Support no_proxy environment variable. #140

[hgiddens]

Sorry if I've done any dumb stuff here. I tried to find a spec, and the nearest I could find was some ancient info from W3C. I've thus implemented a subset of what other popular libraries support.

no_proxy contains a list of domain suffixes, separated by commas. The domain suffixes may optionally have leading periods; the commas may optionally have trailing spaces.

For example, if no_proxy=internal.company.com, .other.company.com, requests to internal.company.com, foo.internal.company.com, and other.company.com will avoid the proxy. Requests to notactuallyinternal.company.com will still go via the proxy.

Differences to other implementations:

Domain suffix vs. string suffix

wget and Python's urllib3 avoid the proxy if one of the no_proxy hosts is a string suffix of the request host, rather than a domain suffix (with special casing so no_proxy=.foo.example avoids the proxy for requests to foo.example).

Ignoring case/spaces

Some implementations ignore all spaces, rather than just 0x20s following a comma. Some implementations also use case-sensitive domain handling.

Port-specific rules

Ruby's stdlib implementation can be made to apply only to specific ports.

Avoiding the proxy for CADR ranges

Python's urllib3 allows you to specify e.g. no_proxy=internal.company.com,192.168.0.0/16.

Avoiding the proxy for all requests

Ruby and cURL avoid the proxy for all requests if no_proxy=* is set.

[snoyberg]

Unless I'm misreading this, this code will require parsing the no_proxy environment variable from scratch on each request. It would be better to explicitly parse it immediately into some intermediate data structure, and then perform lookups on that.

[hgiddens]

Yeah, you're quite right. Would newManager be an appropriate place for the parsing step?

[snoyberg]

It's fine to do it in this function. Just do it outside of the inner function (in the same part of the code where getEnvironment is called).

[hgiddens]

Is there anything else you'd like done on this one?

[snoyberg]

I'll check now. For future reference: Github doesn't send notifications on new commits to a PR, so it's good to add a comment when making such a change.

[snoyberg]

Thanks!