feat: Add multi-provider support #1500

suvaidkhan · 2025-07-01T07:43:28Z

This PR

Added Multiprovider class
Added Strategies
Added a new dependency for JSON

Related Issues

Resolves #1486

Follow-up Tasks

Multiprovider should be removed from the contrib codebase

chrfwow

Looks good so far!
I'm not sure if we want to add a json dependecy (which might also produce the License Compliance error) "just" so that we can build up the metadata name string.

chrfwow · 2025-07-01T08:28:09Z

src/main/java/dev/openfeature/sdk/multiprovider/MultiProvider.java

+    private String metadataName;
+
+    /**
+     * Constructs a MultiProvider with the given list of FeatureProviders, using a default strategy.


I think the comment should say what the default strategy is

chrfwow · 2025-07-01T08:33:01Z

src/main/java/dev/openfeature/sdk/multiprovider/MultiProvider.java

+        json.put("name", NAME);
+        JSONObject providersMetadata = new JSONObject();
+        json.put("originalMetadata", providersMetadata);
+        ExecutorService initPool = Executors.newFixedThreadPool(INIT_THREADS_COUNT);


Suggested change

ExecutorService initPool = Executors.newFixedThreadPool(INIT_THREADS_COUNT);

ExecutorService initPool = Executors.newFixedThreadPool(Math.min(INIT_THREADS_COUNT, providers.size()));

chrfwow · 2025-07-01T08:34:12Z

src/main/java/dev/openfeature/sdk/multiprovider/MultiProvider.java

+                throw new GeneralError("init failed");
+            }
+        }
+        metadataName = json.toString();


If the executer service is unused from this point onwards, we should shut it down

chrfwow · 2025-07-01T08:40:02Z

src/test/java/dev/openfeature/sdk/multiProvider/MultiProviderTest.java

+        assertThrows(FlagNotFoundError.class, () -> finalMultiProvider1.getStringEvaluation("non-existing", "", null));
+
+        multiProvider.shutdown();
+        multiProvider = new MultiProvider(providers, new FirstSuccessfulStrategy());


There should probably be a test file with tests for each strategy. If you want to reduce code duplication by the flag setup, make those test classes extend some common test setup class

have created a BaseStrategyTest for the setup which is extended by the separate test classes for each strategy

codecov · 2025-07-01T08:47:58Z

Codecov Report

❌ Patch coverage is 96.38554% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 93.45%. Comparing base (e67f598) to head (84bc45a).
⚠️ Report is 85 commits behind head on main.

Files with missing lines	Patch %	Lines
...v/openfeature/sdk/multiprovider/MultiProvider.java	94.64%	2 Missing and 1 partial ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #1500      +/-   ##
============================================
+ Coverage     92.97%   93.45%   +0.47%     
- Complexity      488      519      +31     
============================================
  Files            46       50       +4     
  Lines          1182     1253      +71     
  Branches        103      112       +9     
============================================
+ Hits           1099     1171      +72     
+ Misses           53       51       -2     
- Partials         30       31       +1

Flag	Coverage Δ
unittests	`93.45% <96.38%> (+0.47%)`	⬆️

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suvaidkhan · 2025-07-03T08:19:08Z

Looks good so far! I'm not sure if we want to add a json dependecy (which might also produce the License Compliance error) "just" so that we can build up the metadata name string.

Should I construct the json using Strings?

chrfwow · 2025-07-03T11:04:23Z

Maybe it would be worth it.
@toddbaert what do you think?

suvaidkhan · 2025-07-08T18:40:54Z

@chrfwow @toddbaert any updates on this?

aepfli

Thank you, great effort. I am looking forward to having the multiprovider migrated. For me, the added dependency is currently a show stopper, because I think we can handle that with proper and simple data classes, even with better metadata support overall (not losing information from the sub providers). I added simple but untested code snippets to my review. Please let me know what you think about this approach.

src/main/java/dev/openfeature/sdk/multiprovider/MultiProvider.java

suvaidkhan · 2025-07-10T03:30:13Z

Thank you, great effort. I am looking forward to having the multiprovider migrated. For me, the added dependency is currently a show stopper, because I think we can handle that with proper and simple data classes, even with better metadata support overall (not losing information from the sub providers). I added simple but untested code snippets to my review. Please let me know what you think about this approach.

