Server response 100 Continue

HTTP Status Code 100 (Continue)

The HTTP status code 100 (Continue) is a provisional response indicating that the initial part of a request has been received and the client can continue sending the body of the request. This mechanism is especially useful for optimizing interactions with large data volumes.

Key Concepts

• What is Status Code 100 (Continue): It is a temporary status code used in the HTTP protocol, signaling that the server has accepted the request headers and the client should proceed with the request body.
• When and Why is This Code Used: This code is primarily used when a client is uploading a large file or data set. By confirming that the server is ready to receive the data, it helps in preventing unnecessary data transmission in case of a potential error.

Practical Examples of Usage

Example 1: Uploading a Large File

Consider a scenario where a client is attempting to upload a large file. When the client sends the request headers, the server responds with a 100 status code, indicating that it is ready to receive the file body. This confirmation allows the client to proceed with the file upload, thus optimizing the process.

The advantages of using this code in the context of file uploads include:

• Reduced latency in data transfer.
• Minimized risk of sending large amounts of data unnecessarily.

Example 2: Checking Headers Before Sending Data

Status code 100 can also be beneficial when the client needs to ensure that the request headers meet the server's expectations before sending the actual data. For instance, if a client sends a request with specific content-type headers, the server can respond with 100 if it is prepared to accept the data type, thus avoiding a situation where the client sends data that the server cannot process.

Handling Errors Related to Code 100 (Continue)

Example in Python

In situations where a server fails to return a 100 status code, the client must be able to handle this gracefully. Below is a sample implementation in Python using the requests library:

import requests

url = 'http://example.com/upload'
headers = {'Expect': '100-continue'}
response = requests.post(url, headers=headers, data=open('largefile.txt', 'rb'))

if response.status_code == 100:
    print("Server is ready to receive the file.")
elif response.status_code == 200:
    print("File uploaded successfully.")
else:
    print("Error: ", response.status_code)

Example in Java

In Java, if using the HttpURLConnection class, the handling of the status code 100 can be done as follows:

import java.io.*;
import java.net.*;

public class FileUploader {
    public static void main(String[] args) throws Exception {
        String url = "http://example.com/upload";
        HttpURLConnection connection = (HttpURLConnection) new URL(url).openConnection();
        connection.setDoOutput(true);
        connection.setRequestMethod("POST");
        connection.setRequestProperty("Expect", "100-continue");

        connection.connect();
        if (connection.getResponseCode() == HttpURLConnection.HTTP_CONTINUE) {
            // Proceed to send the file
            OutputStream os = connection.getOutputStream();
            FileInputStream fis = new FileInputStream("largefile.txt");
            byte[] buffer = new byte[4096];
            int bytesRead;
            while ((bytesRead = fis.read(buffer)) != -1) {
                os.write(buffer, 0, bytesRead);
            }
            os.close();
            fis.close();
        }
    }
}

Example in JavaScript

In JavaScript, the handling of the 100 status code can be implemented using XMLHttpRequest or the fetch API:

const xhr = new XMLHttpRequest();
xhr.open("POST", "http://example.com/upload");
xhr.setRequestHeader("Expect", "100-continue");

xhr.onload = function() {
    if (xhr.status === 200) {
        console.log("File uploaded successfully.");
    } else {
        console.error("Error: ", xhr.status);
    }
};

xhr.send(file); // Assuming 'file' is a File object

Best Practices

• Always set the "Expect" header when sending large requests to leverage the 100 status code properly.
• Implement error handling to manage cases when the server does not support the 100 status code.
• Regularly test the client and server interactions to ensure compatibility with the 100 status code.

Frequently Asked Questions

1. What behavior is expected from the client upon receiving a 100 status code?

   The client should proceed with sending the request body, as the server has indicated it is ready to accept data.

2. What should be done if the server does not support status code 100?

   If the server does not support the 100 status code, the client should handle this gracefully, possibly by sending the data without waiting for the 100 response.