Each HTTP request contains a URL, a method (like `GET` or `POST`), and a list of headers. Requests may also contain a body: a data stream of a specific content type.

## [Responses](https://square.github.io/okhttp/5.x/okhttp/okhttp3/-response/)

The response answers the request with a code (like 200 for success or 404 for not found), headers, and its own optional body.

## Rewriting Requests

import java.util.Date
import okhttp3.Headers.Companion.headersOf
import org.junit.jupiter.api.Test

class HeadersKotlinTest {
  @Test fun getOperator() {
    val headers = headersOf("a", "b", "c", "d")
    assertThat(headers["a"]).isEqualTo("b")
    assertThat(headers["c"]).isEqualTo("d")
    assertThat(headers["e"]).isNull()
  }

  @Test fun iteratorOperator() {
    val headers = headersOf("a", "b", "c", "d")

 * limitations under the License.
 */
package okhttp3.mockwebserver

import okhttp3.Headers

class PushPromise(
  @get:JvmName("method") val method: String,
  @get:JvmName("path") val path: String,
  @get:JvmName("headers") val headers: Headers,
  @get:JvmName("response") val response: MockResponse,
) {
  @JvmName("-deprecated_method")
  @Deprecated(
    message = "moved to val",

          ),
        ).build()
    server.enqueue(MockResponse())
    get(server.url("/"))
    val request = server.takeRequest()
    assertThat(request.headers["Cookie"]).isEqualTo("Bar=bar; Baz=baz")
    assertThat(request.headers["Cookie2"]).isNull()
    assertThat(request.headers["Quux"]).isNull()
  }

  @Test
  fun acceptOriginalServerMatchesSubdomain() {

// getCanonicalHeaders generate a list of request headers with their values
func getCanonicalHeaders(signedHeaders http.Header) string {
	var headers []string
	vals := make(http.Header, len(signedHeaders))
	for k, vv := range signedHeaders {
		k = strings.ToLower(k)
		headers = append(headers, k)
		vals[k] = vv
	}
	sort.Strings(headers)

	var buf bytes.Buffer
	for _, k := range headers {
		buf.WriteString(k)
		buf.WriteByte(':')

/// warning

Before setting `convert_underscores` to `False`, bear in mind that some HTTP proxies and servers disallow the usage of headers with underscores.

///

## Duplicate headers { #duplicate-headers }

It is possible to receive duplicate headers. That means, the same header with multiple values.

You can define those cases using a list in the type declaration.

        return contentException;
    }

    /**
     * Sets the headers for the response.
     *
     * @param headers the headers to set.
     */
    public void setHeaders(final Map<String, List<String>> headers) {
        if (headers != null) {
            final Map<String, List<String>> map = new HashMap<>();
            headers.entrySet().stream().filter(e -> e.getKey() != null).forEach(

    ) = apply {
      headers.add(name, value)
    }

    /** Removes all headers named [name] on this builder. */
    open fun removeHeader(name: String) =
      apply {
        headers.removeAll(name)
      }

    /** Removes all headers on this builder and adds [headers]. */
    open fun headers(headers: Headers) =
      apply {
        this.headers = headers.newBuilder()
      }

      .build()
  }

  companion object {
    /** Combines cached headers with a network headers as defined by RFC 7234, 4.3.4. */
    private fun combine(
      cachedHeaders: Headers,
      networkHeaders: Headers,
    ): Headers {
      val result = Headers.Builder()

      for (index in 0 until cachedHeaders.size) {
        val fieldName = cachedHeaders.name(index)

    List<Class<? extends AbstractTester>> testers = copyToList(super.getTesters());
    testers.add(SetMultimapAsMapTester.class);
    testers.add(SetMultimapEqualsTester.class);
    testers.add(SetMultimapPutTester.class);
    testers.add(SetMultimapPutAllTester.class);
    testers.add(SetMultimapReplaceValuesTester.class);
    testers.add(SortedSetMultimapAsMapTester.class);
    testers.add(SortedSetMultimapGetTester.class);