Golang - Get HTTP headers from given string, and/or the value from specific header key

urlheaders.go

package main

import (
	"log"
	"net/http"
	"strings"
)

/*
Returns a map array of all available headers.
@param string - URL given
@return map[string]interface{}
*/
func getURLHeaders(url string) map[string]interface {} {
	response, err := http.Head(url)
	if err != nil {
		log.Fatal("Error: Unable to download URL (", url, ") with error: ", err)
	}

	if response.StatusCode != http.StatusOK {
		log.Fatal("Error: HTTP Status = ", response.Status)
	}

	headers := make(map[string]interface{})
	
	for k, v := range response.Header {
		headers[strings.ToLower(k)] = string(v[0])
	}
	
	return headers
}

/*
Returns the header value from a given header key, if available, else returns empty string.
@param string - URL given
@param string - Header key
@return string
*/
func getURLHeaderByKey(url string, key string) string {
	headers := getURLHeaders(url)
	key = strings.ToLower(key)
	
	if value, ok := headers[key]; ok {
		return value.(string)
	}
	
	return ""
}

func main() {
	url := "https://media.kairos.com/test1.jpg"
	
	findByKey := "Content-Type"
	
	contentType := getURLHeaderByKey(url, findByKey)
	
	if contentType == "" {
		log.Fatal(findByKey," is unavailable")
	}
	
	log.Println(findByKey,"=", contentType)
}