Add a utility class for associating IP addresses with ASNs.

service/src/main/java/org/whispersystems/textsecuregcm/util/AsnTable.java

@@ -0,0 +1,80 @@
+/*
+ * Copyright 2021 Signal Messenger, LLC
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+
+package org.whispersystems.textsecuregcm.util;
+
+import com.google.common.annotations.VisibleForTesting;
+import java.io.IOException;
+import java.io.Reader;
+import java.net.Inet4Address;
+import java.nio.ByteBuffer;
+import java.util.NavigableMap;
+import java.util.Optional;
+import java.util.TreeMap;
+import org.apache.commons.csv.CSVFormat;
+import org.apache.commons.csv.CSVParser;
+import org.apache.commons.csv.CSVRecord;
+
+/**
+ * Allows IP->ASN lookup operations using data from https://iptoasn.com/.
+ */
+class AsnTable {
+  private final NavigableMap<Long, AsnRange> asnBlocksByFirstIp;
+
+  private static class AsnRange {
+    private final long rangeStart;
+    private final long rangeEnd;
+
+    private final long asn;
+
+    private AsnRange(long rangeStart, long rangeEnd, long asn) {
+      this.rangeStart = rangeStart;
+      this.rangeEnd = rangeEnd;
+      this.asn = asn;
+    }
+
+    boolean contains(final long address) {
+      return address >= rangeStart && address <= rangeEnd;
+    }
+
+    long getAsn() {
+      return asn;
+    }
+  }
+
+  public AsnTable(final Reader tsvReader) throws IOException {
+    final TreeMap<Long, AsnRange> treeMap = new TreeMap<>();
+
+    try (final CSVParser csvParser = CSVFormat.TDF.parse(tsvReader)) {
+      for (final CSVRecord record : csvParser) {
+        final long start = Long.parseLong(record.get(0), 10);
+        final long end = Long.parseLong(record.get(1), 10);
+        final long asn = Long.parseLong(record.get(2), 10);
+
+        treeMap.put(start, new AsnRange(start, end, asn));
+      }
+    }
+
+    asnBlocksByFirstIp = treeMap;
+  }
+
+  public Optional<Long> getAsn(final Inet4Address address) {
+    final long addressAsLong = ipToLong(address);
+
+    return Optional.ofNullable(asnBlocksByFirstIp.floorEntry(addressAsLong))
+        .filter(entry -> entry.getValue().contains(addressAsLong))
+        .map(entry -> entry.getValue().getAsn());
+  }
+
+  @VisibleForTesting
+  static long ipToLong(final Inet4Address address) {
+    final ByteBuffer buffer = ByteBuffer.allocate(8);
+    buffer.position(4);
+    buffer.put(address.getAddress());
+
+    buffer.flip();
+    return buffer.getLong();
+  }
+}