FileUpload - stream a POST body straight to a file

Layer: L7 Application · Build flags: PC_ENABLE_UPLOAD

What this example teaches

This streams a request body into a LittleFS file in FILE_CHUNK_SIZE pieces via the parser's streaming-body hook - the same mechanism OTA uses - so an upload never has to fit in RAM. A GET route serves the stored file back to verify the round-trip.

One call wires the upload sink. pc_upload_begin(server, path, fs, dest) registers a POST route whose body is streamed to dest as it arrives:

pc_upload_begin(server, "/upload", LittleFS, DEST);     // POST body -> file, chunk by chunk
server.on("/file", HttpMethod::HTTP_GET, [](uint8_t id, HttpReq *) {   // read it back
    server.serve_file(id, LittleFS, DEST, "application/octet-stream");
});

Two important constraints (from the header):

• The upload sink shares the parser's streaming hook with OTA - enable one or the other, not both.
• Enabling upload raises RX_BUF_SIZE to the streaming floor of 8192 (a full TCP receive window) automatically - a smaller ring keeps a large upload in backpressure long enough to trip the idle-timeout reap and the connection resets mid-transfer (HW-measured: a 2048 ring resets a 64 KB upload; 8192 round-trips 256 KB byte-exact). Because that ring is real DRAM per connection, this build dials MAX_CONNS down to 4 so 8192 * MAX_CONNS fits the classic ESP32's ~122 KB internal DRAM; a PSRAM/large-SRAM board can raise it.

Build and run

pio ci --board=esp32dev --project-option="framework=arduino" \
  --project-option="build_flags=-DPC_ENABLE_UPLOAD=1 -DMAX_CONNS=4" \
  --lib="." examples/L7-Application/FileUpload/FileUpload.ino

curl --data-binary @somefile.bin http://<ip>/upload   # 200 OK <n> bytes
curl http://<ip>/file > roundtrip.bin                 # read it back

Annotated source

The complete sketch (FileUpload.ino), reproduced verbatim with added explanatory comments:

// Copyright (C) 2026 Douglas Quigg (dstroy0) <dquigg123@gmail.com>
// SPDX-License-Identifier: AGPL-3.0-or-later
 
#define PC_ENABLE_UPLOAD 1
 
#include "protocore.h"
#include "network_drivers/physical/physical.h"
#include "services/upload_service.h"
#include <LittleFS.h>
 
static const char *SSID = "YOUR_SSID";
static const char *PASSWORD = "YOUR_PASSWORD";
 
static const char *DEST = "/uploaded.bin";
 
PC server;
 
void setup()
{
    Serial.begin(115200);
 
    if (!LittleFS.begin(true)) // format on first use
        Serial.println("LittleFS mount failed");
 
    init_wifi_physical(SSID, PASSWORD);
    Serial.print("Connecting to WiFi");
    while (!wifi_ready())
    {
        delay(250);
        Serial.print('.');
    }
    uint32_t ip = pc_net_egress_ip(); // library egress IP (network byte order), no Arduino WiFi
    Serial.printf("IP: %u.%u.%u.%u\n", (unsigned)(ip & 0xFF), (unsigned)((ip >> 8) & 0xFF),
                  (unsigned)((ip >> 16) & 0xFF), (unsigned)((ip >> 24) & 0xFF));
 
    // POST /upload -> stream the body into DEST on LittleFS (chunked, never in RAM).
    pc_upload_begin(server, "/upload", LittleFS, DEST);
 
    // GET /file -> serve the stored file back.
    server.on("/file", HttpMethod::HTTP_GET,
              [](uint8_t id, HttpReq *) { server.serve_file(id, LittleFS, DEST, "application/octet-stream"); });
 
    int32_t result = server.begin(80);
    if (result < 0)
        Serial.printf("begin() failed (error %d)\n", result);
    else
        Serial.println("Upload server on :80 (curl --data-binary @file http://<ip>/upload)");
}
 
void loop()
{
    server.handle();
}