Persistent

The persistent plugin has been around since thread-local connection pools start being used.

Its inspiration was net-http-persistent, which does something similar.

Usually, single request calls close the connection afterwards. You can extend the lifetime of the connection(s) using .wrap, but that’s about it:

HTTPX.get("https://nghttp2.org")
#=> opens a secure connection to "nghttp2.org"
#=> sends request, gets response back"
#=> closes the connection

HTTPX.wrap do |session|
  session.get("https://nghttp2.org")
  # connection is still alive
end
# connection closed

With the persistent plugin, you can now refrain from closing the connections, as they will be kept open during the lifetime of the process:

session = HTTPX.plugin(:persistent)
session("https://nghttp2.org")
#=> opens a secure connection to "nghttp2.org"
#=> sends request, gets response back"

HTTPX.wrap do |session|
  # will reuse the same connection
  session.get("https://nghttp2.org")
  # connection is still alive
end
# connection still alive

Reconnections

If the connection goes down (because the peer closed it), then the connection will be reopened and requests will be retried in the new connection:

session = HTTPX.plugin(:persistent)
session.get("https://google.com")
... 5 mins have passed, and google shuts down the TCP socket ...
session.get("https://google.com")
# sending request in the connection fails
# new connection is created
# new request is sent, new connection kept alive

When you should use this

You might ask yourself, why isn’t this turned on by default? Of course, keeping connections alive for the duration of a process locates resources indefinitely, and in some edge cases, you might hit limitations of your OS.

You should use it:

  • If you’re connecting always to the same origins;
  • If your process is long lived;

You should not use it:

  • If the number of origins you’re connecting to is unbounded (example: web scraping/web crawler);
  • If your process is short lived (connections will be reaped at the end of the process anyway);

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