Error on creating new XML - Expecting an external pointer

[douglaszickuhr]

Issue Description and Expected Result

When trying to create a new XML body and it has a namespace defined on the root node, xml2 returns an error, even that the namespaces are correctly assigned. It just happens with the root node. An example of a situation like that is a SOAP request XML. The root node will be called soap:Envelope for soap 1.1 or soap12:for soap 1.2.

Reproducible Example

library(magrittr)
#> Warning: package 'magrittr' was built under R version 3.5.1
library(xml2)
#> Warning: package 'xml2' was built under R version 3.5.1

soap_body_xml <- function(){
  body <- xml_new_root( .value = "soap12:Envelope",
                        "xmlns:xsi" = "http://www.w3.org/2001/XMLSchema-instance",
                        "xmlns:xsd" = "http://www.w3.org/2001/XMLSchema",
                        "xmlns:soap12" = "http://www.w3.org/2003/05/soap-envelope") %>%
    xml_add_child("soap12:Body")
  
  body
}

soap_body_xml() %>%
  xml_root()
#> Error in ns_lookup(parent$doc, parent$node, parts[[1]]): Expecting an external pointer: [type=NULL].

^{Created on 2018-11-06 by the reprex package (v0.2.1)}

-->

Session Info

devtools::session_info() # Paste output below
#> output
- Session info --------------------------------------------------------------------------------------------------------------------------------------
 setting  value                       
 version  R version 3.5.0 (2018-04-23)
 os       Windows 7 x64 SP 1          
 system   x86_64, mingw32             
 ui       RStudio                     
 language (EN)                        
 collate  English_Ireland.1252        
 ctype    English_Ireland.1252        
 tz       Europe/London               
 date     2018-11-06                  

- Packages ------------------------------------------------------------------------------------------------------------------------------------------
 package     * version date       lib source        
 assertthat    0.2.0   2017-04-11 [1] CRAN (R 3.5.1)
 backports     1.1.2   2017-12-13 [1] CRAN (R 3.5.0)
 base64enc     0.1-3   2015-07-28 [1] CRAN (R 3.5.0)
 callr         3.0.0   2018-08-24 [1] CRAN (R 3.5.1)
 cli           1.0.1   2018-09-25 [1] CRAN (R 3.5.1)
 clipr         0.4.1   2018-06-23 [1] CRAN (R 3.5.1)
 crayon        1.3.4   2017-09-16 [1] CRAN (R 3.5.1)
 desc          1.2.0   2018-05-01 [1] CRAN (R 3.5.1)
 devtools      2.0.1   2018-10-26 [1] CRAN (R 3.5.1)
 digest        0.6.18  2018-10-10 [1] CRAN (R 3.5.1)
 evaluate      0.12    2018-10-09 [1] CRAN (R 3.5.1)
 fs            1.2.6   2018-08-23 [1] CRAN (R 3.5.1)
 glue          1.3.0   2018-07-17 [1] CRAN (R 3.5.1)
 hms           0.4.2   2018-03-10 [1] CRAN (R 3.5.1)
 htmltools     0.3.6   2017-04-28 [1] CRAN (R 3.5.1)
 httr        * 1.3.1   2017-08-20 [1] CRAN (R 3.5.1)
 janitor     * 1.1.1   2018-07-31 [1] CRAN (R 3.5.1)
 knitr         1.20    2018-02-20 [1] CRAN (R 3.5.1)
 lubridate   * 1.7.4   2018-04-11 [1] CRAN (R 3.5.1)
 magrittr    * 1.5     2014-11-22 [1] CRAN (R 3.5.1)
 memoise       1.1.0   2017-04-21 [1] CRAN (R 3.5.1)
 pillar        1.3.0   2018-07-14 [1] CRAN (R 3.5.1)
 pkgbuild      1.0.2   2018-10-16 [1] CRAN (R 3.5.1)
 pkgconfig     2.0.2   2018-08-16 [1] CRAN (R 3.5.1)
 pkgload       1.0.2   2018-10-29 [1] CRAN (R 3.5.1)
 prettyunits   1.0.2   2015-07-13 [1] CRAN (R 3.5.1)
 processx      3.2.0   2018-08-16 [1] CRAN (R 3.5.1)
 ps            1.2.0   2018-10-16 [1] CRAN (R 3.5.1)
 purrr       * 0.2.5   2018-05-29 [1] CRAN (R 3.5.1)
 R6            2.3.0   2018-10-04 [1] CRAN (R 3.5.1)
 Rcpp          0.12.19 2018-10-01 [1] CRAN (R 3.5.1)
 readr       * 1.1.1   2017-05-16 [1] CRAN (R 3.5.1)
 remotes       2.0.2   2018-10-30 [1] CRAN (R 3.5.1)
 reprex      * 0.2.1   2018-09-16 [1] CRAN (R 3.5.1)
 rlang         0.3.0.1 2018-10-25 [1] CRAN (R 3.5.1)
 rmarkdown     1.10    2018-06-11 [1] CRAN (R 3.5.1)
 rprojroot     1.3-2   2018-01-03 [1] CRAN (R 3.5.1)
 rstudioapi    0.8     2018-10-02 [1] CRAN (R 3.5.1)
 sessioninfo   1.1.0   2018-09-25 [1] CRAN (R 3.5.1)
 stringi       1.2.4   2018-07-20 [1] CRAN (R 3.5.1)
 stringr     * 1.3.1   2018-05-10 [1] CRAN (R 3.5.1)
 tibble        1.4.2   2018-01-22 [1] CRAN (R 3.5.1)
 usethis       1.4.0   2018-08-14 [1] CRAN (R 3.5.1)
 whisker       0.3-2   2013-04-28 [1] CRAN (R 3.5.1)
 withr         2.1.2   2018-03-15 [1] CRAN (R 3.5.1)
 xml2        * 1.2.0   2018-01-24 [1] CRAN (R 3.5.1)
 yaml          2.2.0   2018-07-25 [1] CRAN (R 3.5.1)

