PACKET: constify where possible

The PACKET should hold a 'const unsigned char*' underneath as well
but the legacy code passes the record buffer around as 'unsigned char*'
(to callbacks, too) so that's a bigger refactor.
Reviewed-by: NMatt Caswell <matt@openssl.org>

ssl/packet_locl.h

@@ -82,7 +82,7 @@ typedef struct {
 /*
  * Returns the number of bytes remaining to be read in the PACKET
  */
-__owur static inline size_t PACKET_remaining(PACKET *pkt)
+__owur static inline size_t PACKET_remaining(const PACKET *pkt)
 {
     return (size_t)(pkt->end - pkt->curr);
 }
@@ -113,8 +113,8 @@ static inline int PACKET_buf_init(PACKET *pkt, unsigned char *buf, size_t len)
  * Data is not copied: the |subpkt| packet will share its underlying buffer with
  * the original |pkt|, so data wrapped by |pkt| must outlive the |subpkt|.
  */
-__owur static inline int PACKET_peek_sub_packet(PACKET *pkt, PACKET *subpkt,
-                                               size_t len)
+__owur static inline int PACKET_peek_sub_packet(const PACKET *pkt,
+                                                PACKET *subpkt, size_t len)
 {
     if (PACKET_remaining(pkt) < len)
         return 0;
@@ -143,7 +143,8 @@ __owur static inline int PACKET_get_sub_packet(PACKET *pkt, PACKET *subpkt,
 /* Peek ahead at 2 bytes in network order from |pkt| and store the value in
  * |*data|
  */
-__owur static inline int PACKET_peek_net_2(PACKET *pkt, unsigned int *data)
+__owur static inline int PACKET_peek_net_2(const PACKET *pkt,
+                                           unsigned int *data)
 {
     if (PACKET_remaining(pkt) < 2)
         return 0;
@@ -169,7 +170,8 @@ __owur static inline int PACKET_get_net_2(PACKET *pkt, unsigned int *data)
 /* Peek ahead at 3 bytes in network order from |pkt| and store the value in
  * |*data|
  */
-__owur static inline int PACKET_peek_net_3(PACKET *pkt, unsigned long *data)
+__owur static inline int PACKET_peek_net_3(const PACKET *pkt,
+                                           unsigned long *data)
 {
     if (PACKET_remaining(pkt) < 3)
         return 0;
@@ -196,7 +198,8 @@ __owur static inline int PACKET_get_net_3(PACKET *pkt, unsigned long *data)
 /* Peek ahead at 4 bytes in network order from |pkt| and store the value in
  * |*data|
  */
-__owur static inline int PACKET_peek_net_4(PACKET *pkt, unsigned long *data)
+__owur static inline int PACKET_peek_net_4(const PACKET *pkt,
+                                           unsigned long *data)
 {
     if (PACKET_remaining(pkt) < 4)
         return 0;
@@ -222,7 +225,7 @@ __owur static inline int PACKET_get_net_4(PACKET *pkt, unsigned long *data)
 }
 
 /* Peek ahead at 1 byte from |pkt| and store the value in |*data| */
-__owur static inline int PACKET_peek_1(PACKET *pkt, unsigned int *data)
+__owur static inline int PACKET_peek_1(const PACKET *pkt, unsigned int *data)
 {
     if (!PACKET_remaining(pkt))
         return 0;
@@ -247,7 +250,7 @@ __owur static inline int PACKET_get_1(PACKET *pkt, unsigned int *data)
  * Peek ahead at 4 bytes in reverse network order from |pkt| and store the value
  * in |*data|
  */
-__owur static inline int PACKET_peek_4(PACKET *pkt, unsigned long *data)
+__owur static inline int PACKET_peek_4(const PACKET *pkt, unsigned long *data)
 {
     if (PACKET_remaining(pkt) < 4)
         return 0;
@@ -281,7 +284,7 @@ __owur static inline int PACKET_get_4(PACKET *pkt, unsigned long *data)
  * caller should not free this data directly (it will be freed when the
  * underlying buffer gets freed
  */
-__owur static inline int PACKET_peek_bytes(PACKET *pkt, unsigned char **data,
+__owur static inline int PACKET_peek_bytes(const PACKET *pkt, unsigned char **data,
                                           size_t len)
 {
     if (PACKET_remaining(pkt) < len)
@@ -310,7 +313,7 @@ __owur static inline int PACKET_get_bytes(PACKET *pkt, unsigned char **data,
 }
 
 /* Peek ahead at |len| bytes from |pkt| and copy them to |data| */
-__owur static inline int PACKET_peek_copy_bytes(PACKET *pkt,
+__owur static inline int PACKET_peek_copy_bytes(const PACKET *pkt,
                                                 unsigned char *data, size_t len)
 {
     if (PACKET_remaining(pkt) < len)
@@ -356,7 +359,7 @@ __owur static inline int PACKET_forward(PACKET *pkt, size_t len)
 }
 
 /* Store a bookmark for the current reading position in |*bm| */
-__owur static inline int PACKET_get_bookmark(PACKET *pkt, size_t *bm)
+__owur static inline int PACKET_get_bookmark(const PACKET *pkt, size_t *bm)
 {
     *bm = pkt->curr - pkt->start;
 
@@ -378,7 +381,7 @@ __owur static inline int PACKET_goto_bookmark(PACKET *pkt, size_t bm)
  * Stores the total length of the packet we have in the underlying buffer in
  * |*len|
  */
-__owur static inline int PACKET_length(PACKET *pkt, size_t *len)
+__owur static inline int PACKET_length(const PACKET *pkt, size_t *len)
 {
     *len = pkt->end - pkt->start;
 
@@ -390,4 +393,3 @@ __owur static inline int PACKET_length(PACKET *pkt, size_t *len)
 # endif
 
 #endif /* HEADER_PACKET_LOCL_H */
-