2016-03-24 17:50:18 +00:00
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# FBPortForwarding
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FBPortForwarding lets you expose your Mac's port to iOS device via lightning
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cable. The typical usecase is connecting to a TCP server that runs on OS X
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from an iPhone app without common WiFi network.
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## Benefits:
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1. No need to be on the same WiFi, worry about firewalls (fbguest) or VPN
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2. iOS app doesn't have to know your Mac's IP address
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3. Secure - communication is possible only when connected via USB
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## How it works
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iOS provides a way to connect to device's TCP server from Mac via USBHub, but
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there is no API to connect from iOS to TCP server running on Mac. FBPortForwarding
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uses [Peertalk](https://github.com/rsms/peertalk) to establish communication
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channel from Mac to iOS, creates a TCP server on iOS and multiplexes all
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connections to that server via the peertalk channel. Helper app running on Mac
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listens for commands on the peertalk channel and initializes TCP connections
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to local port and forwards all communication back via the same peertalk channel.
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iOS Device | Mac
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+----------------+ +----------------+
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|Peertalk Server | connect |Peertalk Client |
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| <------------+ |
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| | | |
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| Port 8025| | |
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+----+-----------+ +---------^------+
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incoming +----------------+ | | +--------------+
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connections |Proxy Server | | | |Real Server |
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2016-07-07 21:11:00 +00:00
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------------>> | | +-------------+ commands | | |
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2016-03-24 17:50:18 +00:00
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| Port 8081| | create | | stream | | Port 8081|
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+-+--------------+ +---------> Peertalk <----------+ +-^------------+
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| | Channel | ^
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| +--------+ | | +--------+ | outgoing
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| | | onConnect | | connect | | | connections
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+---> Client +---------------> OpenPipe +---------------> Client +-----+
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| #[tag] | onRead | | write | #[tag] |
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| +---------------> WriteToPipe +---------------> |
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| | onDisconnect | | disconnect | |
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| +---------------> ClosePipe +---------------> |
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| | | | | |
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| | write | | onRead | |
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| <---------------+ WriteToPipe <---------------+ |
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| | close | | onDisconnect | |
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| <---------------+ ClosePipe <---------------+ |
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+--------+ | | +--------+
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+-------------+
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First, the library on iOS device creates a TCP server on the port we want to
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forward (let's say 8081) and a special Peertalk server on port 8025. Mac helper
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app looks for connected iOS devices, and once it finds one it connects to its
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peertalk server. Only *one* channel is created that's going to be used for
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multiplexing data.
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When a socket connects to local proxy server, FBPortForwarding is going to assign
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a tag to the connection and use peertalk channel to tell Mac helper app to connect
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to TCP port 8081 on Mac. Now events and data on both sides of the wire are going
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to be multiplexed and transferred via the peertalk channel.
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