prometheus/vendor/github.com/hashicorp/go-cleanhttp

cleanhttp

Functions for accessing "clean" Go http.Client values

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The Go standard library contains a default http.Client called http.DefaultClient. It is a common idiom in Go code to start with http.DefaultClient and tweak it as necessary, and in fact, this is encouraged; from the http package documentation:

The Client's Transport typically has internal state (cached TCP connections), so Clients should be reused instead of created as needed. Clients are safe for concurrent use by multiple goroutines.

Unfortunately, this is a shared value, and it is not uncommon for libraries to assume that they are free to modify it at will. With enough dependencies, it can be very easy to encounter strange problems and race conditions due to manipulation of this shared value across libraries and goroutines (clients are safe for concurrent use, but writing values to the client struct itself is not protected).

Making things worse is the fact that a bare http.Client will use a default http.Transport called http.DefaultTransport, which is another global value that behaves the same way. So it is not simply enough to replace http.DefaultClient with &http.Client{}.

This repository provides some simple functions to get a "clean" http.Client -- one that uses the same default values as the Go standard library, but returns a client that does not share any state with other clients.