When it comes to customizing HTTP requests and responses, adding custom headers can be a useful tool for passing application-specific data between clients and servers. However, with great power comes great responsibility, and it’s essential to follow established naming conventions and best practices when creating custom HTTP headers.
In the past, it was common to prefix custom header names with "X-", as seen in examples like X-Forwarded-For and X-Requested-With. This convention was initially recommended by the IETF (Internet Engineering Task Force) in RFC 2047. However, this recommendation has since been deprecated, and the current official guidance is outlined in RFC 6648.
According to RFC 6648, it’s recommended to avoid prefixing custom header names with "X-" or similar constructs, as this can lead to naming conflicts when these headers become standardized. Instead, developers should choose sensible, descriptive names for their custom headers that are unlikely to conflict with existing or future standard headers.
That being said, there are cases where using a namespace or vendor prefix is justified, such as when creating implementation-specific and private-use headers. In these situations, adding a unique prefix can help avoid naming conflicts and ensure that the header is clearly identifiable as a custom, non-standard header.
When it comes to formatting custom HTTP headers, the general structure is defined in the HTTP specification (RFC 2616). A message-header consists of a field-name followed by a colon and an optional field-value. The field-name must be composed of a subset of ASCII characters, including alphanumerics and some punctuation marks.
On the other hand, the field-value can contain any octets except control characters, which are explicitly barred. While the specification implies that header values should be interpreted as ISO-8859-1 encoded, it’s generally recommended to stick with ASCII for defensive programming purposes, as not all servers, proxies, and clients may support non-ASCII characters.
Here’s an example of a custom HTTP header:
X-MyApp-UserId: 12345
In this example, the custom header name "X-MyApp-UserId" clearly indicates that it’s a private, application-specific header. The value "12345" is a simple ASCII string.
To illustrate the concept of using custom HTTP headers for debugging purposes, consider the following example:
X-Debug-Variable: some_value
In this case, the custom header name "X-Debug-Variable" indicates that it’s a temporary, debugging-related header. The value "some_value" can be used to pass information about the current state of the application or variables being debugged.
In conclusion, when creating custom HTTP headers, it’s essential to follow established naming conventions and best practices. By choosing sensible, descriptive names and avoiding unnecessary prefixes, developers can ensure that their custom headers are clear, concise, and unlikely to conflict with existing or future standard headers.