Symmetrically, interceptors can rewrite response headers and transform the response body. This is generally more dangerous than rewriting request headers because it may violate the webserver's expectations!

If you're in a tricky situation and prepared to deal with the consequences, rewriting response headers is a powerful way to work around problems. For example, you can fix a server's misconfigured `Cache-Control` response header to enable better response caching:

      assertThat(response.header("h1")).isEqualTo("v1")
      assertThat(source.readUtf8()).isEqualTo("Hello")
      assertThat(response.trailers()).isEqualTo(headersOf("t1", "v2"))
    }

    val call2 = client.newCall(Request(server.url("/")))
    call2.execute().use { response ->
      val source = response.body.source()
      assertThat(response.header("h1")).isEqualTo("v1")

  }

  @Test
  fun headers() {
    var headers: Headers = headersOf("", "")
    headers = mapOf("" to "").toHeaders()
    val get: String? = headers[""]
    val date: Date? = headers.getDate("")
    val instant: Instant? = headers.getInstant("")
    val size: Int = headers.size
    val name: String = headers.name(0)
    val value: String = headers.value(0)
    val names: Set<String> = headers.names()

When writing request headers, use `header(name, value)` to set the only occurrence of `name` to `value`. If there are existing values, they will be removed before the new value is added. Use `addHeader(name, value)` to add a header without removing the headers already present.

    val body = "hello".toRequestBody()
    val headers = headersOf("User-Agent", "RequestTest")
    val method = "PUT"
    val request =
      Request(
        url = url,
        headers = headers,
        method = method,
        body = body,
      )
    assertThat(request.url).isEqualTo(url)
    assertThat(request.headers).isEqualTo(headers)
    assertThat(request.method).isEqualTo(method)

    peer.acceptFrame() // ACK
    peer.acceptFrame() // SYN_STREAM
    peer.sendFrame().headers(false, 3, headerEntries("a", "android"))
    val expectedRequestHeaders =
      listOf(
        Header(Header.TARGET_METHOD, "GET"),
        Header(Header.TARGET_SCHEME, "https"),
        Header(Header.TARGET_AUTHORITY, "squareup.com"),
        Header(Header.TARGET_PATH, "/cached"),
      )

                logger.debug("Apply header {}:{} to response of {}", k, v, mimeType);
            }
            response.header(k, v);
        });
    }

    protected void adjustActionResponseHeaders(final String mimeType, final BiConsumer<String, String> callback) {
        defaultResponseHeaders.forEach(header -> callback.accept(header.getFirst(), header.getSecond()));

      Request
        .Builder()
        .url(server.url("/"))
        .header("", "A")
        .build()
    }
  }

  @Test
  fun emptyResponseHeaderNameIsLenient() {
    val headers = Headers.Builder()
    addHeaderLenient(headers, ":A")
    server.enqueue(
      MockResponse(
        headers = headers.build(),
        body = "body",
      ),
    )

        .header("User-Agent", "OkHttp Headers.java")
        .addHeader("Accept", "application/json; q=0.5")
        .addHeader("Accept", "application/vnd.github.v3+json")
        .build()

    client.newCall(request).execute().use { response ->
      if (!response.isSuccessful) throw IOException("Unexpected code $response")

      println("Server: ${response.header("Server")}")

import mockwebserver3.internal.decodeRequestLine
import okhttp3.Headers
import okhttp3.Headers.Companion.headersOf
import okio.Buffer
import okio.ByteString
import org.junit.jupiter.api.Test
import org.junit.jupiter.api.Timeout

@Timeout(30)
class RecordedRequestTest {
  private val headers: Headers = Headers.EMPTY

  @Test fun testIPv4() {
    val socket =
      MockWebServerSocket(