errors: add errors coder (#946)

* add errors coder

* rename internal http to httputil

* add errors proto

internal/httputil/http.go

@@ -1,4 +1,4 @@
-package http
+package httputil
 
 import (
 	"net/http"
@@ -11,15 +11,6 @@ const (
 	baseContentType = "application"
 )
 
-var (
-	// HeaderAccept is accept header.
-	HeaderAccept = http.CanonicalHeaderKey("Accept")
-	// HeaderContentType is content-type header.
-	HeaderContentType = http.CanonicalHeaderKey("Content-Type")
-	// HeaderAcceptLanguage is accept-language header.
-	HeaderAcceptLanguage = http.CanonicalHeaderKey("Accept-Language")
-)
-
 // ContentType returns the content-type with base prefix.
 func ContentType(subtype string) string {
 	return strings.Join([]string{baseContentType, subtype}, "/")

internal/httputil/http_test.go

@@ -1,4 +1,4 @@
-package http
+package httputil
 
 import "testing"