From da4eca5da56b109b91452ef013456b883034c258 Mon Sep 17 00:00:00 2001
From: Denis Kirillov <denis@nspcc.ru>
Date: Wed, 30 Jun 2021 18:10:11 +0300
Subject: [PATCH] [#94] GetObject support conditional headers

Supported If-Modified-Since and If-Unmodified-Since.

Signed-off-by: Denis Kirillov <denis@nspcc.ru>
---
 api/handler/get.go | 42 ++++++++++++++++++++++++++++++++++++++++++
 api/headers.go     |  4 +++-
 2 files changed, 45 insertions(+), 1 deletion(-)

diff --git a/api/handler/get.go b/api/handler/get.go
index 5113ad85b..2450062c0 100644
--- a/api/handler/get.go
+++ b/api/handler/get.go
@@ -5,6 +5,7 @@ import (
 	"net/http"
 	"strconv"
 	"strings"
+	"time"
 
 	"github.com/gorilla/mux"
 	"github.com/nspcc-dev/neofs-s3-gw/api"
@@ -12,6 +13,11 @@ import (
 	"go.uber.org/zap"
 )
 
+type getObjectArgs struct {
+	IfModifiedSince   time.Time
+	IfUnmodifiedSince time.Time
+}
+
 func fetchRangeHeader(headers http.Header, fullSize uint64) (*layer.RangeParams, error) {
 	const prefix = "bytes="
 	rangeHeader := headers.Get("Range")
@@ -73,10 +79,25 @@ func (h *handler) GetObjectHandler(w http.ResponseWriter, r *http.Request) {
 		rid = api.GetRequestID(r.Context())
 	)
 
+	args, err := parseGetObjectArgs(r.Header)
+	if err != nil {
+		return
+	}
+
 	if inf, err = h.obj.GetObjectInfo(r.Context(), bkt, obj); err != nil {
 		writeError(w, r, h.log, "could not find object", rid, bkt, obj, err)
 		return
 	}
+
+	if !args.IfModifiedSince.IsZero() && inf.Created.Before(args.IfModifiedSince) {
+		w.WriteHeader(http.StatusNotModified)
+		return
+	}
+	if !args.IfUnmodifiedSince.IsZero() && inf.Created.After(args.IfUnmodifiedSince) {
+		w.WriteHeader(http.StatusPreconditionFailed)
+		return
+	}
+
 	if params, err = fetchRangeHeader(r.Header, uint64(inf.Size)); err != nil {
 		writeError(w, r, h.log, "could not parse range header", rid, bkt, obj, err)
 		return
@@ -97,6 +118,27 @@ func (h *handler) GetObjectHandler(w http.ResponseWriter, r *http.Request) {
 	}
 }
 
+func parseGetObjectArgs(headers http.Header) (*getObjectArgs, error) {
+	var err error
+	args := &getObjectArgs{}
+
+	ifModifiedSince := headers.Get(api.IfModifiedSince)
+	if len(ifModifiedSince) > 0 {
+		if args.IfModifiedSince, err = time.Parse(http.TimeFormat, ifModifiedSince); err != nil {
+			return nil, fmt.Errorf("couldn't parse %s header: %w", api.IfModifiedSince, err)
+		}
+	}
+
+	ifUnmodifiedSince := headers.Get(api.IfUnmodifiedSince)
+	if len(ifUnmodifiedSince) > 0 {
+		if args.IfUnmodifiedSince, err = time.Parse(http.TimeFormat, ifUnmodifiedSince); err != nil {
+			return nil, fmt.Errorf("couldn't parse %s header: %w", api.IfUnmodifiedSince, err)
+		}
+	}
+
+	return args, nil
+}
+
 func writeRangeHeaders(w http.ResponseWriter, params *layer.RangeParams, size int64) {
 	w.Header().Set("Accept-Ranges", "bytes")
 	w.Header().Set("Content-Range", fmt.Sprintf("bytes %d-%d/%d", params.Start, params.End, size))
diff --git a/api/headers.go b/api/headers.go
index 085e3f773..4e8380f4e 100644
--- a/api/headers.go
+++ b/api/headers.go
@@ -1,6 +1,6 @@
 package api
 
-// Standard S3 HTTP response constants.
+// Standard S3 HTTP request/response constants.
 const (
 	LastModified       = "Last-Modified"
 	Date               = "Date"
@@ -22,4 +22,6 @@ const (
 	ContentDisposition = "Content-Disposition"
 	Authorization      = "Authorization"
 	Action             = "Action"
+	IfModifiedSince    = "If-Modified-Since"
+	IfUnmodifiedSince  = "If-Unmodified-Since"
 )