frankvicky commented on code in PR #21080:
URL: https://github.com/apache/kafka/pull/21080#discussion_r3628846348
##########
clients/src/main/java/org/apache/kafka/clients/NetworkClient.java:
##########
@@ -1207,6 +1296,155 @@ private boolean isTelemetryApi(ApiKeys apiKey) {
return apiKey == ApiKeys.GET_TELEMETRY_SUBSCRIPTIONS || apiKey ==
ApiKeys.PUSH_TELEMETRY;
}
+ public static class BootstrapConfiguration {
+ public static final BootstrapConfiguration DISABLED =
+ new BootstrapConfiguration(List.of(), null, 0, 0);
+
+ public final List<String> bootstrapServers;
+ public final ClientDnsLookup clientDnsLookup;
+ public final long bootstrapResolveTimeoutMs;
+ public final long retryBackoffMs;
+
+ private BootstrapConfiguration(final List<String> bootstrapServers,
+ final ClientDnsLookup clientDnsLookup,
+ final long bootstrapResolveTimeoutMs,
+ final long retryBackoffMs) {
+ this.bootstrapServers = bootstrapServers;
+ this.clientDnsLookup = clientDnsLookup;
+ this.bootstrapResolveTimeoutMs = bootstrapResolveTimeoutMs;
+ this.retryBackoffMs = retryBackoffMs;
+ }
+
+ public static BootstrapConfiguration enabled(final List<String>
bootstrapServers,
+ final ClientDnsLookup
clientDnsLookup,
+ final long
bootstrapResolveTimeoutMs,
+ final long
retryBackoffMs) {
+ for (String url : bootstrapServers) {
+ if (Utils.getHost(url) == null || Utils.getPort(url) == null)
+ throw new ConfigException("Invalid url in " +
CommonClientConfigs.BOOTSTRAP_SERVERS_CONFIG + ": " + url);
+ }
+ return new BootstrapConfiguration(bootstrapServers,
clientDnsLookup, bootstrapResolveTimeoutMs, retryBackoffMs);
+ }
+ }
+
+ /**
+ * Attempts to resolve bootstrap server addresses via DNS and create an
initial bootstrap cluster.
+ * This method is called from {@link #poll(long, long)} and uses a truly
asynchronous approach
+ * to avoid blocking on DNS resolution.
+ *
+ * <p>DNS resolution is performed on a separate thread via {@link
CompletableFuture}. This ensures
+ * the event loop remains responsive even if DNS lookups block or take a
long time. The bootstrap
+ * timeout can interrupt a pending DNS resolution, unlike synchronous
approaches.
+ *
+ * @param currentTimeMs The current time in milliseconds
+ * @throws BootstrapResolutionException if the bootstrap timeout expires
before DNS resolution succeeds
+ */
+ void ensureBootstrapped(final long currentTimeMs) {
+ if (bootstrapConfiguration == BootstrapConfiguration.DISABLED ||
metadataUpdater.isBootstrapped())
+ return;
+
+ if (bootstrapException != null)
+ return;
+
+ if (Thread.interrupted()) {
+ cancelBootstrapResolution();
+ throw new InterruptException(new InterruptedException());
+ }
+
+ // Start the timer on the first poll so its budget represents "time we
spend on
+ // bootstrap since polling began" — the caller may have created the
client well before
+ // its first API call, and we don't want that idle gap to eat into the
budget.
+ if (bootstrapTimer == null)
+ bootstrapTimer =
time.timer(bootstrapConfiguration.bootstrapResolveTimeoutMs);
+
+ // Check if a pending resolution completed before checking the
timeout, so that a
+ // result arriving at the same time as the deadline is not incorrectly
rejected.
+ if (maybeProcessBootstrapResolutionResult(currentTimeMs))
Review Comment:
`checkBootstrapTimeout` doesn't actually throw — it just records the failure
on the metadata, callers surface it later via `maybeThrowFatalException`. And
on the very first poll, the timer isn't expired yet:
1. `bootstrapTimer = time.timer(1)` → `startMs = time.milliseconds() = T`,
deadline = T+1
2. `maybeProcessBootstrapResolutionResult(currentTimeMs)` — if the eager
pending future already completed (fast DNS), we bootstrap and early-return
3. Otherwise `bootstrapTimer.update(currentTimeMs)` keeps cached time at T
(Timer.update uses max)
4. `checkBootstrapTimeout` → `T >= T+1` → false, nothing recorded
So the first poll always gets a shot: either the eager resolution has
finished (bootstrap succeeds), or we exit without recording a failure. The
timer can only fire from the second poll onward, once ≥1ms of wall-clock has
elapsed. With `bootstrap.resolve.timeout.ms` now enforced to be `atLeast(1L)`,
this gives the "at least one attempt" guarantee.
Also cleaned up a stale comment that still referenced
`bootstrap.resolve.timeout.ms=0`.
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