使用R语言下载FTP链接时遇550错误的技术求助

错误详情 #

尝试访问指定FTP链接时触发如下错误与警告：

Error in download.file(paste(url, filename, sep = ""), paste(getwd(),  :
cannot open URL 'ftp://gdo-dcp.ucllnl.org/pub/dcp/subset/202404050438gr5H_n_1msibTNA'
附加警告信息：
In download.file(paste(url, filename, sep = ""), paste(getwd(),  :
cannot open URL 'ftp://gdo-dcp.ucllnl.org/pub/dcp/subset/202404050438gr5H_n_1msibTNA': FTP status was '550 Requested action not taken; file unavailable'

所用代码 #

library(RCurl)
library(data.table)
# Set the location where data should be saved
setwd("D:/hydrology_climate/access0")
# Change to the FTP url for the subset request. This is provided in the
# DCP notification email (sent from no-reply@gdo4.llnl.gov).
options(download.file.method="libcurl", url.method="libcurl")
url = "ftp://gdo-dcp.ucllnl.org/pub/dcp/subset/202404050438gr5H_n_1msibT"
filenames = getURL(url, ftp.use.epsv = FALSE, dirlistonly = TRUE)
filenames <- strsplit(filenames, "\r\n")
filenames = unlist(filenames)
tmp = data.table(filenames)
zips = tmp[filenames %like% 'zip']
txts = tmp[filenames %like% 'txt']

nzips = as.numeric(nrow(zips))
for (i in 1:nzips) {
filename = zips[i]
download.file(paste(url, filename, sep = ""), paste(getwd(), "/", filename,sep = ""))
}
 ntxts = as.numeric(nrow(txts))
for (i in 1:ntxts) {
filename = txts[i]
download.file(paste(url, filename, sep = ""), paste(getwd(), "/", filename,sep = ""))
}

排查与解决步骤 #

• 修正FTP路径格式：当前url变量末尾缺少斜杠，导致拼接文件名时生成错误路径。给url末尾添加/：

  url = "ftp://gdo-dcp.ucllnl.org/pub/dcp/subset/202404050438gr5H_n_1msibT/"
  

• 优化路径拼接逻辑：用file.path()替代手动拼接，避免分隔符错误：

  # 替换下载循环中的路径拼接代码
  download.file(file.path(url, filename), file.path(getwd(), filename))
  

• 验证文件存在性：用FTP客户端（如FileZilla）或浏览器访问url对应的目录，确认目标zip/txt文件确实存在，且文件名无拼写错误。
• 调整FTP连接参数：给getURL添加被动模式参数，提升兼容性：

  filenames = getURL(url, ftp.use.epsv = FALSE, dirlistonly = TRUE, ftp.passive = TRUE)
  

• 替换下载函数：若download.file仍报错，改用RCurl的curlDownload函数：

  curlDownload(file.path(url, filename), file.path(getwd(), filename))
  

内容的提问来源于stack exchange，提问作者Berama