0xack13 / watchhttp

🌺 Run command periodically and expose latest STDOUT as HTTP endpoint

🌺 watchhttp

Run command periodically and expose latest STDOUT as HTTP endpoint

• <200LOC
• no dependencies
• automatic browser refresh via Refresh header

go install github.com/nikolaydubina/watchhttp@latest

Fetch and transform periodically with curl and jq

watchhttp -t 5s -json -- /bin/sh -c 'curl "https://api.open-meteo.com/v1/forecast?latitude=52.52&longitude=13.41&current_weather=true&hourly=temperature_2m,relativehumidity_2m,windspeed_10m" | jq "del(.hourly)"'

$ curl localhost:9000/
{
  "latitude": 52.52,
  "longitude": 13.419998,
  "generationtime_ms": 0.635981559753418,
  "utc_offset_seconds": 0,
  "timezone": "GMT",
  "timezone_abbreviation": "GMT",
  "elevation": 38,
  "current_weather": {
    "temperature": 1.3,
    "windspeed": 8.4,
    "winddirection": 220,
    "weathercode": 3,
    "time": "2023-03-12T09:00"
  },
  "hourly_units": {
    "time": "iso8601",
    "temperature_2m": "°C",
    "relativehumidity_2m": "%",
    "windspeed_10m": "km/h"
  }
}

watchhttp -t 2s -json -- /bin/sh -c "curl --location 'api.coincap.io/v2/rates/bitcoin' | jq"

Live graph of Kubernetes resources with kubectl and graphviz

go install github.com/nikolaydubina/jsonl-graph@latest

watchhttp -t 3s -p 9000 -- /bin/sh -c "kubectl get pods -o json | jq '.items[] | {to: (.kind + \":\" + .metadata.name), from: (.metadata.ownerReferences[].kind + \":\" + .metadata.ownerReferences[].name)}' | jsonl-graph | dot -Tsvg"

Live status of Kubernetes resource with kubectl

watchhttp -t 3s -p 9000 -- kubectl describe deployment hello-minikube

Live system metrics with vmstat

watchhttp vmstat

$ curl localhost:9000/
Mach Virtual Memory Statistics: (page size of 16384 bytes)
Pages free:                             1616097.
Pages active:                            914186.
Pages inactive:                          579357.
Pages speculative:                       829846.
Pages throttled:                              0.
Pages wired down:                        164337.
Pages purgeable:                         125376.
"Translation faults":                2059157267.
Pages copy-on-write:                   58902729.
Pages zero filled:                   1573609407.
Pages reactivated:                       577992.
Pages purged:                          17881481.
File-backed pages:                      1300312.
Anonymous pages:                        1023077.
Pages stored in compressor:              202931.
Pages occupied by compressor:             35364.
Decompressions:                          973775.
Compressions:                           1404319.
Pageins:                               23222205.
Pageouts:                                 12866.
Swapins:                                 435185.
Swapouts:                                477406.

Watch file tail or cat

watchhttp tail /var/log/system.log

$ curl localhost:9000/            
Mar 12 16:16:07 Nikolays-MacBook-Pro syslogd[532]: ASL Sender Statistics
Mar 12 16:32:06 Nikolays-MacBook-Pro syslogd[532]: ASL Sender Statistics
Mar 12 16:48:15 Nikolays-MacBook-Pro syslogd[532]: ASL Sender Statistics
Mar 12 17:04:22 Nikolays-MacBook-Pro syslogd[532]: ASL Sender Statistics
Mar 12 17:22:24 Nikolays-MacBook-Pro syslogd[532]: ASL Sender Statistics
Mar 12 17:33:45 Nikolays-MacBook-Pro MobileDeviceUpdater[4765]: Entered:_AMMuxedVersion2DeviceConnected, mux-device:4541
Mar 12 17:33:45 Nikolays-MacBook-Pro syslogd[532]: ASL Sender Statistics
Mar 12 17:33:45 Nikolays-MacBook-Pro AMPDeviceDiscoveryAgent[1146]: Entered:_AMMuxedVersion2DeviceConnected, mux-device:4541
Mar 12 17:33:47 Nikolays-MacBook-Pro AMPDevicesAgent[67221]: Entered:_AMMuxedVersion2DeviceConnected, mux-device:4541
Mar 12 17:44:54 Nikolays-MacBook-Pro syslogd[532]: ASL Sender Statistics

---

Appendix A: Existing Tools

• as of 2023-03-12, awesome-go does not mention any tools that can do this
• netcat can not do this

Appendix B: Alternative with file server + bash

Similar effect can be achieved with file server and bash, albeit headers would not be set.

package main

import "net/http"

func main() { http.ListenAndServe(":9000", http.FileServer(http.Dir("."))) }

$ while sleep 5; do <something> > <file> ; done

Appendix C: Paths Not Taken

Expose STDIN as HTTP endpoint

The problem is how to differentate separate responses? Is empty line valid separator of responses? There are clearly interesting eaxmples with UNIX pipes and tail -f, logs, WebSockets. However, that may need separate tool.

Stream top, k9s, datadash to browser in HTML

First, those tools re-render terminal output at their own interval. It would take some effort, but effectivelly this is emulating terminal rendering in browser. Issue of converting terminal escaped ASCII to HTML output colors. As next step, you would want to also pass to STDIN through browser too. Overall, this is separate problem of exposing terminal throuhg browser.

Appendix D: Interesting free real time data sources

• https://github.com/public-apis/public-apis

Stock Sentiment in /r/Wallstreetbets

• https://tradestie.com/apps/reddit/api/
• curl -XGET 'https://tradestie.com/api/v1/apps/reddit'
• no auth
• no limit

Weather forecast

• curl https://api.open-meteo.com/v1/forecast?latitude=52.52&longitude=13.41&current_weather=true&hourly=temperature_2m,relativehumidity_2m,windspeed_10m
• no auth
• no limit

Bitcoin rates

• https://docs.coincap.io/#intro
• curl --location 'api.coincap.io/v2/rates/bitcoin'
• no auth
• no limit