describing the request at a high-level: _“fetch me this URL with these headers.”_ For correctness and efficiency, OkHttp rewrites your request before transmitting it.

OkHttp may add headers that are absent from the original request, including `Content-Length`, `Transfer-Encoding`, `User-Agent`, `Host`, `Connection`, and `Content-Type`. It will add an `Accept-Encoding` header for transparent response compression unless the header is already present. If you’ve got cookies, OkHttp will add a `Cookie`...

from fastapi import FastAPI, Header
from pydantic import BaseModel

app = FastAPI()


class CommonHeaders(BaseModel):
    class Config:
        extra = "forbid"

    host: str
    save_data: bool
    if_modified_since: str | None = None
    traceparent: str | None = None
    x_tag: list[str] = []


@app.get("/items/")
async def read_items(headers: Annotated[CommonHeaders, Header()]):

    get() {
      val result = mutableListOf<Header>()
      for (inputHeader in headers) {
        val (key, value) = inputHeader.entries.iterator().next()
        result.add(Header(key, value))
      }
      return result
    }

  public override fun clone() = Case(seqno, this.wire, headers)

      transparentGzip = true
      requestBuilder.header("Accept-Encoding", "gzip")
    }

    val cookies = cookieJar.loadForRequest(userRequest.url)
    if (cookies.isNotEmpty()) {
      requestBuilder.header("Cookie", cookieHeader(cookies))
    }

    if (userRequest.header("User-Agent") == null) {
      requestBuilder.header("User-Agent", USER_AGENT)
    }

        .build();

    try (Response response = client.newCall(request).execute()) {
      if (!response.isSuccessful()) throw new IOException("Unexpected code " + response);

      Headers responseHeaders = response.headers();
      for (int i = 0; i < responseHeaders.size(); i++) {
        System.out.println(responseHeaders.name(i) + ": " + responseHeaders.value(i));
      }

      System.out.println(response.body().string());

client = TestClient(app)


@pytest.mark.parametrize(
    "path,headers,expected_status,expected_response",
    [
        ("/items", None, 200, {"User-Agent": "testclient"}),
        ("/items", {"X-Header": "notvalid"}, 200, {"User-Agent": "testclient"}),
        ("/items", {"User-Agent": "FastAPI test"}, 200, {"User-Agent": "FastAPI test"}),
    ],
)
def test(path, headers, expected_status, expected_response):

        ),
        (
            "/items",
            {"strange-header": "Not really underscore"},
            200,
            {"strange_header": None},
        ),
    ],
)
def test(path, headers, expected_status, expected_response):
    response = client.get(path, headers=headers)
    assert response.status_code == expected_status
    assert response.json() == expected_response

            200,
            {"X-Token values": ["foo", "bar"]},
        ),
    ],
)
def test(path, headers, expected_status, expected_response):
    response = client.get(path, headers=headers)
    assert response.status_code == expected_status
    assert response.json() == expected_response


def test_openapi_schema():
    response = client.get("/openapi.json")
    assert response.status_code == 200

   readTimeoutMillis, retryOnConnectionFailure, socketFactory, sslSocketFactory, writeTimeoutMillis
 * **PushPromise**: headers, method, path, response
 * **Request**: body, cacheControl, headers, method, url
 * **Response**: body, cacheControl, cacheResponse, code, handshake, headers, message,
   networkResponse, priorResponse, protocol, receivedResponseAtMillis, request, sentRequestAtMillis

        this.sentRequestMillis = cacheResponse.sentRequestAtMillis
        this.receivedResponseMillis = cacheResponse.receivedResponseAtMillis
        val headers = cacheResponse.headers
        for (i in 0 until headers.size) {
          val fieldName = headers.name(i)
          val value = headers.value(i)
          when {
            fieldName.equals("Date", ignoreCase = true) -> {
              servedDate = value.toHttpDateOrNull()