add a README notice on how to work with promo codes (anjlab#220)

* add a README notice on how to work with promo codes

* add UPGRADING.md

README.md

@@ -196,6 +196,18 @@ Call `bp.getSubscriptionTransactionDetails(...)` and check the `purchaseInfo.pur
 It will be set to `False` once subscription gets cancelled.
 Also notice, that you will need to call periodically `bp.loadOwnedPurchasesFromGoogle()` method in order to update subscription information
 
+## Promo Codes Support
+
+You can use promo codes along with this library, they are supported with one extra notice. According to [this issue](https://github.com/googlesamples/android-play-billing/issues/7)
+there is currently a bug in Google Play Services, and it does not respect _Developer Payload_ token made by this library, causing a security validation fault (`BILLING_ERROR_INVALID_DEVELOPER_PAYLOAD` error code).
+While Google engineers are working on fixing this (lets hope so, you can also leave a feedback on this issue to make them work faster).
+
+Still, there are couple of workarounds you can use:
+
+1. Handle `BILLING_ERROR_INVALID_DEVELOPER_PAYLOAD` error code in your `onBillingError` implementation. You can check out [#156](https://github.com/anjlab/android-inapp-billing-v3/issues/156) for a suggested workaround. This does not look nice, but it works.
+2. Avoid using promo codes in a purchase dialog, prefer entering these codes in Google Play's App _Redeem promo code_ menu.
+One way to do this is to distribute your promo codes in form of a redeem link (`https://play.google.com/redeem?code=YOURPROMOCODE`) instead of just a `YOURPROMOCODE` values.
+You can find a sample on how to bundle it inside your app [here](https://gist.github.com/SuperThomasLab/6d44b4920dbdc8482a2467d95f66c5df).
 
 ## Protection Against Fake "Markets"
 

UPGRADING.md

@@ -0,0 +1,12 @@
+## Upgrading Android In-App Billing v3 Library
+
+### Upgrading to >= 1.0.37
+
+If you were supporting promo codes and faced troubled described in #156,
+you will need to change your workaround code:
+
+```java
+errorCode == Constants.BILLING_ERROR_OTHER_ERROR && _billingProcessor.loadOwnedPurchasesFromGoogle() && _billingProcessor.isPurchased(SKU)
+```
+
+`errorCode` needs to be changed to `Constants.BILLING_ERROR_INVALID_DEVELOPER_PAYLOAD`

library/src/main/java/com/anjlab/android/iab/v3/BillingProcessor.java

@@ -467,6 +467,24 @@ public TransactionDetails getSubscriptionTransactionDetails(String productId) {
 		return getPurchaseTransactionDetails(productId, cachedSubscriptions);
 	}
 
+	private String getDeveloperPayloadFromPurchaseData(JSONObject purchase) {
+		String value = null;
+		try
+		{
+			value = purchase.has(Constants.RESPONSE_PAYLOAD)
+					? purchase.getString(Constants.RESPONSE_PAYLOAD) : null;
+		}
+		catch (JSONException e)
+		{
+			Log.e(LOG_TAG, "Failed to extract developer payload value!");
+		}
+		return value != null ? value : "";
+	}
+
+	private boolean validateDeveloperPayload(String expectedValue, String actualValue) {
+		return expectedValue.equals(actualValue);
+	}
+
 	public boolean handleActivityResult(int requestCode, int resultCode, Intent data) {
 		if (requestCode != PURCHASE_FLOW_REQUEST_CODE)
 			return false;
@@ -483,11 +501,9 @@ public boolean handleActivityResult(int requestCode, int resultCode, Intent data
 			try {
 				JSONObject purchase = new JSONObject(purchaseData);
 				String productId = purchase.getString(Constants.RESPONSE_PRODUCT_ID);
-				String developerPayload = purchase.getString(Constants.RESPONSE_PAYLOAD);
-				if (developerPayload == null)
-					developerPayload = "";
+				String developerPayload = getDeveloperPayloadFromPurchaseData(purchase);
 				boolean purchasedSubscription = purchasePayload.startsWith(Constants.PRODUCT_TYPE_SUBSCRIPTION);
-				if (purchasePayload.equals(developerPayload)) {
+				if (validateDeveloperPayload(purchasePayload, developerPayload)) {
 					if (verifyPurchaseSignature(productId, purchaseData, dataSignature)) {
 						BillingCache cache = purchasedSubscription ? cachedSubscriptions : cachedProducts;
 						cache.put(productId, purchaseData, dataSignature);
@@ -501,7 +517,7 @@ public boolean handleActivityResult(int requestCode, int resultCode, Intent data
 				} else {
 					Log.e(LOG_TAG, String.format("Payload mismatch: %s != %s", purchasePayload, developerPayload));
 					if (eventHandler != null)
-						eventHandler.onBillingError(Constants.BILLING_ERROR_INVALID_SIGNATURE, null);
+						eventHandler.onBillingError(Constants.BILLING_ERROR_INVALID_DEVELOPER_PAYLOAD, null);
 				}
 			} catch (Exception e) {
 				Log.e(LOG_TAG, "Error in handleActivityResult", e);
@@ -539,7 +555,7 @@ private boolean isPurchaseHistoryRestored() {
 		return loadBoolean(getPreferencesBaseKey() + RESTORE_KEY, false);
 	}
 
-	public void setPurchaseHistoryRestored() {
+	private void setPurchaseHistoryRestored() {
 		saveBoolean(getPreferencesBaseKey() + RESTORE_KEY, true);
 	}
 

library/src/main/java/com/anjlab/android/iab/v3/Constants.java

@@ -57,6 +57,7 @@ public class Constants {
 	public static final int BILLING_ERROR_INVALID_SIGNATURE = 102;
 	public static final int BILLING_ERROR_LOST_CONTEXT = 103;
 	public static final int BILLING_ERROR_INVALID_MERCHANT_ID = 104;
+	public static final int BILLING_ERROR_INVALID_DEVELOPER_PAYLOAD = 105;
 	public static final int BILLING_ERROR_OTHER_ERROR = 110;
 	public static final int BILLING_ERROR_CONSUME_FAILED = 111;
 	public static final int BILLING_ERROR_SKUDETAILS_FAILED = 112;