From f80681815422865fbe0e9b637f38553fa965004a Mon Sep 17 00:00:00 2001
From: Solomon Hykes <solomon@dotcloud.com>
Date: Sun, 8 Dec 2013 07:33:23 +0000
Subject: [PATCH] Engine: convenience http transport for simple remote job
 execution

---
 engine/http.go | 40 ++++++++++++++++++++++++++++++++++++++++
 1 file changed, 40 insertions(+)
 create mode 100644 engine/http.go

diff --git a/engine/http.go b/engine/http.go
new file mode 100644
index 0000000000..6391b3ff5a
--- /dev/null
+++ b/engine/http.go
@@ -0,0 +1,40 @@
+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()
+}