Summary

This PR adds live log streaming via Log Cache to cf-java-client – the Java equivalent of
cf tail --follow and the Go [logcache.Walk()][go-walk] API.

Previously, the only Log Cache read path was logsRecent (a single snapshot GET /api/v1/read).
There was no way to continuously stream new log envelopes without polling manually.
This change introduces a first-class logsTail API across all three relevant modules
(cloudfoundry-client, cloudfoundry-client-reactor, cloudfoundry-operations).

Motivation

Cloud Foundry dropped the legacy Loggregator Doppler streaming endpoint
(DopplerClient.stream()) in Loggregator ≥ 107.0 (CFD ≥ 24.3 / TAS ≥ 4.0).
The Go CF CLI replaced it with a polling loop over the Log Cache
[/api/v1/read][log-cache-read] endpoint – that is what cf tail --follow does today.
This PR brings the same capability to Java consumers.

Changes

/**
 * Continuously polls Log Cache /api/v1/read and streams new Envelopes as they appear.
 * Equivalent to the Go logcache.Walk() API and `cf tail --follow`.
 * The Flux never completes on its own – cancel the subscription to stop streaming.
 */
Flux<Envelope> logsTail(TailLogsRequest request);

Flux.defer(buildReadRequest)
    .onErrorReturn(ReadResponse.empty())
    .flatMapMany(sortAndAdvanceCursor)
    .repeatWhen(count == 0 → Mono.delay(pollInterval), else → immediate)

@Override
public Flux<org.cloudfoundry.logcache.v1.Envelope> logsTail(TailLogsRequest request) {
    return this.logCacheClient
            .flatMapMany(client -> client.logsTail(request))
            .transform(OperationsLogging.log("Tail Application Logs"))
            .checkpoint();
}

/**
 * Continuously streams application log envelopes from Log Cache.
 * The returned Flux is infinite – cancel it to stop streaming.
 * Java equivalent of `cf tail --follow`.
 */
Flux<Envelope> logsTail(TailLogsRequest request);

Tests

Four unit tests cover logsTail in DefaultApplicationsTest:

Tests run: 120, Failures: 0, Errors: 0, Skipped: 0

Usage Example

// Stream live logs for an application
TailLogsRequest request = TailLogsRequest.builder()
        .sourceId(applicationGuid)
        .envelopeTypes(List.of(EnvelopeType.LOG))   // optional: logs only
        .pollInterval(Duration.ofMillis(250))        // optional: default 250 ms
        .build();

logCacheClient.logsTail(request)
        .filter(e -> e.getLog() != null)
        .map(e -> e.getLog().getPayloadAsText())
        .subscribe(System.out::println);             // cancel() to stop

Or via the high-level Operations API:

cloudFoundryOperations.applications()
        .logsTail(TailLogsRequest.builder().sourceId(appGuid).build())
        .filter(e -> e.getLog() != null)
        .map(e -> e.getLog().getPayloadAsText())
        .subscribe(System.out::println);

Relation to existing API

Checklist

• New _TailLogsRequest Immutables value object
• LogCacheClient.logsTail() interface method
• ReactorLogCacheEndpoints.logsTail() — fully non-blocking Reactor implementation
• _ReactorLogCacheClient.logsTail() — delegate override
• Applications.logsTail() — high-level Operations API method
• DefaultApplications.logsTail() — implementation
• Unit test logsTailLogCache in DefaultApplicationsTest
• All 117 DefaultApplicationsTest tests pass
• Execute the integration tests

Notes

• go-walk
• log-cache-read
• Work was done with the assistance of Claude (claude-sonnet-4-6, Anthropic) via GitHub Copilot.