1 files changed, 46 insertions, 0 deletions
diff --git a/core/readbuf.c b/core/readbuf.c
new file mode 100644
index 0000000..ee10362
--- /dev/null
+++ b/core/readbuf.c
@@ -0,0 +1,46 @@
+/*
+ * Copyright (c) 2026, Chloe M.
+ * Provided under the BSD-3 clause
+ */
+
+#include <stdint.h>
+#include <stddef.h>
+#include <errno.h>
+#include <unistd.h>
+#include "cescal/readbuf.h"
+
+int
+readbuf_init(struct readbuf *rb)
+{
+    if (rb == NULL) {
+        errno = EINVAL;
+        return -1;
+    }
+
+    rb->size = 0;
+    rb->tail = 0;
+    return 0;
+}
+
+char
+readbuf_read(struct readbuf *rb, int fd)
+{
+    ssize_t nread = -1;
+
+    if (rb == NULL || fd < 0) {
+        errno = EINVAL;
+        return '\0';
+    }
+
+#define N_RESIDUAL(rb) ((rb)->size - (rb)->tail)
+    if (N_RESIDUAL(rb) == 0 || rb->size == 0) {
+        if ((nread = read(fd, rb->buf, READBUF_CAP)) <= 0)
+            return nread;
+
+        rb->size = nread;
+        rb->tail = 0;
+    }
+#undef N_RESIDUAL
+
+    return rb->buf[rb->tail++];
+}