Move header lowercasing from the per-request start() path to config time:
- Python codegen now lowercases collect_headers values before passing to C++
- add_collect_header() stores values as-is (already lowered by Python)
- start() with std::vector is now a direct passthrough to perform()
- Deprecated std::set overload still lowercases for external callers
Rename collect_headers_ to lower_case_collect_headers_ and update all
parameter names throughout the chain to make the lowercase invariant
explicit in the API contract.
This eliminates per-request allocation of a temporary vector and
str_lower_case() calls on every HTTP request, reducing stack usage
in the perform() call chain where stack space is critical for HTTPS
TLS handshakes.
The template only existed to share a loop between set and vector
iterators. Instead, have the deprecated set overload forward to
the vector overload, and inline the loop there.
start() already lowercases all collect_headers via lowercase_headers(),
so pre-lowercasing at insertion time was redundant double work on
every request.
Both start() overloads now use a shared lowercase_headers() template
that does a single pass from any iterator range, avoiding the extra
vector copy that the set overload was doing.
The vector overload of start() was passing collect_headers directly
to perform() without lowercasing. This meant callers using get()/post()
with mixed-case header names (e.g. {"ETag"}) would fail to match
against the lowercased header names from the HTTP response.
The no-collect-headers start() overload calls perform() directly
instead of the vector start() overload to avoid ambiguity with
the deprecated std::set overload.
- Change get()/post() collect_headers param from std::set to std::vector
(initializer list callers like online_image work unchanged)
- Add ESPDEPRECATED on start() std::set overload with clear message
about the collect_headers parameter
Replace heavy STL containers with simple std::vector and linear scan
for response header collection. This eliminates red-black tree (_Rb_tree)
and hash table template instantiations that are unnecessary for the small
number of headers typically collected (1-5 elements).
Changes:
- response_headers_: std::map<string, list<string>> -> std::vector<Header>
- collect_headers_: std::set<string> -> std::vector<string>
- perform() signature: std::set -> std::vector
- Add should_collect_header() inline helper for linear scan
- Lowercase collect_headers at config/insertion time instead of per-request
- IDF UserData now holds references to container's vector instead of
owning a separate map that gets moved after the request
- Reuse existing Header struct instead of std::pair
Reduces stack usage in perform() and eliminates STL container overhead
on memory-constrained ESP devices.
