Getheader

Getheader is a term used to describe a function or method that retrieves the value of a header by name from a collection of headers in HTTP messages or other structured data. The name of the function commonly appears as getHeader, getheader, or a language-specific variant, and it is widely used across web programming libraries, HTTP clients, and email/MIME parsers.

Most header systems treat header names as case-insensitive in HTTP contexts. A typical getheader implementation returns a single value—the first value associated with the header key—while some headers can have multiple values. Depending on the API, a caller may receive a string, a list of strings, or a null/None when the header is absent. Many implementations allow supplying a default value to use if the header is missing.

Examples: In Python's http.client.HTTPResponse, the method getheader(name) returns the value or None. In Go's net/http package, the Header type has a Get method that returns the first value for a key. In the JavaScript Fetch API, the Headers interface exposes get(name) to obtain the first header value. Some libraries offer a get_all or getAll function to retrieve all values for a multi-valued header.

Because header values may be multi-valued or modified by intermediaries, applications should avoid assuming a single authoritative value and should consider the cache, proxy, and encoding implications when using getheader.