Re: [lwip-devel] [RFC] Extend httpd.c to support REST services more easily

[address@hidden]

Am 29.10.2020 um 23:13 schrieb tinic-lwip-devel@tinic.org:
> I present a patch which adds support for REST services over HTTP in a
> relatively user 
> friendly manner. 
>
> Rationale: REST is the standard for most interesting Javascript
> frameworks. 
> My use case was a vue.js based configuration UI built into a STM32
> microcontroller.
>
> This is primarily a variation of the existing LWIP_HTTPD_SUPPORT_POST
> code
> but different enough to where extending or mashing it together was not
> pratical. The two
> new #ifdefs are LWIP_HTTPD_SUPPORT_REST and LWIP_HTTPD_REST_MANUAL_WND.
> You either enable LWIP_HTTPD_SUPPORT_POST or LWIP_HTTPD_SUPPORT_REST but
> not both.
>
> My question is: Is there any interest in merging such functionality into
> upstream LwIP?
> If so I'd be willing to clean up and explain the code; add
> documentation, examples and a
> few test cases. On the other hand I am also happy to just move on :-)

Being able to easily support REST would be nice, but I'm not sure if
there's enough man-power available for lwIP at the moment to integrate
this. A clean patch would of course help.

>
> My fork is here: https://github.com/tinic/lwip-ajax
> A patch is attached to this email.
>
>  From a user perspective a minimal REST service can be implemented as
> such:
>
> ----
> #define SERVICE_GET_STATUS 1
> #define SERVICE_POST_SETTINGS 2
>
> static int method = 0;

This won't work: you cannot use a global variable. REST calls may come
interleaved, depending on segment size. You have to pass everything as
arguments, not using globals.

>
> err_t httpd_rest_begin(void *handle, rest_method_t method, const char
> *url, const char *, u16_t, int, u8_t *) {

This won't work either: you have 2 variables named 'method' here.

Regards,
Simon

>     switch(method) {
>         case REST_METHOD_GET: {
>             if (strcmp(url, "/status") == 0) {
>                 method = SERVICE_GET_STATUS;
>                 return ERR_OK;
>             }
>         } break;
>
>         case REST_METHOD_POST: {
>             if (strcmp(url, "/settings") == 0) {
>                 method = SERVICE_POST_SETTINGS;
>                 return ERR_OK;
>             }
>         } break;
>
>         case REST_METHOD_PUT:
>         case REST_METHOD_PATCH:
>         case REST_METHOD_DELETE:
>         case REST_METHOD_OPTIONS: {
>         } break;
>     }
>     method = 0;
>     return ERR_ARG;
> }
>
>
> err_t httpd_rest_receive_data(void *handle, struct pbuf *p) {
>     if (method == SERVICE_POST_SETTINGS) {
>     
>         // user: send data to json parser
>
>         return ERR_OK;
>     }
> }
>
> err_t httpd_rest_finished(void *handle, const char **data, u16_t
> *dataLen) {
>     if (method == SERVICE_POST_SETTINGS) {
>
>         // Minimal set of fields for most browsers to work correctly in
> 2020
>         // Response string is user controlled as it is security
> sensitive
>         const char *okResponse = 
>             "HTTP/1.0 200 OK" CRLF
>             "Access-Control-Allow-Origin: *" CRLF; // Wildcard is a
> potential security risk
>
>         *data = okResponse;
>         *dataLen = strlen(okResponse);
>         
>         return ERR_OK;
>     }
>
>     if (method == SERVICE_GET_STATUS) {
>         
>         static char response[1024];        
>
>         memset(response, 0, sizeof(response))
>         
>         // Minimal set of fields for most browsers to work correctly in
> 2020
>         // Response string is user controlled as it is security
> sensitive
>         const char *responsePrototype = 
>             "HTTP/1.0 200 OK" CRLF 
>             "Access-Control-Allow-Origin: *" CRLF // Wildcard is a
> potential security risk
>             "Content-Type: application/json; charset=utf-8" CRLF 
>             "X-Content-Type-Options: nosniff" CRLF
>             "Vary: Origin, Accept-Encoding" CRLF
>             "Content-Length: @@@@@@@@@@@" CRLF // Needs to be patched
> after JSON data is added
>             "Cache-Control: no-cache" CRLF
>             CRLF;
>             
>         strncpy(response, responsePrototype, sizeof(response) - 1);
>         
>         // user: safely add json to response
>
>         // user: safely patch content length field in response
>         
>         *data = response;
>         *dataLen = strlen(response);
>
>         return ERR_OK;
>     }
>
>     return ERR_ARG;
> }
> ---