Repository: scrapy/scrapy (python)

Issue:
Sitemap spider not robust against wrong sitemap URLs in robots.txt
[The "specs"](http://www.sitemaps.org/protocol.html#submit_robots) do say that the URL should be a "full URL":

> You can specify the location of the Sitemap using a robots.txt file. To do this, simply add the following line including the full URL to the sitemap:
> `Sitemap: http://www.example.com/sitemap.xml`

But some robots.txt use relative ones.

Example: http://www.asos.com/robots.txt

```
User-agent: *
Sitemap: /sitemap.ashx
Sitemap: http://www.asos.com/sitemap.xml
Disallow: /basket/
(...)
```

Spider:
```
from scrapy.spiders import SitemapSpider


class TestSpider(SitemapSpider):
    name = "test"
    sitemap_urls = [
        'http://www.asos.com/robots.txt',
    ]

    def parse(self, response):
        self.logger.info('parsing %r' % response.url)
```
Logs:

```
$ scrapy runspider spider.py
Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/54.0.2840.90 Safari/537.36'
2016-11-09 17:46:19 [scrapy] INFO: Scrapy 1.2.1 started (bot: scrapybot)
(...)
2016-11-09 17:46:19 [scrapy] DEBUG: Crawled (200) <GET http://www.asos.com/robots.txt> (referer: None)
2016-11-09 17:46:19 [scrapy] ERROR: Spider error processing <GET http://www.asos.com/robots.txt> (referer: None)
Traceback (most recent call last):
  File "/home/paul/.virtualenvs/scrapy12/local/lib/python2.7/site-packages/scrapy/utils/defer.py", line 102, in iter_errback
    yield next(it)
  File "/home/paul/.virtualenvs/scrapy12/local/lib/python2.7/site-packages/scrapy/spidermiddlewares/offsite.py", line 29, in process_spider_output
    for x in result:
  File "/home/paul/.virtualenvs/scrapy12/local/lib/python2.7/site-packages/scrapy/spidermiddlewares/referer.py", line 22, in <genexpr>
    return (_set_referer(r) for r in result or ())
  File "/home/paul/.virtualenvs/scrapy12/local/lib/python2.7/site-packages/scrapy/spidermiddlewares/urllength.py", line 37, in <genexpr>
    return (r for r in result or () if _filter(r))
  File "/home/paul/.virtualenvs/scrapy12/local/lib/python2.7/site-packages/scrapy/spidermiddlewares/depth.py", line 58, in <genexpr>
    return (r for r in result or () if _filter(r))
  File "/home/paul/.virtualenvs/scrapy12/local/lib/python2.7/site-packages/scrapy/spiders/sitemap.py", line 36, in _parse_sitemap
    yield Request(url, callback=self._parse_sitemap)
  File "/home/paul/.virtualenvs/scrapy12/local/lib/python2.7/site-packages/scrapy/http/request/__init__.py", line 25, in __init__
    self._set_url(url)
  File "/home/paul/.virtualenvs/scrapy12/local/lib/python2.7/site-packages/scrapy/http/request/__init__.py", line 57, in _set_url
    raise ValueError('Missing scheme in request url: %s' % self._url)
ValueError: Missing scheme in request url: /sitemap.ashx
2016-11-09 17:46:19 [scrapy] INFO: Closing spider (finished)
2016-11-09 17:46:19 [scrapy] INFO: Dumping Scrapy stats:
{'downloader/request_bytes': 291,
 'downloader/request_count': 1,
 'downloader/request_method_count/GET': 1,
 'downloader/response_bytes': 1857,
 'downloader/response_count': 1,
 'downloader/response_status_count/200': 1,
 'finish_reason': 'finished',
 'finish_time': datetime.datetime(2016, 11, 9, 16, 46, 19, 332383),
 'log_count/DEBUG': 2,
 'log_count/ERROR': 1,
 'log_count/INFO': 7,
 'response_received_count': 1,
 'scheduler/dequeued': 1,
 'scheduler/dequeued/memory': 1,
 'scheduler/enqueued': 1,
 'scheduler/enqueued/memory': 1,
 'spider_exceptions/ValueError': 1,
 'start_time': datetime.datetime(2016, 11, 9, 16, 46, 19, 71714)}
2016-11-09 17:46:19 [scrapy] INFO: Spider closed (finished)
```

