libos: Make os::File a wrapper around stdio's FILE

This way, os::File benefits from the same buffering as stdio.h does.

libos/include/os/File.h

@@ -14,6 +14,7 @@
 #include <luna/SharedPtr.h>
 #include <luna/StringView.h>
 #include <os/Path.h>
+#include <stdio.h>
 #include <sys/types.h>
 
 namespace os
@@ -164,9 +165,14 @@ namespace os
          */
         int fd() const
         {
-            return m_fd;
+            return fileno(m_file);
         }
 
+        /**
+         * @brief Flushes the stream's buffers.
+         */
+        void flush();
+
         /**
          * @brief Move this File's file pointer back to the beginning.
          */
@@ -182,7 +188,7 @@ namespace os
         Result<usize> raw_read(u8* buf, usize length);
         Result<usize> raw_write(const u8* buf, usize length);
 
-        int m_fd { -1 };
+        FILE* m_file { nullptr };
     };
 
     /**

libos/src/File.cpp

@@ -7,6 +7,7 @@
  *
  */
 
+#include <errno.h>
 #include <luna/StringBuilder.h>
 #include <os/File.h>
 #include <sys/syscall.h>
@@ -16,6 +17,21 @@ static SharedPtr<os::File> g_stdin = {};
 static SharedPtr<os::File> g_stdout = {};
 static SharedPtr<os::File> g_stderr = {};
 
+static const char* stdio_mode_from_openmode(int mode)
+{
+    mode &= ~(O_CREAT | O_EXCL);
+
+    switch (mode)
+    {
+    case os::File::ReadOnly: return "r";
+    case os::File::ReadWrite: return "w+";
+    case os::File::WriteOnly: return "w";
+    case os::File::ReadAppend: return "a+";
+    case os::File::Append: return "a";
+    default: fail("Mode incompatible with fdopen()");
+    }
+}
+
 namespace os
 {
     File::File(Badge<File>)
@@ -24,22 +40,22 @@ namespace os
 
     File::~File()
     {
-        if (m_fd >= 0) close(m_fd);
+        if (m_file) fclose(m_file);
     }
 
     void File::initialize_standard_streams()
     {
         g_stdin = adopt_shared_if_nonnull(new (std::nothrow) File({}))
                       .expect_release_value("Cannot open standard input stream");
-        g_stdin->m_fd = STDIN_FILENO;
+        g_stdin->m_file = stdin;
 
         g_stdout = adopt_shared_if_nonnull(new (std::nothrow) File({}))
                        .expect_release_value("Cannot open standard output stream");
-        g_stdout->m_fd = STDOUT_FILENO;
+        g_stdout->m_file = stdout;
 
         g_stderr = adopt_shared_if_nonnull(new (std::nothrow) File({}))
                        .expect_release_value("Cannot open standard error stream");
-        g_stderr->m_fd = STDERR_FILENO;
+        g_stderr->m_file = stderr;
     }
 
     SharedPtr<File> File::standard_input()
@@ -70,7 +86,8 @@ namespace os
         long rc = syscall(SYS_openat, path.dirfd(), path.name().chars(), flags, mode);
         int fd = TRY(Result<int>::from_syscall(rc));
 
-        file->m_fd = fd;
+        file->m_file = fdopen(fd, stdio_mode_from_openmode(flags));
+        if (!file->m_file) return err(errno);
 
         return file;
     }
@@ -99,14 +116,16 @@ namespace os
 
     Result<usize> File::raw_read(u8* buf, usize length)
     {
-        long rc = syscall(SYS_read, m_fd, buf, length);
-        return Result<usize>::from_syscall(rc);
+        size_t nread = fread(buf, 1, length, m_file);
+        if (nread == 0 && ferror(m_file)) return err(errno);
+        return nread;
     }
 
     Result<usize> File::raw_write(const u8* buf, usize length)
     {
-        long rc = syscall(SYS_write, m_fd, buf, length);
-        return Result<usize>::from_syscall(rc);
+        size_t nwrite = fwrite(buf, 1, length, m_file);
+        if (nwrite == 0 && ferror(m_file)) return err(errno);
+        return nwrite;
     }
 
     Result<void> File::write(StringView str)
@@ -130,7 +149,7 @@ namespace os
         int current;
         while (true)
         {
-            current = TRY(getchar());
+            current = fgetc(m_file);
 
             if (current == -1) break;
 
@@ -189,29 +208,31 @@ namespace os
 
     Result<int> File::getchar()
     {
-        u8 value;
-
-        usize nread = TRY(raw_read(&value, 1));
-        if (!nread) return -1;
-
-        return value;
+        return fgetc(m_file);
     }
 
     void File::set_close_on_exec()
     {
-        fcntl(m_fd, F_SETFD, FD_CLOEXEC);
+        fcntl(fd(), F_SETFD, FD_CLOEXEC);
     }
 
     void File::rewind()
     {
-        lseek(m_fd, 0, SEEK_SET);
+        ::rewind(m_file);
+    }
+
+    void File::flush()
+    {
+        fflush(m_file);
     }
 
     // FIXME: Do not allocate memory for printing.
     Result<void> print_impl(SharedPtr<File> f, StringView fmt, va_list ap)
     {
         auto str = TRY(String::vformat(fmt, ap));
-        return f->write(str.view());
+        auto rc = f->write(str.view());
+        f->flush();
+        return rc;
     }
 
     Result<void> print(StringView fmt, ...)