Implement S3 Style ErrorCodes and Response

This patchset also brings in lot of cleanup in terms of minioapi codebase

pkg/api/minioapi/headers.go

@@ -0,0 +1,61 @@
+package minioapi
+
+import (
+	"bytes"
+	"encoding/json"
+	"encoding/xml"
+	"net/http"
+	"strconv"
+	"time"
+
+	mstorage "github.com/minio-io/minio/pkg/storage"
+)
+
+// Write Common Header helpers
+func writeCommonHeaders(w http.ResponseWriter, acceptsType string) {
+	w.Header().Set("Server", "Minio")
+	w.Header().Set("Content-Type", acceptsType)
+}
+
+func writeErrorResponse(w http.ResponseWriter, response interface{}, acceptsType contentType) []byte {
+	var bytesBuffer bytes.Buffer
+	var encoder encoder
+	// write common headers
+	writeCommonHeaders(w, getContentString(acceptsType))
+	switch acceptsType {
+	case xmlType:
+		encoder = xml.NewEncoder(&bytesBuffer)
+	case jsonType:
+		encoder = json.NewEncoder(&bytesBuffer)
+	}
+	encoder.Encode(response)
+	return bytesBuffer.Bytes()
+}
+
+// Write Object Header helper
+func writeObjectHeaders(w http.ResponseWriter, metadata mstorage.ObjectMetadata) {
+	lastModified := metadata.Created.Format(time.RFC1123)
+	// write common headers
+	writeCommonHeaders(w, metadata.ContentType)
+	w.Header().Set("ETag", metadata.ETag)
+	w.Header().Set("Last-Modified", lastModified)
+	w.Header().Set("Content-Length", strconv.FormatInt(metadata.Size, 10))
+	w.Header().Set("Connection", "close")
+}
+
+func writeObjectHeadersAndResponse(w http.ResponseWriter, response interface{}, acceptsType contentType) []byte {
+	var bytesBuffer bytes.Buffer
+	var encoder encoder
+	// write common headers
+	writeCommonHeaders(w, getContentString(acceptsType))
+	switch acceptsType {
+	case xmlType:
+		encoder = xml.NewEncoder(&bytesBuffer)
+	case jsonType:
+		encoder = json.NewEncoder(&bytesBuffer)
+	}
+
+	w.Header().Set("Connection", "close")
+	encoder.Encode(response)
+	return bytesBuffer.Bytes()
+}