tcpw

tcpw

tcpw (TCP Wait) is a tool that waits until TCP endpoints are open.

It is useful for synchronizing the spin-up of interdependent services, such as linked docker containers.

That is yet another alternative to wait-for-it.sh.

Rationale

• available as a binary executable without any dependencies (file size <1M).
  • Optimized with: -ldflags="-s -w" -trimpath and upx
  • Pre-built binaries:
    • tcpw-linux-x86_64
    • tcpw-linux-aarch64
    • tcpw-linux-armv7l
• available on PyPI (x86_64 only)
• additionally, you can set:
  • more than one endpoint: -a google.com:80 -a booble.gum:8080 ...
  • command, which can be executed only after success, failure or any result: -on f -a google.com:9999 echo "Endpoint is down"
  • polling interval: -i 500ms
  • timeout/interval in different time units: ns,ms,s,m,h

Installation

Download executable file:

sh -c "wget -O tcpw https://raw.githubusercontent.com/jackcvr/tcpw/main/bin/$(uname -m)/tcpw && chmod +x tcpw"

or:

pip install tcpw

Usage

Usage: tcpw [-t timeout] [-i interval] [-on (s|f|any)] [-q] [-v] [-a host:port ...] [command [args]]

  -a value
    	Endpoint to await, in the form 'host:port'
  -i duration
    	Interval between retries in format N{ns,ms,s,m,h} (default 1s)
  -on string
    	Condition for command execution. Possible values: 's' - after success, 'f' - after failure, 'any' - always (default "s")
  -q	Do not print anything (default false)
  -t duration
    	Timeout in format N{ns,ms,s,m,h}, e.g. '5s' == 5 seconds. Zero for no timeout (default 0)
  -v	Verbose mode (default false)
  command args
    	Execute command with arguments after the test finishes (default: if connection succeeded)

Examples

Wait 5 seconds for port 80 on www.google.com, and if it is available, echo the message Google is up:

$ tcpw -t 5s -a www.google.com:80 echo "Google is up"
2024/08/26 20:06:47.209012 successfully connected to www.google.com:80
Google is up

Next command waits 2 seconds for www.google.com:80 and localhost:5000, checking them every 500 milliseconds with enabled verbose mode and executes echo regardless of the result:

$ tcpw -t 2s -i 500ms -v -on any -a www.google.com:80 -a localhost:5000 echo "Printed anyway"
2024/08/26 20:08:24.153240 connecting to localhost:5000...
2024/08/26 20:08:24.153327 connecting to www.google.com:80...
2024/08/26 20:08:24.153541 dial tcp 127.0.0.1:5000: connect: connection refused
2024/08/26 20:08:24.179927 successfully connected to www.google.com:80
2024/08/26 20:08:24.654984 dial tcp 127.0.0.1:5000: connect: connection refused
2024/08/26 20:08:25.155997 dial tcp 127.0.0.1:5000: connect: connection refused
2024/08/26 20:08:25.661397 dial tcp 127.0.0.1:5000: connect: connection refused
2024/08/26 20:08:26.161613 dial tcp: lookup localhost: i/o timeout
timeout error
Printed anyway

License

MIT