[1] C:/Users/ST9DZ1/Documents/R/win-library/3.5
[2] C:/Program Files/R/R-3.5.0/library
```r
</details>

[nuest]

I have the same problem creating documents with a namespace prefix on the root node. My workaround is to create a suitable string and then read that in to start with:

body <- xml2::read_xml('<soap12:Envelope xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:soap12="http://www.w3.org/2003/05/soap-envelope" />')
xml2::xml_add_child(body, "soap12:Body")
body

{xml_document}
<Envelope xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:soap12="http://www.w3.org/2003/05/soap-envelope">
[1] <soap12:Body/>

With some pointers how to start I'd be happy to attempt a PR to fix this. My first guess it the ... have to be used in

xml2/R/xml_modify.R

Line 125 in 7ed7218

namespace <- ns_lookup(parent$doc, parent$node, parts[[1]])

.

[douglaszickuhr]

Hey @nuest your solution seems way more elegant than mine. I've been creating an empty XML Body just containing a simple Body tag and later I replace it for soap12:Body using str_replace_all function from stringr package.

Anyway, it's been working here as a workaround but I'd love to contribute to fix this on xml2 package.

Cheers

soap_body_xml() %>%
      xml_add_child(method, xmlns = "http://ultraasp.net/") %>%
      xml_add_child("domain", domain) %>%
      xml_add_sibling("sessionToken", session_token) %>%
      xml_add_sibling("xmlMessage", xml_message) %>%
      xml_root() %>%
      as("character") %>%
      str_replace_all("Envelope", "soap12:Envelope") %>%
      str_replace_all("Body", "soap12:Body")

[douglaszickuhr]

I have gone through the code and it looks like the problem is exactly what you pointed. There is a problem when the namespace is being looked up.

My guess is that there is no point in validate that if the parent node is not a node, right? Like when creating a root node. I've tried the following solution, just adding a new condition to ignore the ns_lookup call if the parent$node is null.

What do you think? It might be too simplistic but it could fix the problem. :)

parts <- strsplit(.value, ":")[[1]]
  if ((length(parts) == 2) & !is.null(parent$node)) {
    namespace <- ns_lookup(parent$doc, parent$node, parts[[1]])
    node <- structure(list(node = node_new_ns(parts[[2]], namespace), doc = parent$doc), class = "xml_node")
  } else {
    node <- structure(list(node = node_new(.value), doc = parent$doc), class = "xml_node")
  }

[cderv]

I know that for adding a node, you can use xml_set_namespace to set the namespace after it has been defined. See #176
However, it does not seem to work for root node , but you can use xml_name to rename the node after creation.
I would create your soap xml like this

library(magrittr)
library(xml2)

root <- xml_new_root( .value = "Envelope",
                      "xmlns:xsi" = "http://www.w3.org/2001/XMLSchema-instance",
                      "xmlns:xsd" = "http://www.w3.org/2001/XMLSchema",
                      "xmlns:soap12" = "http://www.w3.org/2003/05/soap-envelope")
xml_name(root) <- "soap12:Envelope"
root %>%
  xml_add_child("Body") %>%
  xml_set_namespace("soap12") %>%
  xml_root()
#> {xml_document}
#> <soap12:Envelope xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:soap12="http://www.w3.org/2003/05/soap-envelope">
#> [1] <soap12:Body/>

^{Created on 2019-03-31 by the reprex package (v0.2.1.9000)}