Static allocated WifiClientSecureBearSSL

[gnalbandian]

Hi everyone.
Having BearSSL free of dynamic memory allocations, wouldn't be sensible to also have a wrapper around it (such as WifiClientSecureBearSSL) that doesn't do dynamic allocations?

I understand the drawback of this setup, but sometimes, where memory budget is limited it would be pretty handy.
Let me know if that would be feasible and how hard it would be.

@earlephilhower I would certainly appreciate your comments regarding this topic

[earlephilhower]

So where exactly are you seeing WiFiClientBearSSL allocating memory? If you include a WiFiClientSecure as a global variable, the extra stack allocation will be performed at C runtime init, before main, and stay forever. OTW, I can't think of a spot off the top of my head where it's alloc'ing things. Maybe when you add a certificate (but that's always at runtime so there's no possibility of doing it statically).

[gnalbandian]

Well, i am having crashes concerning memory allocation in the wrapper WifiClientSecureBearSSL.
This happens (sometimes) while attempting to reconnect (connect() of WiFiClientSecure lib).
Here is the decoded dump:

User exception (panic/abort/assert)
--------------- CUT HERE FOR EXCEPTION DECODER ---------------

Unhandled C++ exception: OOM

>>>stack>>>

ctx: cont
sp: 3ffffde0 end: 3fffffd0 offset: 0010
3ffffdf0:  c014c00a c031c02d 00000c08 4022e6a0  
3ffffe00:  c02ac026 3ffffe20 3fff359c 40215d4d  
3ffffe10:  00000000 00000000 3fff359c 40215e9b
3ffffe20:  00000000 c00dc003 3fff000a 40215a34
3ffffe30:  00000000 00000000 00000d60 3ffe8e96
3ffffe40:  00000000 3fff6564 3fff359c 40216269
3ffffe50:  00000000 001180ab afdf3b64 143cc683
3ffffe60:  00000000 00000000 00000034 001180ab
3ffffe70:  00003a98 3fff5da4 3fff359c 402150a3
3ffffe80:  3fff5f74 0000007f 49ba5e35 4022ff14
3ffffe90:  00000000 3ffe988e 3ffffea0 3fff25e8 <
3ffffea0:  000001bb 3ffe8e96 3fff359c 402163f5
3ffffeb0:  4023b844 dca79a95 4023b844 dca79a95
3ffffec0:  3fff1f10 3fff23c0 3fff240c 402111cc
3ffffed0:  00000000 00000000 00000000 fffffffe
3ffffee0:  ffffffff 3fffc6fc 00000001 3fffdab0
3ffffef0:  00000000 3fffdad0 3fff27c8 00000030
3fffff00:  00000000 3fffdad0 3fff27c8 00000030
3fffff10:  00000000 3fffdad0 3fff27c8 00000030
3fffff20:  0000000b 65682065 3ffe8e4c 00000006
3fffff30:  72463e01 3fff7de4 3ffffed0 3fffff08  
3fffff40:  3ffffed0 3fff7db4 3ffffed0 3fff7dac
3fffff50:  3ffffed0 3fff7da4 3ffffed0 3fff7d9c
3fffff60:  3ffffed0 3fff7d94 3ffffed0 3fff7d8c
3fffff70:  3ffffed0 3fff7d84 3ffffed0 3fff7d7c
3fffff80:  00000000 3fff7d74 3ffffed0 40275350
3fffff90:  3fff25e8 40291b4c 3fffffa0 3fff27c8 <

