+/*
+ * This function examines a saved game file just far enough to
+ * determine which game type it contains. It returns NULL on success
+ * and the game name string in 'name' (which will be dynamically
+ * allocated and should be caller-freed), or an error message on
+ * failure.
+ */
+char *identify_game(char **name, int (*read)(void *ctx, void *buf, int len),
+ void *rctx)
+{
+ int nstates = 0, statepos = -1, gotstates = 0;
+ int started = FALSE;
+
+ char *val = NULL;
+ /* Initially all errors give the same report */
+ char *ret = "Data does not appear to be a saved game file";
+
+ *name = NULL;
+
+ /*
+ * Loop round and round reading one key/value pair at a time from
+ * the serialised stream, until we've found the game name.
+ */
+ while (nstates <= 0 || statepos < 0 || gotstates < nstates-1) {
+ char key[9], c;
+ int len;
+
+ do {
+ if (!read(rctx, key, 1)) {
+ /* unexpected EOF */
+ goto cleanup;
+ }
+ } while (key[0] == '\r' || key[0] == '\n');
+
+ if (!read(rctx, key+1, 8)) {
+ /* unexpected EOF */
+ goto cleanup;
+ }
+
+ if (key[8] != ':') {
+ if (started)
+ ret = "Data was incorrectly formatted for a saved game file";
+ goto cleanup;
+ }
+ len = strcspn(key, ": ");
+ assert(len <= 8);
+ key[len] = '\0';
+
+ len = 0;
+ while (1) {
+ if (!read(rctx, &c, 1)) {
+ /* unexpected EOF */
+ goto cleanup;
+ }
+
+ if (c == ':') {
+ break;
+ } else if (c >= '0' && c <= '9') {
+ len = (len * 10) + (c - '0');
+ } else {
+ if (started)
+ ret = "Data was incorrectly formatted for a"
+ " saved game file";
+ goto cleanup;
+ }
+ }
+
+ val = snewn(len+1, char);
+ if (!read(rctx, val, len)) {
+ if (started)
+ goto cleanup;
+ }
+ val[len] = '\0';
+
+ if (!started) {
+ if (strcmp(key, "SAVEFILE") || strcmp(val, SERIALISE_MAGIC)) {
+ /* ret already has the right message in it */
+ goto cleanup;
+ }
+ /* Now most errors are this one, unless otherwise specified */
+ ret = "Saved data ended unexpectedly";
+ started = TRUE;
+ } else {
+ if (!strcmp(key, "VERSION")) {
+ if (strcmp(val, SERIALISE_VERSION)) {
+ ret = "Cannot handle this version of the saved game"
+ " file format";
+ goto cleanup;
+ }
+ } else if (!strcmp(key, "GAME")) {
+ *name = dupstr(val);
+ ret = NULL;
+ goto cleanup;
+ }
+ }
+
+ sfree(val);
+ val = NULL;
+ }
+
+ cleanup:
+ sfree(val);
+ return ret;
+}
+