sd-dhcp: refactor dhcp_option_append

Store a pointer to the options in the DHCPMessage struct, and pass
this together with an offset around, rather than a uint8_t**.

This avoids us having to (re)compute the pointer; and changes
dhcp_option_append from adjusting both the pointer to the next
option and the remaining size of the options, to just adjusting
the current offset.

This makes the code a bit simpler to follow IMHO, but there should
be no functional change.

6 files changed, 74 insertions, 96 deletions

diff --git a/src/libsystemd-network/dhcp-internal.h b/src/libsystemd-network/dhcp-internal.h
index eb4a6cdce2..56423a2cce 100644
--- a/src/libsystemd-network/dhcp-internal.h
+++ b/src/libsystemd-network/dhcp-internal.h
@@ -36,8 +36,8 @@ int dhcp_network_send_raw_socket(int s, const union sockaddr_union *link,
 int dhcp_network_send_udp_socket(int s, be32_t address, uint16_t port,
                                  const void *packet, size_t len);
 
-int dhcp_option_append(uint8_t **buf, size_t *buflen, uint8_t code,
-                       size_t optlen, const void *optval);
+int dhcp_option_append(uint8_t options[], size_t size, size_t *offset,
+                       uint8_t code, size_t optlen, const void *optval);
 
 typedef int (*dhcp_option_cb_t)(uint8_t code, uint8_t len,
                                 const uint8_t *option, void *user_data);
@@ -46,7 +46,7 @@ int dhcp_option_parse(DHCPMessage *message, size_t len,
                       dhcp_option_cb_t cb, void *user_data);
 
 int dhcp_message_init(DHCPMessage *message, uint8_t op, uint32_t xid, uint8_t type,
-                      uint8_t **opt, size_t *optlen);
+                      uint8_t options[], size_t optlen, size_t *optoffset);
 
 uint16_t dhcp_packet_checksum(void *buf, size_t len);
 
diff --git a/src/libsystemd-network/dhcp-option.c b/src/libsystemd-network/dhcp-option.c
index 1b92e8616b..7bf8812676 100644
--- a/src/libsystemd-network/dhcp-option.c
+++ b/src/libsystemd-network/dhcp-option.c
@@ -26,37 +26,33 @@
 
 #include "dhcp-internal.h"
 
-int dhcp_option_append(uint8_t **buf, size_t *buflen, uint8_t code,
-                       size_t optlen, const void *optval)
-{
-        if (!buf || !buflen)
-                return -EINVAL;
+int dhcp_option_append(uint8_t options[], size_t size, size_t *offset,
+                       uint8_t code, size_t optlen, const void *optval) {
+        assert(options);
+        assert(offset);
 
         switch (code) {
 
         case DHCP_OPTION_PAD:
         case DHCP_OPTION_END:
-                if (*buflen < 1)
+                if (size - *offset < 1)
                         return -ENOBUFS;
 
-                (*buf)[0] = code;
-                *buf += 1;
-                *buflen -= 1;
+                options[*offset] = code;
+                *offset += 1;
                 break;
 
         default:
-                if (*buflen < optlen + 2)
+                if (size - *offset < optlen + 2)
                         return -ENOBUFS;
 
-                if (!optval)
-                        return -EINVAL;
+                assert(optval);
 
-                (*buf)[0] = code;
-                (*buf)[1] = optlen;
-                memcpy(&(*buf)[2], optval, optlen);
+                options[*offset] = code;
+                options[*offset + 1] = optlen;
+                memcpy(&options[*offset + 2], optval, optlen);
 
-                *buf += optlen + 2;
-                *buflen -= (optlen + 2);
+                *offset += optlen + 2;
 
                 break;
         }
@@ -143,7 +139,6 @@ int dhcp_option_parse(DHCPMessage *message, size_t len,
 {
         uint8_t overload = 0;
         uint8_t message_type = 0;
-        uint8_t *opt = (uint8_t *)(message + 1);
         int res;
 
         if (!message)
@@ -154,7 +149,7 @@ int dhcp_option_parse(DHCPMessage *message, size_t len,
 
         len -= sizeof(DHCPMessage);
 
-        res = parse_options(opt, len, &overload, &message_type,
+        res = parse_options(message->options, len, &overload, &message_type,
                             cb, user_data);
         if (res < 0)
                 return res;
diff --git a/src/libsystemd-network/dhcp-packet.c b/src/libsystemd-network/dhcp-packet.c
index d72d7a686d..10b645759e 100644
--- a/src/libsystemd-network/dhcp-packet.c
+++ b/src/libsystemd-network/dhcp-packet.c
@@ -38,8 +38,9 @@
 #define DHCP_CLIENT_MIN_OPTIONS_SIZE            312
 
 int dhcp_message_init(DHCPMessage *message, uint8_t op, uint32_t xid,
-                      uint8_t type, uint8_t **opt, size_t *optlen) {
-        int err;
+                      uint8_t type, uint8_t options[], size_t optlen, size_t *optoffset) {
+        size_t offset = 0;
+        int r;
 
         assert(op == BOOTREQUEST || op == BOOTREPLY);
 
