set parser failed with attempt to apply non-function

[jangorecki]

Using latest CRAN plumber. Consulted news file and my issue does not seem to be solved in devel.

System details

R version 4.3.2 (2023-10-31)
Platform: x86_64-redhat-linux-gnu (64-bit)
Running under: Fedora Linux 39 (Workstation Edition)

Matrix products: default
BLAS/LAPACK: FlexiBLAS OPENBLAS-OPENMP;  LAPACK version 3.11.0

locale:
 [1] LC_CTYPE=en_US.UTF-8       LC_NUMERIC=C              
 [3] LC_TIME=en_US.UTF-8        LC_COLLATE=en_US.UTF-8    
 [5] LC_MONETARY=en_US.UTF-8    LC_MESSAGES=en_US.UTF-8   
 [7] LC_PAPER=en_US.UTF-8       LC_NAME=C                 
 [9] LC_ADDRESS=C               LC_TELEPHONE=C            
[11] LC_MEASUREMENT=en_US.UTF-8 LC_IDENTIFICATION=C       

time zone: Europe/Zurich
tzcode source: system (glibc)

attached base packages:
[1] stats     graphics  grDevices utils     datasets  methods   base     

loaded via a namespace (and not attached):
 [1] plumber_1.2.1   compiler_4.3.2  ellipsis_0.3.2  magrittr_2.0.3 
 [5] R6_2.5.1        cli_3.6.1       later_1.3.1     promises_1.2.1 
 [9] tools_4.3.2     swagger_3.33.1  Rcpp_1.0.11     stringi_1.8.1  
[13] jsonlite_1.8.7  webutils_1.2.0  httpuv_1.6.12   lifecycle_1.0.4
[17] rlang_1.1.2  

no {sessioninfo} pkg

Reproduce

create r.R file:

#* test
#* @post /test
function(x) {
  cat("input str(x):\n")
  cat(capture.output(str(x)), sep="\n")
  x
}

try setting parser

plumber::plumb("r.R")$setParser(list(json=list(simplifyMatrix=FALSE, simplifyDataFrame=FALSE), rds=list()))
#Error: attempt to apply non-function

Describe the problem in detail

Setting parser for json type to not simplify to matrix or data.frame is failing. Using according to manual of setParser method at https://www.rplumber.io/reference/Plumber.html?q=parser#method-setparsers-

Background

I need to set json parser because otherwise my API is not type stable (giving matrix or list depending on the length of vectors in the input), see without the parser:

plumber::plumb("r.R")$run(host="0.0.0.0", port=8000)

curl -H "Content-Type: application/json" --data '{"x":[[1,2,3], [4,5,6]]}' http://localhost:8000/test
curl -H "Content-Type: application/json" --data '{"x":[[1,2,3], [4,5]]}' http://localhost:8000/test

input str(x):
 int [1:2, 1:3] 1 4 2 5 3 6
input str(x):
List of 2
 $ : int [1:3] 1 2 3
 $ : int [1:2] 4 5