If you are looking for the feature that allows you to utilize more than one capability in HTTP requests or applications, you might not be familiar with trailer fields. These are one of the attractive abilities of HTTP that allows you to add some information after sending an HTTP message. Now why might you need this capability? Well, it might sometimes be useful to provide more information after this data has been sent, especially in large datasets or when it is necessary to ensure that this data has been properly rendered, it should be obvious.
Using trailer fields is usually seen in HTTP/1.1 and mostly for HTTP/2 and after that it is common. This helps you ensure that headers, which require more time for processing, or for the next stages of data transfer are included in the Trailer field. For example, assume that you have information that needs to be processed after receiving the original message, such as digital signatures or data analysis.
A key point is that you should be cautious about using trailer fields only when you take into account their processing. That is to say, if you want to use this capability, you need to ensure that they are ready for processing in HTTP/2 or newer versions.
Now let's explore more with an example of practical usage of trailer fields. Here’s a simple example of configuring and using trailer fields:
GET /example HTTP/1.1
Host: example.com
TE: trailers
Transfer-Encoding: chunked
4
Wiki
5
pedia
0
Trailer: X-Custom-Header
X-Custom-Header: my-custom-value
Line-by-line explanation of the above code:
GET /example HTTP/1.1: This is a GET request for the path /example. Host: example.com: This line specifies the domain or the address of the target website. TE: trailers: This line indicates that the requester is capable of processing trailer fields. Transfer-Encoding: chunked: This allows for chunked transfer encoding that supports the use of trailer fields. 4: This is the length of the first chunk of data which is 4 bytes. Wiki and pedia: These are the actual data in each chunk. 0: This indicates the end of the chunked data. Trailer: X-Custom-Header: This informs that a trailer field called X-Custom-Header will be added. X-Custom-Header: my-custom-value: This is the actual value of the trailer field that has been added.