// The header remains for subsequent tests due to static request handling
        // Different matching header added to same request
        request.addHeader("X-Forwarded-Host", "test.com");
        result = virtualHostHelper.getVirtualHostPath(page);
        assertEquals("/site1/search", result.getRoutingPath()); // Still site1 due to header precedence
    }

    @Test
    public void test_getVirtualHostBasePath() {

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:

// For forward compatibility, users that retrieve a Header from Reader.Next,
// mutate it in some ways, and then pass it back to Writer.WriteHeader
// should do so by creating a new Header and copying the fields
// that they are interested in preserving.
type Header struct {
	// Typeflag is the type of header entry.
	// The zero value is automatically promoted to either TypeReg or TypeDir
	// depending on the presence of a trailing slash in Name.

def test_read_nonexistent_item():
    response = client.get("/items/baz", headers={"X-Token": "coneofsilence"})
    assert response.status_code == 404
    assert response.json() == {"detail": "Item not found"}


def test_create_item():
    response = client.post(
        "/items/",
        headers={"X-Token": "coneofsilence"},

from fastapi import FastAPI, Header
from pydantic import BaseModel

app = FastAPI()


class CommonHeaders(BaseModel):
    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: CommonHeaders = Header(convert_underscores=False)):

from fastapi import Cookie, FastAPI, Header, Query
from fastapi.testclient import TestClient
from pydantic import BaseModel

app = FastAPI()


class Model(BaseModel):
    param: str

    model_config = {"extra": "allow"}


@app.get("/query")
async def query_model_with_extra(data: Model = Query()):
    return data


@app.get("/header")
async def header_model_with_extra(data: Model = Header()):
    return data

from fastapi import FastAPI, Header
from pydantic import BaseModel

app = FastAPI()


class CommonHeaders(BaseModel):
    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(convert_underscores=False)],
):

      value: String,
    ) = 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()
      }

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`...

	}
	if err != nil {
		return n, err
	}
	return n, err
}

// Write the headers into the given buffer
func (lrw *ResponseRecorder) writeHeaders(w io.Writer, statusCode int, headers http.Header) {
	n, _ := fmt.Fprintf(w, "%d %s\n", statusCode, http.StatusText(statusCode))
	lrw.headerBytesWritten += n
	for k, v := range headers {
		n, _ := fmt.Fprintf(w, "%s: %s\n", k, v[0])
		lrw.headerBytesWritten += n
	}
}