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Re: [lwip-devel] httpd and CGI handler call

From: address@hidden
Subject: Re: [lwip-devel] httpd and CGI handler call
Date: Thu, 23 Nov 2017 21:52:43 +0100
User-agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:45.0) Gecko/20100101 Thunderbird/45.8.0

Honestly, I can't really follow all your mails here. I lost trace of what's good and what's bad.
I'm in the process of adding httpd examples to the contrib repository. Your CGI/generated file combination is one of the next.

I'd suggest that I push my example (hopefully next week) and then let's discuss your thoughts again by sharing diffs. Looking at diffs is *much* easier than following 5 emails of textual descriptions...


Giuseppe Modugno:

I need to answer to GET /login.cgi?user=admin&pwd=admin request with JSON data. The answer depends on parameters user and pwd passed as query string.

I can't create the answer in fs_open_custom(), because parameters aren't available. Even the answer buffer can't be allocated in fs_open_custom(), because the answer length isn't known yet. In CGI handler I can allocate and create the answer, however I can't set the file content, because I can't access file structure.

One solution is to use LWIP_HTTPD_DYNAMIC_FILE_READ and implement a trivial fs_read_custom(). I think a better solution could be to use LWIP_HTTPD_FILE_STATE, set file->state as file in fs_open_custom() and set file content in CGI handler.

int fs_open_custom(struct fs_file *file, const char *name) {
  if (!strcmp(name, "/login.cgi")) {
        file->state = file;

void httpd_cgi_handler(const char *filename, int iNumParams, char **pcParam, char **pcValue, void *file_state) {
  if (!strcmp(filename, "/login.cgi")) {
    struct fs_file *file = (struct fs_file *)file_state;
    void *reply_buf = malloc(answer_length);
    file->data = "">
    file->len = file->index = strlen(reply_buf);

This doesn't work, because in http_init_file() hs->handle, hs->file and hs->left are assigned before calling CGI httpd_cgi_handler().

However this could work if httpd_cgi_handler() is moved before assigning hs->handle, hs->file and hs->left. I tried and it seems it works.

IMHO another good modification could be to pass file to httpd_cgi_handler(), instead of only file->state. In the handler, you will have the access to file and file->state. With this change, you could avoid assigning file->state=file in fs_open_custom() that could be empty.

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