Use fallback API hosts when receiving server down response #4970

ajpallares · 2025-04-08T16:58:50Z

Checklist

If applicable, unit tests
If applicable, create follow-up issues for purchases-android and hybrids

Description

This PR implements a retry mechanism using fallback URL hosts for supported requests that fail with a server down error

Notes

Only some requests support a fallback API host. Currently only getCustomerInfo and getProductEntitlementMapping support it.
HTTPRequestPaths serverHostURLs is now an array containing the list of hosts, in order of preference, to use for supported requests.
When a request's response is a server error (5XX), the same request is immediately retried with the next host of the array.
The logic is implemented per-request: that is, if a request fails with a server-down error for host 1 and then falls back and succeeds for host 2, then all future requests will use again host 1 initially. No state is held between different requests.
No fallback retries happen when using a proxy URL

Android PR counterpart --> RevenueCat/purchases-android#2368

Copilot

Copilot reviewed 9 out of 9 changed files in this pull request and generated no comments.

Comments suppressed due to low confidence (2)

Tests/BackendIntegrationTests/StoreKitIntegrationTests.swift:991

This line still references 'serverHostURL' even though the API now uses 'serverHostURLs'; update it to 'HTTPRequest.Path.serverHostURLs.first?.host' for consistency.

let host = try XCTUnwrap(HTTPRequest.Path.serverHostURL.first?.host)

Tests/BackendIntegrationTests/StoreKitIntegrationTests.swift:1012

This line should also be updated to use 'serverHostURLs' instead of 'serverHostURL' to ensure consistency with the new fallback API host implementation.

let host = try XCTUnwrap(HTTPRequest.Path.serverHostURL.first?.host)

ajpallares · 2025-04-10T13:11:16Z

Sources/Networking/HTTPClient/HTTPClient.swift

+                retryScheduled = self.retryRequestWithNextHostIfNeeded(request: request,
+                                                                       httpURLResponse: httpURLResponse)
+                if !retryScheduled {
+                    retryScheduled = self.retryRequestIfNeeded(request: request,
+                                                               httpURLResponse: httpURLResponse)
+                }


These lines are the actual changes in this method. The other changes in this method are to accommodate the linter (function_body_length).

ajpallares · 2025-04-10T13:11:43Z

Sources/Diagnostics/Networking/DiagnosticsHTTPRequestPath.swift

@@ -16,7 +16,7 @@ import Foundation
 extension HTTPRequest.DiagnosticsPath: HTTPRequestPath {

    // swiftlint:disable:next force_unwrapping
-    static let serverHostURL = URL(string: "https://api-diagnostics.revenuecat.com")!
+    static let serverHostURLs = [URL(string: "https://api-diagnostics.revenuecat.com")!]


TODO: add final hosts list

ajpallares · 2025-04-10T13:11:56Z

Sources/Networking/HTTPClient/HTTPRequestPath.swift

+    static let serverHostURLs = [
+        "https://api.revenuecat.com",
+        "https://api2.revenuecat.com", // TODO: Add real values
+        "https://api3.revenuecat.com"


TODO: add final hosts list

ajpallares · 2025-04-10T13:12:02Z

Sources/Paywalls/Events/Networking/PaywallHTTPRequestPath.swift

@@ -16,7 +16,7 @@ import Foundation
 extension HTTPRequest.PaywallPath: HTTPRequestPath {

    // swiftlint:disable:next force_unwrapping
-    static let serverHostURL = URL(string: "https://api-paywalls.revenuecat.com")!
+    static let serverHostURLs = [URL(string: "https://api-paywalls.revenuecat.com")!]


TODO: add final hosts list

Copilot

Copilot reviewed 8 out of 8 changed files in this pull request and generated no comments.

Comments suppressed due to low confidence (2)

Sources/Networking/HTTPClient/HTTPClient.swift:296

[nitpick] Consider adding a clarifying comment in the requestWithNextFallbackPath() method to indicate that the safe subscript on fallbackPaths intentionally returns nil when the fallback index is out of bounds.

func requestWithNextFallbackPath() -> Self? {

Sources/Networking/HTTPClient/HTTPClient.swift:288

[nitpick] The retriedRequest() method preserves the fallbackPathIndex when creating a retried request. Adding a comment to clarify this intentional behavior would improve code readability.

func retriedRequest() -> Self {

tonidero

LGTM!

Sources/Networking/HTTPClient/HTTPRequestPath.swift

tonidero · 2025-04-14T06:44:15Z

Sources/Networking/HTTPClient/HTTPClient.swift

+            path: nextRequest.path
+        ))
+        self.state.modify {
+            $0.queuedRequests.insert(nextRequest, at: 0)


Hmm nothing to do for this PR since I believe this could actually happen already, but I wonder if we should dedupe any queued requests here... In android we do something like that, and just "hook" the callbacks to the existing queued/in progress request if it exists.

tonidero · 2025-04-14T06:47:09Z

Sources/Networking/HTTPClient/HTTPClient.swift

+    ///   - request: The original `HTTPClient.Request` that may need to be retried.
+    ///   - httpURLResponse: An optional `HTTPURLResponse` that contains the status code of the response.
+    /// - Returns: A Boolean value indicating whether the request was retried.
+    internal func retryRequestWithNextFallbackPathIfNeeded(


Again, nothing to do in this PR, but I was thinking it would be great to have a way to test this more easily. One thing that came to mind would be to add an option to our test proxy to block only these endpoints in the main host...

