Expose precondition error code header

Co-authored-by: Pijus Kamandulis <pikami@users.noreply.github.com>

api/handlers/documents.go

@@ -105,6 +105,7 @@ func (h *Handlers) ReplaceDocument(c *gin.Context) {
 
 	if ifMatch := c.GetHeader(headers.IfMatch); ifMatch != "" {
 		if existingDocument["_etag"] != ifMatch {
+			c.Header(headers.ErrorCode, "PreconditionFailed")
 			c.JSON(http.StatusPreconditionFailed, constants.PreconditionFailedResponse)
 			return
 		}

api/headers/headers.go

@@ -4,6 +4,7 @@ const (
 	AIM                = "A-Im"
 	Authorization      = "authorization"
 	CosmosLsn          = "x-ms-cosmos-llsn"
+	ErrorCode          = "x-ms-error-code"
 	ETag               = "etag"
 	GlobalCommittedLsn = "x-ms-global-committed-lsn"
 	IfMatch            = "if-match"

api/tests/documents_test.go

@@ -403,7 +403,7 @@ func Test_Documents(t *testing.T) {
 			var respErr *azcore.ResponseError
 			if errors.As(err, &respErr) {
 				assert.Equal(t, http.StatusPreconditionFailed, respErr.StatusCode)
-				assert.Equal(t, "PreconditionFailed", respErr.ErrorCode)
+				assert.Equal(t, "PreconditionFailed", respErr.RawResponse.Header.Get("x-ms-error-code"))
 
 				responseBody, readErr := io.ReadAll(respErr.RawResponse.Body)
 				assert.Nil(t, readErr)