Summary

Adds live log streaming via Log Cache — the Java equivalent of cf tail --follow.

Previously the only Log Cache read path was logsRecent, a single snapshot request. There was no way to continuously receive new log envelopes without polling manually. This change introduces a logsTail API across all three relevant modules.

Motivation

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

Changes

cloudfoundry-client — new TailLogsRequest and LogCacheClient.logsTail()

New _TailLogsRequest.java (Immutables @Value.Immutable):

New method on LogCacheClient:

/**
 * 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);

cloudfoundry-client-reactor — non-blocking polling implementation

ReactorLogCacheEndpoints.logsTail() mirrors the Go logcache.Walk() algorithm, fully non-blocking:

1. An AtomicLong cursor starts at startTime (or now − 5 s).
2. Flux.defer builds a fresh ReadRequest from the current cursor on every repetition and calls GET /api/v1/read/{sourceId}?start_time=cursor.
3. Envelopes are sorted ascending by timestamp; the cursor advances to lastTimestamp + 1; each envelope is emitted individually downstream.
4. When the batch is empty, repeatWhen inserts a Mono.delay(pollInterval) before the next poll. When envelopes arrive, the next poll starts immediately.
5. The Flux is infinite; the caller cancels the subscription to stop.

Transient network errors are logged and retried. HTTP errors (4xx/5xx) are propagated to the subscriber.

cloudfoundry-operations — Applications.logsTail()

DefaultApplications delegates to LogCacheClient:

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

Tests

Usage

TailLogsRequest request = TailLogsRequest.builder()
        .sourceId(applicationGuid)
        .envelopeTypes(List.of(EnvelopeType.LOG))
        .pollInterval(Duration.ofMillis(250))
        .build();

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

Or via the 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

• _TailLogsRequest Immutables value object
• LogCacheClient.logsTail() interface method
• ReactorLogCacheEndpoints.logsTail() — non-blocking Reactor implementation
• _ReactorLogCacheClient.logsTail() — delegate override
• Applications.logsTail() — Operations API method
• DefaultApplications.logsTail() — implementation
• Unit tests in DefaultApplicationsTest (120 passing)
• Integration tests