Prompt for a username when an HTTP request 401s

When an HTTP request returns a 401, Git will currently fail with a
confusing message saying that it got a 401, which is not very
descriptive.

Currently if a user wants to use Git over HTTP, they have to use one
URL with the username in the URL (e.g. "http://user@host.com/repo.git")
for write access and another without the username for unauthenticated
read access (unless they want to be prompted for the password each
time). However, since the HTTP servers will return a 401 if an action
requires authentication, we can prompt for username and password if we
see this, allowing us to use a single URL for both purposes.

This patch changes http_request to prompt for the username and password,
then return HTTP_REAUTH so http_get_strbuf can try again.  If it gets
a 401 even when a user/pass is supplied, http_request will now return
HTTP_NOAUTH which remote_curl can then use to display a more
intelligent error message that is less confusing.

Signed-off-by: Scott Chacon <schacon@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

http.c

@@ -815,7 +815,21 @@ static int http_request(const char *url, void *result, int target, int options)
 			ret = HTTP_OK;
 		else if (missing_target(&results))
 			ret = HTTP_MISSING_TARGET;
-		else
+		else if (results.http_code == 401) {
+			if (user_name) {
+				ret = HTTP_NOAUTH;
+			} else {
+				/*
+				 * git_getpass is needed here because its very likely stdin/stdout are
+				 * pipes to our parent process.  So we instead need to use /dev/tty,
+				 * but that is non-portable.  Using git_getpass() can at least be stubbed
+				 * on other platforms with a different implementation if/when necessary.
+				 */
+				user_name = xstrdup(git_getpass("Username: "));
+				init_curl_http_auth(slot->curl);
+				ret = HTTP_REAUTH;
+			}
+		} else
 			ret = HTTP_ERROR;
 	} else {
 		error("Unable to start HTTP request for %s", url);
@@ -831,7 +845,11 @@ static int http_request(const char *url, void *result, int target, int options)
 
 int http_get_strbuf(const char *url, struct strbuf *result, int options)
 {
-	return http_request(url, result, HTTP_REQUEST_STRBUF, options);
+	int http_ret = http_request(url, result, HTTP_REQUEST_STRBUF, options);
+	if (http_ret == HTTP_REAUTH) {
+		http_ret = http_request(url, result, HTTP_REQUEST_STRBUF, options);
+	}
+	return http_ret;
 }
 
 /*

http.h

@@ -126,6 +126,8 @@ extern char *get_remote_object_url(const char *url, const char *hex,
 #define HTTP_MISSING_TARGET	1
 #define HTTP_ERROR		2
 #define HTTP_START_FAILED	3
+#define HTTP_REAUTH	4
+#define HTTP_NOAUTH	5
 
 /*
  * Requests an url and stores the result in a strbuf.

remote-curl.c

@@ -132,6 +132,8 @@ static struct discovery* discover_refs(const char *service)
 	case HTTP_MISSING_TARGET:
 		die("%s not found: did you run git update-server-info on the"
 		    " server?", refs_url);
+	case HTTP_NOAUTH:
+		die("Authentication failed");
 	default:
 		http_error(refs_url, http_ret);
 		die("HTTP request failed");