# README
Mid - Assorted middleware for HTTP services.
This is mid, a collection of useful middleware for HTTP services.
Err
The Err function turns a func(http.ResponseWriter, *http.Request) error
into an http.Handler,
allowing handler functions to return errors in a more natural fashion.
These errors result in the handler producing an HTTP 500 status code,
but CodeErr and Responder allow you to control this behavior
(see below).
A nil return produces a 200,
or a 204 (“no content”) if no bytes were written to the response object.
Usage:
func main() {
http.Handle("/foo", Err(fooHandler))
http.ListenAndServe(":8080", nil)
}
func fooHandler(w http.ResponseWriter, req *http.Request) error {
if x := req.FormValue("x"); x != "secret password" {
return CodeErr{C: http.StatusUnauthorized}
}
fmt.Fprintf(w, "You know the secret password")
return nil
}
JSON
The JSON function turns a func(context.Context, X) (Y, error)
into an http.Handler,
where X is the type of a parameter into which the HTTP request body is automatically JSON-unmarshaled,
and Y is the type of a result that is automatically JSON-marshaled into the HTTP response.
Any error is handled as with Err
(see above).
All parts of the func signature are optional:
the context.Context parameter,
the X parameter,
the Y result,
and the error result.
Usage:
func main() {
// Parses the request body as a JSON-encoded array of strings,
// then sorts, re-encodes, and returns that array.
http.Handle("/bar", JSON(barHandler))
http.ListenAndServe(":8080", nil)
}
func barHandler(inp []string) []string {
sort.Strings(inp)
return inp
}
CodeErr and Responder
CodeErr is an error type suitable for returning from Err- and JSON-wrapped handlers that can control the HTTP status code that gets returned.
It contains an HTTP status code field and a nested error.
Responder is an interface
(implemented by CodeErr)
that allows an error type to control how Err- and JSON-wrapped handlers respond to the pending request.
ResponseWrapper
ResponseWrapper is an http.ResponseWriter that wraps a nested http.ResponseWriter and also records the status code and number of bytes sent in the response.
Trace
The Trace function wraps an http.Handler and decorates the context.Context in its *http.Request with any “trace ID” string found in the request header.
Log
The Log function wraps an http.Handler with a function that writes a simple log line on the way into and out of the handler.
The log line includes any “trace ID” found in the request’s context.Context.