When to use HTTP HEAD request

HTTP (Hypertext Transfer Protocol) is an application layer protocol for transporting hypertext, which defines how clients and servers communicate. In HTTP, the HEAD request is one of the common HTTP request methods and has some key differences from the GET request. This article will delve into the purpose of HEAD requests and their differences from GET requests, and illustrate them with specific examples.

Purpose of HTTP HEAD request:

HEADThe request is similar to the GET request, but the difference is that the HEAD request only obtains the header information of the target resource but not the specific resource content. The header information includes metadata related to the resource, such as Content-Type, Content-Length, Last-Modified, etc., but does not contain actual data. Therefore, HEAD requests are mainly used to obtain meta-information about resources without transmitting actual data content, thereby saving bandwidth and improving performance.

The difference between HTTP GET request and HEAD request:

1. data transmission:

   • GETThe request is used to obtain the complete content of the target resource, including header information and actual data.
   • HEADThe request only obtains the header information of the target resource and does not transmit the actual data.

2. Bandwidth consumption:

   • GETThe request consumes more bandwidth because it transfers the contents of the entire resource.
   • HEADThe request only transmits header information, so it consumes less bandwidth.

3. Response time:

   • BecauseHEADthe request does not transmit actual data, you can usually get a faster response, especially for large resources.
   • GETThe request needs to wait for the server to transfer the entire resource, so the response time is relatively long.

4. Caching processing:

   • GETThe response to the request can be cached, including header information and actual data.
   • HEADThe response to the request can usually also be cached, but the cache only contains the header information, not the actual data.

Specific examples:

Consider a simple scenario, assuming there is an image resource on a website, we use GET and HEAD requests to obtain information about the resource.

1. Use GET request:

   GET /images/example.jpg HTTP/1.1
   Host: example.com
   

   response:

   HTTP/1.1 200 OK
   Date: Tue, 14 Dec 2023 12:00:00 GMT
   Content-Type: image/jpeg
   Content-Length: 10240
   
   <binary data of the image>
   

   In the above example, GET requested to obtain the header information and actual data of example.jpg the image.

2. Use HEAD request:

   HEAD /images/example.jpg HTTP/1.1
   Host: example.com
   

   response:

   HTTP/1.1 200 OK
   Date: Tue, 14 Dec 2023 12:01:00 GMT
   Content-Type: image/jpeg
   Content-Length: 10240
   

   In this example,HEAD the request obtains the same header information, but does not transmit the actual image data.

Summarize:

HEADThe request is an efficient way to obtain only meta-information about a resource without transmitting actual data. It has obvious advantages in reducing bandwidth consumption, improving performance and accelerating caching. However, it is important to note that not all servers provide the same response to HEAD requests as to GET requests, so when using HEAD When requesting, you must ensure that the target server implements this functionality correctly.

By in-depth understanding of HEAD requests and their characteristics that differ from GET requests, developers can better optimize network performance and improve the efficiency of resource acquisition. , while reducing the load on the server and network.