@@ -49,12 +50,12 @@ int dhcp_message_init(DHCPMessage *message, uint8_t op, uint32_t xid,
         message->xid = htobe32(xid);
         message->magic = htobe32(DHCP_MAGIC_COOKIE);
 
-        *opt = (uint8_t *)(message + 1);
+        r = dhcp_option_append(message->options, optlen, &offset,
+                                 DHCP_OPTION_MESSAGE_TYPE, 1, &type);
+        if (r < 0)
+                return r;
 
-        err = dhcp_option_append(opt, optlen, DHCP_OPTION_MESSAGE_TYPE, 1,
-                                 &type);
-        if (err < 0)
-                return err;
+        *optoffset = offset;
 
         return 0;
 }
diff --git a/src/libsystemd-network/dhcp-protocol.h b/src/libsystemd-network/dhcp-protocol.h
index 539606cff6..11de186297 100644
--- a/src/libsystemd-network/dhcp-protocol.h
+++ b/src/libsystemd-network/dhcp-protocol.h
@@ -44,6 +44,7 @@ struct DHCPMessage {
         uint8_t sname[64];
         uint8_t file[128];
         be32_t magic;
+        uint8_t options[0];
 } _packed_;
 
 typedef struct DHCPMessage DHCPMessage;
diff --git a/src/libsystemd-network/sd-dhcp-client.c b/src/libsystemd-network/sd-dhcp-client.c
index 94235cf2f5..cee4ccf784 100644
--- a/src/libsystemd-network/sd-dhcp-client.c
+++ b/src/libsystemd-network/sd-dhcp-client.c
@@ -257,19 +257,18 @@ static sd_dhcp_client *client_stop(sd_dhcp_client *client, int error) {
 }
 
 static int client_message_init(sd_dhcp_client *client, DHCPMessage *message,
-                               uint8_t type, uint8_t **opt, size_t *optlen) {
+                               uint8_t type, size_t optlen, size_t *optoffset) {
         be16_t max_size;
         int r;
 
         assert(client);
         assert(client->secs);
         assert(message);
-        assert(opt);
-        assert(optlen);
+        assert(optoffset);
         assert(type == DHCP_DISCOVER || type == DHCP_REQUEST);
 
-        r = dhcp_message_init(message, BOOTREQUEST, client->xid, type, opt,
-                              optlen);
+        r = dhcp_message_init(message, BOOTREQUEST, client->xid, type,
+                              message->options, optlen, optoffset);
         if (r < 0)
                 return r;
 
@@ -285,7 +284,8 @@ static int client_message_init(sd_dhcp_client *client, DHCPMessage *message,
 
         /* Some DHCP servers will refuse to issue an DHCP lease if the Client
            Identifier option is not set */
-        r = dhcp_option_append(opt, optlen, DHCP_OPTION_CLIENT_IDENTIFIER,
+        r = dhcp_option_append(message->options, optlen, optoffset,
+                               DHCP_OPTION_CLIENT_IDENTIFIER,
                                sizeof(client->client_id), &client->client_id);
         if (r < 0)
                 return r;
@@ -299,10 +299,9 @@ static int client_message_init(sd_dhcp_client *client, DHCPMessage *message,
            it MUST include that list in any subsequent DHCPREQUEST
            messages.
          */
-        r = dhcp_option_append(opt, optlen,
+        r = dhcp_option_append(message->options, optlen, optoffset,
                                DHCP_OPTION_PARAMETER_REQUEST_LIST,
-                               client->req_opts_size,
-                               client->req_opts);
+                               client->req_opts_size, client->req_opts);
         if (r < 0)
                 return r;
 
@@ -316,7 +315,7 @@ static int client_message_init(sd_dhcp_client *client, DHCPMessage *message,
          */
         max_size = htobe16(DHCP_IP_UDP_SIZE + DHCP_MESSAGE_SIZE +
                            DHCP_MIN_OPTIONS_SIZE);
-        r = dhcp_option_append(opt, optlen,
+        r = dhcp_option_append(message->options, optlen, optoffset,
                                DHCP_OPTION_MAXIMUM_MESSAGE_SIZE,
                                2, &max_size);
         if (r < 0)
@@ -336,8 +335,7 @@ static int dhcp_client_send_raw(sd_dhcp_client *client, DHCPPacket *packet,
 
 static int client_send_discover(sd_dhcp_client *client) {
         _cleanup_free_ DHCPPacket *discover = NULL;
-        size_t optlen, len;
-        uint8_t *opt;
+        size_t optoffset, optlen, len;
         usec_t time_now;
         int r;
 
