MINOR: quic: Variable-length integer encoding/decoding into/from buffer struct.

Add a function to encode a QUIC varint into a buffer struct. Samething for the
deconding part.

include/haproxy/xprt_quic.h

@@ -412,6 +412,46 @@ static inline int quic_dec_int(uint64_t *val,
 	return 1;
 }
 
+/* Decode a QUIC variable-length integer from <b> buffer into <val> supporting wrapping.
+ * Note that the result is a 64-bits integer but with the less significant
+ * 62 bits as relevant information. The most significant 2 bits encode
+ * the length of the integer.
+ * Note that this function update <b> buffer when a variable-length integer
+ * has successfully been parsed.
+ * Returns 1 and if succeeded (there was enough data in <buf>), 0 if not.
+ * If <retlen> is not null, increment <*retlen> by the number of bytes consumed to decode
+ * the varint.
+ */
+static inline size_t b_quic_dec_int(uint64_t *val, struct buffer *b, size_t *retlen)
+{
+	const unsigned char *pos = (const unsigned char *)b_head(b);
+	const unsigned char *end = (const unsigned char *)b_wrap(b);
+	size_t size = b_size(b);
+	size_t data = b_data(b);
+	size_t save_len, len;
+
+	if (!data)
+		return 0;
+
+	save_len = len = 1 << (*pos >> QUIC_VARINT_BYTE_0_SHIFT);
+	if (data < len)
+		return 0;
+
+	*val = *pos & QUIC_VARINT_BYTE_0_BITMASK;
+	if (++pos == end)
+		pos -= size;
+	while (--len) {
+		*val = (*val << 8) | *pos;
+		if (++pos == end)
+			pos -= size;
+	}
+	if (retlen)
+		*retlen += save_len;
+	b_del(b, save_len);
+
+	return 1;
+}
+
 /* Encode a QUIC variable-length integer from <val> into <buf> buffer with <end> as first
  * byte address after the end of this buffer.
  * Returns 1 if succeeded (there was enough room in buf), 0 if not.
@@ -439,6 +479,43 @@ static inline int quic_enc_int(unsigned char **buf, const unsigned char *end, ui
 	return 1;
 }
 
+/* Encode a QUIC variable-length integer <val> into <b> buffer.
+ * Returns 1 if succeeded (there was enough room in buf), 0 if not.
+ */
+static inline int b_quic_enc_int(struct buffer *b, uint64_t val)
+{
+	unsigned int shift;
+	unsigned char size_bits, *head, *pos, *wrap;
+	size_t save_len, len;
+	size_t data = b_data(b);
+	size_t size = b_size(b);
+
+	if (data == size)
+		return 0;
+
+	save_len = len = quic_int_getsize(val);
+	if (!len)
+		return 0;
+
+	shift = (len - 1) * 8;
+	/* set the bits of byte#0 which gives the length of the encoded integer */
+	size_bits = quic_log2(len) << QUIC_VARINT_BYTE_0_SHIFT;
+	pos = head = (unsigned char *)b_head(b);
+	wrap = (unsigned char *)b_wrap(b);
+	while (len--) {
+		*pos++ = val >> shift;
+		shift -= 8;
+		if (pos == wrap)
+			pos -= size;
+		if (++data == size && len)
+			return 0;
+	}
+	*head |= size_bits;
+	b_add(b, save_len);
+
+	return 1;
+}
+
 /* Return the length in bytes of <pn> packet number depending on
  * <largest_acked_pn> the largest ackownledged packet number.
  */