The Go os package connects applications to operating-system facilities. Use it to read environment-based configuration, inspect host details, obtain process information, and select portable path separators. section 2.2.2 section 12.4.1
Common operations include:
- Read configuration with os.Getenv; missing variables return an empty string, so critical values can be validated before startup. section 2.2.2
- Convert string configuration with strconv.ParseInt when an environment value, such as PORT, must become an integer. section 2.2.2
- Inspect the runtime host with os.Hostname, os.Getpid, os.Getwd, os.PathSeparator, and os.PathListSeparator. section 12.4.1
- Combine os.Hostname with net.LookupHost to discover addresses associated with the machine’s system-known hostname. section 12.4.1
Fail fast on missing server configuration
Read PORT with os.Getenv, panic when it is empty, and pass the configured value to http.ListenAndServe. Namespace variables such as MYAPP_PORT to reduce conflicts, and treat environment contents as potentially visible to subprocesses. section 2.2.2
Listing 2.12 Environment variable-based configuration
package main
import (
"fmt"
"net/http"
"os"
)
func main() {
var port string
if port = os.Getenv("PORT"); port == "" { #1
panic("environment variable PORT has not been set!") #2
}
http.HandleFunc("/", homePage)
http.ListenAndServe(":"+port, nil) #3
}
func homePage(res http.ResponseWriter, req *http.Request) {
if req.URL.Path != "/" {
http.NotFound(res, req)
return
}
fmt.Fprint(res, "The homepage.")
}
Runnable Go example showing environment-variable validation followed by HTTP server startup. section 2.2.2
Listing 12.10 Looking up the host’s IP addresses via the hostname
func main() {
name, err := os.Hostname() #1
if err != nil { #1
fmt.Println(err) #1
return #1
} #1
addrs, err := net.LookupHost(name) #2
if err != nil { #2
fmt.Println(err) #2
return #2
} #2
for _, a := range addrs { #3
fmt.Println(a) #3
}
Runnable Go example showing hostname retrieval, error handling, address lookup, and iteration over returned addresses. section 12.4.1