@@ -364,7 +362,7 @@ static int client_send_discover(sd_dhcp_client *client) {
                 return -ENOMEM;
 
         r = client_message_init(client, &discover->dhcp, DHCP_DISCOVER,
-                                &opt, &optlen);
+                                optlen, &optoffset);
         if (r < 0)
                 return r;
 
@@ -375,22 +373,21 @@ static int client_send_discover(sd_dhcp_client *client) {
            option to suggest the lease time it would like.
          */
         if (client->last_addr != INADDR_ANY) {
-                r = dhcp_option_append(&opt, &optlen,
-                                         DHCP_OPTION_REQUESTED_IP_ADDRESS,
-                                         4, &client->last_addr);
+                r = dhcp_option_append(discover->dhcp.options, optlen, &optoffset,
+                                       DHCP_OPTION_REQUESTED_IP_ADDRESS,
+                                       4, &client->last_addr);
                 if (r < 0)
                         return r;
         }
 
-        r = dhcp_option_append(&opt, &optlen, DHCP_OPTION_END, 0, NULL);
-        if (r < 0)
-                return r;
+        r = dhcp_option_append(discover->dhcp.options, optlen, &optoffset,
+                               DHCP_OPTION_END, 0, NULL);
 
         /* We currently ignore:
            The client SHOULD wait a random time between one and ten seconds to
            desynchronize the use of DHCP at startup.
          */
-        r = dhcp_client_send_raw(client, discover, len - optlen);
+        r = dhcp_client_send_raw(client, discover, sizeof(DHCPPacket) + optoffset);
         if (r < 0)
                 return r;
 
@@ -401,8 +398,7 @@ static int client_send_discover(sd_dhcp_client *client) {
 
 static int client_send_request(sd_dhcp_client *client) {
         _cleanup_free_ DHCPPacket *request;
-        size_t optlen, len;
-        uint8_t *opt;
+        size_t optoffset, optlen, len;
         int r;
 
         optlen = DHCP_MIN_OPTIONS_SIZE;
@@ -412,8 +408,8 @@ static int client_send_request(sd_dhcp_client *client) {
         if (!request)
                 return -ENOMEM;
 
-        r = client_message_init(client, &request->dhcp, DHCP_REQUEST, &opt,
-                                &optlen);
+        r = client_message_init(client, &request->dhcp, DHCP_REQUEST,
+                                optlen, &optoffset);
         if (r < 0)
                 return r;
 
@@ -428,13 +424,13 @@ static int client_send_request(sd_dhcp_client *client) {
                    filled in with the yiaddr value from the chosen DHCPOFFER.
                  */
 
-                r = dhcp_option_append(&opt, &optlen,
+                r = dhcp_option_append(request->dhcp.options, optlen, &optoffset,
                                        DHCP_OPTION_SERVER_IDENTIFIER,
                                        4, &client->lease->server_address);
                 if (r < 0)
                         return r;
 
-                r = dhcp_option_append(&opt, &optlen,
+                r = dhcp_option_append(request->dhcp.options, optlen, &optoffset,
                                        DHCP_OPTION_REQUESTED_IP_ADDRESS,
                                        4, &client->lease->address);
                 if (r < 0)
@@ -447,7 +443,7 @@ static int client_send_request(sd_dhcp_client *client) {
                    option MUST be filled in with client’s notion of its previously
                    assigned address. ’ciaddr’ MUST be zero.
                  */
-                r = dhcp_option_append(&opt, &optlen,
+                r = dhcp_option_append(request->dhcp.options, optlen, &optoffset,
                                        DHCP_OPTION_REQUESTED_IP_ADDRESS,
                                        4, &client->last_addr);
                 if (r < 0)
@@ -480,7 +476,8 @@ static int client_send_request(sd_dhcp_client *client) {
                 return -EINVAL;
         }
 
-        r = dhcp_option_append(&opt, &optlen, DHCP_OPTION_END, 0, NULL);
+        r = dhcp_option_append(request->dhcp.options, optlen, &optoffset,
+                               DHCP_OPTION_END, 0, NULL);
         if (r < 0)
                 return r;
 
