问题
I have a list of URLs (more than 4000) from a specific domain (pixilink.com) and what I want to do is to figure out if the provided domain is a picture or a video. To do this, I used the solutions provided here: How to write trycatch in R and Check whether a website provides photo or video based on a pattern in its URL and wrote the code shown below:
#Function to get the value of initial_mode from the URL
urlmode <- function(x){
mycontent <- readLines(x)
mypos <- grep("initial_mode = ", mycontent)
if(grepl("0", mycontent[mypos])){
return("picture")
} else if(grepl("tour", mycontent[mypos])){
return("video")
} else{
return(NA)
}
}
Also, in order to prevent having error for URLs that don't exist, I used the code below:
readUrl <- function(url) {
out <- tryCatch(
{
readLines(con=url, warn=FALSE)
return(1)
},
error=function(cond) {
return(NA)
},
warning=function(cond) {
return(NA)
},
finally={
message( url)
}
)
return(out)
}
Finally, I separated the list of URLs and pass it into the functions (here for instance, I used 1000 values from URL list) described above:
a <- subset(new_df, new_df$host=="www.pixilink.com")
vec <- a[['V']]
vec <- vec[1:1000] # only chose first 1000 rows
tt <- numeric(length(vec)) # checking validity of url
for (i in 1:length(vec)){
tt[i] <- readUrl(vec[i])
print(i)
}
g <- data.frame(vec,tt)
g2 <- g[which(!is.na(g$tt)),] #only valid url
dd <- numeric(nrow(g2))
for (j in 1:nrow(g2)){
dd[j] <- urlmode(g2[j,1])
}
Final <- cbind(g2,dd)
Final <- left_join(g, Final, by = c("vec" = "vec"))
I ran this code on a sample list of URLs with 100, URLs and it worked; however, after I ran it on whole list of URLs, it returned an error. Here is the error : Error in textConnection("rval", "w", local = TRUE) : all connections are in use Error in textConnection("rval", "w", local = TRUE) : all connections are in use
And after this even for sample URLs (100 samples that I tested before) I ran the code and got this error message : Error in file(con, "r") : all connections are in use
I also tried closeAllConnection after each recalling each function in the loop, but it didn't work.
Can anyone explain what this error is about? is it related to the number of requests we can have from the website? what's the solution?
回答1:
So, my guess as to why this is happening is because you're not closing the connections that you're opening via tryCatch() and via urlmode() through the use of readLines(). I was unsure of how urlmode() was going to be used in your previous post so it had made it as simple as I could (and in hindsight, that was badly done, my apologies). So I took the liberty of rewriting urlmode() to try and make it a little bit more robust for what appears to be a more expansive task at hand.
I think the comments in the code should help, so take a look below:
#Updated URL mode function with better
#URL checking, connection handling,
#and "mode" investigation
urlmode <- function(x){
#Check if URL is good to go
if(!httr::http_error(x)){
#Test cases
#x <- "www.pixilink.com/3"
#x <- "https://www.pixilink.com/93320"
#x <- "https://www.pixilink.com/93313"
#Then since there are redirect shenanigans
#Get the actual URL the input points to
#It should just be the input URL if there is
#no redirection
#This is important as this also takes care of
#checking whether http or https need to be prefixed
#in case the input URL is supplied without those
#(this can cause problems for url() below)
myx <- httr::HEAD(x)$url
#Then check for what the default mode is
mycon <- url(myx)
open(mycon, "r")
mycontent <- readLines(mycon)
mypos <- grep("initial_mode = ", mycontent)
#Close the connection since it's no longer
#necessary
close(mycon)
#Some URLs with weird formats can return
#empty on this one since they don't
#follow the expected format.
