#http-proxy #proxy #http


HTTP proxy adapters that respect the system proxy configuration

1 unstable release

0.1.0 Aug 4, 2021

#423 in HTTP client


376 lines


crates.io Rust Documentation

HTTP proxy adapters that respect the system's proxy configuration.

View documentation.


# Cargo.toml
mz-http-proxy = { version = "0.1", features = ["hyper", "reqwest"] }


HTTP proxy adapters.

This crate constructs HTTP clients that respect the system's proxy configuration.


This crate is developed as part of Materialize, the streaming data warehouse. Contributions are encouraged:


All features are disabled by default. You will likely want to enable at least one of the following features depending on the HTTP client library you use:

  • The hyper feature enables the proxy adapters for use with the hyper crate.

  • The reqwest feature enables the proxy adapters for use with the reqwest crate.

Note that reqwest by default will perform its own determination of the system proxy configuration, but its support for no_proxy is not as complete as the implementation in this crate.

System proxy configuration

The system's proxy configuration is governed by four environment variables, http_proxy, https_proxy, all_proxy, and no_proxy, whose meanings are nonstandard and vary widely from tool to tool. Materialize implements a subset of the behavior that has been empirically determined to be common to many other HTTP clients.

With the exception of http_proxy, environment variables may be specified in all lowercase, as written above, or in all uppercase (e.g, HTTPS_PROXY). http_proxy is accepted in lowercase only because the variable HTTP_PROXY can be controlled by attackers in CGI environments, as in golang/go#16405. If an environment variable is specified in both lowercase and uppercase, the lowercase variable takes precedence.

Proxy selection

The http_proxy and https_proxy environment variables specify the URL of a proxy server to use when routing HTTP and HTTPS traffic, respectively. The all_proxy environment variable specifies a proxy server that applies to both HTTP and HTTPS traffic. http_proxy and https_proxy take precedence over all_proxy.

Proxy exclusions

The no_proxy environment variable is a comma-separated list specifying hosts to exclude from proxying. It takes precedence over the other environment variables. Each entry in the list must be:

  • an IP address followed by an optional port (e.g.,,, ::1, [::1], or [::1]:80),
  • an IP address prefix in CIDR notation (e.g.,, or
  • a domain name followed by an optional port (e.g., foo.com).

Whitespace surrounding an entry is ignored.

IPv6 addresses cannot contain whitespace inside the [ and ] characters or they will be treated as domains. IPv6 addresses that are followed by a port specification must be surrounded by [ and ] or the port will be considered part of the IPv6 address. (The implementation technically allows IPv4 addresses to be wrapped in square brackets as well, for compatibility with other tools, but this should not be relied upon.)

no_proxy matching never involves DNS resolution, so a no_proxy value of will exclude requests that literally mention the IP in the URL (e.g., from proxying, but not requests to http://domainthatresolvesto1234.

Domain names in no_proxy match all subdomains, so a no_proxy value of materialize.com will exclude requests to both materialize.com and cloud.materialize.com from proxying. For compatibility with other tools, domain names can include one optional . character at the start, which is ignored.

Invalid entries in the list are silently ignored.

If the no_proxy environment variable is set to the special value *, then all addresses will be excluded from proxying.

See also

For further details on these environment variables, see the GitLab blog article "We need to talk: can we standardize NO_PROXY?".


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