1 files changed, 133 insertions, 0 deletions
diff --git a/paste/cascade.py b/paste/cascade.py
new file mode 100644
index 0000000..8207ae3
--- /dev/null
+++ b/paste/cascade.py
@@ -0,0 +1,133 @@
+# (c) 2005 Ian Bicking and contributors; written for Paste (http://pythonpaste.org)
+# Licensed under the MIT license: http://www.opensource.org/licenses/mit-license.php
+
+"""
+Cascades through several applications, so long as applications
+return ``404 Not Found``.
+"""
+from paste import httpexceptions
+from paste.util import converters
+import tempfile
+from cStringIO import StringIO
+
+__all__ = ['Cascade']
+
+def make_cascade(loader, global_conf, catch='404', **local_conf):
+    """
+    Entry point for Paste Deploy configuration
+
+    Expects configuration like::
+
+        [composit:cascade]
+        use = egg:Paste#cascade
+        # all start with 'app' and are sorted alphabetically
+        app1 = foo
+        app2 = bar
+        ...
+        catch = 404 500 ...
+    """
+    catch = map(int, converters.aslist(catch))
+    apps = []
+    for name, value in local_conf.items():
+        if not name.startswith('app'):
+            raise ValueError(
+                "Bad configuration key %r (=%r); all configuration keys "
+                "must start with 'app'"
+                % (name, value))
+        app = loader.get_app(value, global_conf=global_conf)
+        apps.append((name, app))
+    apps.sort()
+    apps = [app for name, app in apps]
+    return Cascade(apps, catch=catch)
+
+class Cascade(object):
+
+    """
+    Passed a list of applications, ``Cascade`` will try each of them
+    in turn.  If one returns a status code listed in ``catch`` (by
+    default just ``404 Not Found``) then the next application is
+    tried.
+
+    If all applications fail, then the last application's failure
+    response is used.
+
+    Instances of this class are WSGI applications.
+    """
+
+    def __init__(self, applications, catch=(404,)):
+        self.apps = applications
+        self.catch_codes = {}
+        self.catch_exceptions = []
+        for error in catch:
+            if isinstance(error, str):
+                error = int(error.split(None, 1)[0])
+            if isinstance(error, httpexceptions.HTTPException):
+                exc = error
+                code = error.code
+            else:
+                exc = httpexceptions.get_exception(error)
+                code = error
+            self.catch_codes[code] = exc
+            self.catch_exceptions.append(exc)
+        self.catch_exceptions = tuple(self.catch_exceptions)
+
+    def __call__(self, environ, start_response):
+        """
+        WSGI application interface
+        """
+        failed = []
+        def repl_start_response(status, headers, exc_info=None):
+            code = int(status.split(None, 1)[0])
+            if code in self.catch_codes:
+                failed.append(None)
+                return _consuming_writer
+            return start_response(status, headers, exc_info)
+
+        try:
+            length = int(environ.get('CONTENT_LENGTH', 0) or 0)
+        except ValueError:
+            length = 0
+        if length > 0:
+            # We have to copy wsgi.input
+            copy_wsgi_input = True
+            if length > 4096 or length < 0:
+                f = tempfile.TemporaryFile()
+                if length < 0:
+                    f.write(environ['wsgi.input'].read())
+                else:
+                    copy_len = length
+                    while copy_len > 0:
+                        chunk = environ['wsgi.input'].read(min(copy_len, 4096))
+                        if not chunk:
+                            raise IOError("Request body truncated")
+                        f.write(chunk)
+                        copy_len -= len(chunk)
+                f.seek(0)
+            else:
+                f = StringIO(environ['wsgi.input'].read(length))
+            environ['wsgi.input'] = f
+        else:
+            copy_wsgi_input = False
+        for app in self.apps[:-1]:
+            environ_copy = environ.copy()
+            if copy_wsgi_input:
+                environ_copy['wsgi.input'].seek(0)
+            failed = []
+            try:
+                v = app(environ_copy, repl_start_response)
+                if not failed:
+                    return v
+                else:
+                    if hasattr(v, 'close'):
+                        # Exhaust the iterator first:
+                        list(v)
+                        # then close:
+                        v.close()
+            except self.catch_exceptions:
+                pass
+        if copy_wsgi_input:
+            environ['wsgi.input'].seek(0)
+        return self.apps[-1](environ, start_response)
+
+def _consuming_writer(s):
+    pass