Proxies in Neckoby Christian Biesinger <firstname.lastname@example.org>
Proxies are implemented transparently to necko users. This means that callers can just create an nsIChannel, not needing to worry about whether the channel will use a proxy or not
nsIProxyInfo is a simple helper which stores information about the
type of the proxy, its host and its port.
The decision whether to use a proxy is made in
nsIOService::NewChannelFromURI. It first asks the
nsIProtocolProxyService for an nsIProxyInfo. Depending on the type of
the proxy info, it either asks the HTTP Protocol Handler or the
protocol handler for the requested URI for a new channel with the
nsIProxyInfo - if the channel supports
Otherwise, the proxy info is discarded.
The most important function on nsIProtocolProxyService is
resolve. It checks whether the passed-in URI should use a
proxy, and returns an
nsIProxyInfo if so.
This works by examining the
protocolFlags of the protocol handler
for the given URI. If this protocol handler does not support proxies,
resolve returns null. Alternatively, if proxies are disabled,
or this host is in the list of hosts for which no proxy should be used,
null is also returned.
If PAC (proxy autoconfiguration) is enabled, it is asked for the proxy string for the given URI, which determines whether to use a proxy. Note that the PROXY method is only used when the protocol handler supports HTTP proxies, as indicated by its protocol flags.
Finally, depending on the protocol, the proxy info will be created with the appropriate type, host and port.
The aforementioned methods work very well for application-level proxies. However, SOCKS is transparent to upper-level protocols, and can transport any other TCP- or UDP-based protocol.
nsISocketTransportService supports creating socket
transports using an
nsIProxyInfo. This proxy info will only be used if
it specifies a SOCKS proxy, through which the connection is then made.
Note that SOCKS is implemented as an
nsISocketProvider, and the
socket transport service will therefore use it as as the downmost
XXX missing paragraphs are about PAC, and more details about HTTP proxying, and maybe some more details about SOCKS proxies.