feat: IOB structures and iob_init()

src/io_backend/io_backend.c

@@ -0,0 +1,34 @@
+#include "io_backend.h"
+
+#include <stdio.h>
+
+static struct iob_context context;
+static FILE *input;
+
+int iob_init(struct iob_context *ctx)
+{
+    context = *ctx;
+
+    switch (context.mode)
+    {
+    IOB_MODE_STDIN:
+        input = stdin;
+        return 0;
+
+    IOB_MODE_SCRIPT:
+        if (context.args == NULL)
+            return -2;
+        input = fopen(context.args, "r");
+        if (input == NULL)
+            return -4;
+
+    IOB_MODE_CMD:
+        if (context.args != NULL)
+            return -2;
+        else
+            return 0;
+
+    default:
+        return -1;
+    }
+}