0x4022e6a0 in operator new(unsigned int) at C:\Users\gonza\.platformio\packages\framework-arduinoespressif8266\cores\esp8266/abi.cpp:47
0x40215d4d in __gnu_cxx::new_allocator<std::_Sp_counted_ptr_inplace<br_x509_minimal_context, std::allocator<br_x509_minimal_context>, (__gnu_cxx::_Lock_policy)0> >::allocate(unsigned int, void const*) at c:\users\gonza\.platformio\packages\toolchain-xtensa\xtensa-lx106-elf\include\c++\10.3.0\ext/new_allocator.h:115
 (inlined by) std::allocator_traits<std::allocator<std::_Sp_counted_ptr_inplace<br_x509_minimal_context, std::allocator<br_x509_minimal_context>, (__gnu_cxx::_Lock_policy)0> > >::allocate(std::allocator<std::_Sp_counted_ptr_inplace<br_x509_minimal_context, std::allocator<br_x509_minimal_context>, (__gnu_cxx::_Lock_policy)0> >&, unsigned int) at c:\users\gonza\.platformio\packages\toolchain-xtensa\xtensa-lx106-elf\include\c++\10.3.0\bits/alloc_traits.h:460
 (inlined by) std::__allocated_ptr<std::allocator<std::_Sp_counted_ptr_inplace<br_x509_minimal_context, std::allocator<br_x509_minimal_context>, (__gnu_cxx::_Lock_policy)0> > > std::__allocate_guarded<std::allocator<std::_Sp_counted_ptr_inplace<br_x509_minimal_context, std::allocator<br_x509_minimal_context>, (__gnu_cxx::_Lock_policy)0> > >(std::allocator<std::_Sp_counted_ptr_inplace<br_x509_minimal_context, std::allocator<br_x509_minimal_context>, (__gnu_cxx::_Lock_policy)0> >&) at c:\users\gonza\.platformio\packages\toolchain-xtensa\xtensa-lx106-elf\include\c++\10.3.0\bits/allocated_ptr.h:97
 (inlined by) std::__shared_count<(__gnu_cxx::_Lock_policy)0>::__shared_count<br_x509_minimal_context, std::allocator<br_x509_minimal_context>>(br_x509_minimal_context*&, std::_Sp_alloc_shared_tag<std::allocator<br_x509_minimal_context> >) at c:\users\gonza\.platformio\packages\toolchain-xtensa\xtensa-lx106-elf\include\c++\10.3.0\bits/shared_ptr_base.h:680
 (inlined by) std::__shared_ptr<br_x509_minimal_context, (__gnu_cxx::_Lock_policy)0>::__shared_ptr<std::allocator<br_x509_minimal_context>>(std::_Sp_alloc_shared_tag<std::allocator<br_x509_minimal_context> >) at c:\users\gonza\.platformio\packages\toolchain-xtensa\xtensa-lx106-elf\include\c++\10.3.0\bits/shared_ptr_base.h:1371
 (inlined by) std::shared_ptr<br_x509_minimal_context>::shared_ptr<std::allocator<br_x509_minimal_context>>(std::_Sp_alloc_shared_tag<std::allocator<br_x509_minimal_context> >) at c:\users\gonza\.platformio\packages\toolchain-xtensa\xtensa-lx106-elf\include\c++\10.3.0\bits/shared_ptr.h:408
 (inlined by) std::shared_ptr<br_x509_minimal_context> std::allocate_shared<br_x509_minimal_context, std::allocator<br_x509_minimal_context>>(std::allocator<br_x509_minimal_context> const&) at c:\users\gonza\.platformio\packages\toolchain-xtensa\xtensa-lx106-elf\include\c++\10.3.0\bits/shared_ptr.h:860
 (inlined by) std::shared_ptr<br_x509_minimal_context> std::make_shared<br_x509_minimal_context>() at c:\users\gonza\.platformio\packages\toolchain-xtensa\xtensa-lx106-elf\include\c++\10.3.0\bits/shared_ptr.h:876
0x40215e9b in std::shared_ptr<br_x509_minimal_context>::operator=(std::shared_ptr<br_x509_minimal_context>&&) at c:\users\gonza\.platformio\packages\toolchain-xtensa\xtensa-lx106-elf\include\c++\10.3.0\bits/shared_ptr.h:384
 (inlined by) BearSSL::WiFiClientSecureCtx::_installClientX509Validator() at C:\Users\gonza\.platformio\packages\framework-arduinoespressif8266\libraries\ESP8266WiFi\src/WiFiClientSecureBearSSL.cpp:1087
0x40215a34 in std::__shared_ptr<unsigned char, (__gnu_cxx::_Lock_policy)0>::operator=(std::__shared_ptr<unsigned char, (__gnu_cxx::_Lock_policy)0>&&) at c:\users\gonza\.platformio\packages\toolchain-xtensa\xtensa-lx106-elf\include\c++\10.3.0\bits/shared_ptr_base.h:1281
0x40216269 in BearSSL::WiFiClientSecureCtx::_connectSSL(char const*) at C:\Users\gonza\.platformio\packages\framework-arduinoespressif8266\libraries\ESP8266WiFi\src/WiFiClientSecureBearSSL.cpp:1158
0x402150a3 in void esp_delay<ClientContext::connect(ip4_addr*, unsigned short)::{lambda()#1}>(unsigned int, ClientContext::connect(ip4_addr*, unsigned short)::{lambda()#1}&&, unsigned int) at C:\Users\gonza\.platformio\packages\framework-arduinoespressif8266\cores\esp8266/coredecls.h:69
 (inlined by) void esp_delay<ClientContext::connect(ip4_addr*, unsigned short)::{lambda()#1}>(unsigned int, ClientContext::connect(ip4_addr*, unsigned short)::{lambda()#1}&&) at C:\Users\gonza\.platformio\packages\framework-arduinoespressif8266\cores\esp8266/coredecls.h:78
 (inlined by) ClientContext::connect(ip4_addr*, unsigned short) at C:\Users\gonza\.platformio\packages\framework-arduinoespressif8266\libraries\ESP8266WiFi\src/include/ClientContext.h:147
 (inlined by) WiFiClient::connect(IPAddress, unsigned short) at C:\Users\gonza\.platformio\packages\framework-arduinoespressif8266\libraries\ESP8266WiFi\src/WiFiClient.cpp:164 
0x4022ff14 in uart_write at C:\Users\gonza\.platformio\packages\framework-arduinoespressif8266\cores\esp8266/uart.cpp:545
0x402163f5 in BearSSL::WiFiClientSecureCtx::connect(char const*, unsigned short) at C:\Users\gonza\.platformio\packages\framework-arduinoespressif8266\libraries\ESP8266WiFi\src/WiFiClientSecureBearSSL.cpp:229
0x4023b844 in std::__uniq_ptr_impl<WiFiClient, std::default_delete<WiFiClient> >::reset(WiFiClient*) at ??:?
0x4023b844 in std::__uniq_ptr_impl<WiFiClient, std::default_delete<WiFiClient> >::reset(WiFiClient*) at ??:?
0x402111cc in loop at src/main.cpp:4024
0x40275350 in umm_fragmentation_metric at C:\Users\gonza\.platformio\packages\framework-arduinoespressif8266\cores\esp8266\umm_malloc/umm_info.c:248

