A smattering of other related changes

CL: STM32 OTA support for L475-IOT01 and DISCO-F746

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CL: Mongoose 6.12

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h/t @M4GNV5

Fixes https://github.com/cesanta/mongoose/issues/943
Closes https://github.com/cesanta/mongoose/issues/944

CL: mg: Don't touch send_mbuf when sending MQTT messages

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Fixes https://nvd.nist.gov/vuln/detail/CVE-2018-10945

CL: mg: Fix body length calculation in mg_handle_cgi

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Closes https://github.com/cesanta/mongoose/pull/955

CL: mg: Add host name verification for OpenSSL

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CL: Make esp8266 compilation a little less verbose

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Closes https://github.com/cesanta/mongoose/pull/945

CL: Fix build with CS_ENABLE_STDIO=0

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CL: Add mg_strstrip: trims whitespace at the ends of s

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Use vararg macros for this.

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h/t @YankunLi

Closes https://github.com/cesanta/mongoose/pull/939

CL: mg: Fix a bug in mg_mgr_init_opt with opts.num_ifaces

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CL: mos support for LFS (littlefs) https://github.com/ARMmbed/littlefs

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Do not clear buffer at the end of multipart request to allow following request to proceed.

Closes https://github.com/cesanta/mongoose/pull/940

CL: mg: Fix pipelining issue with multipart upload

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CL: Add missing CC3220 sub-header to mongoose.h

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curl -F file1 -F file2 ...

Add a unit test and fix a minor memory leak when returning an error.

CL: mg_file_upload_handler: Support multiple files

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Set CLOSE_IMMEDIATELY flag when destroying conn.
This avoid some races in LWIP adapter.

CL: mg_lwip: Fix race during clean conenction teardown

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startup cleanup on CC3220

CL: none

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Closes https://github.com/cesanta/mos-libs/pull/2

CL: Add MG_HIDE_SERVER_INFO

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CL: Fix TZ on ESP8266

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CL: none

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mgos_dlsym needs to include mg_str for ffi_exports to be able to use it

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Enables extra compile-time checks

CL: none

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Also remove `-O3` optimization flasg, it negates `-Os`. Saves ~400 bytes.

CL: none

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CL: Add `mg_url_encode_opt()` - a parametrized version of `mg_url_encode()`

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Per standard, cookies are delimited by `; `.

CL: Fix mg_http_parse_header: treat ";" as a delimiter.

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CL: Apache license to common/

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A major cleanup, disentangling net_if and ssl_if.
Pulled a lot of common logic into the core and reduced size of net_if implementations.

CL: Mongoose net_if and ssl_if refactoring

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Consume buffer as soon as we know there is no boundary there, no need to delay until next chunk arrives.
This prevents stall where buffer fills up in one go and next chunk never arrives.

CL: Fix an edge case in multipart HTTP upload parsing

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In preparation for making moving to lib.
Reduce amount of makefile copypasta a bit.

CL: none

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 * Limit total amount of headroom, in absolute terms (`MBUF_SIZE_MAX_HEADROOM`).
 * If unable to allocate with headroom, fall back to allocating the required minimum.
 * For mOS, set default `MBUF_SIZE_MULTIPLIER` to 2 to avoid floating point operations.
   Since max headroom size is now capped to 128 bytes, this will not result in much of a bloat.

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mongoose: fix formatting

mongoose: fix formatting

mongoose: remove debugging messages

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freshen: implement ota rollback

freshen: api for rpc

freshen: implement rpc api (without transport)

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CL: Fix mg_socketpair for lwip + UDP

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Fixes https://github.com/cesanta/mongoose-os/issues/394

CL: Fix buffer size passed to inet_ntop()

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E.g. if `ASSERT_EQ(myfunc(), 123)` fails, `myfunc()` would be invoked again to print the actual value.
This can cause confusion sometimes.
To avoid this, we cast arguments to double, which is wide enough for most cases and we provide a variant for 64 bit value types for when it's not.
We also perform a check and fail if argument to the check results in loss of precision.

CL: none

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