# Header Parameter Models { #header-parameter-models }

If you have a group of related **header parameters**, you can create a **Pydantic model** to declare them.

This would allow you to **re-use the model** in **multiple places** and also to declare validations and metadata for all the parameters at once. 😎

/// note

This is supported since FastAPI version `0.115.0`. 🤓

///

				}
				got := buf.Bytes()
				if !bytes.Equal(want, got) {
					t.Fatalf("incorrect result: (-got +want)\n%v", bytediff(got, want))
				}
			}
		})
	}
}

func TestPax(t *testing.T) {
	// Create an archive with a large name
	fileinfo, err := os.Stat("testdata/small.txt")
	if err != nil {
		t.Fatal(err)
	}
	hdr, err := FileInfoHeader(fileinfo, "")
	if err != nil {
		t.Fatalf("os.Stat: %v", err)
	}

// 32-bit decimal input.
func ExampleScanner_custom() {
	// An artificial input source.
	const input = "1234 5678 1234567901234567890"
	scanner := bufio.NewScanner(strings.NewReader(input))
	// Create a custom split function by wrapping the existing ScanWords function.
	split := func(data []byte, atEOF bool) (advance int, token []byte, err error) {
		advance, token, err = bufio.ScanWords(data, atEOF)

	}

	initAllSubsystems(ctx)

	initConfigSubsystem(ctx, objLayer)

	creds, err := auth.CreateCredentials("myuser", "mypassword")
	if err != nil {
		t.Fatalf("unable create credential, %s", err)
	}

	globalActiveCred = creds

	globalIAMSys.Init(ctx, objLayer, globalEtcdClient, 2*time.Second)

	// List of test cases for validating http request authentication.

---> 100%
```

</div>

**Note**: Make sure you put `"fastapi[standard]"` in quotes to ensure it works in all terminals.

## Example { #example }

### Create it { #create-it }

Create a file `main.py` with:

```Python
from typing import Union

from fastapi import FastAPI

app = FastAPI()


@app.get("/")
def read_root():
    return {"Hello": "World"}

    /** User agent string */
    protected String userAgent = "Crawler";

    /** HTTP client context for requests */
    protected HttpClientContext httpClientContext = HttpClientContext.create();

    /** Proxy host name */
    protected String proxyHost;

    /** Proxy port number */
    protected Integer proxyPort;

    /** Proxy authentication scheme */

// This is usually orders of magnitude faster than actually sorting.
func (m metaCacheEntries) isSorted() bool {
	return sort.SliceIsSorted(m, m.less)
}

// shallowClone will create a shallow clone of the array objects,
// but object metadata will not be cloned.
func (m metaCacheEntries) shallowClone() metaCacheEntries {
	dst := make(metaCacheEntries, len(m))
	copy(dst, m)
	return dst
}

            InetAddress serverAddress,
            WitnessNotificationListener listener) {
        
        return CompletableFuture.supplyAsync(() -> {
            try {
                // Create registration
                WitnessRegistration registration = new WitnessRegistration(
                    shareName, serverAddress, WitnessServiceType.FILE_SERVER_WITNESS);
                

        SimpleCircuitBreaker breaker = new SimpleCircuitBreaker("concurrent", 5, 3, 100);
        AtomicInteger successCount = new AtomicInteger(0);
        AtomicInteger failureCount = new AtomicInteger(0);

        // Create multiple threads
        Thread[] threads = new Thread[10];
        for (int i = 0; i < threads.length; i++) {
            final int index = i;
            threads[i] = new Thread(() -> {

      "coverage" : {
        "per_commit" : [ "linux" ]
      }
    } ]
  }, {
    "testId" : "org.gradle.performance.regression.corefeature.DeprecationCreationPerformanceTest.create many deprecation warnings",
    "groups" : [ {
      "testProject" : "generateLotsOfDeprecationWarnings",
      "coverage" : {
        "per_day" : [ "linux" ]
      }
    } ]
  }, {