c: move c files into nostrdb in prep for switchover

nostrdb/utf8.h

@@ -0,0 +1,57 @@
+/* MIT (BSD) license - see LICENSE file for details */
+#ifndef CCAN_UTF8_H
+#define CCAN_UTF8_H
+#include <inttypes.h>
+#include <stdbool.h>
+#include <string.h>
+
+/* Unicode is limited to 21 bits. */
+#define UTF8_MAX_LEN    4
+
+struct utf8_state {
+    /* How many characters we are expecting as part of this Unicode point */
+    uint16_t total_len;
+    /* How many characters we've already seen. */
+    uint16_t used_len;
+    /* Compound character, aka Unicode point. */
+    uint32_t c;
+};
+
+#define UTF8_STATE_INIT { 0, 0, 0 }
+
+static inline void utf8_state_init(struct utf8_state *utf8_state)
+{
+    memset(utf8_state, 0, sizeof(*utf8_state));
+}
+
+/**
+ * utf8_decode - continue UTF8 decoding with this character.
+ * @utf8_state - initialized UTF8 state.
+ * @c - the character.
+ *
+ * Returns false if it needs another character to give results.
+ * Otherwise returns true, @utf8_state can be reused without initializeation,
+ * and sets errno:
+ * 0: success
+ * EINVAL: bad encoding (including a NUL character).
+ * EFBIG: not a minimal encoding.
+ * ERANGE: encoding of invalid character.
+ *
+ * You can extract the character from @utf8_state->c; @utf8_state->used_len
+ * indicates how many characters have been consumed.
+ */
+bool utf8_decode(struct utf8_state *utf8_state, char c);
+
+/**
+ * utf8_encode - encode a point into UTF8.
+ * @point - Unicode point to include.
+ * @dest - buffer to fill.
+ *
+ * Returns 0 if point was invalid, otherwise bytes of dest used.
+ * Sets errno to ERANGE if point was invalid.
+ */
+size_t utf8_encode(uint32_t point, char dest[UTF8_MAX_LEN]);
+
+/* Check for valid UTF-8 */
+bool utf8_check(const void *vbuf, size_t buflen);
+#endif /* CCAN_UTF8_H */