libc: Add fdopen()

libs/libc/include/stdio.h

@@ -32,6 +32,9 @@ extern "C"
     /* Opens the file specified by pathname. Returns the file handle on success, or NULL on error. */
     FILE* fopen(const char* pathname, const char* mode);
 
+    /* Returns a new file associated with the file descriptor fd. */
+    FILE* fdopen(int fd, const char* mode);
+
     /* Writes formatted output according to the string format to the file stream. */
     int fprintf(FILE* stream, const char* format, ...);
 

libs/libc/src/file.cpp

@@ -40,6 +40,19 @@ extern "C"
         return stream;
     }
 
+    FILE* fdopen(int fd, const char*)
+    {
+        if (fd < 0) // FIXME: Also check if the mode string is compatible with how fd was opened.
+        {
+            errno = EBADF;
+            return 0;
+        }
+        FILE* stream = (FILE*)malloc(sizeof(FILE));
+        stream->f_fd = fd;
+        clearerr(stream);
+        return stream;
+    }
+
     size_t fread(void* buf, size_t size, size_t nmemb, FILE* stream)
     {
         ssize_t status = read(stream->f_fd, buf, size * nmemb);