* Added a sha256 method to module_common

* Added a sha256sum parameter to the get_url module to enable
cryptographic verification of downloaded files
* Fixed a few typos in the documentation

network/get_url

@@ -33,7 +33,7 @@ description:
        server I(must) have direct access to the remote resource.
      - By default, if an environment variable C(<protocol>_proxy) is set on
        the target host, requests will be sent through that proxy. This
-       behaviour can be overriden by setting a variable for this task
+       behaviour can be overridden by setting a variable for this task
        (see `setting the environment
        <http://ansible.cc/docs/playbooks2.html#setting-the-environment-and-working-with-proxies>`_),
        or by using the use_proxy option.
@@ -53,19 +53,26 @@ options:
     default: null
   force:
     description:
-      - if C(yes), will download the file every time and replace the
+      - If C(yes), will download the file every time and replace the
         file if the contents change. If C(no), the file will only be downloaded if
         the destination does not exist. Generally should be C(yes) only for small
-        local files. prior to 0.6, acts if C(yes) by default.
+        local files. Prior to 0.6, this module behaved as if C(yes) was the default.
     version_added: "0.7"
     required: false
     choices: [ "yes", "no" ]
     default: "no"
     aliases: [ "thirsty" ]
+  sha256sum:
+    description:
+      - If a SHA-256 checksum is passed to this parameter, the digest of the
+        destination file will be calculated after it is downloaded to ensure
+        its integrity and verify that the transfer completed successfully.
+    required: false
+    default: null
   use_proxy:
     description:
-      - if C(no), it will not use a proxy, even if one is defined by
+      - if C(no), it will not use a proxy, even if one is defined in
-        in an environment variable on the target hosts.
+        an environment variable on the target hosts.
     required: false
     default: 'yes'
     choices: ['yes', 'no']
@@ -81,20 +88,30 @@ author: Jan-Piet Mens
 '''
 
 EXAMPLES='''
+# Download file.conf to /etc/foo.conf with read permissions set for the user and group
 get_url: url=http://example.com/path/file.conf dest=/etc/foo.conf mode=0440
+
+# Download file.conf to /etc/foo.conf and ensure that it matches the specified SHA-256 checksum
+get_url: url=http://example.com/path/file.conf dest=/etc/foo.conf sha256sum=b5bb9d8014a0f9b1d61e21e796d78dccdf1352f23cd32812f4850b878ae4944c
 '''
 
 
-HAS_URLLIB2 = True
+try:
+    import hashlib
+    HAS_HASHLIB=True
+except ImportError:
+    HAS_HASHLIB=False
+
 try:
     import urllib2
+    HAS_URLLIB2 = True
 except ImportError:
     HAS_URLLIB2 = False
-HAS_URLPARSE = True
 
 try:
     import urlparse
     import socket
+    HAS_URLPARSE = True
 except ImportError:
     HAS_URLPARSE=False
 
@@ -217,6 +234,7 @@ def main():
             url = dict(required=True),
             dest = dict(required=True),
             force = dict(default='no', aliases=['thirsty'], type='bool'),
+            sha256sum = dict(default=''),
             use_proxy = dict(default='yes', type='bool')
         ),
         add_file_common_args=True
@@ -225,6 +243,7 @@ def main():
     url  = module.params['url']
     dest = os.path.expanduser(module.params['dest'])
     force = module.params['force']
+    sha256sum = module.params['sha256sum']
     use_proxy = module.params['use_proxy']
 
     if os.path.isdir(dest):
@@ -273,6 +292,16 @@ def main():
     else:
         changed = False
 
+    # Check the digest of the destination file and ensure that it matches the 
+    # sha256sum parameter if it is present
+    if sha256sum != '':
+        if not HAS_HASHLIB:
+            os.remove(dest)
+            module.fail_json(msg="The sha256sum parameter requires hashlib, which is available in Python 2.5 and higher")
+        if sha256sum != module.sha256(dest):
+            os.remove(dest)
+            module.fail_json(msg="The SHA-256 checksum for %s did not match %s" % (dest, sha256sum))
+
     os.remove(tmpsrc)
 
     # allow file attribute changes
@@ -283,7 +312,7 @@ def main():
 
     # Mission complete
     module.exit_json(url=url, dest=dest, src=tmpsrc, md5sum=md5sum_src,
-        changed=changed, msg=info.get('msg', ''))
+        sha256sum=sha256sum, changed=changed, msg=info.get('msg', ''))
 
 # this is magic, see lib/ansible/module_common.py
 #<<INCLUDE_ANSIBLE_MODULE_COMMON>>