Looks good to me.
I'll add these changes and some UTs to make sure it's working correctly.

chrfwow

Looks good

src/main/java/dev/openfeature/sdk/multiprovider/MultiProvider.java

src/test/java/dev/openfeature/sdk/multiProvider/MultiProviderTest.java

suvaidkhan · 2025-07-22T06:03:55Z

Hey @aepfli @chrfwow this is ready for review

aepfli

Thank you, the basic implementation looks good to me. But i took a closer look at the two strategies. The strategies seem to be a little inconsistent in exception handling, logging and returning. I think we should normalize this a little for consistency (no need for more abstraction, but it should log the same way, it should handle all the possible exceptions the same way, etc).

src/test/java/dev/openfeature/sdk/multiProvider/MultiProviderTest.java

src/main/java/dev/openfeature/sdk/multiprovider/MultiProvider.java

src/main/java/dev/openfeature/sdk/multiprovider/FirstMatchStrategy.java

src/main/java/dev/openfeature/sdk/multiprovider/FirstSuccessfulStrategy.java

Signed-off-by: suvaidkhan <[email protected]>

… removed json dep Signed-off-by: suvaidkhan <[email protected]>

Signed-off-by: suvaidkhan <[email protected]>

sonarqubecloud · 2025-08-11T17:27:28Z

Quality Gate passed

Issues
3 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

aepfli

Sorry for the delay @suvaidkhan - i was on vacation - thank you for incoporating all the changes, i will give other maintainers the chance to also take a look for 2 more days, and else i will merge it.

Thank you this contribution is highly appreciated!

aepfli · 2025-08-26T11:14:35Z

/gemini review

gemini-code-assist

Code Review

This pull request introduces multi-provider support, a significant and valuable feature. The implementation includes different provider evaluation strategies and a MultiProvider class to manage them. The code is well-structured and includes a good set of tests. I've identified a few issues, including a critical one in the initialize method related to resource handling and edge cases, as well as some medium-severity items around error reporting and immutability. I've provided detailed suggestions to address these points. Overall, this is a great addition, and with these fixes, it will be even more robust.

gemini-code-assist · 2025-08-26T11:16:37Z

src/main/java/dev/openfeature/sdk/multiprovider/MultiProvider.java

+    public void initialize(EvaluationContext evaluationContext) throws Exception {
+        var metadataBuilder = MultiProviderMetadata.builder();
+        metadataBuilder.name(NAME);
+        HashMap<String, Metadata> providersMetadata = new HashMap<>();
+        ExecutorService executorService = Executors.newFixedThreadPool(Math.min(INIT_THREADS_COUNT, providers.size()));
+        Collection<Callable<Boolean>> tasks = new ArrayList<>(providers.size());
+        for (FeatureProvider provider : providers.values()) {
+            tasks.add(() -> {
+                provider.initialize(evaluationContext);
+                return true;
+            });
+            Metadata providerMetadata = provider.getMetadata();
+            providersMetadata.put(providerMetadata.getName(), providerMetadata);
+        }
+        metadataBuilder.originalMetadata(providersMetadata);
+        List<Future<Boolean>> results = executorService.invokeAll(tasks);
+        for (Future<Boolean> result : results) {
+            if (!result.get()) {
+                executorService.shutdown();
+                throw new GeneralError("init failed");
+            }
+        }
+        executorService.shutdown();
+        metadata = metadataBuilder.build();
+    }


The initialize method has a few critical issues:

Crash on empty provider list: If MultiProvider is created with an empty list of providers, providers.size() will be 0, and Executors.newFixedThreadPool(0) will throw an IllegalArgumentException.

Resource leak: If any provider's initialize method throws an exception, the ExecutorService is not shut down, leading to a resource leak.

Unreachable code: The if (!result.get()) block is unreachable because result.get() will either return true or throw an exception.

Mutable state: The providersMetadata map is passed to the builder without being made unmodifiable, which could lead to modification of internal state.

I suggest refactoring the method to handle these issues.

public void initialize(EvaluationContext evaluationContext) throws Exception { var metadataBuilder = MultiProviderMetadata.builder().name(NAME); HashMap<String, Metadata> providersMetadata = new HashMap<>(); if (providers.isEmpty()) { metadataBuilder.originalMetadata(providersMetadata); metadata = metadataBuilder.build(); return; } ExecutorService executorService = Executors.newFixedThreadPool(Math.min(INIT_THREADS_COUNT, providers.size())); try { Collection<Callable<Void>> tasks = new ArrayList<>(providers.size()); for (FeatureProvider provider : providers.values()) { tasks.add(() -> { provider.initialize(evaluationContext); return null; }); Metadata providerMetadata = provider.getMetadata(); providersMetadata.put(providerMetadata.getName(), providerMetadata); } // Make the metadata map unmodifiable to protect internal state. metadataBuilder.originalMetadata(Collections.unmodifiableMap(providersMetadata)); List<Future<Void>> results = executorService.invokeAll(tasks); for (Future<Void> result : results) { // This will re-throw any exception from the provider's initialize method, // wrapped in an ExecutionException. result.get(); } } finally { executorService.shutdown(); } metadata = metadataBuilder.build(); }

gemini-code-assist · 2025-08-26T11:16:37Z

src/main/java/dev/openfeature/sdk/multiprovider/FirstMatchStrategy.java

+        return ProviderEvaluation.<T>builder()
+                .errorMessage("No provider successfully responded")
+                .errorCode(ErrorCode.GENERAL)
+                .build();
+    }


When all providers return FLAG_NOT_FOUND, the strategy currently returns a GENERAL error. It would be more accurate to return a FLAG_NOT_FOUND error code to reflect that the flag was not found in any of the providers. The error message could also be more specific.

Note that this change will require updating FirstMatchStrategyTest.shouldThrowFlagNotFoundWhenAllProvidersReturnFlagNotFound and MultiProviderTest.shouldUseDefaultFirstMatchStrategy to assert for FLAG_NOT_FOUND instead of GENERAL.

Suggested change

return ProviderEvaluation.<T>builder()

.errorMessage("No provider successfully responded")

.errorCode(ErrorCode.GENERAL)

.build();

}

return ProviderEvaluation.<T>builder()

.errorMessage("Flag not found in any provider")

.errorCode(ErrorCode.FLAG_NOT_FOUND)

.build();

gemini-code-assist · 2025-08-26T11:16:37Z

src/main/java/dev/openfeature/sdk/multiprovider/MultiProviderMetadata.java

+@Data
+@Builder
+public class MultiProviderMetadata implements Metadata {
+    String name;
+    Map<String, Metadata> originalMetadata;
+
+    @Override
+    public String getName() {
+        return name;
+    }
+}


The MultiProviderMetadata class is currently mutable due to Lombok's @Data annotation, which generates setters. This could allow external code to modify the metadata of the MultiProvider, which is generally undesirable. To ensure immutability, I recommend using @Value instead of @Data. @Value creates an immutable class with private final fields and getters. The explicit getName() override also becomes unnecessary as @Value will generate it.