3fffffa0:  3fffdad0 00000000 3fff279c 3fff27c8
3fffffb0:  3fffdad0 00000000 3fff279c 4022ea84
3fffffc0:  feefeffe feefeffe 3fffdab0 4010149d
<<<stack<<<

last failed alloc call: 40215D4D(3080)

--------------- CUT HERE FOR EXCEPTION DECODER ---------------

[mcspr]

nit: if the object of the assignment is not freed beforehand or (still) referenced somewhere, obviously there is no RAM in such constrained environment. I wonder if there is a _x509_minimal = null / .reset() missing somewhere before the make_shared happens?

[earlephilhower]

Logically, I would say no. But practically on this machine, good point.

The RHS will be executed (alloc new smart pointer data) and then assigned to the LHS (which would trigger the free of the old smart pointer data) unless there's some STL magic. So theoretically you'd be able to re-use the same chunk of heap assuming nothing weird in the allocator...

@gnalbandian you can try adding

_x509_insecure = nullptr;

as the 1st line of

Arduino/libraries/ESP8266WiFi/src/WiFiClientSecureBearSSL.cpp

Line 1054 in 4cc20a9

bool WiFiClientSecureCtx::_installClientX509Validator() {

Might be a few other std::make_shareds where that could also be done, but the validator has a lot of state compared to other bits.

[gnalbandian]

Sorry I forgot to mention that I am using a certificate with setTrustAnchors(cert) and also a BearSSL session for fast reconnection.
All of these are globally declared in main.cpp.

[gnalbandian]

Would you suggest to set _x509_minimal = nullptr before line 1086:

#WiFiClientSecureBearSSL.cpp#L1086

[earlephilhower]

Sure. In fact you could try clearing them all out explicitly right at the beginning of the function (line 1055)

    // Ensure we free any existing validators before trying to re-allocate one so we can use the memory of the old one for the new one
    _x509_insecure = nullptr;
    _x509_knownkey = nullptr;
    _x509_minimal = nullptr;

This isn't really guaranteeing your own low memory situation will work out, but it may help and won't hurt.