I've written a very quick blast script in r to enable interfacing with the NCBI blast API. Sometimes however, the result url takes a while to load and my script throws an error until the url is ready. Is there an elegant way (i.e. a tryCatch option) to handle the error until the result is returned or timeout after a specified time?
library(rvest)
## Definitive set of blast API instructions can be found here: https://www.ncbi.nlm.nih.gov/staff/tao/URLAPI/new/BLAST_URLAPI.html
## Generate query URL
query_url <-
function(QUERY,
PROGRAM = "blastp",
DATABASE = "nr",
...) {
put_url_stem <-
'https://www.ncbi.nlm.nih.gov/blast/Blast.cgi?CMD=Put'
arguments = list(...)
paste0(
put_url_stem,
"&QUERY=",
QUERY,
"&PROGRAM=",
PROGRAM,
"&DATABASE=",
DATABASE,
arguments
)
}
blast_url <- query_url(QUERY = "NP_001117.2") ## test query
blast_session <- html_session(blast_url) ## create session
blast_form <- html_form(blast_session)[[1]] ## pull form from session
RID <- blast_form$fields$RID$value ## extract RID identifier
get_url <- function(RID, ...) {
get_url_stem <-
"https://www.ncbi.nlm.nih.gov/blast/Blast.cgi?CMD=Get"
arguments = list(...)
paste0(get_url_stem, "&RID=", RID, "&FORMAT_TYPE=XML", arguments)
}
hits_xml <- read_xml(get_url(RID)) ## this is the sticky part
Sometimes it takes several minutes for the get_url to go live so what I would like is to do is to keep trying let's say every 20-30 seconds until it either produces the url or times out after a pre-specified time.
