From: Brian Warner Date: Sat, 19 Jul 2008 01:06:50 +0000 (-0700) Subject: web: for GET save=true, don't interpret the filename= arg with any character set... X-Git-Url: https://git.rkrishnan.org/architecture.txt?a=commitdiff_plain;h=572c848d983db04087b8396a9b26273ae566515b;p=tahoe-lafs%2Ftahoe-lafs.git web: for GET save=true, don't interpret the filename= arg with any character set, just copy the bytes back into the Content-Disposition header. This seems to make it maximally compatible with Firefox and IE7 --- diff --git a/docs/webapi.txt b/docs/webapi.txt index 05621292..ea5a4eca 100644 --- a/docs/webapi.txt +++ b/docs/webapi.txt @@ -443,6 +443,12 @@ GET /uri/$DIRCAP/[SUBDIRS../]FILENAME most browsers will refuse to display it inline). "true", "t", "1", and other case-insensitive equivalents are all treated the same. + Character-set handling in URLs and HTTP headers is a dubious art[1]. For + maximum compatibility, Tahoe simply copies the bytes from the filename= + argument into the Content-Disposition header's filename= parameter, without + trying to interpret them in any particular way. + + GET /named/$FILECAP/FILENAME This is an alternate download form which makes it easier to get the correct @@ -910,3 +916,57 @@ For more details, please see the "Consistency vs Availability" and "The Prime Coordination Directive" sections of mutable.txt, in the same directory as this file. + +[1]: URLs and HTTP and UTF-8, Oh My + + HTTP does not provide a mechanism to specify the character set used to + encode non-ascii names in URLs (rfc2396#2.1). We prefer the convention that + the filename= argument shall be a URL-encoded UTF-8 encoded unicode object. + For example, suppose we want to provoke the server into using a filename of + "f i a n c e-acute e" (i.e. F I A N C U+00E9 E). The UTF-8 encoding of this + is 0x66 0x69 0x61 0x6e 0x63 0xc3 0xa9 0x65 (or "fianc\xC3\xA9e", as python's + repr() function would show). To encode this into a URL, the non-printable + characters must be escaped with the urlencode '%XX' mechansim, giving us + "fianc%C3%A9e". Thus, the first line of the HTTP request will be "GET + /uri/CAP...?save=true&filename=fianc%C3%A9e HTTP/1.1". Not all browsers + provide this: IE7 uses the Latin-1 encoding, which is fianc%E9e. + + The response header will need to indicate a non-ASCII filename. The actual + mechanism to do this is not clear. For ASCII filenames, the response header + would look like: + + Content-Disposition: attachment; filename="english.txt" + + If Tahoe were to enforce the utf-8 convention, it would need to decode the + URL argument into a unicode string, and then encode it back into a sequence + of bytes when creating the response header. One possibility would be to use + unencoded utf-8. Developers suggest that IE7 might accept this: + + #1: Content-Disposition: attachment; filename="fianc\xC3\xA9e" + (note, the last four bytes of that line, not including the newline, are + 0xC3 0xA9 0x65 0x22) + + RFC2231#4 (dated 1997): suggests that the following might work, and some + developers (http://markmail.org/message/dsjyokgl7hv64ig3) have reported that + it is supported by firefox (but not IE7): + + #2: Content-Disposition: attachment; filename*=utf-8''fianc%C3%A9e + + My reading of RFC2616#19.5.1 (which defines Content-Disposition) says that + the filename= parameter is defined to be wrapped in quotes (presumeably to + allow spaces without breaking the parsing of subsequent parameters), which + would give us: + + #3: Content-Disposition: attachment; filename*=utf-8''"fianc%C3%A9e" + + However this is contrary to the examples in the email thread listed above. + + Developers report that IE7 (when it is configured for UTF-8 URL encoding, + which is not the default in asian countries), will accept: + + #4: Content-Disposition: attachment; filename=fianc%C3%A9e + + However, for maximum compatibility, Tahoe simply copies bytes from the URL + into the response header, rather than enforcing the utf-8 convention. This + means it does not try to decode the filename from the URL argument, nor does + it encode the filename into the response header. diff --git a/src/allmydata/web/filenode.py b/src/allmydata/web/filenode.py index 21ede7e2..7996e757 100644 --- a/src/allmydata/web/filenode.py +++ b/src/allmydata/web/filenode.py @@ -157,8 +157,19 @@ class FileNodeHandler(RenderMixin, rend.Page, ReplaceMeMixin): t = get_arg(req, "t", "").strip() if not t: # just get the contents - filename = get_arg(req, "filename", self.name) or "unknown" save_to_file = boolean_of_arg(get_arg(req, "save", "False")) + # the filename arrives as part of the URL or in a form input + # element, and will be sent back in a Content-Disposition header. + # Different browsers use various character sets for this name, + # sometimes depending upon how language environment is + # configured. Firefox sends the equivalent of + # urllib.quote(name.encode("utf-8")), while IE7 sometimes does + # latin-1. Browsers cannot agree on how to interpret the name + # they see in the Content-Disposition header either, despite some + # 11-year old standards (RFC2231) that explain how to do it + # properly. So we assume that at least the browser will agree + # with itself, and echo back the same bytes that we were given. + filename = get_arg(req, "filename", self.name) or "unknown" return FileDownloader(self.node, filename, save_to_file) if t == "json": return FileJSONMetadata(ctx, self.node) @@ -294,12 +305,13 @@ class WebDownloadTarget: self._req.setHeader("content-encoding", self._content_encoding) self._req.setHeader("content-length", str(size)) if self._save_to_filename is not None: - # tell the browser to save the file rather display it - # TODO: indicate charset of filename= properly - filename = self._save_to_filename.encode("utf-8") + # tell the browser to save the file rather display it we don't + # try to encode the filename, instead we echo back the exact same + # bytes we were given in the URL. See the comment in + # FileNodeHandler.render_GET for the sad details. + filename = self._save_to_filename self._req.setHeader("content-disposition", - 'attachment; filename="%s"' - % filename) + 'attachment; filename="%s"' % filename) def write(self, data): self._req.write(data)