From 0982ad2613d4ace40c5d14b0815f1285eac69451 Mon Sep 17 00:00:00 2001
From: Sargun Dhillon <sargun@netflix.com>
Date: Wed, 12 Apr 2017 02:27:36 -0700
Subject: [PATCH] Add FD swap / redirect stderr code

---
 src/tini.c | 32 ++++++++++++++++++++++++++++++++
 1 file changed, 32 insertions(+)

diff --git a/src/tini.c b/src/tini.c
index a0d6328..5d8c42b 100644
--- a/src/tini.c
+++ b/src/tini.c
@@ -136,8 +136,29 @@ int isolate_child() {
 
 
 int spawn(const signal_configuration_t* const sigconf_ptr, char* const argv[], int* const child_pid_ptr) {
+	int new_stdout_fd = 1;
+	int new_stderr_fd = 2;
+	char *redir_path;
 	pid_t pid;
 
+	redir_path = getenv("REDIR_STDOUT");
+	if (redir_path) {
+		new_stdout_fd = open(redir_path, O_WRONLY | O_CREAT | O_APPEND);
+		if (new_stdout_fd == -1) {
+			PRINT_FATAL("Failed to open stdout redirect path: %s", strerror(errno));
+			return 1;
+		}
+	}
+
+	redir_path = getenv("REDIR_STDERR");
+	if (redir_path) {
+		new_stderr_fd = open(redir_path, O_WRONLY | O_CREAT | O_APPEND);
+		if (new_stderr_fd == -1) {
+			PRINT_FATAL("Failed to open stderr redirect path: %s", strerror(errno));
+			return 1;
+		}
+	}
+
 	// TODO: check if tini was a foreground process to begin with (it's not OK to "steal" the foreground!")
 
 	pid = fork();
@@ -156,6 +177,17 @@ int spawn(const signal_configuration_t* const sigconf_ptr, char* const argv[], i
 			return 1;
 		}
 
+		// Do the FD swap
+		// No need to set CLO_EXEC on existing stdout, stderr FDs, because we're closing them anyway
+		if (dup2(new_stdout_fd, 1) == -1) {
+			PRINT_FATAL("Failed to duplicate stdout FD: %s", strerror(errno));
+			return 1;
+		}
+		if (dup2(new_stderr_fd, 2) == -1) {
+			PRINT_FATAL("Failed to duplicate stdout FD: %s", strerror(errno));
+			return 1;
+		}
+
 		execvp(argv[0], argv);
 
 		// execvp will only return on an error so make sure that we check the errno