Add README. allow to turn of geohash. still use main.go

README.md

@@ -0,0 +1,73 @@
+# endlessh-go
+
+Golang implementation of [endlessh](https://nullprogram.com/blog/2019/03/22/).
+
+## Purpose
+
+Endlessh is a great idea that not only blocks the brute force SSH attackers, but also wastes their time that I consider as a kind of counter-attack. Besides trapping the attackers, I also want to virtualize the Geolocations and other statistics of the sources of attacks. Unfortunately the wonderful [C implementation of endlessh](https://github.com/skeeto/endlessh) only provides text based log, but I do not like the solution that writing extra scripts to parse the log outputs, then exporting the results to a dashboard, which would introduce extra layers in my current setup and would depend on the format of the text log file rather than some structured data. Thus I create this golang implementation of endlessh to export [Prometheus](https://prometheus.io/) metrics and a [Grafana](https://grafana.com/) dashboard to virtualize them.
+
+If you do not mind the endlessh server, besides trapping the attackers, does extra things including
+
+* Translating IP to Geohash
+* Exporting Prometheus metrics
+* Using more memory (about 10MB)
+
+and want a dashboard of sources of attacks, this is the solution for you.
+
+
+## Usage
+
+Usage of `./endlessh-go`
+
+* -alsologtostderr
+  * log to standard error as well as files
+* -conn_type string
+  * Connection type. Possible values are tcp, tcp4, tcp6 (default "tcp")
+* -enable_prometheus
+  * Enable prometheus
+* -geoip_supplier string
+  * Supplier to obtain Geohash of IPs. Possible values are "off", "ip-api", "freegeoip" (default "off")
+* -host string
+  * Listening address (default "0.0.0.0")
+* -interval_ms int
+  * Message millisecond delay (default 1000)
+* -line_length int
+  * Maximum banner line length (default 32)
+* -log_backtrace_at value
+  * when logging hits line file:N, emit a stack trace
+* -log_dir string
+  * If non-empty, write log files in this directory
+* -logtostderr
+  * log to standard error instead of files
+* -max_clients int
+  * Maximum number of clients (default 4096)
+* -port string
+  * Listening port (default "2222")
+* -prometheus_entry string
+  * Entry point for prometheus (default "metrics")
+* -prometheus_port string
+  * The port for prometheus (default "2112")
+* -stderrthreshold value
+  * logs at or above this threshold go to stderr
+* -v value
+  * log level for V logs
+* -vmodule value
+  * comma-separated list of pattern=N settings for file-filtered logging
+
+## Metrics
+
+This golang implementation export the following Prometheus metrics.
+
+| Metric                               | Type  | Description  |
+|--------------------------------------|-------|--------------|
+| endlessh_client_open_count_total     | count | Total number of clients that tried to connect to this host. |
+| endlessh_client_closed_count_total   | count | Total number of clients that stopped connecting to this host. |
+| endlessh_sent_bytes_total            | count | Total bytes sent to clients that tried to connect to this host. |
+| endlessh_trapped_time_seconds_total  | count | Total seconds clients spent on endlessh. |
+| endlessh_client_open_count           | count | Number of connections of clients. |
+| endlessh_client_trapped_time_seconds | count | Seconds a client spends on endlessh. |
+
+The metrics is off by default, you can turn it via the CLI argument `-enable_prometheus`. If you want log like the [C implementation](https://github.com/skeeto/endlessh), you need to set both `-logtostderr` and `-v=1`
+
+The endlessh-go server stores the geohash of attackers as a label on `endlessh_client_open_count`, which is also off by default. You can turn it on via the CLI argument `-geoip_supplier`. The endlessh-go uses service from either [ip-api](https://ip-api.com/) or [freegeoip](https://freegeoip.live/), which may enforce a query rate and limit commercial use. Visit their website for their terms and policies.
+

geoip.go

@@ -118,6 +118,8 @@ func geohashAndLocationFromIpapi(address string) (string, string, string, error)
 
 func geohashAndLocation(address string, geoipSupplier string) (string, string, string, error) {
 	switch geoipSupplier {
+	case "off":
+		return "s000", "Geohash off", "Geohash off", nil
 	case "ip-api":
 		return geohashAndLocationFromIpapi(address)
 	case "freegeoip":