LDStreamingMode.streaming incompatible with some Proxy servers

[swhitty]

Describe the bug LDStreamingMode.streaming can cause start() / setOnline(true) to timeout behind some proxy servers.

We observe that 2% of our customers appear to be behind proxy servers that cause this issue. While cached flags values are available, falling back to polling mode is more reliable for these users.

To reproduce

Add device to a network with an incompatible proxy server and attempt start in streaming mode (which is default):

var config = LDConfig(mobileKey: "")
config.startOnline = false
config.streamingMode = .streaming
LDClient.start(config: config, context: context, startWaitSeconds: 5) { timedOut in
   ...
}

Request is sent to https://clientstream.launchdarkly.com and headers are returned but no data is ever received within the body, timeout occurs and completion handler is called.

Expected behavior It would be great to detect this and switch to polling somehow.

It's unclear how one could try with streaming then fall back to polling. Its possible to use CFNetworkCopyProxiesForURL to detect upfront if the config.streamingURL will be handled via a proxy, this

Logs If applicable, add any log output related to your problem.

Library version 9.8.2

XCode and Swift version Xcode 15.4 Swift 5.10

Platform the issue occurs on iOS