nanocoap: added function for finding options #18

haukepetersen · 2017-07-26T17:17:57Z

After receiving a packet, I needed to be able to read out certain options (COAP_OPT_LOCATION_PATH in my case), and to copy their content into some user defined buffers. This was not able with the current interface, so I added a function that allows for finding certain options.

The usage is quite easy (I hope):

coap_opt_t *opt;

// for finding the first occurrence of a certain option:
uint8_t *bufpos = coap_find_opt(pdu, pdu->options, &opt, COAP_OPT_LOCATION_PATH);

// for finding the next occurrence of the same option:
while (bufpos) {
    bufpos = coap_find_opt(pdu, bufpos, &opt, 0);
    ...
}

With this function one can read ANY option and do with its values whatever they like...

haukepetersen · 2017-08-07T08:26:51Z

@kaspar030: ping

kaspar030

minor comments...

kaspar030 · 2017-08-15T11:57:41Z

nanocoap/nanocoap.c

@@ -369,3 +377,65 @@ ssize_t coap_well_known_core_default_handler(coap_pkt_t* pkt, uint8_t *buf, \

    return coap_build_reply(pkt, COAP_CODE_205, buf, len, payload_len);
 }
+
+size_t get_lenval(uint8_t *buf, uint16_t *val)


make static, add underscore, maybe rename to "_decode_optlen" to be in line with the other coap decode functions?

yes, forgot the static. Will do both.

kaspar030 · 2017-08-15T11:58:05Z

nanocoap/nanocoap.c

+    return len;
+}
+
+int parse_opt(uint8_t *optpos, coap_opt_t *opt)


static, too?

kaspar030 · 2017-08-15T12:01:39Z

nanocoap/nanocoap.c

+
+    uint16_t delta = 0;
+
+    do {


Can we add packet length checks here? Seems like a bogus header leads to crashes here.

kaspar030 · 2017-08-15T12:04:09Z

nanocoap/nanocoap.h

@@ -172,6 +180,8 @@ size_t coap_put_option(uint8_t *buf, uint16_t lastonum, uint16_t onum, uint8_t *
 size_t coap_put_option_ct(uint8_t *buf, uint16_t lastonum, uint16_t content_type);
 size_t coap_put_option_url(uint8_t *buf, uint16_t lastonum, const char *url);

+uint8_t *coap_find_opt(coap_pkt_t *pkt, uint8_t *bufpos, coap_opt_t *opt, uint16_t optnum);


the other public functions carry "option" written out, so maybe rename?

bergzand · 2017-08-15T22:40:44Z

I'm trying to use your coap_find_opt function for #21 and I'm running into some issues with the arguments where I want to find a previously inserted option to readjust the value of the option, but a coap_pkt_t variable is not yet created for the packet.

For the context, I'm implementing block2 support (rfc7959). Before constructing the packet payload I insert a block2 header. This header consists of a block number (known), a size exponent (known) and a "more" bit flag. This more bit flag is set if there are more blocks following the current block. I currently set this flag if the payload of the reply exceeds the current block. This flag thus have to be adjusted after the payload is added and I would like to use the coap_find_opt function to retrieve the header from the headers.

So at that moment a coap_pkt_t struct of the reply is not yet available (it is created in the coap_build_reply. Would this not be more flexible if the coap_pkt_t argument would be an uint8_t* to the payload, seeing that it is only used for the payload position. This way the function can also be used to retrieve previously set options in the construction of a packet.

haukepetersen · 2017-08-16T11:38:26Z

@kaspar030 fixed your remarks, better now?

haukepetersen · 2017-08-16T11:40:10Z

@bergzand yes, that makes sense ineed: see last commit

kaspar030 · 2017-08-16T21:38:01Z

@kaspar030 fixed your remarks, better now?

yes! (I guess we leave the size validity check for later?)

haukepetersen · 2017-08-17T07:28:10Z

I guess we leave the size validity check for later?

why? It should be fixed now, is it not?

haukepetersen · 2017-08-17T07:32:49Z

I thought the check in line 428

        if (bufpos >= payload_pos) {
            return NULL;
        }

is doing that?!

kaspar030 · 2017-08-17T08:09:21Z

nanocoap/nanocoap.c

+        len = 1;
+    }
+    else if (*val == 14) {
+        memcpy(val, buf, 2);


this might read past packet length

kaspar030 · 2017-08-17T08:10:12Z

nanocoap/nanocoap.c

+        return -1;
+    }
+
+    opt->val += _decode_optlen(opt->val, &opt->delta);


through _decode_optlen(), this might read past the packet

kaspar030 · 2017-08-17T08:15:38Z

For _decode_value() I added the packet end as parameter in order to be able to check if the decoding would read past end.

haukepetersen · 2017-08-17T14:28:00Z

Ah, I see...

emmanuelsearch · 2017-09-08T09:55:14Z

@haukepetersen @kaspar030 would love to see this in ;)
(and it would bring us closer to blockwise support, if I understand correctly ?)

haukepetersen · 2018-04-12T07:07:51Z

closing in favor of #8920 and #8772

kb2ma mentioned this pull request Jul 30, 2017

net/gcoap: add Uri-Query strings for requests RIOT-OS/RIOT#7402

Merged

bergzand mentioned this pull request Aug 1, 2017

nanocoap: Add blockwise transfer block2 support #21

Closed

kaspar030 requested changes Aug 15, 2017

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haukepetersen added 2 commits August 16, 2017 13:37

nanocoap: added function for finding options

a6def23

fixup! nanocoap: fixed things

ca04f1e

haukepetersen force-pushed the add_nanocoap_findopt branch from 0ca72be to ca04f1e Compare August 16, 2017 11:37

fixup! pass payload position directly to find_option()

45918ad

kaspar030 reviewed Aug 17, 2017

View reviewed changes

nanocoap/nanocoap.c

len = 1;

}

else if (*val == 14) {

memcpy(val, buf, 2);

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this might read past packet length

kaspar030 reviewed Aug 17, 2017

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haukepetersen closed this Apr 12, 2018

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nanocoap: added function for finding options #18

nanocoap: added function for finding options #18

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nanocoap: added function for finding options #18

nanocoap: added function for finding options #18

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bergzand commented Aug 15, 2017

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