add httpcat utility

cmd/httpcat/README.md

@@ -0,0 +1,5 @@
+# HTTP Cat
+
+An HTTP server that returns the HTTP request as text in the response body.
+Useful for debugging proxy configurations.
+

cmd/httpcat/main.go

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+package main
+
+import (
+	"flag"
+	"fmt"
+	"io"
+	"log"
+	"net/http"
+	"strings"
+)
+
+var (
+	ports = flag.String("ports", "", "comma-separated list of ports to listen on")
+)
+
+type CatHandler struct{}
+
+var _ http.Handler = &CatHandler{}
+
+func (cs *CatHandler) ServeHTTP(w http.ResponseWriter, req *http.Request) {
+	log.Printf("[%s] %s %s", req.Host, req.Method, req.URL.Path)
+
+	w.Write([]byte(fmt.Sprintf("HTTP1.1 %s %s\n", req.Method, req.URL.Path)))
+	for k, v := range req.Header {
+		w.Write([]byte(fmt.Sprintf("%s: %s\n", k, strings.Join(v, ", "))))
+	}
+	w.Write([]byte{'\n'})
+
+	if req.Body != nil {
+		io.Copy(w, req.Body)
+	}
+}
+
+func main() {
+	flag.Parse()
+
+	errch := make(chan error)
+	done := make(chan struct{})
+	for _, p := range strings.Split(*ports, ",") {
+		port := strings.TrimSpace(p)
+		if port[0] != ':' {
+			port = ":" + port
+		}
+		go func() {
+			log.Printf("listening on %s\n", port)
+			if err := http.ListenAndServe(port, new(CatHandler)); err != nil {
+				log.Println(err)
+				errch <- err
+			}
+		}()
+	}
+
+	go func() {
+		<-errch
+		done <- struct{}{}
+	}()
+
+	<-done
+}