Oh I like that! In fact I'm trying to add these fallback endpoints to our backend tests and I'm really struggling so far 😅

JayShortway

Looks good! Just have some general questions about naming consistency.

Sources/Networking/HTTPClient/HTTPClient.swift

JayShortway · 2025-04-14T10:35:51Z

Sources/Networking/HTTPClient/HTTPClient.swift

+        private func getCurrentPath() -> HTTPRequestPath? {
+            if let fallbackPathIndex = self.fallbackPathIndex {
+                return self.httpRequest.path.fallbackPaths[safe: fallbackPathIndex]
+            } else {
+                return self.httpRequest.path
+            }
+        }


So only the path changes in a fallback scenario? I'm a bit confused as this PR title mentions hosts (and the Diagnostics PR does too), but I don't see hosts being changed. Maybe I'm misunderstanding something.

Sorry about that. Originally, the host would only change, but we realized that the fallback backend had different paths. In the end, after talking with COIN, they've added a mapping in the fallback backend which means that the original premise was correct: only the host will change.
I'll put this back as a draft until I've made the changes back. Sorry again!

No worries at all! Thanks for explaining 😄

…equests support a fallback host For those requests that support a fallback host, the path, headers and response structure remain the same

emerge-tools · 2025-04-17T10:29:18Z

📸 Snapshot Test

192 unchanged

Name	Added	Removed	Modified	Renamed	Unchanged	Errored	Approval
RevenueCat com.revenuecat.PaywallsTester	0	0	0	0	192	0	N/A

🛸 Powered by Emerge Tools

### Checklist - [x] If applicable, unit tests - [ ] If applicable, create follow-up issues for `purchases-ios` and hybrids ### Description This PR implements a retry mechanism using fallback URL hosts for supported requests that fail with a server down error ### Notes * Only some requests support a fallback API host. Currently only getCustomerInfo and getProductEntitlementMapping support it. * `AppConfig` now has a `fallbackBaseURLs` containing the list of hosts, in order of preference, to use for supported requests. * When a request's response is a server error (5XX), the same request is immediately retried with the next host of the array. * The logic is implemented per-request: that is, if a request fails with a server-down error for host 1 and then falls back and succeeds for host 2, then all future requests will use again host 1 initially. No state is held between different requests. * No fallback retries happen when using a proxy URL iOS PR counterpart --> RevenueCat/purchases-ios#4970

feat: implement fallback host in all URL requests

9577ba5

ajpallares added the pr:other label Apr 8, 2025

ajpallares added 6 commits April 9, 2025 19:21

cleanup fallback host API implementation

85267dc

Adapt existing tests to changes in HTTPRequestPath

720b3cd

fix implementation

b7ae271

add unit tests for fallback API host

f51040c

add extra unit test

23420f1

Merge branch 'main' into fallback-api-host

e149e07

ajpallares requested a review from Copilot April 10, 2025 08:30

Copilot AI reviewed Apr 10, 2025

View reviewed changes

ajpallares added 2 commits April 10, 2025 10:42

fix tests

be78693

fix lint

5146304

ajpallares commented Apr 10, 2025

View reviewed changes

ajpallares requested a review from a team April 10, 2025 13:13

ajpallares and others added 3 commits April 11, 2025 13:51

change the logic from fallback hosts to fallback paths

a18a382

fix test

1c365cd

Merge branch 'main' into fallback-api-host

88b9c03

ajpallares requested a review from Copilot April 11, 2025 11:55

Copilot AI reviewed Apr 11, 2025

View reviewed changes

ajpallares marked this pull request as ready for review April 11, 2025 12:32

fix fallback endpoint for get product entitlement mapping

0c9e623

tonidero approved these changes Apr 14, 2025

View reviewed changes

fix backend integration tests not building after changes

c2facde

JayShortway approved these changes Apr 14, 2025

View reviewed changes

ajpallares marked this pull request as draft April 14, 2025 11:59

ajpallares added 2 commits April 14, 2025 18:45

rewrite fallback host functionality knowing that only some specific r…

a9275b6

…equests support a fallback host For those requests that support a fallback host, the path, headers and response structure remain the same

Merge branch 'main' into fallback-api-host

89e8d79

ajpallares added 2 commits April 15, 2025 09:31

Merge branch 'main' into fallback-api-host

3c5a9d3

Merge branch 'main' into fallback-api-host

854a9f6

fix text name

ba66359

ajpallares mentioned this pull request Apr 21, 2025

Use fallback API hosts when receiving server down response RevenueCat/purchases-android#2368

Merged

2 tasks

Merge branch 'main' into fallback-api-host

cafbf9c

ajpallares marked this pull request as ready for review April 25, 2025 11:08

Merge branch 'main' into fallback-api-host

cd0dc1c

ajpallares requested review from a team, tonidero and JayShortway April 25, 2025 11:09

ajpallares enabled auto-merge April 25, 2025 11:54

ajpallares added this pull request to the merge queue Apr 25, 2025

Merged via the queue into main with commit e991e07 Apr 25, 2025
12 checks passed

ajpallares deleted the fallback-api-host branch April 25, 2025 12:15

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Use fallback API hosts when receiving server down response #4970

Use fallback API hosts when receiving server down response #4970

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Use fallback API hosts when receiving server down response #4970

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ajpallares commented Apr 8, 2025 • edited Loading

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emerge-tools bot commented Apr 17, 2025 • edited Loading

📸 Snapshot Test

192 unchanged

ajpallares commented Apr 8, 2025 •

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