Creating RetryAfterParser

Author: LikeTheSalad

opamp-client/src/main/java/io/opentelemetry/opamp/client/internal/connectivity/http/RetryAfterParser.java

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+package io.opentelemetry.opamp.client.internal.connectivity.http;
+
+import io.opentelemetry.opamp.client.internal.tools.SystemTime;
+import java.text.ParseException;
+import java.text.SimpleDateFormat;
+import java.time.Duration;
+import java.util.Locale;
+import java.util.regex.Pattern;
+
+public final class RetryAfterParser {
+  private final SystemTime systemTime;
+  public static final Pattern SECONDS_PATTERN = Pattern.compile("\\d+");
+  public static final Pattern DATE_PATTERN =
+      Pattern.compile(
+          "^([A-Za-z]{3}, [0-3][0-9] [A-Za-z]{3} [0-9]{4} [0-2][0-9]:[0-5][0-9]:[0-5][0-9] GMT)$");
+  private static final SimpleDateFormat dateFormat =
+      new SimpleDateFormat("EEE, dd MMM yyyy HH:mm:ss z", Locale.US);
+
+  public static RetryAfterParser getInstance() {
+    return new RetryAfterParser(SystemTime.getInstance());
+  }
+
+  RetryAfterParser(SystemTime systemTime) {
+    this.systemTime = systemTime;
+  }
+
+  public Duration parse(String value) {
+    if (SECONDS_PATTERN.matcher(value).matches()) {
+      return Duration.ofSeconds(Long.parseLong(value));
+    } else if (DATE_PATTERN.matcher(value).matches()) {
+      return Duration.ofMillis(toMilliseconds(value) - systemTime.getCurrentTimeMillis());
+    }
+    throw new IllegalArgumentException("Invalid Retry-After value: " + value);
+  }
+
+  @SuppressWarnings({"JavaUtilDate", "ThrowSpecificExceptions"})
+  private static long toMilliseconds(String value) {
+    try {
+      return dateFormat.parse(value).getTime();
+    } catch (ParseException e) {
+      throw new RuntimeException(e);
+    }
+  }
+}

opamp-client/src/main/java/io/opentelemetry/opamp/client/internal/tools/SystemTime.java

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+package io.opentelemetry.opamp.client.internal.tools;
+
+/** Utility to be able to mock the current system time for testing purposes. */
+public final class SystemTime {
+  private static final SystemTime INSTANCE = new SystemTime();
+
+  public static SystemTime getInstance() {
+    return INSTANCE;
+  }
+
+  private SystemTime() {}
+
+  public long getCurrentTimeMillis() {
+    return System.currentTimeMillis();
+  }
+}

opamp-client/src/test/java/io/opentelemetry/opamp/client/internal/connectivity/http/RetryAfterParserTest.java

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+package io.opentelemetry.opamp.client.internal.connectivity.http;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.when;
+
+import io.opentelemetry.opamp.client.internal.tools.SystemTime;
+import java.time.Duration;
+import org.junit.jupiter.api.Test;
+
+class RetryAfterParserTest {
+
+  @Test
+  void verifyParsing() {
+    SystemTime systemTime = mock();
+    long currentTimeMillis = 1577836800000L;
+    when(systemTime.getCurrentTimeMillis()).thenReturn(currentTimeMillis);
+
+    RetryAfterParser parser = new RetryAfterParser(systemTime);
+
+    assertThat(parser.parse("123")).isEqualTo(Duration.ofSeconds(123));
+    assertThat(parser.parse("Wed, 01 Jan 2020 01:00:00 GMT")).isEqualTo(Duration.ofHours(1));
+  }
+}