Fix .onion link linkification.

Fixes #11458.

app/src/main/java/org/thoughtcrime/securesms/util/LinkUtil.java

@@ -0,0 +1,87 @@
+package org.thoughtcrime.securesms.util;
+
+import android.text.TextUtils;
+
+import androidx.annotation.NonNull;
+import androidx.annotation.Nullable;
+
+import org.signal.core.util.SetUtil;
+import org.thoughtcrime.securesms.stickers.StickerUrl;
+
+import java.util.Objects;
+import java.util.Set;
+import java.util.regex.Matcher;
+import java.util.regex.Pattern;
+
+import okhttp3.HttpUrl;
+
+public final class LinkUtil {
+
+  private static final Pattern DOMAIN_PATTERN             = Pattern.compile("^(https?://)?([^/]+).*$");
+  private static final Pattern ALL_ASCII_PATTERN          = Pattern.compile("^[\\x00-\\x7F]*$");
+  private static final Pattern ALL_NON_ASCII_PATTERN      = Pattern.compile("^[^\\x00-\\x7F]*$");
+  private static final Pattern ILLEGAL_CHARACTERS_PATTERN = Pattern.compile("[\u202C\u202D\u202E\u2500-\u25FF]");
+
+  private static final Set<String> INVALID_TOP_LEVEL_DOMAINS = SetUtil.newHashSet("onion", "i2p");
+
+  private LinkUtil() {}
+
+  /**
+   * @return True if URL is valid for link previews.
+   */
+  public static boolean isValidPreviewUrl(@Nullable String linkUrl) {
+    if (linkUrl == null) {
+      return false;
+    }
+
+    if (StickerUrl.isValidShareLink(linkUrl)) {
+      return true;
+    }
+
+    HttpUrl url = HttpUrl.parse(linkUrl);
+    return url != null &&
+           !TextUtils.isEmpty(url.scheme()) &&
+           "https".equals(url.scheme()) &&
+           isLegalUrl(linkUrl, false);
+  }
+
+  /**
+   * @return True if URL is valid, mostly useful for linkifying.
+   */
+  public static boolean isLegalUrl(@NonNull String url) {
+    return isLegalUrl(url, true);
+  }
+
+  private static boolean isLegalUrl(@NonNull String url, boolean skipTopLevelDomainValidation) {
+    if (ILLEGAL_CHARACTERS_PATTERN.matcher(url).find()) {
+      return false;
+    }
+
+    Matcher matcher = DOMAIN_PATTERN.matcher(url);
+
+    if (matcher.matches()) {
+      String domain         = Objects.requireNonNull(matcher.group(2));
+      String cleanedDomain  = domain.replaceAll("\\.", "");
+      String topLevelDomain = parseTopLevelDomain(domain);
+
+      boolean validCharacters = ALL_ASCII_PATTERN.matcher(cleanedDomain).matches() ||
+                                ALL_NON_ASCII_PATTERN.matcher(cleanedDomain).matches();
+
+      boolean validTopLevelDomain = skipTopLevelDomainValidation || !INVALID_TOP_LEVEL_DOMAINS.contains(topLevelDomain);
+
+      return validCharacters && validTopLevelDomain;
+    } else {
+      return false;
+    }
+  }
+
+  private static @Nullable String parseTopLevelDomain(@NonNull String domain) {
+    int periodIndex = domain.lastIndexOf(".");
+
+    if (periodIndex >= 0 && periodIndex < domain.length() - 1) {
+      return domain.substring(periodIndex + 1);
+    } else {
+      return null;
+    }
+  }
+}