único de Factura) - unique invoice code generated using models.CompraVenta.GenerarCUF()
​
WithCufd
func(string)
required
CUFD (Código Único de Factura Diario) - daily invoice code
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WithCodigoSucursal
func(int)
required
Branch/office code registered in SIAT
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WithCodigoPuntoVenta
func(int)
required
Point of sale code
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WithFechaEmision
func(string)
required
Emission date and time in format: "2006-01-02T15:04:05.000"
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WithCodigoDocumentoSector
func(int)
required
Document sector type code from SIAT catalogs

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Customer Information

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WithNombreRazonSocial
func(string)
Customer’s name or legal name (optional)
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WithCodigoTipoDocumentoIdentidad
func(int)
required
Document type code:
  • 1 = CI (Cédula de Identidad)
  • 2 = CEX (Cédula de Extranjero)
  • 3 = Pasaporte
  • 4 = NIT
  • 5 = Otro
​
WithNumeroDocumento
func(string)
required
Customer’s document number
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WithComplemento
func(string)
Document complement (e.g., “1A”) - optional
​
WithCodigoCliente
func(string)
required
Internal customer code in your system

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Payment Information

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WithCodigoMetodoPago
func(int)
required
Payment method code:
  • 1 = Efectivo
  • 2 = Tarjeta
  • 3 = Cheque
  • 4 = Otro
​
WithNumeroTarjeta
func(int64)
Card number (last 4 digits) - required if payment method is card
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WithMontoTotal
func(float64)
required
Total invoice amount including taxes
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WithMontoTotalSujetoIva
func(float64)
required
Total amount subject to VAT
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WithCodigoMoneda
func(int)
required
Currency code:
  • 1 = Boliviano (BOB)
  • 2 = Dólar (USD)
  • 3 = Euro (EUR)
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WithTipoCambio
func(float64)
required
Exchange rate (use 1.0 for BOB)
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WithMontoTotalMoneda
func(float64)
required
Total amount in the specified currency
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WithMontoGiftCard
func(float64)
Gift card amount applied (optional)
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WithDescuentoAdicional
func(float64)
Additional discount amount (optional)

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Additional Fields

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WithLeyenda
func(string)
required
Legal legend text (e.g., “Ley N° 453: El proveedor deberá suministrar el servicio…”)
​
WithUsuario
func(string)
required
Username of the person issuing the invoice
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WithCodigoExcepcion
func(int64)
Exception code for offline invoicing (optional)
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WithCafc
func(string)
CAFC code for offline contingency mode (optional)

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Detalle Builder Methods

Complete reference for all DetalleBuilder methods:
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WithActividadEconomica
func(string)
required
Economic activity code associated with the product/service
​
WithCodigoProductoSin
func(string)
required
SIN product code from SIAT catalogs
​
WithCodigoProducto
func(string)
required
Internal product code in your system
​
WithDescripcion
func(string)
required
Product or service description
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WithCantidad
func(float64)
required
Quantity sold
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WithUnidadMedida
func(int)
required
Unit of measure code from SIAT catalogs:
  • 57 = Unidad
  • 58 = Kilogramo
  • 59 = Metro
  • 62 = Servicio
  • (see SIAT catalogs for complete list)
​
WithPrecioUnitario
func(float64)
required
Unit price of the product/service
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WithSubTotal
func(float64)
required
Line item subtotal (quantity × unit price - discount)
​
WithMontoDescuento
func(float64)
Discount amount applied to this line item (optional)
​
WithNumeroSerie
func(string)
Serial number for serialized products (optional)
​
WithNumeroImei
func(string)
IMEI number for mobile devices (optional)

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Complete Example

Here’s a complete example building an invoice with multiple line items: 
package main

import (
    "encoding/xml"
    "fmt"
    "log"
    "time"

    "github.com/ron86i/go-siat/pkg/models"
)

func main() {
    // Generate CUF
    nit := int64(123456789)
    fechaEmision := time.Now()
    cuf, err := models.CompraVenta.GenerarCUF(
        nit, fechaEmision, 0, 1, 1, 1, 1, 1, 0, "XYZ789",
    )
    if err != nil {
        log.Fatal(err)
    }

