package engine
 
 import (
 	"path"
 	"net/http"
 )
 
 // ServeHTTP executes a job as specified by the http request `r`, and sends the
 // result as an http response.
 // This method allows an Engine instance to be passed as a standard http.Handler interface.
 //
 // Note that the protocol used in this methid is a convenience wrapper and is not the canonical
 // implementation of remote job execution. This is because HTTP/1 does not handle stream multiplexing,
 // and so cannot differentiate stdout from stderr. Additionally, headers cannot be added to a response
 // once data has been written to the body, which makes it inconvenient to return metadata such
 // as the exit status.
 //
 func (eng *Engine) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 	jobName := path.Base(r.URL.Path)
 	jobArgs, exists := r.URL.Query()["a"]
 	if !exists {
 		jobArgs = []string{}
 	}
 	w.Header().Set("Job-Name", jobName)
 	for _, arg := range(jobArgs) {
 		w.Header().Add("Job-Args", arg)
 	}
 	job := eng.Job(jobName, jobArgs...)
 	job.Stdout.Add(w)
 	job.Stderr.Add(w)
 	// FIXME: distinguish job status from engine error in Run()
 	// The former should be passed as a special header, the former
 	// should cause a 500 status
 	w.WriteHeader(http.StatusOK)
 	// The exit status cannot be sent reliably with HTTP1, because headers
 	// can only be sent before the body.
 	// (we could possibly use http footers via chunked encoding, but I couldn't find
 	// how to use them in net/http)
 	job.Run()
 }