extmod/modlwip: Return EAGAIN from a non-blocking send on ERR_MEM. - #19708
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Code size report: Reference: esp32/boards/SEEED_XIAO_ESP32C5: Use 0x2000 as the flash offset. [b0310f5]
Comparison: extmod/modlwip: Return EAGAIN from a non-blocking send on ERR_MEM. [merge of a4cc2b0]
mpy-cross: +0 +0.000%
bare-arm: +0 +0.000%
minimal x86: +0 +0.000%
unix x64: +0 +0.000% standard
stm32: +0 +0.000% PYBV10
esp32: +0 +0.000% ESP32_GENERIC
mimxrt: +0 +0.000% TEENSY40
rp2: +8 +0.001% RPI_PICO_W
samd: +0 +0.000% ADAFRUIT_ITSYBITSY_M4_EXPRESS
qemu rv32: +0 +0.000% VIRT_RV32
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Codecov Report✅ All modified and coverable lines are covered by tests. @@ Coverage Diff @@
## master #19708 +/- ##
=======================================
Coverage 98.55% 98.55%
=======================================
Files 182 182
Lines 23335 23335
Branches 5 5
=======================================
Hits 22998 22998
Misses 336 336
Partials 1 1
Flags with carried forward coverage won't be shown. Click here to find out more. ☔ View full report in Codecov by Harness.
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tcp_sndbuf counts bytes, so it can report room while the segment or heap pool is exhausted and tcp_write returns ERR_MEM. lwip_tcp_send then waited in its retry loop for up to 10 seconds even for a non-blocking socket, stalling a single-threaded event loop. Nothing is queued on ERR_MEM, so a non-blocking socket can return EAGAIN there, as it already does when tcp_sndbuf is 0. Blocking sockets are unchanged. Fixes issue micropython#19704. Signed-off-by: Tejas Nagmote <tejasnagmote520@gmail.com>
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September 18, 2026 14:17
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tcp_sndbuf counts bytes, so it can report room while the segment or heap pool is exhausted and tcp_write returns ERR_MEM. lwip_tcp_send then waited in its retry loop for up to 10 seconds even for a non-blocking socket, stalling a single-threaded event loop.
Nothing is queued on ERR_MEM, so a non-blocking socket can return EAGAIN there, as it already does when tcp_sndbuf is 0. Blocking sockets are unchanged.
Fixes issue #19704.
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