#See for example: "https://www.pixilink.com/clients/899/#3"
#which is actually
#redirected from "https://www.pixilink.com/3"
#After that, evaluate what's at mypos, and always
#return the actual URL
#along with the result
if(!purrr::is_empty(mypos)){
#mystr<- stringr::str_extract(mycontent[mypos], "(?<=initial_mode\\s\\=).*")
mystr <- stringr::str_extract(mycontent[mypos], "(?<=\').*(?=\')")
return(c(myx, mystr))
#return(mystr)
#So once all that is done, check if the line at mypos
#contains a 0 (picture), tour (video)
#if(grepl("0", mycontent[mypos])){
# return(c(myx, "picture"))
#return("picture")
#} else if(grepl("tour", mycontent[mypos])){
# return(c(myx, "video"))
#return("video")
#}
} else{
#Valid URL but not interpretable
return(c(myx, "uninterpretable"))
#return("uninterpretable")
}
} else{
#Straight up invalid URL
#No myx variable to return here
#Just x
return(c(x, "invalid"))
#return("invalid")
}
}
#--------
#Sample code execution
library(purrr)
library(parallel)
library(future.apply)
library(httr)
library(stringr)
library(progressr)
library(progress)
#All future + progressr related stuff
#learned courtesy
#https://stackoverflow.com/a/62946400/9494044
#Setting up parallelized execution
no_cores <- parallel::detectCores()
#The above setup will ensure ALL cores
#are put to use
clust <- parallel::makeCluster(no_cores)
future::plan(cluster, workers = clust)
#Progress bar for sanity checking
progressr::handlers(progressr::handler_progress(format="[:bar] :percent :eta :message"))
#Website's base URL
baseurl <- "https://www.pixilink.com"
#Using future_lapply() to recursively apply urlmode()
#to a sequence of the URLs on pixilink in parallel
#and storing the results in sitetype
#Using a future chunk size of 10
#Everything is wrapped in with_progress() to enable the
#progress bar
#
range <- 93310:93350
#range <- 1:10000
progressr::with_progress({
myprog <- progressr::progressor(along = range)
sitetype <- do.call(rbind, future_lapply(range, function(b, x){
myprog() ##Progress bar signaller
myurl <- paste0(b, "/", x)
cat("\n", myurl, " ")
myret <- urlmode(myurl)
cat(myret, "\n")
return(c(myurl, myret))
}, b = baseurl, future.chunk.size = 10))
})
#Converting into a proper data.frame
#and assigning column names
sitetype <- data.frame(sitetype)
names(sitetype) <- c("given_url", "actual_url", "mode")
#A bit of wrangling to tidy up the mode column
sitetype$mode <- stringr::str_replace(sitetype$mode, "0", "picture")
head(sitetype)
# given_url actual_url mode
# 1 https://www.pixilink.com/93310 https://www.pixilink.com/93310 invalid
# 2 https://www.pixilink.com/93311 https://www.pixilink.com/93311 invalid
# 3 https://www.pixilink.com/93312 https://www.pixilink.com/93312 floorplan2d
# 4 https://www.pixilink.com/93313 https://www.pixilink.com/93313 picture
# 5 https://www.pixilink.com/93314 https://www.pixilink.com/93314 floorplan2d
# 6 https://www.pixilink.com/93315 https://www.pixilink.com/93315 tour
unique(sitetype$mode)
# [1] "invalid" "floorplan2d" "picture" "tour"
#--------
Basically, urlmode() now opens and closes connections only when necessary, checks for URL validity, URL redirection, and also "intelligently" extracts the value assigned to initial_mode. With the help of future.lapply(), and the progress bar from the progressr package, this can now be applied quite conveniently in parallel to as many pixilink.com/<integer> URLs as desired. With a bit of wrangling thereafter, the results can be presented very tidily as a data.frame as shown.
As an example, I've demonstrated this for a small range in the code above. Note the commented out 1:10000 range in the code in this context: I let this code run the last couple of hours over this (hopefully sufficiently) large range of URLs to check for errors and problems. I can attest that I encountered no errors (only the regular warnings In readLines(mycon) : incomplete final line found on 'https://www.pixilink.com/93334'). For proof, I have the data from all 10000 URLs written to a CSV file that I can provide upon request (I don't fancy uploading that to pastebin or elsewhere unnecessarily). Due to oversight on my part, I forgot to benchmark that run, but I suppose I could do that later if performance metrics are desired/would be considered interesting.
For your purposes, I believe you can simply take the entire code snippet below and run it verbatim (or with modifications) by just changing the range assignment right before the with_progress(do.call(...)) step to a range of your liking. I believe this approach is simpler and does away with having to deal with multiple functions and such (and no tryCatch() messes to deal with).
来源：https://stackoverflow.com/questions/64613433/how-to-properly-close-connection-so-i-wont-get-error-in-filecon-r-all-c