ui-shared: add support for NO_HTTP=1/--nohttp

cgit_print_http_headers() used to do nothing if 'embedded' was
specified in cgitrc, but that was wrong - we never want to skip the
headers when invoked as a CGI app. Sadly, there's no easy way to
detect if we're invoked as a CGI app or if we're invoked by another
CGI app, so for the latter case cgit needs to be invoked with either
--nohttp on the command line or NO_HTTP=1 in the environment.

Signed-off-by: Lars Hjemli <hjemli@gmail.com>

cgit.c

@@ -253,6 +253,7 @@ static void prepare_context(struct cgit_context *ctx)
 	ctx->env.cgit_config = xstrdupn(getenv("CGIT_CONFIG"));
 	ctx->env.http_host = xstrdupn(getenv("HTTP_HOST"));
 	ctx->env.https = xstrdupn(getenv("HTTPS"));
+	ctx->env.no_http = xstrdupn(getenv("NO_HTTP"));
 	ctx->env.path_info = xstrdupn(getenv("PATH_INFO"));
 	ctx->env.query_string = xstrdupn(getenv("QUERY_STRING"));
 	ctx->env.request_method = xstrdupn(getenv("REQUEST_METHOD"));
@@ -445,6 +446,9 @@ static void cgit_parse_args(int argc, const char **argv)
 		if (!strcmp(argv[i], "--nocache")) {
 			ctx.cfg.nocache = 1;
 		}
+		if (!strcmp(argv[i], "--nohttp")) {
+			ctx.env.no_http = "1";
+		}
 		if (!strncmp(argv[i], "--query=", 8)) {
 			ctx.qry.raw = xstrdup(argv[i]+8);
 		}

cgit.h

@@ -211,6 +211,7 @@ struct cgit_environment {
 	char *cgit_config;
 	char *http_host;
 	char *https;
+	char *no_http;
 	char *path_info;
 	char *query_string;
 	char *request_method;

ui-shared.c

@@ -455,7 +455,7 @@ void cgit_print_age(time_t t, time_t max_relative, char *format)
 
 void cgit_print_http_headers(struct cgit_context *ctx)
 {
-	if (ctx->cfg.embedded)
+	if (ctx->env.no_http && !strcmp(ctx->env.no_http, "1"))
 		return;
 
 	if (ctx->page.status)