From 97273ac0b89ab4d54cb82fcc8a296b910cba1556 Mon Sep 17 00:00:00 2001
From: oreo639 <31916379+Oreo639@users.noreply.github.com>
Date: Fri, 14 Jan 2022 15:52:45 -0800
Subject: [PATCH] Add 3dslink stdio redirection

---
 libctru/include/3ds.h            |  1 +
 libctru/include/3ds/3dslink.h    | 34 ++++++++++++++++++++++
 libctru/source/3dslink.c         | 48 ++++++++++++++++++++++++++++++++
 libctru/source/system/initArgv.c | 12 ++++++++
 4 files changed, 95 insertions(+)
 create mode 100644 libctru/include/3ds/3dslink.h
 create mode 100644 libctru/source/3dslink.c

diff --git a/libctru/include/3ds.h b/libctru/include/3ds.h
index dc7c6caf4..9aeb842d6 100644
--- a/libctru/include/3ds.h
+++ b/libctru/include/3ds.h
@@ -99,6 +99,7 @@ extern "C" {
 #include <3ds/mii.h>
 
 #include <3ds/gdbhio_dev.h>
+#include <3ds/3dslink.h>
 
 #ifdef __cplusplus
 }
diff --git a/libctru/include/3ds/3dslink.h b/libctru/include/3ds/3dslink.h
new file mode 100644
index 000000000..234f941f4
--- /dev/null
+++ b/libctru/include/3ds/3dslink.h
@@ -0,0 +1,34 @@
+/**
+ * @file 3dslink.h
+ * @brief Netloader (3dslink) utilities
+ */
+
+#pragma once
+
+#include <stdbool.h>
+
+struct in_addr;
+
+/// Address of the host connected through 3dslink
+extern struct in_addr __3dslink_host;
+
+#define LINK3DS_COMM_PORT 17491 ///< 3dslink TCP server port
+
+/**
+ * @brief Connects to the 3dslink host, setting up an output stream.
+ * @param[in] redirStdout Whether to redirect stdout to nxlink output.
+ * @param[in] redirStderr Whether to redirect stderr to nxlink output.
+ * @return Socket fd on success, negative number on failure.
+ * @note The socket should be closed with close() during application cleanup.
+ */
+int link3dsConnectToHost(bool redirStdout, bool redirStderr);
+
+/// Same as \ref link3dsConnectToHost but redirecting both stdout/stderr.
+static inline int link3dsStdio(void) {
+    return link3dsConnectToHost(true, true);
+}
+
+/// Same as \ref link3dsConnectToHost but redirecting only stderr.
+static inline int link3dsStdioForDebug(void) {
+    return link3dsConnectToHost(false, true);
+}
diff --git a/libctru/source/3dslink.c b/libctru/source/3dslink.c
new file mode 100644
index 000000000..8dc038137
--- /dev/null
+++ b/libctru/source/3dslink.c
@@ -0,0 +1,48 @@
+#include <string.h>
+#include <stdio.h>
+#include <sys/socket.h>
+#include <sys/errno.h>
+#include <arpa/inet.h>
+#include <unistd.h>
+
+#include <3ds/3dslink.h>
+
+struct in_addr __3dslink_host = {0};
+
+static int sock = -1;
+
+int link3dsConnectToHost(bool redirStdout, bool redirStderr)
+{
+	int ret = -1;
+	struct sockaddr_in srv_addr;
+
+	sock = socket(AF_INET, SOCK_STREAM, 0);
+	if (!sock) {
+		return ret;
+	}
+
+	bzero(&srv_addr, sizeof srv_addr);
+	srv_addr.sin_family = AF_INET;
+	srv_addr.sin_addr = __3dslink_host;
+	srv_addr.sin_port = htons(LINK3DS_COMM_PORT);
+
+	ret = connect(sock, (struct sockaddr *) &srv_addr, sizeof(srv_addr));
+	if (ret != 0) {
+		close(sock);
+		return -1;
+	}
+
+	if (redirStdout) {
+		// redirect stdout
+		fflush(stdout);
+		dup2(sock, STDOUT_FILENO);
+	}
+
+	if (redirStderr) {
+		// redirect stderr
+		fflush(stderr);
+		dup2(sock, STDERR_FILENO);
+	}
+
+	return sock;
+}
diff --git a/libctru/source/system/initArgv.c b/libctru/source/system/initArgv.c
index c34843e01..a91b851ad 100644
--- a/libctru/source/system/initArgv.c
+++ b/libctru/source/system/initArgv.c
@@ -1,7 +1,10 @@
 #include <3ds/types.h>
 #include <3ds/env.h>
+#include <3ds/3dslink.h>
 
 #include <string.h>
+#include <stdlib.h>
+#include <arpa/inet.h>
 
 // System globals we define here
 int __system_argc;
@@ -47,5 +50,14 @@ void __attribute__((weak)) __system_initArgv(void)
 		for (; *temp; temp ++);
 		temp ++;
 	}
+
+	// Grab 3dslink host address if avaliable
+	if ( __system_argc > 1 &&
+         strlen(__system_argv[__system_argc - 1]) == 17 &&
+         strncmp(&__system_argv[__system_argc - 1][8], "_3DSLINK_", 8) == 0 )
+	{
+		__system_argc--;
+		__3dslink_host.s_addr = strtoul(__system_argv[__system_argc], NULL, 16);
+	}
 	__system_argv[__system_argc] = NULL;
 }