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Add utilities to detect and replace broken links. #1366

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Add utilities to detect and replace broken links. #1366

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9004e6b
Add utilities to detect and replace broken links.
barsh404error Dec 29, 2025
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barsh404error Dec 31, 2025
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43 changes: 42 additions & 1 deletion application/src/main/java/org/togetherjava/tjbot/features/utils/LinkDetection.java
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Original file line number Diff line number Diff line change
Expand Up @@ -4,9 +4,14 @@
import com.linkedin.urls.detection.UrlDetector;
import com.linkedin.urls.detection.UrlDetectorOptions;

import java.net.URI;
import java.net.http.HttpClient;
import java.net.http.HttpRequest;
import java.net.http.HttpResponse;
import java.util.List;
import java.util.Optional;
import java.util.Set;
import java.util.concurrent.CompletableFuture;

/**
* Utility class to detect links.
Expand Down Expand Up @@ -58,6 +63,43 @@ public static boolean containsLink(String content) {
return !(new UrlDetector(content, UrlDetectorOptions.BRACKET_MATCH).detect().isEmpty());
}

public static CompletableFuture<Boolean> isLinkBroken(String url) {
HttpClient client = HttpClient.newHttpClient();

HttpRequest request = HttpRequest.newBuilder(URI.create(url))
.method("HEAD", HttpRequest.BodyPublishers.noBody())
.build();

return client.sendAsync(request, HttpResponse.BodyHandlers.discarding())
.thenApply(response -> response.statusCode() >= 400)
.exceptionally(ignored -> true);
}

public static CompletableFuture<String> replaceDeadLinks(String text, String replacement) {
Set<LinkFilter> filters = Set.of(LinkFilter.SUPPRESSED, LinkFilter.NON_HTTP_SCHEME);

List<String> links = extractLinks(text, filters);

if (links.isEmpty()) {
return CompletableFuture.completedFuture(text);
}

StringBuilder result = new StringBuilder(text);
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@tj-wazei tj-wazei Dec 30, 2025

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This implementation is not thread-safe. StringBuilder is mutated from multiple async callbacks, causing data races and invalid index calculations. Async HTTP completion order is nondeterministic, so index-based replacements are unsafe.

The correct approach is to separate concurrent link checks from sequential string mutation: perform all HTTP checks first, then apply replacements in a single thread once all futures complete.


List<CompletableFuture<Void>> checks =
links.stream().map(link -> isLinkBroken(link).thenAccept(isDead -> {
if (isDead) {
int index = result.indexOf(link);
if (index != -1) {
result.replace(index, index + link.length(), replacement);
}
}
})).toList();

return CompletableFuture.allOf(checks.toArray(new CompletableFuture[0]))
.thenApply(v -> result.toString());
}

private static Optional<String> toLink(Url url, Set<LinkFilter> filter) {
String raw = url.getOriginalUrl();
if (filter.contains(LinkFilter.SUPPRESSED) && raw.contains(">")) {
Expand All @@ -76,7 +118,6 @@ private static Optional<String> toLink(Url url, Set<LinkFilter> filter) {
// Remove trailing punctuation
link = link.substring(0, link.length() - 1);
}

return Optional.of(link);
}

Expand Down