Set correct buffer size in into_options() on libcoap<4.3.5rc2

[pulsastrix]

Versions of libcoap older than 4.3.5rc2 used a user-provided buffer for temporarily storing the options during conversion.

This buffer, however, must be larger than what the libcoap documentation originally suggested, as this buffer area must also hold the option headers.
If this is not done, trailing elements of the URI are silently removed.

This PR increases the used buffer size for this temporary buffer to a value that should be large enough to store all options that could be created from this URI.

Additionally, it adds a check for newer libcoap versions that don't use this buffer anymore.
In that case, we just pass an empty buffer instead, saving memory and avoiding some iterations over the URI path and query string to determine the buffer size.

[github-actions]

Workflow Status Report

Generated for commit 722fddc on Fri Aug 23 12:44:20 UTC 2024.

Linting Report

Clippy check result: success

Refer to the "Files Changed" tab for identified issues.

Code Coverage Report

Filename                                    Stmts    Miss  Cover    Missing
----------------------------------------  -------  ------  -------  -----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
libcoap/src/session/client.rs                 135      62  54.07%   69-74, 76-84, 88-94, 96, 100, 111, 114, 119, 140, 146, 152-153, 155, 174, 180, 186-187, 189, 211, 213, 215, 217-223, 265-266, 272-282, 293-303, 314-324, 371-376
libcoap/src/session/mod.rs                    154      86  44.16%   61-67, 96-97, 111-225, 236-252, 268-270, 289-291, 301-311, 347, 362, 377-396, 419, 427, 451, 455, 476-480, 558, 564
libcoap/src/session/server.rs                  48      12  75.00%   71-73, 140-141, 149-150, 181-186
libcoap-sys/src/lib.rs                         91      32  64.84%   115-151, 183, 188, 193, 198, 228, 233, 238, 243, 248, 253, 258, 263, 268, 278, 320-337, 459-460
libcoap/src/context.rs                        217     114  47.47%   51, 105, 110-115, 121-122, 127, 132, 134, 136, 138, 140, 142-148, 184-227, 236-244, 261, 297, 380, 385, 401, 409-542, 567-574, 589-599, 612-619, 630-657
libcoap/src/crypto.rs                          31       2  93.55%   109, 183
libcoap/src/error.rs                            4       4  0.00%    87-166
libcoap/src/event.rs                            9       0  100.00%
libcoap/src/mem.rs                            118      49  58.47%   144-158, 192-193, 206-207, 267-293, 315-319, 349-350, 363-365, 377-388, 448-484, 503, 521-523, 526-527
libcoap/src/prng.rs                            18      14  22.22%   67-179
libcoap/src/protocol.rs                       150     110  26.67%   145-146, 152-157, 159-174, 176-177, 184-189, 191-206, 208-209, 266-267, 289, 303-304, 347-352, 361-380, 437-482, 515, 517
libcoap/src/resource.rs                       139      69  50.36%   96-98, 173-208, 216-221, 248, 251, 254, 257, 268-289, 302-304, 329-333, 340-341, 350-352, 358-360, 366-374, 496, 498-509
libcoap/src/transport.rs                       10       3  70.00%   28-33, 54
libcoap/src/types.rs                          235     160  31.91%   77-122, 129-158, 201-276, 286, 352, 426-466, 519-593, 651, 677-727, 781, 796, 826-846, 868-869, 902-986
libcoap/tests/dtls_client_server_test.rs       10       0  100.00%
libcoap/src/message/mod.rs                    245     124  49.39%   107-110, 112-133, 141-147, 149-170, 174, 176, 210, 212, 215-224, 227-245, 247-251, 267-276, 297-303, 400, 443, 449, 480, 488, 490-492, 499-500, 508, 513-526, 531, 551-552, 563-564
libcoap/src/message/request.rs                220     150  31.82%   52, 69-202, 229-257, 265-375, 381, 384-386, 390, 397-401, 412, 416, 431-432, 437, 440-441, 445-446, 450, 453, 456, 459, 462, 473-477
libcoap/src/message/response.rs               143     111  22.38%   33-156, 162, 165, 168, 171, 174, 192-322, 326-330, 356-357
libcoap/tests/common/mod.rs                    43       5  88.37%   66, 91, 93-94, 97
TOTAL                                        2020    1107  45.20%

Diff against main

Filename                Stmts    Miss  Cover
--------------------  -------  ------  -------
libcoap/src/mem.rs          0      +1  -0.85%
libcoap/src/types.rs       -2      +8  -3.95%
TOTAL                      -2      +9  -0.50%

Results for commit: 906e151

Coverage target is 80%

[JKRhb]

Great work finding and solving the issue here :) See a couple of small suggestions below, other than that: Looks good to me :)