Pull request description:
[MRG+1] Handle relative sitemap URLs in robots.txt
Fixes #2390

Patch:
diff --git a/scrapy/spiders/sitemap.py b/scrapy/spiders/sitemap.py
index 89d96c330..9e45637c3 100644
--- a/scrapy/spiders/sitemap.py
+++ b/scrapy/spiders/sitemap.py
@@ -32,7 +32,7 @@ class SitemapSpider(Spider):
 
     def _parse_sitemap(self, response):
         if response.url.endswith('/robots.txt'):
-            for url in sitemap_urls_from_robots(response.text):
+            for url in sitemap_urls_from_robots(response.text, base_url=response.url):
                 yield Request(url, callback=self._parse_sitemap)
         else:
             body = self._get_sitemap_body(response)
diff --git a/scrapy/utils/sitemap.py b/scrapy/utils/sitemap.py
index 008196435..4742b3e13 100644
--- a/scrapy/utils/sitemap.py
+++ b/scrapy/utils/sitemap.py
@@ -4,7 +4,9 @@ Module for processing Sitemaps.
 Note: The main purpose of this module is to provide support for the
 SitemapSpider, its API is subject to change without notice.
 """
+
 import lxml.etree
+from six.moves.urllib.parse import urljoin
 
 
 class Sitemap(object):
@@ -34,10 +36,11 @@ class Sitemap(object):
                 yield d
 
 
-def sitemap_urls_from_robots(robots_text):
+def sitemap_urls_from_robots(robots_text, base_url=None):
     """Return an iterator over all sitemap urls contained in the given
     robots.txt file
     """
     for line in robots_text.splitlines():
         if line.lstrip().lower().startswith('sitemap:'):
-            yield line.split(':', 1)[1].strip()
+            url = line.split(':', 1)[1].strip()
+            yield urljoin(base_url, url)


Test patch:
diff --git a/tests/test_spider.py b/tests/test_spider.py
index 1d22c1212..079734a69 100644
--- a/tests/test_spider.py
+++ b/tests/test_spider.py
@@ -332,13 +332,17 @@ class SitemapSpiderTest(SpiderTest):
         robots = b"""# Sitemap files
 Sitemap: http://example.com/sitemap.xml
 Sitemap: http://example.com/sitemap-product-index.xml
+Sitemap: HTTP://example.com/sitemap-uppercase.xml
+Sitemap: /sitemap-relative-url.xml
 """
 
         r = TextResponse(url="http://www.example.com/robots.txt", body=robots)
         spider = self.spider_class("example.com")
         self.assertEqual([req.url for req in spider._parse_sitemap(r)],
                          ['http://example.com/sitemap.xml',
-                          'http://example.com/sitemap-product-index.xml'])
+                          'http://example.com/sitemap-product-index.xml',
+                          'http://example.com/sitemap-uppercase.xml',
+                          'http://www.example.com/sitemap-relative-url.xml'])
 
 
 class BaseSpiderDeprecationTest(unittest.TestCase):
diff --git a/tests/test_utils_sitemap.py b/tests/test_utils_sitemap.py
index bd2677956..716bb44eb 100644
--- a/tests/test_utils_sitemap.py
+++ b/tests/test_utils_sitemap.py
@@ -119,13 +119,18 @@ Disallow: /s*/*tags
 # Sitemap files
 Sitemap: http://example.com/sitemap.xml
 Sitemap: http://example.com/sitemap-product-index.xml
+Sitemap: HTTP://example.com/sitemap-uppercase.xml
+Sitemap: /sitemap-relative-url.xml
 
 # Forums
 Disallow: /forum/search/
 Disallow: /forum/active/
 """
-        self.assertEqual(list(sitemap_urls_from_robots(robots)),
-             ['http://example.com/sitemap.xml', 'http://example.com/sitemap-product-index.xml'])
+        self.assertEqual(list(sitemap_urls_from_robots(robots, base_url='http://example.com')),
+                         ['http://example.com/sitemap.xml',
+                          'http://example.com/sitemap-product-index.xml',
+                          'http://example.com/sitemap-uppercase.xml',
+                          'http://example.com/sitemap-relative-url.xml'])
 
     def test_sitemap_blanklines(self):
         """Assert we can deal with starting blank lines before <xml> tag"""