Visz11 patch 1

[visz11]

The downloads in AbstractActionInputPrefetcher#prefetchInputs reported lost inputs that are symlinks to other artifacts with the exec path of the target, which results in a crash when the target is not also an input to the action. This is fixed by always reporting the exec path of the symlink.

Fixes bazelbuild#25841

[arvi18]

/refacto-test

[refacto-test]

Refacto is reviewing this PR. Please wait for the review comments to be posted.

[refacto-test]

Code Review: Symlink Error Handling Enhancement

👍 Well Done

Improved Error Reporting

Enhanced error handling for symlinked inputs improves failure recovery and diagnostics.

Path Information Preservation

Setting exec path ensures accurate error reporting for rewinding.

📝 Additional Comments

src/main/java/com/google/devtools/build/lib/remote/AbstractActionInputPrefetcher.java (1)

Error Propagation Enhancement

Error handler doesn't log the exception before propagating. Missing logging reduces observability of cache misses affecting symlinks, making troubleshooting more difficult during production incidents.

              .onErrorResumeNext(
                  t -> {
                    if (t instanceof CacheNotFoundException cacheNotFoundException) {
                      // Only the symlink itself is guaranteed to be an input to the action, so
                      // report its path for rewinding.
                      cacheNotFoundException.setExecPath(input.getExecPath());
                      logger.atFine().withCause(cacheNotFoundException)
                          .log("Cache miss for symlinked input %s", input.getExecPath());
                      return Completable.error(cacheNotFoundException);
                    }
                    return Completable.error(t);
                  });

Standards:

• ISO-IEC-25010-Reliability-Recoverability
• SRE-Observability

[refacto-test]

Missing ExecPath Propagation

Cache errors lack proper path information for symlinked inputs. Without ExecPath propagation, action rewinding fails to identify missing files correctly, potentially causing build failures.

Suggested change

	action,
	downloadFileNoCheckRx(
	action,
	execRoot.getRelative(execPath),
	treeRootExecPath != null ? execRoot.getRelative(treeRootExecPath) : null,
	dirsWithOutputPermissions,
	input,
	metadata,
	priority,
	reason)
	.onErrorResumeNext(
	t -> {
	if (t instanceof CacheNotFoundException cacheNotFoundException) {
	// Only the symlink itself is guaranteed to be an input to the action, so
	// report its path for rewinding.
	cacheNotFoundException.setExecPath(input.getExecPath());
	return Completable.error(cacheNotFoundException);
	}
	return Completable.error(t);
	})

Standards

• CWE-755
• OWASP-A06