LwM2M Server Read Returns Timeout

In this tutorial, you'll learn about LwM2M Server Read Returns Timeout. We cover key concepts, practical examples, and best practices.

The Problem

LwM2M server read request to a client resource times out.

Quick Fix

Wrong

# Server sends READ request but no response from client

Read request times out with no data returned.

Right

# Client implementation — Anjay
#include <anjay/anjay.h>

static int read_temperature(
  anjay_t *anjay, const anjay_rid_t *rid,
  anjay_output_ctx_t *ctx) {
  
  float temp = read_sensor_sync();  // Must return quickly
  anjay_ret_float(ctx, temp);
  return 0;  // 0 = success
}

static int read_humidity(
  anjay_t *anjay, const anjay_rid_t *rid,
  anjay_output_ctx_t *ctx) {
  
  float hum = 60.0;
  anjay_ret_float(ctx, hum);
  return ANJAY_ERR_NOT_FOUND;  // Wrong! Returns 4.04
}

# Response codes: 0 = success (2.05), negative = error (4.00-5.00)

Server receives 2.05 Content with temperature value.

Prevention

Client read handlers must return promptly (< 1s). Blocking operations cause timeouts. Use asynchronous I/O for slow sensors. Return 0 for success, negative values for errors (-1 = 5.01, -2 = 4.00, -3 = 4.04, -5 = 4.01). The read handler is called on each server READ request.

DodaTech engineers apply these same patterns across Doda Browser, DodaZIP, and Durga Antivirus Pro for production IoT reliability.

FAQ