Add a captcha short-code expander

service/src/main/java/org/whispersystems/textsecuregcm/captcha/CaptchaChecker.java

@@ -29,9 +29,15 @@ public class CaptchaChecker {
   @VisibleForTesting
   static final String SEPARATOR = ".";
 
+  private static final String SHORT_SUFFIX = "-short";
+
+  private final ShortCodeExpander shortCodeExpander;
   private final Map<String, CaptchaClient> captchaClientMap;
 
-  public CaptchaChecker(final List<CaptchaClient> captchaClients) {
+  public CaptchaChecker(
+      final ShortCodeExpander shortCodeRetriever,
+      final List<CaptchaClient> captchaClients) {
+    this.shortCodeExpander = shortCodeRetriever;
     this.captchaClientMap = captchaClients.stream()
         .collect(Collectors.toMap(CaptchaClient::scheme, Function.identity()));
   }
@@ -63,9 +69,17 @@ public class CaptchaChecker {
     final String prefix = parts[0];
     final String siteKey = parts[1].toLowerCase(Locale.ROOT).strip();
     final String action = parts[2];
-    final String token = parts[3];
+    String token = parts[3];
 
-    final CaptchaClient client = this.captchaClientMap.get(prefix);
+    String provider = prefix;
+    if (prefix.endsWith(SHORT_SUFFIX)) {
+      // This is a "short" solution that points to the actual solution. We need to fetch the
+      // full solution before proceeding
+      provider = prefix.substring(0, prefix.length() - SHORT_SUFFIX.length());
+      token = shortCodeExpander.retrieve(token).orElseThrow(() -> new BadRequestException("invalid shortcode"));
+    }
+
+    final CaptchaClient client = this.captchaClientMap.get(provider);
     if (client == null) {
       throw new BadRequestException("invalid captcha scheme");
     }
@@ -92,7 +106,7 @@ public class CaptchaChecker {
     Metrics.counter(ASSESSMENTS_COUNTER_NAME,
             "action", action,
             "score", result.getScoreString(),
-            "provider", prefix)
+            "provider", provider)
         .increment();
     return result;
   }

service/src/main/java/org/whispersystems/textsecuregcm/captcha/ShortCodeExpander.java

@@ -0,0 +1,49 @@
+/*
+ * Copyright 2023 Signal Messenger, LLC
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+
+package org.whispersystems.textsecuregcm.captcha;
+
+import io.micrometer.core.instrument.Metrics;
+import org.apache.http.HttpStatus;
+import java.io.IOException;
+import java.net.URI;
+import java.net.http.HttpClient;
+import java.net.http.HttpRequest;
+import java.net.http.HttpResponse;
+import java.util.Optional;
+
+import static org.whispersystems.textsecuregcm.metrics.MetricsUtil.name;
+
+public class ShortCodeExpander {
+  private static final String EXPAND_COUNTER_NAME = name(ShortCodeExpander.class, "expand");
+
+  private final HttpClient client;
+  private final URI shortenerHost;
+
+  public ShortCodeExpander(final HttpClient client, final String shortenerHost) {
+    this.client = client;
+    this.shortenerHost = URI.create(shortenerHost);
+  }
+
+  public Optional<String> retrieve(final String shortCode) throws IOException {
+    final URI uri = shortenerHost.resolve("/" + shortCode);
+    final HttpRequest request = HttpRequest.newBuilder().uri(uri).GET().build();
+
+    try {
+      final HttpResponse<String> response = this.client.send(request, HttpResponse.BodyHandlers.ofString());
+      Metrics.counter(EXPAND_COUNTER_NAME, "responseCode", Integer.toString(response.statusCode())).increment();
+      return switch (response.statusCode()) {
+        case HttpStatus.SC_OK -> Optional.of(response.body());
+        case HttpStatus.SC_NOT_FOUND -> Optional.empty();
+        default -> throw new IOException("Failed to look up shortcode");
+      };
+    } catch (InterruptedException e) {
+      throw new IOException(e);
+    }
+  }
+
+
+
+}