Move StringInput into its own file

src/runtime/string_input.c

@@ -0,0 +1,37 @@
+#include "runtime/string_input.h"
+#include <string.h>
+
+typedef struct {
+  const char *string;
+  size_t position;
+  size_t length;
+} TSStringInput;
+
+const char *ts_string_input_read(void *d, size_t *bytes_read) {
+  TSStringInput *data = (TSStringInput *)d;
+  if (data->position >= data->length) {
+    *bytes_read = 0;
+    return "";
+  }
+  size_t previous_position = data->position;
+  data->position = data->length;
+  *bytes_read = data->position - previous_position;
+  return data->string + previous_position;
+}
+
+int ts_string_input_seek(void *d, size_t position) {
+  TSStringInput *data = (TSStringInput *)d;
+  data->position = position;
+  return (position < data->length);
+}
+
+TSInput ts_string_input_make(const char *string) {
+  TSStringInput *data = malloc(sizeof(TSStringInput));
+  data->string = string;
+  data->position = 0;
+  data->length = strlen(string);
+  return (TSInput) { .data = (void *)data,
+                     .read_fn = ts_string_input_read,
+                     .seek_fn = ts_string_input_seek,
+                     .release_fn = free };
+}