    // Build header
    cabecera := models.CompraVenta.NewCabecera().
        WithNitEmisor(nit).
        WithRazonSocialEmisor("ACME Corporation S.A.").
        WithMunicipio("La Paz").
        WithDireccion("Av. 16 de Julio #1234").
        WithTelefono("+591 2 1234567").
        WithNumeroFactura(1001).
        WithCuf(cuf).
        WithCufd("CUFD123456789").
        WithCodigoSucursal(0).
        WithCodigoPuntoVenta(0).
        WithFechaEmision(fechaEmision.Format("2006-01-02T15:04:05.000")).
        WithNombreRazonSocial("Juan Pérez").
        WithCodigoTipoDocumentoIdentidad(1).
        WithNumeroDocumento("12345678").
        WithComplemento("1A").
        WithCodigoCliente("CUST-001").
        WithCodigoMetodoPago(1).
        WithMontoTotal(250.0).
        WithMontoTotalSujetoIva(250.0).
        WithCodigoMoneda(1).
        WithTipoCambio(1.0).
        WithMontoTotalMoneda(250.0).
        WithLeyenda("Ley N° 453: El proveedor deberá suministrar el servicio...").
        WithUsuario("admin").
        WithCodigoDocumentoSector(1).
        Build()

    // Build line items
    detalle1 := models.CompraVenta.NewDetalle().
        WithActividadEconomica("461000").
        WithCodigoProductoSin("12345").
        WithCodigoProducto("LAPTOP-001").
        WithDescripcion("Laptop Dell Inspiron 15").
        WithCantidad(1.0).
        WithUnidadMedida(57).
        WithPrecioUnitario(200.0).
        WithSubTotal(200.0).
        WithNumeroSerie("SN123456789").
        Build()

    detalle2 := models.CompraVenta.NewDetalle().
        WithActividadEconomica("461000").
        WithCodigoProductoSin("67890").
        WithCodigoProducto("MOUSE-001").
        WithDescripcion("Mouse inalámbrico").
        WithCantidad(2.0).
        WithUnidadMedida(57).
        WithPrecioUnitario(30.0).
        WithMontoDescuento(10.0).
        WithSubTotal(50.0).
        Build()

    // Assemble invoice
    factura := models.CompraVenta.NewFactura().
        WithCabecera(cabecera).
        AddDetalle(detalle1).
        AddDetalle(detalle2).
        Build()

    // Marshal to XML
    xmlData, err := xml.MarshalIndent(factura, "", "  ")
    if err != nil {
        log.Fatal(err)
    }

    fmt.Println(string(xmlData))
}

​
Working with Optional Fields

Some fields use the Nilable[T] type internally to support SIAT’s requirement for explicit nil values. The builders handle this automatically: 
// Optional string field
cabecera := models.CompraVenta.NewCabecera().
    WithTelefono("+591 2 1234567"). // Sets value
    // ... other fields
    Build()

// Optional numeric field
detalle := models.CompraVenta.NewDetalle().
    WithMontoDescuento(15.5). // Sets value
    // ... other fields
    Build()

// Omitting optional fields is fine - they will be nil in the XML
detalle := models.CompraVenta.NewDetalle().
    // No WithMontoDescuento() call
    // ... other fields
    Build()

​
XML Output

The built invoice marshals to XML compatible with SIAT’s XSD schema: 
<facturaElectronicaCompraVenta 
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:noNamespaceSchemaLocation="facturaElectronicaCompraVenta.xsd">
  <cabecera>
    <nitEmisor>123456789</nitEmisor>
    <razonSocialEmisor>Mi Empresa S.A.</razonSocialEmisor>
    <municipio>La Paz</municipio>
    <telefono>+591 2 1234567</telefono>
    <!-- ... more fields ... -->
  </cabecera>
  <detalle>
    <actividadEconomica>461000</actividadEconomica>
    <codigoProductoSin>12345</codigoProductoSin>
    <!-- ... more fields ... -->
  </detalle>
</facturaElectronicaCompraVenta>

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Next Steps

After building your invoice:
  1. Marshal to XML: Use xml.Marshal(factura)
  2. Sign: Use models.CompraVenta.SignXML()
  3. Compress: Use gzip compression
  4. Hash: Calculate SHA256 hash
  5. Submit: Use RecepcionFactura service method
See the RecepcionFactura page for the complete submission workflow.

RecepcionFactura

Submit invoices to SIAT

Overview

CompraVenta service overview

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