CIODevice: Add some basic output facilities: write() and printf().

Being able to do file.printf() is extremely comfy, I have to say. :^)

LibCore/CIODevice.cpp

@@ -2,6 +2,7 @@
 #include <unistd.h>
 #include <sys/select.h>
 #include <stdio.h>
+#include <AK/printf.cpp>
 
 CIODevice::CIODevice(CObject* parent)
     : CObject(parent)
@@ -185,3 +186,25 @@ bool CIODevice::seek(signed_qword offset)
     m_eof = false;
     return true;
 }
+
+bool CIODevice::write(const byte* data, int size)
+{
+    int rc = ::write(m_fd, data, size);
+    if (rc < 0) {
+        perror("CIODevice::write: write");
+        return false;
+    }
+    return rc == size;
+}
+
+int CIODevice::printf(const char* format, ...)
+{
+    va_list ap;
+    va_start(ap, format);
+    // FIXME: We're not propagating write() failures to client here!
+    int ret = printf_internal([this] (char*&, char ch) {
+        write((const byte*)&ch, 1);
+    }, nullptr, format, ap);
+    va_end(ap);
+    return ret;
+}

LibCore/CIODevice.h

@@ -30,6 +30,8 @@ public:
     ByteBuffer read_line(int max_size);
     ByteBuffer read_all();
 
+    bool write(const byte*, int size);
+
     // FIXME: I would like this to be const but currently it needs to call populate_read_buffer().
     bool can_read_line();
 
@@ -40,6 +42,8 @@ public:
     virtual bool open(CIODevice::OpenMode) = 0;
     virtual bool close();
 
+    int printf(const char*, ...);
+
     virtual const char* class_name() const override { return "CIODevice"; }
 
 protected: