Add logic to continue on bad HEAD

Some services won't support `HEAD` requests so if `HEAD` request fails, a notice message is logged but the program continues to try and download.

closes #5

README.md

@@ -1,6 +1,6 @@
 Package go-download
 ===================
-![Project status](https://img.shields.io/badge/version-2.0.0-green.svg)
+![Project status](https://img.shields.io/badge/version-2.1.0-green.svg)
 [![Build Status](https://travis-ci.org/joeybloggs/go-download.svg?branch=master)](https://travis-ci.org/joeybloggs/go-download)
 [![Coverage Status](https://coveralls.io/repos/github/joeybloggs/go-download/badge.svg?branch=master)](https://coveralls.io/github/joeybloggs/go-download?branch=master)
 [![Go Report Card](https://goreportcard.com/badge/github.com/joeybloggs/go-download)](https://goreportcard.com/report/github.com/joeybloggs/go-download)

download.go

@@ -7,6 +7,7 @@ import (
 	"fmt"
 	"io"
 	"io/ioutil"
+	"log"
 	"net/http"
 	"os"
 	"path/filepath"
@@ -112,15 +113,19 @@ func OpenContext(ctx context.Context, url string, options *Options) (*File, erro
 	}
 
 	if resp.StatusCode != http.StatusOK {
-		return nil, &InvalidResponseCode{got: resp.StatusCode, expected: http.StatusOK}
-	}
-
-	f.size = resp.ContentLength
-
-	if t := resp.Header.Get("Accept-Ranges"); t == "bytes" {
-		err = f.downloadRangeBytes(ctx)
-	} else {
+		// not all services support HEAD requests
+		// so if this fails just move along to the
+		// GET portion, with a warning
+		log.Printf("notice: unexpected HEAD response code '%d', proceeding with download.", resp.StatusCode)
 		err = f.download(ctx)
+	} else {
+		f.size = resp.ContentLength
+
+		if t := resp.Header.Get("Accept-Ranges"); t == "bytes" {
+			err = f.downloadRangeBytes(ctx)
+		} else {
+			err = f.download(ctx)
+		}
 	}
 
 	if err != nil {

download_test.go

@@ -85,6 +85,18 @@ func TestBadOptions(t *testing.T) {
 
 		w.WriteHeader(http.StatusNotFound)
 	})
+	mux.HandleFunc("/testdata/bad-head-good-get", func(w http.ResponseWriter, r *http.Request) {
+
+		if r.Method == http.MethodHead {
+			w.WriteHeader(http.StatusMethodNotAllowed)
+			return
+		}
+
+		f, _ := os.Open(data)
+		defer f.Close()
+
+		io.Copy(w, f)
+	})
 	mux.HandleFunc("/testdata/bad-content-length", func(w http.ResponseWriter, r *http.Request) {
 
 		fi, _ := os.Stat(data)
@@ -182,6 +194,13 @@ func TestBadOptions(t *testing.T) {
 	if err != nil {
 		t.Fatal(err)
 	}
+	f.Close()
+
+	url = server.URL + "/testdata/bad-head-good-get"
+	f, err = Open(url, nil)
+	if err != nil {
+		t.Fatal(err)
+	}
 	defer f.Close()
 }