libc: Add freopen()

libc/include/stdio.h

@@ -41,6 +41,9 @@ extern "C"
     /* Bind a stream to a file descriptor. */
     FILE* fdopen(int fd, const char* mode);
 
+    /* Change the underlying file and mode of a stream. */
+    FILE* freopen(const char* path, const char* mode, FILE* stream);
+
     /* Close a file and frees up its stream. */
     int fclose(FILE* stream);
 

libc/src/stdio.cpp

@@ -85,6 +85,25 @@ extern "C"
         return f;
     }
 
+    FILE* freopen(const char* path, const char* mode, FILE* stream)
+    {
+        int flags;
+
+        if ((flags = fopen_parse_mode(mode)) < 0) return nullptr;
+
+        close(stream->_fd);
+
+        if (!path) { fail("FIXME: freopen() called with path=nullptr"); }
+
+        int fd = open(path, flags, 0666);
+        if (fd < 0) { return nullptr; }
+
+        stream->_fd = fd;
+        clearerr(stream);
+
+        return stream;
+    }
+
     int fclose(FILE* stream)
     {
         if (close(stream->_fd) < 0) return EOF;