feat: add X-LaunchDarkly-Instance-Id header (SDK-2359)#170
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Generate a v4 UUID once per SDK instance in ConfigBuilder::build and stamp it on the X-LaunchDarkly-Instance-Id header sent by the streaming data source, polling feature requester, and event processor. The header value is stable for the lifetime of the SDK instance and unique across instances, satisfying SCMP-server-connection-minutes-polling section 1.1. The instance id is plumbed through the existing DataSourceFactory, FeatureRequesterFactory (via HttpFeatureRequesterBuilder), and EventProcessorFactory build paths so streaming, polling, and event requests all carry the same identifier without per-channel plumbing. Registers the "instance-id" capability with the contract-test service so the cross-SDK harness can verify the header on each request type.
DataSourceFactory::build and EventProcessorFactory::build are public traits; adding an `instance_id` parameter is a breaking change for any external implementor. This commit reverts that and instead adds a `set_instance_id(&mut self, String)` method on each trait with a default no-op implementation, so external implementors are unaffected. LD-owned builders (StreamingDataSourceBuilder, PollingDataSourceBuilder, EventProcessorBuilder) override the setter to store the value, and use it in build() to stamp the `X-LaunchDarkly-Instance-Id` header on outbound requests. Client::build calls `.to_owned().set_instance_id(id)` on each builder before invoking build(). HttpFeatureRequesterBuilder::new also reverted to its prior signature; the instance id is now applied via a fluent with_instance_id() setter. StreamingDataSource::new and the polling feature requester now treat the instance id as Option<&str> and skip the header when absent -- consistent with the no-op default on the trait setter. cargo fmt --check / clippy --all-targets -- -D warnings / cargo test (304 unit + 12 doctests) all pass.
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Summary
Adds the
X-LaunchDarkly-Instance-Idheader to every outbound polling, streaming, and event request. Value is a v4 UUID generated once per SDK instance inConfigBuilder::buildand stable for that instance's lifetime.The UUID is stored on
Config(exposed viaConfig::instance_id()for diagnostics) and threaded into LD's own builders via a newset_instance_idsetter on theDataSourceFactoryandEventProcessorFactorytraits. The setter has a default no-op implementation, so adding it is non-breaking for external implementors of those traits — only LD's own builders (Streaming/Polling/Event) override it.`Client::build` calls `.to_owned().set_instance_id(id)` on each factory before invoking `.build()`. `HttpFeatureRequesterBuilder` likewise keeps its original `::new()` signature; the instance id is applied via a fluent `with_instance_id()` setter.
`StreamingDataSource::new` and the polling feature requester now treat the instance id as `Option<&str>` and simply skip the header when absent — consistent with the no-op default on the trait setter.
Test plan
Note
Medium Risk
Touches client construction and request-building for streaming, polling, and event delivery; mistakes could break network communication or tests, but the change is additive and guarded with optional/no-op defaults.
Overview
Adds a per-SDK-instance UUID (
X-LaunchDarkly-Instance-Id) to all outbound streaming, polling, and event HTTP requests.ConfigBuilder::buildnow generates and stores a stable v4 UUID onConfig(exposed viaConfig::instance_id()), andClient::buildinjects it into the data source and event processor via new default-no-opset_instance_idhooks onDataSourceFactoryandEventProcessorFactory(implemented by LD’s built-in builders). Contract tests register the newinstance-idcapability, and new unit tests assert the header is present and UUID-v4-shaped for streaming/polling and propagated for event POSTs.Reviewed by Cursor Bugbot for commit 3fa8c78. Bugbot is set up for automated code reviews on this repo. Configure here.