@lombok.Value @Builder public class MultiProviderMetadata implements Metadata { String name; Map<String, Metadata> originalMetadata; }

gemini-code-assist · 2025-08-26T11:16:37Z

src/test/java/dev/openfeature/sdk/multiProvider/MultiProviderTest.java

+import lombok.SneakyThrows;
+import org.junit.jupiter.api.Test;
+
+class MultiProviderTest extends BaseStrategyTest {


The test suite for MultiProvider is missing a test case for initialization with an empty list of providers. This is an important edge case that currently causes a crash in the submitted code. Please add a test to cover this scenario and ensure it's handled gracefully (i.e., it should not throw an exception).

Here is an example of what such a test could look like:

@Test void shouldInitializeWithEmptyProvidersList() { MultiProvider multiProvider = new MultiProvider(new ArrayList<>()); assertDoesNotThrow(() -> multiProvider.initialize(null)); assertNotNull(multiProvider.getMetadata()); assertEquals(MultiProvider.getNAME(), multiProvider.getMetadata().getName()); }

aepfli · 2025-08-26T11:21:06Z

okay @suvaidkhan - as we now have gemini support, i executed the gemini review, and i think the initialization issue seems to be critical. We do have two options here - first we add the feedback for gemini now, and wait for your implementation before merging, or second option, we are merging this, and create an issue to address the gemini feedback regarding initialization. wdyt?

suvaidkhan · 2025-08-26T22:57:52Z

okay @suvaidkhan - as we now have gemini support, i executed the gemini review, and i think the initialization issue seems to be critical. We do have two options here - first we add the feedback for gemini now, and wait for your implementation before merging, or second option, we are merging this, and create an issue to address the gemini feedback regarding initialization. wdyt?

I'm fine with both
But I think it makes more sense to fix the issue before merging

suvaidkhan requested review from a team as code owners July 1, 2025 07:43

suvaidkhan force-pushed the suvaidkhan/add-multiprovider-support branch from 8710a52 to f07dd25 Compare July 1, 2025 07:46

chrfwow requested changes Jul 1, 2025

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aepfli reviewed Jul 9, 2025

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src/main/java/dev/openfeature/sdk/multiprovider/MultiProvider.java Outdated Show resolved Hide resolved

suvaidkhan force-pushed the suvaidkhan/add-multiprovider-support branch from 97f6dc9 to 1103949 Compare July 17, 2025 00:07

chrfwow reviewed Jul 17, 2025

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src/main/java/dev/openfeature/sdk/multiprovider/MultiProvider.java Show resolved Hide resolved

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suvaidkhan requested review from aepfli and chrfwow July 18, 2025 23:24

aepfli reviewed Jul 23, 2025

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suvaidkhan force-pushed the suvaidkhan/add-multiprovider-support branch from ff27ce8 to fc8c18f Compare August 11, 2025 17:14

suvaidkhan added 4 commits August 11, 2025 12:25

MultiProvider: Added strategies, unit tests and documentation

1b3db82

Signed-off-by: suvaidkhan <[email protected]>

MultiProvider: Added MultiProviderMetadata.java, refactored tests and…

dd809d2

… removed json dep Signed-off-by: suvaidkhan <[email protected]>

Multiprovider: review comments incorporated

5e30d12

Signed-off-by: suvaidkhan <[email protected]>

Multiprovider: fixed log messages and exception handling

84bc45a

Signed-off-by: suvaidkhan <[email protected]>

suvaidkhan force-pushed the suvaidkhan/add-multiprovider-support branch from fc8c18f to 84bc45a Compare August 11, 2025 17:27

aepfli approved these changes Aug 24, 2025

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gemini-code-assist bot reviewed Aug 26, 2025

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chrfwow approved these changes Aug 26, 2025

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	ExecutorService initPool = Executors.newFixedThreadPool(INIT_THREADS_COUNT);
	ExecutorService initPool = Executors.newFixedThreadPool(Math.min(INIT_THREADS_COUNT, providers.size()));

feat: Add multi-provider support #1500

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feat: Add multi-provider support #1500

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suvaidkhan commented Jul 1, 2025

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