What causes "Could not forward client stdin." in gradle/gradle?

Check the attached exception - if the build was already aborting or finished, the warning is harmless

Could not forward client stdin.

Error message

Could not forward client stdin.

What it means

The daemon multiplexes the client's stdin over the connection as ForwardInput/CloseInput/UserResponse commands and dispatches them to the build's StdinHandler inside a command queue. If handler.onInput(...), handler.onEndOfInput(), or handler.onUserResponse(...) throws, the exception is caught, this warning is logged, and the queue moves on (returns true, command consumed).

Source

Thrown at platforms/core-runtime/launcher/src/main/java/org/gradle/launcher/daemon/server/DefaultDaemonConnection.java:308

    private static class StdinQueue extends CommandQueue<InputMessage, StdinHandler> {

        private StdinQueue(ExecutorFactory executorFactory) {
            super(executorFactory, "Stdin handler");
        }

        @Override
        protected boolean doHandleCommand(final StdinHandler handler, InputMessage command) {
            try {
                if (command instanceof CloseInput) {
                    handler.onEndOfInput();
                    return true;
                } else if (command instanceof UserResponse) {
                    handler.onUserResponse((UserResponse) command);
                } else {
                    handler.onInput((ForwardInput) command);
                }
            } catch (Exception e) {
                LOGGER.warn("Could not forward client stdin.", e);
                return true;
            }
            return false;
        }

        @Override
        protected void doHandleDisconnect() {
            queue.clear();
            queue.add(new CloseInput());
        }
    }

    private static class CancelQueue extends CommandQueue<Cancel, Runnable> {

        private CancelQueue(ExecutorFactory executorFactory) {
            super(executorFactory, "Cancel handler");
        }

View on GitHub (pinned to 534f27719b)

Solutions

Check the attached exception - if the build was already aborting or finished, the warning is harmless
Do not feed stdin to non-interactive/daemon builds; use -q, --console=plain, or close the pipe
For prompts, prefer passing answers via properties or a file instead of live stdin through the daemon
Re-run the build - stdin forwarding state is per-connection and resets

Example fix

# before: CI pipes stdin into a daemon build that never reads it
cat answers.txt | ./gradlew ask

# after: pass answers as a property, keep stdin closed
./gradlew ask -PanswersFile=answers.txt < /dev/null

Defensive patterns

Strategy: validation

Validate before calling

// only forward stdin for builds that actually read it
boolean buildReadsStdin = Boolean.getBoolean("mybuild.interactive");
if (!buildReadsStdin) System.in.close(); // daemon gets no stdin to mis-forward

Prevention

Redirect stdin from /dev/null for non-interactive daemon builds ('< /dev/null')
Pass interactive answers via -P properties or files instead of piping them through the daemon
Remember stdin handling is per-client-connection; a fresh build resets it

When it happens

Trigger: A stdin command arrives but the build-side stdin handler fails - build input stream already closed, console/encoding errors, or an interactive build that finished while further stdin commands were still queued.

Common situations: Piping stdin into a Gradle build that prompts interactively while running in the daemon; CI jobs with closed stdin; pressing Ctrl+C during an interactive prompt; tools streaming input to 'gradle' after the build completed.

Related errors

AI-assisted analysis of gradle/gradle@534f27719b (2026-08-22). Data as JSON: /api/errors/5841f259b50ceba6. Report an issue: GitHub.