Configuration - sizing the server for your build

Layer: Foundation (tutorial) · Build flags: core (this example overrides defaults rather than enabling features)

What this example teaches

Everything in the library is sized at compile time, and this example is the reference for the knobs. It strips optional features down to a lean REST-only profile, tightens every capacity constant, exposes routes that echo the active configuration so you can confirm your overrides took effect, and demonstrates a runtime config struct. The sketch's header comment is itself a cheat-sheet of every flag and constant.

Overrides go BEFORE the include. Each #define must appear before #include "protocore.h" so the library compiles with your value instead of the default. Here the optional subsystems are stripped and the buffers are shrunk for a small sensor node:

#define PC_ENABLE_WEBSOCKET 0   // strip features entirely: no code, no RAM, no flash
#define PC_ENABLE_SSE 0
#define PC_ENABLE_MULTIPART 0
#define PC_ENABLE_FILE_SERVING 0
#define PC_ENABLE_AUTH 0
#define MAX_CONNS 2                 // tighten capacity to roughly halve RAM
#define RX_BUF_SIZE 512
#define BODY_BUF_SIZE 128
#include "protocore.h"

‍When compiling with pio ci (separate library translation units), these in-sketch #defines only affect the sketch. Pass them as build_flags so the library compiles with them too - see the build-flag tree and the repository's contributing notes.

Capacity constants are visible at runtime. GET /config serializes the active sizing constants as JSON, so you can verify a build without a debugger:

snprintf(body, sizeof(body), "{\"MAX_CONNS\":%u,\"RX_BUF_SIZE\":%u,\"BODY_BUF_SIZE\":%u,...}",
         (unsigned)MAX_CONNS, (unsigned)RX_BUF_SIZE, (unsigned)BODY_BUF_SIZE, ...);

The limits are real. With BODY_BUF_SIZE=128, a POST body over 128 bytes is rejected with an automatic 413 before your handler runs. With MAX_QUERY_PARAMS=4, a fifth query parameter is parsed but silently dropped - GET /search echoes exactly what was kept so you can see the boundary.

Runtime config struct. A WebServerConfig passed to begin() overrides the idle timeout without a rebuild (pass nullptr to use the built-in default, CONN_TIMEOUT_MS):

WebServerConfig cfg = {.conn_timeout_ms = CONN_TIMEOUT_MS};
int32_t result = server.begin(80, &cfg);

The header comment also documents the feature-dependency tree (a child flag needs its parent; illegal combinations fail with a compile-time #error).

Build and run

pio ci --board=esp32dev --project-option="framework=arduino" \
  --project-option="build_flags=-DPC_ENABLE_DIAG=1" \
  --lib="." examples/Foundation/Configuration/Configuration.ino

curl http://<ip>/config                          # see the active sizing constants
curl -X POST http://<ip>/echo -d "hello"         # bodies > BODY_BUF_SIZE get a 413
curl "http://<ip>/search?q=esp32&sort=date"      # extra params past MAX_QUERY_PARAMS are dropped

Annotated source

The complete sketch (Configuration.ino). The long header comment (a full flag/constant reference) is kept verbatim; the C++ is annotated.

// Copyright (C) 2026 Douglas Quigg (dstroy0) <dquigg123@gmail.com>
// SPDX-License-Identifier: AGPL-3.0-or-later
 
/**
 * @file Configuration.ino
 * @brief Reference for every user-configurable flag and constant, plus runnable
 *        routes that echo the active configuration so you can confirm your
 *        overrides took effect.
 *
 * All #defines must appear BEFORE the library include (or be supplied as
 * -D build flags in platformio.ini).  Any that are omitted get their documented
 * defaults.  Illegal combinations (e.g. pool sizes that exceed MAX_CONNS)
 * produce a #error in the compiler output rather than a silent misbehavior.
 *
 *   FEATURE FLAGS, CAPACITY CONSTANTS, FEATURE DEPENDENCIES, and RUNTIME CONFIG
 *   are all cataloged in the .ino header - keep it open as a reference.
 */
 
// -------------------------------------------------------------------
// A low-footprint REST-only profile: no WS, SSE, multipart, or file IO.
// These values roughly halve RAM use versus the defaults; good for sensor
// nodes sharing the heap with other subsystems. Each #define MUST precede the
// library include to take effect.
// -------------------------------------------------------------------
#define PC_ENABLE_WEBSOCKET 0
#define PC_ENABLE_SSE 0
#define PC_ENABLE_MULTIPART 0
#define PC_ENABLE_FILE_SERVING 0
#define PC_ENABLE_AUTH 0
 
// Diagnostic endpoint: exposes the compile-time config; disable in production.
#define PC_ENABLE_DIAG 1
 
