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Universal Content Broker (UCB)

Universal Content Broker (has ucps) which do things like convert files to strings in content broker world, or connect LibreOffice with various DMS and fileshare systems like WebDAV, CMIS, or GIO.

The UCPs implement the Universal Content Provider UNO interfaces in C++, in particular the com.sun.star.ucb.ContentProvider service.

WebDAV ucp

The WebDAV content provider is based on libcurl for much of the network and protocol stuff, including authentication.

WebDAV as implemented here is defined in an IETF RFC 4918 extensions, and the code supports both unencrypted HTTP/1.1 (IETF RFC 2616) as well as TLS 1.2 or later.

Our WebDAV com.sun.star.ucb.ContentProvider service implementation registers the vnd.sun.star.webdav and http URI schemes (and their encrypted TLS variants). See here for the specification: https://wiki.openoffice.org/wiki/Documentation/DevGuide/AppendixC/The_WebDAV_Content_Provider

Historically, webdav had two ucps, one based on neon, the second one based on serf. Both are superseded by the current libcurl implementation (since LibreOffice 7.3), but in case of behavioural differences, go hunt for code differences (ucb/source/ucp/webdav-neon and ucb/source/ucp/webdav).

The WebDAV protocol is implemented on top of libcurl basic http GET, PUT, and POST requests (and is relatively straight-forward - see ucb/source/ucp/webdav-curl/webdavcontent.cxx for the main functionality), but incorporates custom handling for a number of server idiosyncrasies:

Nextcloud will reply to a PROPFIND request with “100 Continue” and then after the data is uploaded it will send a “401 Unauthorized” if the auth header is missing in the headers to which it replied with “100 Continue”. So we reuse that.
Sharepoint 16 responds to PROPFIND with “Transfer-Encoding: chunked” with “HTTP/1.1 200 OK” and an actual error message in the response body.
- apparently setting Content-Length works better, so we use that
- Sharepoint 16 has the same problem with PROPFIND.
- and for when using chunked encoding for LOCK
Sharepoint returns redirect urls that curl can’t parse, so we encode them (check WebDAVResponseParser for the code)
avoiding chunked encoding for PUT, since for Nextcloud:
- Transfer-Encoding: chunked creates a 0 byte file with response “201 Created”
- see upstream bug: https://github.com/nextcloud/server/issues/7995
- apparently this doesn’t happen with header Content-Length: 8347, so we use that