LibC: Implement popen() and pclose().

I feel reasonably confident that I might have gotten these right. :^)

AK/ValueRestorer.h

@@ -0,0 +1,26 @@
+#pragma once
+
+namespace AK {
+
+template<typename T>
+class ValueRestorer {
+public:
+ ValueRestorer(T& variable)
+ : m_variable(variable)
+ , m_saved_value(variable)
+ {
+ }
+
+ ~ValueRestorer()
+ {
+ m_variable = m_saved_value;
+ }
+
+private:
+ T& m_variable;
+ T m_saved_value;
+};
+
+}
+
+using AK::ValueRestorer;

LibC/stdio.cpp

@@ -10,6 +10,7 @@
 #include <fcntl.h>
 #include <AK/printf.cpp>
 #include <AK/StdLibExtras.h>
+#include <AK/ValueRestorer.h>
 #include <Kernel/Syscall.h>
 
 extern "C" {
@@ -458,14 +459,70 @@ char* tmpnam(char*)
 
 FILE* popen(const char* command, const char* type)
 {
- (void)command;
- (void)type;
- ASSERT_NOT_REACHED();
+ if (!type || (*type != 'r' && *type != 'w')) {
+ errno = EINVAL;
+ return nullptr;
+ }
+
+ int pipe_fds[2];
+
+ int rc = pipe(pipe_fds);
+ if (rc < 0) {
+ ValueRestorer restorer(errno);
+ perror("pipe");
+ return nullptr;
+ }
+
+ pid_t child_pid = fork();
+ if (!child_pid) {
+ if (*type == 'r') {
+ int rc = dup2(pipe_fds[1], STDOUT_FILENO);
+ if (rc < 0) {
+ perror("dup2");
+ exit(1);
+ }
+ close(pipe_fds[0]);
+ close(pipe_fds[1]);
+ } else if (*type == 'w') {
+ int rc = dup2(pipe_fds[0], STDIN_FILENO);
+ if (rc < 0) {
+ perror("dup2");
+ exit(1);
+ }
+ close(pipe_fds[0]);
+ close(pipe_fds[1]);
+ }
+
+ int rc = execl("/bin/sh", "sh", "-c", command, nullptr);
+ if (rc < 0)
+ perror("execl");
+ exit(1);
+ }
+
+ FILE* fp = nullptr;
+ if (*type == 'r') {
+ fp = make_FILE(pipe_fds[0]);
+ close(pipe_fds[1]);
+ } else if (*type == 'w') {
+ fp = make_FILE(pipe_fds[1]);
+ close(pipe_fds[0]);
+ }
+
+ fp->popen_child = child_pid;
+ return fp;
 }
 
-int pclose(FILE*)
+int pclose(FILE* fp)
 {
- ASSERT_NOT_REACHED();
+ ASSERT(fp);
+ ASSERT(fp->popen_child != 0);
+
+ int wstatus = 0;
+ int rc = waitpid(fp->popen_child, &wstatus, 0);
+ if (rc < 0)
+ return rc;
+
+ return wstatus;
 }
 
 int remove(const char* pathname)

LibC/stdio.h

@@ -29,6 +29,7 @@ struct __STDIO_FILE {
  int eof;
  int error;
  int mode;
+ pid_t popen_child;
  char* buffer;
  size_t buffer_size;
  size_t buffer_index;