[#13] Rename go module name according to NSPCC standards

- refactoring s3 gate structure
- cleanup unused code
- rename go module to `github.com/nspcc-dev/neofs-s3-gate`

closes #13

Signed-off-by: Evgeniy Kulikov <kim@nspcc.ru>

api/reqinfo.go

@@ -0,0 +1,112 @@
+package api
+
+import (
+	"context"
+	"sync"
+)
+
+type (
+	// KeyVal - appended to ReqInfo.Tags
+	KeyVal struct {
+		Key string
+		Val string
+	}
+
+	// ReqInfo stores the request info.
+	ReqInfo struct {
+		sync.RWMutex
+		RemoteHost   string   // Client Host/IP
+		Host         string   // Node Host/IP
+		UserAgent    string   // User Agent
+		DeploymentID string   // x-minio-deployment-id
+		RequestID    string   // x-amz-request-id
+		API          string   // API name - GetObject PutObject NewMultipartUpload etc.
+		BucketName   string   // Bucket name
+		ObjectName   string   // Object name
+		tags         []KeyVal // Any additional info not accommodated by above fields
+	}
+)
+
+// Key used for Get/SetReqInfo
+type contextKeyType string
+
+const ctxRequestInfo = contextKeyType("NeoFS-S3-Gate")
+
+// NewReqInfo :
+func NewReqInfo(remoteHost, userAgent, deploymentID, requestID, api, bucket, object string) *ReqInfo {
+	req := ReqInfo{}
+	req.RemoteHost = remoteHost
+	req.UserAgent = userAgent
+	req.API = api
+	req.DeploymentID = deploymentID
+	req.RequestID = requestID
+	req.BucketName = bucket
+	req.ObjectName = object
+	return &req
+}
+
+// AppendTags - appends key/val to ReqInfo.tags
+func (r *ReqInfo) AppendTags(key string, val string) *ReqInfo {
+	if r == nil {
+		return nil
+	}
+	r.Lock()
+	defer r.Unlock()
+	r.tags = append(r.tags, KeyVal{key, val})
+	return r
+}
+
+// SetTags - sets key/val to ReqInfo.tags
+func (r *ReqInfo) SetTags(key string, val string) *ReqInfo {
+	if r == nil {
+		return nil
+	}
+	r.Lock()
+	defer r.Unlock()
+	// Search of tag key already exists in tags
+	var updated bool
+	for _, tag := range r.tags {
+		if tag.Key == key {
+			tag.Val = val
+			updated = true
+			break
+		}
+	}
+	if !updated {
+		// Append to the end of tags list
+		r.tags = append(r.tags, KeyVal{key, val})
+	}
+	return r
+}
+
+// GetTags - returns the user defined tags
+func (r *ReqInfo) GetTags() []KeyVal {
+	if r == nil {
+		return nil
+	}
+	r.RLock()
+	defer r.RUnlock()
+	return append([]KeyVal(nil), r.tags...)
+}
+
+// SetReqInfo sets ReqInfo in the context.
+func SetReqInfo(ctx context.Context, req *ReqInfo) context.Context {
+	if ctx == nil {
+		return nil
+	}
+	return context.WithValue(ctx, ctxRequestInfo, req)
+}
+
+// GetReqInfo returns ReqInfo if set.
+func GetReqInfo(ctx context.Context) *ReqInfo {
+	if ctx != nil {
+		r, ok := ctx.Value(ctxRequestInfo).(*ReqInfo)
+		if ok {
+			return r
+		}
+		r = &ReqInfo{}
+		SetReqInfo(ctx, r)
+		return r
+	}
+	return nil
+}