I won’t describe how to install the library and use it, but here is the link to the documentation where it is described in detail.
At first glance, it is a trivial task. Scrapy can work with FTP and handle files.
A simple example:
import scrapy
from scrapy.http import Request
class FtpSpider(scrapy.Spider):
name = "mozilla"
allowed_domains = ["ftp.mozilla.org"]
handle_httpstatus_list = [404]
def start_requests(self):
yield Request('ftp://ftp.mozilla.org/pub/firefox/releases/9.0b4/contrib/solaris_pkgadd/README.txt',
meta={'ftp_user': '', 'ftp_password': ''})
def parse(self, response):
print response.bodyAs you can see, we simply put link with ftp:// and add data for authorization. Scrapy understands that it deals with the FTP server and uses FTPDownloadHandler that is able connect and download files. The difficulty here is that Scrapy can download a file using a specific link to it, but it can’t download a list of files from the directory and walk the directory tree.
In my case it is the FTP server with a list of files and I need to get a list of links and deal with each link separately. Default FTP handler in Scrapy can’t work with the file list.
After googling a couple of articles and libraries, I came across ftptree. After analyzing the code, it became clear that the default FTP handler is replaced by their own one, which can download a list of files, but can not handle the files separately,
import json
from twisted.protocols.ftp import FTPFileListProtocol
from scrapy.http import Response
from scrapy.core.downloader.handlers.ftp import FTPDownloadHandler
class FtpListingHandler(FTPDownloadHandler):
def gotClient(self, client, request, filepath):
self.client = client
protocol = FTPFileListProtocol()
return client.list(filepath, protocol).addCallbacks(
callback=self._build_response,
callbackArgs=(request, protocol),
errback=self._failed,
errbackArgs=(request,))
def _build_response(self, result, request, protocol):
self.result = result
body = json.dumps(protocol.files)
return Response(url=request.url, status=200, body=body)To replace the default scrapy handler, you need to write your handler in the parser settings:
DOWNLOAD_HANDLERS = {'ftp': '.FtpListingHandler'}While writing the parser (spider) we decided to combine the two approaches as follows. When the link was pointed not to the file, but to the server itself, the code from ftptree was used, which retrieved and returned a list of all links to the file. Then this list was transmitted and each link from it was handled by the default handler in Scrapy.
Everything worked as it should, all links to files were received and each file was handled, and articles were received. But each time while running it, all the files were received and handled, even those that had already been handled, so we had to do something with that. Meta-data was transmitted with each file, for example: owner, creation date, etc. We decided to define new files by Date Modified indicator. While handling, I saved the most recent date when the file was created, and used it to filter files in the next operation. As a result, only the newest files were handled. This is an example of how a list of links to all files was received:
import scrapy
class FtpMetaRequest(scrapy.http.Request):
# add user with password to ftp meta request
user_meta = {'ftp_user': 'username', 'ftp_password': ''}
def init(self, args, **kwargs):
super(FtpMetaRequest, self).init(args, **kwargs)
self.meta.update(self.user_meta)
class FileFtpRequest(FtpMetaRequest):
pass
class ListFtpRequest(FtpMetaRequest):
pass
class MedisumSpider(scrapy.Spider):
name = "articlespider"
def start_requests(self):
# start request to get all files
yield ListFtpRequest("ftp:///")
def parse(self, response):
# get response with all files
files = json.loads(response.body)
# filter files
with open("article_max_date.txt", "r") as outfile:
date = outfile.read()
if date:
scrp_time = parser.parse(date)
files = filter(
lambda i: parser.parse(i['date']) >= scrp_time, files)
# get max date
date_max = max([parser.parse(fl['date']) for fl in files])
with open("article_max_date.txt", "w") as outfile:
outfile.write(date_max.isoformat())
# get data from each file
for f in files:
path = os.path.join(response.url, f['filename'])
request = FileFtpRequest(path, callback=self.parse_item)
yield request
def parse_item(self, response):
# do some actions
passLet's analyze the code:
FtpMetaRequest- adds user and password for requests to the server tometaFileFtpRequest,ListFtpRequest- with the help of these classes ourFtpListingHandlerdetects when it is necessary to get a single file, and when to get a list. This detection is also possible by adding your own flag to therequest.meta, but we prefer individual classes.MedisumSpider- parser (spider) itself
And here is the code of the handler itself:
import json
from twisted.protocols.ftp import FTPFileListProtocol
from scrapy.http import Response
from scrapy.core.downloader.handlers.ftp import FTPDownloadHandler
class FtpListingHandler(FTPDownloadHandler):
# get files list or one file
def gotClient(self, client, request, filepath):
# check what class sent a request
if isinstance(request, 'FileFtpRequest'):
return super(FtpListingHandler, self).gotClient(
client, request, filepath)
protocol = FTPFileListProtocol()
return client.list(filepath, protocol).addCallbacks(
callback=self._build_response,
callbackArgs=(request, protocol),
errback=self._failed,
errbackArgs=(request,))
def _build_response(self, result, request, protocol):
# get files list or one file
# check what class sent a request
if request.class.name == 'FtpMetaRequest':
return super(FtpListingHandler, self)._build_response(
result, request, protocol)
self.result = result
body = json.dumps(protocol.files)
return Response(url=request.url, status=200, body=body)Let’s analyze the handler code. As we can see, the FtpListingHandler itself is inherited from the default Scrapy FTP handler and it overrides two methods - gotClient and _build_response. When FileFtpRequest is received, it falls back to base handler behaior to process single file, in other cases it uses custom methods to work with list of files.
This example shows that we can add and change logic of handlers, which are available in Scrapy, in the way we need. Yet, the code remains understandable, concise and it is easy to maintain or extend it further if necessary. But Scrapy has more than enough standard solutions, which cover 99% of needs when writing a parser (spider).
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