// Tightened capacity to match a small REST API (every value sizes a BSS array).
#define MAX_CONNS 2
#define EVT_QUEUE_DEPTH 8 // must be >= MAX_CONNS * 4
#define RX_BUF_SIZE 512
#define BODY_BUF_SIZE 128
#define MAX_ROUTES 8
#define MAX_HEADERS 6
#define MAX_PATH_LEN 48
#define MAX_KEY_LEN 16
#define MAX_VAL_LEN 32
#define MAX_QUERY_LEN 64
#define MAX_QUERY_PARAMS 4
#define QUERY_KEY_LEN 16
#define QUERY_VAL_LEN 24
#define CONN_TIMEOUT_MS 3000
 
#include "protocore.h"
#include "network_drivers/physical/physical.h"
 
static const char *SSID = "YOUR_SSID";
static const char *PASSWORD = "YOUR_PASSWORD";
 
PC server;
 
// GET /config - return every active sizing constant as JSON so you can verify
// your build flags / #defines took effect without a debugger.
void handle_config(uint8_t slot_id, HttpReq *req)
{
    char body[384];
    snprintf(body, sizeof(body),
             "{"
             "\"MAX_CONNS\":%u,"
             "\"RX_BUF_SIZE\":%u,"
             "\"CONN_TIMEOUT_MS\":%u,"
             "\"MAX_HEADERS\":%u,"
             "\"MAX_PATH_LEN\":%u,"
             "\"MAX_KEY_LEN\":%u,"
             "\"MAX_VAL_LEN\":%u,"
             "\"MAX_QUERY_LEN\":%u,"
             "\"MAX_QUERY_PARAMS\":%u,"
             "\"QUERY_KEY_LEN\":%u,"
             "\"QUERY_VAL_LEN\":%u,"
             "\"BODY_BUF_SIZE\":%u,"
             "\"MAX_ROUTES\":%u"
             "}",
             (unsigned)MAX_CONNS, (unsigned)RX_BUF_SIZE, (unsigned)CONN_TIMEOUT_MS, (unsigned)MAX_HEADERS,
             (unsigned)MAX_PATH_LEN, (unsigned)MAX_KEY_LEN, (unsigned)MAX_VAL_LEN, (unsigned)MAX_QUERY_LEN,
             (unsigned)MAX_QUERY_PARAMS, (unsigned)QUERY_KEY_LEN, (unsigned)QUERY_VAL_LEN, (unsigned)BODY_BUF_SIZE,
             (unsigned)MAX_ROUTES);
 
    server.send(slot_id, 200, "application/json", body);
}
 
// POST /echo - echo the body. With BODY_BUF_SIZE=128, a body over 128 bytes is
// auto-rejected with 413 BEFORE this handler is ever called.
void handle_echo(uint8_t slot_id, HttpReq *req)
{
    server.send(slot_id, 200, "text/plain", (const char *)req->body);
}
 
// GET /search - echo the parsed query parameters. With MAX_QUERY_PARAMS=4, a
// fifth parameter is parsed but silently dropped: this shows what was kept.
void handle_search(uint8_t slot_id, HttpReq *req)
{
    char body[256] = "params: ";
    for (uint8_t i = 0; i < req->query_count; i++)
    {
        if (i > 0)
            strncat(body, ", ", sizeof(body) - strlen(body) - 1);
        strncat(body, req->query_params[i].key, sizeof(body) - strlen(body) - 1);
        strncat(body, "=", sizeof(body) - strlen(body) - 1);
        strncat(body, req->query_params[i].val, sizeof(body) - strlen(body) - 1);
    }
    server.send(slot_id, 200, "text/plain", body);
}
 
void setup()
{
    Serial.begin(115200);
 
    // Print the active config so you can confirm overrides without curl.
    Serial.println("\n--- Active PC config ---");
    Serial.printf("  MAX_CONNS        = %u\n", (unsigned)MAX_CONNS);
    Serial.printf("  RX_BUF_SIZE      = %u\n", (unsigned)RX_BUF_SIZE);
    Serial.printf("  CONN_TIMEOUT_MS  = %u\n", (unsigned)CONN_TIMEOUT_MS);
    Serial.printf("  BODY_BUF_SIZE    = %u\n", (unsigned)BODY_BUF_SIZE);
    Serial.printf("  MAX_QUERY_PARAMS = %u\n", (unsigned)MAX_QUERY_PARAMS);
    Serial.println("----------------------------------");
 
    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));
 
    server.on("/config", HttpMethod::HTTP_GET, handle_config);
    server.on("/echo", HttpMethod::HTTP_POST, handle_echo);
    server.on("/search", HttpMethod::HTTP_GET, handle_search);
 
    // Diagnostic route (PC_ENABLE_DIAG=1): remove or protect in production.
    server.on("/diag", HttpMethod::HTTP_GET, [](uint8_t id, HttpReq *) { server.diag(id); });
 
    // Pass a runtime config to override the idle timeout without a rebuild.
    WebServerConfig cfg = {.conn_timeout_ms = CONN_TIMEOUT_MS};
    int32_t result = server.begin(80, &cfg);
    if (result < 0)
    {
        Serial.printf("begin() failed (error %d)\n", result);
        return;
    }
    Serial.println("Server started on port 80");
}
 
void loop()
{
    server.handle();
}