Output buffer difference between `Shelter.captureR()` and `Console()`

[James J Balamuta]

Relevant ticket: coatless/quarto-webr#208

The main issue is the lines from writing a data.frame with gt() to STDOUT are exceeding the buffer associated with Shelter.captureR() but not Console().

So, the webR REPL is able to correctly output the results; but, the Shelter.captureR() is not able to.

webr::install("gt")
gt::gt(mtcars) |> print(view = FALSE)

Under REPL:

Under Shelter.captureR():

[George Stagg]

This is a consequence of how R output is captured when running in the non-console context.

See:

webr/packages/webr/src/outputconnection.c

Lines 46 to 51 in c07d899

 #define BUFSIZE 10000 
 struct output_con_data { 
   SEXP output; 
   char buf[BUFSIZE]; 
   char *line, *cur; 
 }; 

and:

webr/packages/webr/src/outputconnection.c

Lines 98 to 105 in c07d899

 if (res < 0) { 
   data->cur[0] = '\0'; 
 } else if (res >= BUFSIZE - curlen) { 
   Rf_warning("printing of extremely long output is truncated"); 
   data->buf[BUFSIZE - 1] = '\0'; 
   res = BUFSIZE - curlen - 1; 
 } 
 data->cur += res < 0 ? 0 : res; 

---

We should consider:

• Increasing BUFSIZE in the short term.
• Adding a mechanism to dynamically grow output_con_data in the longer term.

---

The OP issue would also be solved by handling htmlwidget output correctly, avoiding need to capture raw HTML and output: asis. I'm working on this separately as part of our previously discussed Quarto/webR integration project.