web/http.py

"""
HTTP Utilities
(from web.py)
"""

__all__ = [
  "expires", "lastmodified", 
  "prefixurl", "modified", 
  "changequery", "url",
  "profiler",
]

import sys, os, threading, urllib, urlparse
try: import datetime
except ImportError: pass
import net, utils, webapi as web

def prefixurl(base=''):
    """
    Sorry, this function is really difficult to explain.
    Maybe some other time.
    """
    url = web.ctx.path.lstrip('/')
    for i in xrange(url.count('/')): 
        base += '../'
    if not base: 
        base = './'
    return base

def expires(delta):
    """
    Outputs an `Expires` header for `delta` from now. 
    `delta` is a `timedelta` object or a number of seconds.
    """
    if isinstance(delta, (int, long)):
        delta = datetime.timedelta(seconds=delta)
    date_obj = datetime.datetime.utcnow() + delta
    web.header('Expires', net.httpdate(date_obj))

def lastmodified(date_obj):
    """Outputs a `Last-Modified` header for `datetime`."""
    web.header('Last-Modified', net.httpdate(date_obj))

def modified(date=None, etag=None):
    """
    Checks to see if the page has been modified since the version in the
    requester's cache.
    
    When you publish pages, you can include `Last-Modified` and `ETag`
    with the date the page was last modified and an opaque token for
    the particular version, respectively. When readers reload the page, 
    the browser sends along the modification date and etag value for
    the version it has in its cache. If the page hasn't changed, 
    the server can just return `304 Not Modified` and not have to 
    send the whole page again.
    
    This function takes the last-modified date `date` and the ETag `etag`
    and checks the headers to see if they match. If they do, it returns 
    `True`, or otherwise it raises NotModified error. It also sets 
    `Last-Modified` and `ETag` output headers.
    """
    try:
        from __builtin__ import set
    except ImportError:
        # for python 2.3
        from sets import Set as set

    n = set([x.strip('" ') for x in web.ctx.env.get('HTTP_IF_NONE_MATCH', '').split(',')])
    m = net.parsehttpdate(web.ctx.env.get('HTTP_IF_MODIFIED_SINCE', '').split(';')[0])
    validate = False
    if etag:
        if '*' in n or etag in n:
            validate = True
    if date and m:
        # we subtract a second because 
        # HTTP dates don't have sub-second precision
        if date-datetime.timedelta(seconds=1) <= m:
            validate = True
    
    if date: lastmodified(date)
    if etag: web.header('ETag', '"' + etag + '"')
    if validate:
        raise web.notmodified()
    else:
        return True

def urlencode(query, doseq=0):
    """
    Same as urllib.urlencode, but supports unicode strings.
    
        >>> urlencode({'text':'foo bar'})
        'text=foo+bar'
        >>> urlencode({'x': [1, 2]}, doseq=True)
        'x=1&x=2'
    """
    def convert(value, doseq=False):
        if doseq and isinstance(value, list):
            return [convert(v) for v in value]
        else:
            return utils.safestr(value)
        
    query = dict([(k, convert(v, doseq)) for k, v in query.items()])
    return urllib.urlencode(query, doseq=doseq)

def changequery(query=None, **kw):
    """
    Imagine you're at `/foo?a=1&b=2`. Then `changequery(a=3)` will return
    `/foo?a=3&b=2` -- the same URL but with the arguments you requested
    changed.
    """
    if query is None:
        query = web.rawinput(method='get')
    for k, v in kw.iteritems():
        if v is None:
            query.pop(k, None)
        else:
            query[k] = v
    out = web.ctx.path
    if query:
        out += '?' + urlencode(query, doseq=True)
    return out

def url(path=None, doseq=False, **kw):
    """
    Makes url by concatenating web.ctx.homepath and path and the 
    query string created using the arguments.
    """
    if path is None:
        path = web.ctx.path
    if path.startswith("/"):
        out = web.ctx.homepath + path
    else:
        out = path

    if kw:
        out += '?' + urlencode(kw, doseq=doseq)
    
    return out

def profiler(app):
    """Outputs basic profiling information at the bottom of each response."""
    from utils import profile
    def profile_internal(e, o):
        out, result = profile(app)(e, o)
        return list(out) + ['<pre>' + net.websafe(result) + '</pre>']
    return profile_internal

if __name__ == "__main__":
    import doctest
    doctest.testmod()