Make command parsing more robust

include/cmdbuf.h

@@ -0,0 +1,22 @@
+#ifndef RDBSERVER_CMDBUF_H_
+#define RDBSERVER_CMDBUF_H_
+
+#include <stdbool.h>
+#include <stdint.h>
+#include <stdlib.h>
+
+typedef struct CommandBuf {
+    char *buf;
+    size_t len;
+} CommandBuf;
+
+/* Try to consume a string literal. */
+bool cmd_match_str(CommandBuf *cmd, const char *str);
+/* Try to consume a string literal, if it is the only thing left in the buffer. */
+bool cmd_match_only_str(CommandBuf *cmd, const char *str);
+/* Try to consume a base-16 number, and return the value. */
+bool cmd_match_hex_number(CommandBuf *cmd, uint32_t *value);
+/* Try to consume a hex-encoded list of bytes, and return the value. */
+bool cmd_match_hex_bytes(CommandBuf *cmd, const uint32_t count, char *value);
+
+#endif