breaking change: modify API for working with response metadata (#213)

* implement functions to append/get metadata and set/get status code

* сhanged behavior to return nil instead of empty metadata for getResponseMetadata()

* сhanged work with HTTP headers to use direct array assignment instead of for-range

* fix linters

* fix meter handler

* fix uninitialized response metadata for incoming context

* removed a useless test

* metrics handler has been fixed to work with compressed data

response_test.go

@@ -0,0 +1,79 @@
+package http
+
+import (
+	"context"
+	"net/http"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestSetResponseStatusCode(t *testing.T) {
+	tests := []struct {
+		name     string
+		ctx      context.Context
+		code     int
+		expected context.Context
+	}{
+		{
+			name:     "context without response status code key",
+			ctx:      context.Background(),
+			code:     http.StatusOK,
+			expected: context.Background(),
+		},
+		{
+			name:     "context with incorrect type in response status code value",
+			ctx:      context.WithValue(context.Background(), rspStatusCodeKey{}, struct{}{}),
+			code:     http.StatusOK,
+			expected: context.WithValue(context.Background(), rspStatusCodeKey{}, struct{}{}),
+		},
+		{
+			name:     "successfully set response status code",
+			ctx:      context.WithValue(context.Background(), rspStatusCodeKey{}, &rspStatusCodeVal{}),
+			code:     http.StatusOK,
+			expected: context.WithValue(context.Background(), rspStatusCodeKey{}, &rspStatusCodeVal{code: http.StatusOK}),
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			SetResponseStatusCode(tt.ctx, tt.code)
+			require.Equal(t, tt.expected, tt.ctx)
+		})
+	}
+}
+
+func TestGetResponseStatusCode(t *testing.T) {
+	tests := []struct {
+		name     string
+		ctx      context.Context
+		expected int
+	}{
+		{
+			name:     "no value in context, should return 200",
+			ctx:      context.Background(),
+			expected: http.StatusOK,
+		},
+		{
+			name:     "context with nil value",
+			ctx:      context.WithValue(context.Background(), rspStatusCodeKey{}, nil),
+			expected: http.StatusOK,
+		},
+		{
+			name:     "context with wrong type",
+			ctx:      context.WithValue(context.Background(), rspStatusCodeKey{}, struct{}{}),
+			expected: http.StatusOK,
+		},
+		{
+			name:     "context with valid status code",
+			ctx:      context.WithValue(context.Background(), rspStatusCodeKey{}, &rspStatusCodeVal{code: http.StatusNotFound}),
+			expected: http.StatusNotFound,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			require.Equal(t, tt.expected, GetResponseStatusCode(tt.ctx))
+		})
+	}
+}