@@ -489,9 +486,9 @@ static int client_send_request(sd_dhcp_client *client) {
                                                  client->lease->server_address,
                                                  DHCP_PORT_SERVER,
                                                  &request->dhcp,
-                                                 len - optlen - DHCP_IP_UDP_SIZE);
+                                                 sizeof(DHCPMessage) + optoffset);
         } else {
-                r = dhcp_client_send_raw(client, request, len - optlen);
+                r = dhcp_client_send_raw(client, request, sizeof(DHCPPacket) + optoffset);
         }
         if (r < 0)
                 return r;
diff --git a/src/libsystemd-network/test-dhcp-option.c b/src/libsystemd-network/test-dhcp-option.c
index 35db8c1c0a..eaf6a535e6 100644
--- a/src/libsystemd-network/test-dhcp-option.c
+++ b/src/libsystemd-network/test-dhcp-option.c
@@ -85,16 +85,14 @@ static void test_invalid_buffer_length(void)
 static void test_message_init(void)
 {
         _cleanup_free_ DHCPMessage *message = NULL;
-        size_t optlen = 3;
+        size_t optlen = 3, optoffset;
         size_t len = sizeof(DHCPMessage) + optlen;
-        uint8_t *opt, *magic;
+        uint8_t *magic;
 
         message = malloc0(len);
 
-        opt = (uint8_t *)(message + 1);
-
         assert_se(dhcp_message_init(message, BOOTREQUEST, 0x12345678,
-                  DHCP_DISCOVER, &opt, &optlen) >= 0);
+                  DHCP_DISCOVER, message->options, optlen, &optoffset) >= 0);
 
         assert_se(message->xid == htobe32(0x12345678));
         assert_se(message->op == BOOTREQUEST);
@@ -115,13 +113,11 @@ static DHCPMessage *create_message(uint8_t *options, uint16_t optlen,
 {
         DHCPMessage *message;
         size_t len = sizeof(DHCPMessage) + optlen;
-        uint8_t *opt;
 
         message = malloc0(len);
-        opt = (uint8_t *)(message + 1);
 
         if (options && optlen)
-                memcpy(opt, options, optlen);
+                memcpy(&message->options, options, optlen);
 
         if (file && filelen <= 128)
                 memcpy(&message->file, file, filelen);
@@ -308,46 +304,34 @@ static uint8_t options[64] = {
 
 static void test_option_set(void)
 {
-        size_t len, oldlen;
-        int pos, i;
-        uint8_t *opt;
-
-        assert_se(dhcp_option_append(NULL, NULL, 0, 0, NULL) == -EINVAL);
-
-        len = 0;
-        opt = &result[0];
-        assert_se(dhcp_option_append(&opt, NULL, 0, 0, NULL) == -EINVAL);
-        assert_se(opt == &result[0] && len == 0);
+        size_t offset = 0, len, pos;
+        unsigned i;
 
-        assert_se(dhcp_option_append(&opt, &len, DHCP_OPTION_PAD,
+        assert_se(dhcp_option_append(result, 0, &offset, DHCP_OPTION_PAD,
                                   0, NULL) == -ENOBUFS);
-        assert_se(opt == &result[0] && len == 0);
+        assert_se(offset == 0);
 
-        opt = &result[4];
-        len = 1;
-        assert_se(dhcp_option_append(&opt, &len, DHCP_OPTION_PAD,
+        offset = 4;
+        assert_se(dhcp_option_append(result, 1, &offset, DHCP_OPTION_PAD,
                                     0, NULL) >= 0);
-        assert_se(opt == &result[5] && len == 0);
+        assert_se(offset == 5);
 
-        pos = 4;
+        offset = pos = 4;
         len = 60;
         while (pos < 64 && options[pos] != DHCP_OPTION_END) {
-                opt = &result[pos];
-                oldlen = len;
+                offset = pos;
 
-                assert_se(dhcp_option_append(&opt, &len, options[pos],
-                                          options[pos + 1],
-                                          &options[pos + 2]) >= 0);
+                assert_se(dhcp_option_append(result, len, &offset,
+                                             options[pos],
+                                             options[pos + 1],
+                                             &options[pos + 2]) >= 0);
 
-                if (options[pos] == DHCP_OPTION_PAD) {
-                        assert_se(opt == &result[pos + 1]);
-                        assert_se(len == oldlen - 1);
+                if (options[pos] == DHCP_OPTION_PAD)
                         pos++;
-                } else {
-                        assert_se(opt == &result[pos + 2 + options[pos + 1]]);
-                        assert_se(len == oldlen - 2 - options[pos + 1]);
+                else
                         pos += 2 + options[pos + 1];
-                }
+
+                assert_se(offset == pos);
         }
 
         for (i = 0; i < pos; i++) {