Why http POST form allows only 32 postArgs elements?

[drschlaumeier]

Basic Infos

My Webserver Configuration Page needs to POST a form with >32 elements. Why ESP8266WebServer::_parseForm allows only 32 postArgs elements?

Hardware

Hardware: ESP-8285
Core Version: 2.4.0 ...

Description

I'm building a WebServer around my home light control based on Sonoff Touch device. The flexible configuration page of the webserver uses a html page with form and tables filled with some postArgs elements (some input - type text, some select, some input - type checkbox). All together I have 37 postArgs elements to POST back to my WebServer. After long debugging the esp CRASH I found that the ESP8266WebServer::_parseForm allows only 32 postArgs elements. ... see below code from "Parsing.cpp"
Why only 32? Can someone change to higher value? Any other idea what I can do? Is splitting the config page into several pages the right way?

Thanks in advance

bool ESP8266WebServer::_parseForm(WiFiClient& client, String boundary, uint32_t len){
  (void) len;
#ifdef DEBUG_ESP_HTTP_SERVER
  DEBUG_OUTPUT.print("Parse Form: Boundary: ");
  DEBUG_OUTPUT.print(boundary);
  DEBUG_OUTPUT.print(" Length: ");
  DEBUG_OUTPUT.println(len);
#endif
  String line;
  int retry = 0;
  do {
    line = client.readStringUntil('\r');
    ++retry;
  } while (line.length() == 0 && retry < 3);

  client.readStringUntil('\n');
  //start reading the form
  if (line == ("--"+boundary)){
    RequestArgument* postArgs = new RequestArgument[32];
    int postArgsLen = 0;
    while(1){
      String argName;
      String argValue;
      String argType;
      String argFilename;
      bool argIsFile = false;

.......

Settings in IDE

Module: Generic ESP8266 Module
Flash Size: 1MB
CPU Frequency: 80Mhz
Flash Mode: DOUT
Flash Frequency: 40Mhz
Upload Using: OTA / SERIAL
Reset Method: ck

################################################

[igrr]

The value of 32 was chosen as a compromise between supporting forms with a lot of fields and not having to allocate large postArgs array.

Possible solutions:

• introduce a run-time setting (e.g. ESP8266WebServer::setMaxPostArgs(size_t))
• do a two-pass parsing: count the number of arguments on the first pass, allocate the array, fill it on the second pass
• replace an array with a vector which will grow dynamically as the arguments are added

[drschlaumeier]

Many thanks.
I personally prefer the third solution since i do not need to care on setting the max postArgs and not wasting time with two-pass.
However, I manually changed to postArgs array to 64 for now. Waiting for enhancement ...

[igrr]

Please feel free to submit a PR with the 3rd solution :)

[drschlaumeier]

Hmm, I somehow expected that comment :-)
I'm not a good c programmer but I can try ...The first solution is easy :-) The third is tricky ... e.g. to catch all the possible errors.
Can I PR the first solution ?

[devyte]

@drschlaumeier using a std::vector is far easier than an array that gets allocated/deallocated. For this, you would need something along these lines:
#include
...

replace:

  int              _currentArgCount;
  RequestArgument* _currentArgs;

with
std::vector<RequestArgument> _currentArgs;

Don't init _currentArgs(0) in the constructor, don't alloc it anywhere, clear it wherever it gets deleted.

Replace references to _currentArgCount with _currentArgs.size().

When a new RequestArgument is added, do something like this:
_currentArgs.emplace_back(key, value);

Likely some additional changes, but the above should cover the important stuff.

Be aware that there is currently a bug in Arduino.h that makes #include not compile sometimes. To make certain:

#ifdef min
#undef min
#endif
#ifdef max
#undef max
#endif
#include <vector>

[yoursunny]

Be aware that there is currently a bug in Arduino.h that makes #include not compile sometimes. To make certain:
#undef min
#undef max

I wonder why Arduino.h #defines min and max, instead of using standard library's version?

#include <algorithm>
using std::min;
using std::max;

[devyte]

@yoursunny that has already been fixed, and 3rd party libs have also been fixed to comply.