paypal

paypal is a Go package that allows you to access PayPal APIs, with optional Google AppEngine support, using the "PayPal NVP" format.

Included is a method for using the Digital Goods for Express Checkout payment option.

This fork lets you choose to use AppEngine's urlfetch package to create the HTTP Client

Quick Start: Setting Up a PayPal Charge (Redirect)

####### Standard Go Usage

import (
  "fmt"
  "paypal"
)

func paypalExpressCheckoutHandler(w http.ResponseWriter, r *http.Request) {
  // An example to setup paypal express checkout for digital goods
  currencyCode := "USD"
  isSandbox    := true
  returnURL    := "http://example.com/returnURL"
  cancelURL    := "http://example.com/cancelURL"
  
  // Create the paypal Client with default http client
  client := paypal.NewDefaultClient("Your_Username", "Your_Password", "Your_Signature", isSandbox)
  
  // Make a array of your digital-goods
  testGoods := []paypal.PayPalDigitalGood{paypal.PayPalDigitalGood{
    Name: "Test Good", 
    Amount: 200.000,
    Quantity: 5,
  }}
  
  // Sum amounts and get the token!
  response, err := client.SetExpressCheckoutDigitalGoods(paypal.SumPayPalDigitalGoodAmounts(&testGoods), 
    currencyCode, 
    returnURL, 
    cancelURL, 
    testGoods,
  )
  
  if err != nil {
    // ... gracefully handle error
  } else { // redirect to paypal
    http.Redirect(w, r, response.CheckoutUrl(), 301)
  }
}

####### App Engine Usage

import (
	"fmt"
	"paypal"
	"appengine"
	"appengine/urlfetch"
)

func paypalExpressCheckoutHandler(w http.ResponseWriter, r *http.Request) {
	// An example to setup paypal express checkout for digital goods
	currencyCode := "USD"
	isSandbox    := true
	returnURL    := "http://example.com/returnURL"
	cancelURL    := "http://example.com/cancelURL"
	
	// Create the paypal Client with urlfetch
	client := paypal.NewClient("Your_Username", "Your_Password", "Your_Signature", isSandbox, urlfetch.Client(appengine.NewContext(r)))

  // Make a array of your digital-goods
  testGoods := []paypal.PayPalDigitalGood{paypal.PayPalDigitalGood{
    Name: "Test Good", 
    Amount: 200.000,
    Quantity: 5,
  }}
  
  // Sum amounts and get the token!
  response, err := client.SetExpressCheckoutDigitalGoods(paypal.SumPayPalDigitalGoodAmounts(&testGoods), 
    currencyCode, 
    returnURL, 
    cancelURL, 
    testGoods,
  )
  
  if err != nil {
  // ... gracefully handle error
  } else { // redirect to paypal
    http.Redirect(w, r, response.CheckoutUrl(), 301)
  }
}

Quick Start: Completing a PayPal Charge

According to their documentation (see bottom of page), you'll have to call their DoExpressCheckoutPayment api to successfully charge a transaction.

In the Return URL, PayPal will append a token and PayerId to your return URL as parameters, like this: token=XX-XXXXXXXXXXXXXXXXXX&PayerID=XXXXXXXXXXXXX.

Your controller for the Return URL typically will call the DoExpressCheckoutSale (or DoExpressCheckoutPayment for more control), as follows:

client := paypal.NewDefaultClient("Your_Username", "Your_Password", "Your_Signature", isSandbox)
response, err := client.DoExpressCheckoutSale(r.FormValue("token"), r.FormValue("PayerID"), "USD", AMOUNT_OF_SALE)

if err != nil { // handle error in charging
  http.Redirect(w, r, MY_CHARGE_ERROR_URL, 301)
} else { // success!
  // ... handle successful charge
  http.Redirect(w, r, fmt.Sprintf("%s?receipt-id=%s", MY_RECEIPT_URL, response.Values["PAYMENTREQUEST_0_TRANSACTIONID"][0]), 301)
}

Running Tests

There's a test suite included. To run it, simply run:

go test paypal_test.go

You'll have to have set the following environment variables to run the tests:

export PAYPAL_TEST_USERNAME=XXX
export PAYPAL_TEST_PASSWORD=XXX
export PAYPAL_TEST_SIGNATURE=XXX

Tests currently run in sandbox.

PayPal Documentation

PayPal documentation is scattered at best. Here's the best link I've found that describes it: How to Create One-Time Payments Using Express Checkout