Fix CORS problems due to added headers on JS target

Before this change, missing User-Agent and Accept headers were automatically
added on all platforms. Setting the User-Agent header forces the browser to
do a CORS preflight (see 1) which fails if the HTTP endpoint is not
configured appropriate. It's not neccesary to set either header as the
browser sets them and so this commit disables that functionality on the JS
target.

1: https://developer.mozilla.org/en-US/docs/Web/HTTP/CORS#Simple_requests

core/io/http_client.cpp

@@ -30,6 +30,7 @@
 
 #include "http_client.h"
 #include "io/stream_peer_ssl.h"
+#include "version.h"
 
 const char *HTTPClient::_methods[METHOD_MAX] = {
 	"GET",
@@ -121,16 +122,30 @@ Error HTTPClient::request_raw(Method p_method, const String &p_url, const Vector
 		request += "Host: " + conn_host + ":" + itos(conn_port) + "\r\n";
 	}
 	bool add_clen = p_body.size() > 0;
+	bool add_uagent = true;
+	bool add_accept = true;
 	for (int i = 0; i < p_headers.size(); i++) {
 		request += p_headers[i] + "\r\n";
-		if (add_clen && p_headers[i].find("Content-Length:") == 0) {
+		if (add_clen && p_headers[i].findn("Content-Length:") == 0) {
 			add_clen = false;
 		}
+		if (add_uagent && p_headers[i].findn("User-Agent:") == 0) {
+			add_uagent = false;
+		}
+		if (add_accept && p_headers[i].findn("Accept:") == 0) {
+			add_accept = false;
+		}
 	}
 	if (add_clen) {
 		request += "Content-Length: " + itos(p_body.size()) + "\r\n";
 		// Should it add utf8 encoding?
 	}
+	if (add_uagent) {
+		request += "User-Agent: GodotEngine/" + String(VERSION_FULL_BUILD) + " (" + OS::get_singleton()->get_name() + ")\r\n";
+	}
+	if (add_accept) {
+		request += "Accept: */*\r\n";
+	}
 	request += "\r\n";
 	CharString cs = request.utf8();
 
@@ -173,17 +188,31 @@ Error HTTPClient::request(Method p_method, const String &p_url, const Vector<Str
 	} else {
 		request += "Host: " + conn_host + ":" + itos(conn_port) + "\r\n";
 	}
+	bool add_uagent = true;
+	bool add_accept = true;
 	bool add_clen = p_body.length() > 0;
 	for (int i = 0; i < p_headers.size(); i++) {
 		request += p_headers[i] + "\r\n";
-		if (add_clen && p_headers[i].find("Content-Length:") == 0) {
+		if (add_clen && p_headers[i].findn("Content-Length:") == 0) {
 			add_clen = false;
 		}
+		if (add_uagent && p_headers[i].findn("User-Agent:") == 0) {
+			add_uagent = false;
+		}
+		if (add_accept && p_headers[i].findn("Accept:") == 0) {
+			add_accept = false;
+		}
 	}
 	if (add_clen) {
 		request += "Content-Length: " + itos(p_body.utf8().length()) + "\r\n";
 		// Should it add utf8 encoding?
 	}
+	if (add_uagent) {
+		request += "User-Agent: GodotEngine/" + String(VERSION_FULL_BUILD) + " (" + OS::get_singleton()->get_name() + ")\r\n";
+	}
+	if (add_accept) {
+		request += "Accept: */*\r\n";
+	}
 	request += "\r\n";
 	request += p_body;
 

scene/main/http_request.cpp

@@ -30,8 +30,6 @@
 
 #include "http_request.h"
 
-#include "version.h"
-
 void HTTPRequest::_redirect_request(const String &p_new_url) {
 }
 
@@ -106,28 +104,10 @@ Error HTTPRequest::request(const String &p_url, const Vector<String> &p_custom_h
 
 	validate_ssl = p_ssl_validate_domain;
 
-	bool has_user_agent = false;
-	bool has_accept = false;
 	headers = p_custom_headers;
 
 	request_data = p_request_data;
 
-	for (int i = 0; i < headers.size(); i++) {
-
-		if (headers[i].findn("user-agent:") == 0)
-			has_user_agent = true;
-		if (headers[i].findn("Accept:") == 0)
-			has_accept = true;
-	}
-
-	if (!has_user_agent) {
-		headers.push_back("User-Agent: GodotEngine/" + String(VERSION_FULL_BUILD) + " (" + OS::get_singleton()->get_name() + ")");
-	}
-
-	if (!has_accept) {
-		headers.push_back("Accept: */*");
-	}
-
 	requesting = true;
 
 	if (use_threads) {