reftable/record: extract function to decode key lengths

We're about to refactor the binary search over restart points so that it
does not need to fully decode the record keys anymore. To do so we will
need to decode the record key lengths, which is non-trivial logic.

Extract the logic to decode these lengths from `refatble_decode_key()`
so that we can reuse it.

Signed-off-by: Patrick Steinhardt <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: pks-t

reftable/record.c

@@ -159,26 +159,42 @@ int reftable_encode_key(int *restart, struct string_view dest,
 	return start.len - dest.len;
 }
 
-int reftable_decode_key(struct strbuf *last_key, uint8_t *extra,
-			struct string_view in)
+int reftable_decode_keylen(struct string_view in,
+			   uint64_t *prefix_len,
+			   uint64_t *suffix_len,
+			   uint8_t *extra)
 {
-	int start_len = in.len;
-	uint64_t prefix_len = 0;
-	uint64_t suffix_len = 0;
+	size_t start_len = in.len;
 	int n;
 
-	n = get_var_int(&prefix_len, &in);
+	n = get_var_int(prefix_len, &in);
 	if (n < 0)
 		return -1;
 	string_view_consume(&in, n);
 
-	n = get_var_int(&suffix_len, &in);
+	n = get_var_int(suffix_len, &in);
 	if (n <= 0)
 		return -1;
 	string_view_consume(&in, n);
 
-	*extra = (uint8_t)(suffix_len & 0x7);
-	suffix_len >>= 3;
+	*extra = (uint8_t)(*suffix_len & 0x7);
+	*suffix_len >>= 3;
+
+	return start_len - in.len;
+}
+
+int reftable_decode_key(struct strbuf *last_key, uint8_t *extra,
+			struct string_view in)
+{
+	int start_len = in.len;
+	uint64_t prefix_len = 0;
+	uint64_t suffix_len = 0;
+	int n;
+
+	n = reftable_decode_keylen(in, &prefix_len, &suffix_len, extra);
+	if (n < 0)
+		return -1;
+	string_view_consume(&in, n);
 
 	if (in.len < suffix_len ||
 	    prefix_len > last_key->len)

reftable/record.h

@@ -86,6 +86,12 @@ int reftable_encode_key(int *is_restart, struct string_view dest,
 			struct strbuf prev_key, struct strbuf key,
 			uint8_t extra);
 
+/* Decode a record's key lengths. */
+int reftable_decode_keylen(struct string_view in,
+			   uint64_t *prefix_len,
+			   uint64_t *suffix_len,
+			   uint8_t *extra);
+
 /*
  * Decode into `last_key` and `extra` from `in`. `last_key` is expected to
  * contain the decoded key of the preceding record, if any.