Downloadhandler not working on published server - r

Question

I am creating an app to allow user to upload two excel files and carry over the comments one to the other one, then to download the merged file. The downloadhandler is not working when I tried to run it on the published server, however it running properly locally in rstudio. Any thoughts/suggestions?
library(plyr)
library(dplyr)
library(tidyr)
library(readxl)
library(xlsx)
library(openxlsx)
ui <- fluidPage(
br(),
titlePanel("Excel File Merging Tool"),
br(),
br(),
sidebarLayout(
sidebarPanel(
fileInput("file1", label = h3("Upload New File"), multiple = FALSE, buttonLabel = "Browse", placeholder = "No file selected"),
fileInput("file2", label = h3("Upload Old File"), multiple = FALSE, buttonLabel = "Browse", placeholder = "No file selected"),
actionButton("actionMerge", label = "Merge Uploaded Files"),
hr(),
downloadButton('downloadData', 'Download Merged File')
),
mainPanel(
)
)
)
#Defined Funtions
read_excel_allsheets <- function(filename, tibble = FALSE) {
sheets <- readxl::excel_sheets(filename)
x <- lapply(sheets, function(X) readxl::read_excel(filename, sheet = X))
if(!tibble) x <- lapply(x, as.data.frame)
names(x) <- sheets
x
}
server <- function(input, output) {
getData <- eventReactive(input$actionMerge, {
inFile1 <- input$file1
if (is.null(inFile1)){
return(NULL)
} else {
mydata1= read_excel_allsheets(inFile1$datapath)}
inFile2 <- input$file2
if (is.null(inFile2)){
return(NULL)
} else {
mydata2= read_excel_allsheets(inFile2$datapath)}
wb <- createWorkbook()
#find tabs not in old file
newSheets <- (names(mydata1))[which(!(names(mydata1)) %in% (names(mydata2)))]
if (length(newSheets) > 0){
for (n in newSheets)
{
mydata6 <- bind_rows(mydata1[n])
addWorksheet(wb, sheetName = names(mydata1[n]))
writeData(wb, names(mydata1[n]), mydata6)
}}
for (i in names(mydata1)){
for (j in names(mydata2)){
if (i == j ){
if ((nrow(as.data.frame(mydata1[i]))) == 0 | (nrow(as.data.frame(mydata2[j]))) == 0 )
{
mydata6 <- bind_rows(mydata1[i])
addWorksheet(wb, sheetName = names(mydata1[i]))
writeData(wb, names(mydata1[i]), mydata6)
}
else {
if (ncol(bind_rows(mydata1[i])) == ncol(bind_rows(mydata2[j])) )
{
mydata6 <- bind_rows(mydata1[i])
addWorksheet(wb, sheetName = names(mydata1[i]))
writeData(wb, names(mydata1[i]), mydata6)
}
else {
# validate(
# column_mismatch(mydata1[i], mydata2[j])
# )
drop_in_key <- c("Earliest data creation time", "Latest data update time", "Timestamp of last save in clinical views", "Date time value from the source file name",
"Lowest Date of Rec, Pg, Inst or Subj", "Record Minimum Created Datetime Stamp", "Record Maximum Updated Datetime Stamp", "Accessible to Jreview Timestamp")
mydatax0 = bind_rows(mydata1[i])
mydatax = bind_rows(mydata1[i])[,!(names(bind_rows(mydata1[i])) %in% drop_in_key)]
mydatanew <- mydatax %>% unite(col="Key", 1:(ncol(mydatax)-1), sep=";", remove=FALSE)
mydatanew$Newflag <- "New"
mydatanew0 = mydatanew %>% select(Key, Newflag)
mydatanew1 = bind_cols(mydatanew0,mydatax0)
mydatay0 = bind_rows(mydata2[j])
mydatay = bind_rows(mydata2[j])[,!(names(bind_rows(mydata2[j])) %in% drop_in_key)]
mydataold <- mydatay %>% unite(col="Key", 1:(ncol(mydatay)-1), sep=";", remove=FALSE)
mydataold$Oldflag <- "Old"
mydataold0 <- mydataold %>% select(Oldflag, Key)
mydataold1 <- bind_cols(mydataold0,mydatay0)
mydataold2 = select(mydataold1, Key, Oldflag, (ncol(bind_rows(mydata1[i]))+3):((ncol(mydataold1))))
mydata3 <- merge(x=mydatanew0, y=mydataold2, by="Key", all=TRUE)
mydata4 <- subset(mydata3, Newflag == "New")
mydata5 <- merge(x=mydatanew1, y=mydata4, by="Key", all.y=TRUE)
drop <- c("Key", "Newflag.x", "Oldflag", "Newflag.y")
mydata6 = mydata5[,!(names(mydata5) %in% drop)]
addWorksheet(wb, sheetName = names(mydata1[i]))
writeData(wb, names(mydata1[i]), mydata6)
}}}
else
NULL
}
}
saveWorkbook(wb, file = "aaa.xlsx" , overwrite = TRUE)
})
output$downloadData <- downloadHandler(
filename = function() {
paste0(input$file2, ".xlsx")
},
content = function(file) {
file.copy("aaa.xlsx", file)
})
}
shinyApp(ui = ui, server = server)```

Answer 1

Here's a toy shiny app that provides a solution that is safe for concurrent users. All operations are done on either (a) temporary files that shiny controls, or (b) in the directory of one of these temp files, using tempfile to create the new filename. Both of those assure new-file uniqueness, so no filename collisions. (I believe shiny's method is temporary directories under a temp-directory, at least that's what I'm seeing in my dev env here. So ... seemingly robust.)
The some_magic_function function is mostly because I didn't want to generate an example with openxlsx and sample datas and such, mostly my laziness. For your code, remove all of the if (runif... within the tryCatch and replace with whatever you need, ensuring your code ends by returning the filename with the new data (or updated) data.
... but keep the tryCatch! It will ensure that the function always returns "something". If all code succeeds, then the function will return the filename with new/updated data. If something goes wrong, it returns a class "error" string that can be used to communicate to the user (or otherwise react/recover).
Last thing, though it's just icing on my cupcake here: I use the shinyjs package to disable the 'merge' and 'download' buttons until there is valid data. Frankly, once the two file-selection inputs have something set, the "merge" button will likely never be disabled. However, if there's ever a problem during the merge/update, then the download button will be disabled (until a merge/update happens without error).
library(shiny)
library(shinyjs)
# a naive function that just concatenates the files, first removing
# the header row from the second file
some_magic_function <- function(f1, f2) {
# put the output file in the same directory as 'f2'
d <- dirname(f2)
if (!length(d)) d <- "."
output_file <- tempfile(tmpdir = d, fileext = paste0(".", tools::file_ext(f2)))
tryCatch({
if (runif(1) < 0.2) {
# purely for StackOverflow demonstration
stop("Something went wrong")
} else {
# add your stuff here (and remove the runif if/else)
writeLines(c(readLines(f1), readLines(f2)[-1]), output_file)
output_file # you must return this filename
}
}, error = function(e) e)
# implicitly returning the output_file or an error (text with class 'error')
}
shinyApp(
ui = fluidPage(
shinyjs::useShinyjs(),
titlePanel("Tool"),
sidebarLayout(
sidebarPanel(
fileInput("file1", label = "File #1", multiple = FALSE, placeholder = "No file selected"),
fileInput("file2", label = "File #2", multiple = FALSE, placeholder = "No file selected"),
actionButton("btn", label = "Merge uploaded files"),
hr(),
downloadButton("dnld", "Download merged file")
),
mainPanel(
tableOutput("tbl"),
hr(),
verbatimTextOutput("bigtext")
)
)
),
server = function(input, output, session) {
# start with neither button enabled
for (el in c("btn", "dnld")) shinyjs::disable(el)
# disable the 'merge' button until both files are set
observeEvent({
input$file1
input$file2
}, {
req(input$file1, input$file2)
shinyjs::toggleState("btn", isTRUE(file.exists(input$file1$datapath) && file.exists(input$file2$datapath)))
})
# this is the "workhorse" of the shiny app
newfilename <- eventReactive(input$btn, {
req(input$file1, input$file2)
some_magic_function(input$file1$datapath, input$file2$datapath)
})
# prevent the download handler from being used if the new file does not exist
observeEvent(newfilename(), {
cond <- !is.null(newfilename()) &&
!inherits(newfilename(), "error") &&
file.exists(newfilename())
shinyjs::toggleState("dnld", cond)
})
output$dnld <- downloadHandler(
filename = function() paste0("merged_", input$file2),
content = function(f) {
file.copy(newfilename(), f)
}
)
# some sample output, for fun
output$tbl <- renderTable({
req(newfilename(),
!inherits(newfilename(), "error"),
file.exists(newfilename()))
read.csv(newfilename(), nrows = 10, stringsAsFactors = FALSE)
})
output$bigtext <- renderText({
if (inherits(newfilename(), "error")) {
# if we get here then there was a problem
as.character(newfilename())
} else "(No problem)"
})
}
)
Notes:
shiny::req is supposed to ensure the data has something useful and "truthy" in it (see shiny::isTruthy). Normally it is good with detecting nulls, NA, empty variables, etc ... but it "passes" something that has class "error", perhaps counter-intuitive. That's why I had to be a little more explicit with conditions in some of the reactive blocks.
One impetus for having the merge/update functionality within an external not-shiny-requiring function (some_magic_function here) is that it facilitates testing of the merge functionality before adding the shiny scaffolding. It's difficult to test basic functionality when one is required to interact with a browser for every debugging step of basic functionality.