ESP-IDF

https://docs.espressif.com/projects/esp-idf/en/master/
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ESP-IDF is Espressif's IoT Development Framework, providing a comprehensive programming guide for...
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### TCP Server Example - C

Source: https://docs.espressif.com/projects/esp-idf/en/master/projects/esp-idf/en/stable/esp32/api-guides/lwip

Illustrates how to create a TCP server that accepts client connection requests and receives data using the BSD Sockets API.

```c
/* This example is not provided in the text */
// Placeholder for tcp_server example
```

--------------------------------

### UDP Server Example - C

Source: https://docs.espressif.com/projects/esp-idf/en/master/projects/esp-idf/en/stable/esp32/api-guides/lwip

Explains how to create a UDP server that receives client connection requests and data using the BSD Sockets API.

```c
/* This example is not provided in the text */
// Placeholder for udp_server example
```

--------------------------------

### UDP Multicast Example - C

Source: https://docs.espressif.com/projects/esp-idf/en/master/projects/esp-idf/en/stable/esp32/api-guides/lwip

Demonstrates using IPv4 and IPv6 UDP multicast features via the BSD-style sockets interface.

```c
/* This example is not provided in the text */
// Placeholder for udp_multicast example
```

--------------------------------

### Multi-Network TCP Client Example - C

Source: https://docs.espressif.com/projects/esp-idf/en/master/projects/esp-idf/en/stable/esp32/api-guides/lwip

Demonstrates using Ethernet and Wi-Fi interfaces simultaneously, creating a TCP client for each, and sending basic HTTP requests/responses.

```c
/* This example is not provided in the text */
// Placeholder for tcp_client_multi_net example
```

--------------------------------

### TCP Client Example - C

Source: https://docs.espressif.com/projects/esp-idf/en/master/projects/esp-idf/en/stable/esp32/api-guides/lwip

Shows how to create a TCP client that connects to a server using a predefined IP address and port via the BSD Sockets API.

```c
/* This example is not provided in the text */
// Placeholder for tcp_client example
```

--------------------------------

### UDP Client Example - C

Source: https://docs.espressif.com/projects/esp-idf/en/master/projects/esp-idf/en/stable/esp32/api-guides/lwip

Details how to create a UDP client that connects to a server using a predefined IP address and port with the BSD Sockets API.

```c
/* This example is not provided in the text */
// Placeholder for udp_client example
```

--------------------------------

### Socket API Error Handling using errno - C

Source: https://docs.espressif.com/projects/esp-idf/en/master/projects/esp-idf/en/stable/esp32/api-guides/lwip

Provides an example of detecting socket API failures and obtaining the error reason code by accessing the 'errno' variable.

```c
int err;
int sockfd;

if ((sockfd = socket(AF_INET, SOCK_STREAM, 0)) < 0) {
    // the error code is obtained from errno
    err = errno;
    return err;
}
```

--------------------------------

### Non-blocking TCP Client/Server with IPv4/IPv6 - C

Source: https://docs.espressif.com/projects/esp-idf/en/master/projects/esp-idf/en/stable/esp32/api-guides/lwip

Demonstrates configuring and running a non-blocking TCP client and server, supporting both IPv4 and IPv6 protocols using BSD Sockets API.

```c
/* This example is not provided in the text */
// Placeholder for non_blocking TCP client/server example
```

--------------------------------

### Select() Exception Error Handling using getsockopt - C

Source: https://docs.espressif.com/projects/esp-idf/en/master/projects/esp-idf/en/stable/esp32/api-guides/lwip

Illustrates how to handle socket errors indicated by 'select()' by using 'getsockopt()' to retrieve the specific error code, as 'errno' is not set in this case.

```c
int err;

if (select(sockfd + 1, NULL, NULL, &exfds, &tval) <= 0) {
    err = errno;
    return err;
} else {
    if (FD_ISSET(sockfd, &exfds)) {
        // select() exception set using getsockopt()
        int optlen = sizeof(int);
        getsockopt(sockfd, SOL_SOCKET, SO_ERROR, &err, &optlen);
        return err;
    }
}
```

--------------------------------

### Handle DHCP Extra Option Hook in C

Source: https://docs.espressif.com/projects/esp-idf/en/master/projects/esp-idf/en/stable/esp32/api-guides/lwip

This C code snippet demonstrates how to implement a hook function in ESP-IDF to handle extra DHCP options. It specifically shows how to capture and log a Captive Portal URI option. This requires including 'esp_netif.h' and 'lwip/dhcp.h'.

```c
#include "esp_netif.h"
#include "lwip/dhcp.h"

void lwip_dhcp_on_extra_option(struct dhcp *dhcp, uint8_t state,
                               uint8_t option, uint8_t len,
                               struct pbuf* p, uint16_t offset)
{
    if (option == ESP_NETIF_CAPTIVEPORTAL_URI) {
        char *uri = (char *)p->payload + offset;
        ESP_LOGI(TAG, "Captive Portal URI: %s", uri);
    }
}

```

--------------------------------

### Initialize and Deinitialize lwIP Timers API

Source: https://docs.espressif.com/projects/esp-idf/en/master/projects/esp-idf/en/stable/esp32/api-guides/lwip

These API functions are used to manage lwIP timers, particularly for power saving when not using Wi-Fi. `sys_timeouts_init()` initializes the timer system, and `sys_timeouts_deinit()` deinitializes it, turning off the timers to reduce power consumption.

```c
/* Initialize lwIP timers */
sys_timeouts_init();

/* ... application logic ... */

/* Deinitialize lwIP timers */
sys_timeouts_deinit();

```

--------------------------------

### Enable DHCPv6 Stateless Configuration in lwIP

Source: https://docs.espressif.com/projects/esp-idf/en/master/projects/esp-idf/en/stable/esp32/api-guides/lwip

This code snippet demonstrates how to enable stateless DHCPv6 configuration for a given network interface (netif). It requires that IPv6 autoconfiguration is also enabled. This is necessary for configuring DNS servers via DHCPv6.

```c
#include "lwip/dhcp.h"
#include "lwip/netif.h"

// Assuming 'netif' is a valid pointer to a network interface
struct netif *netif;

// Enable stateless DHCPv6 for the given netif
dhcp6_enable_stateless(netif);

```

--------------------------------

### Define Project-Wide Macros with add_definitions() in ESP-IDF

Source: https://docs.espressif.com/projects/esp-idf/en/master/projects/esp-idf/en/stable/esp32/api-guides/lwip

This snippet shows how to use CMake's add_definitions() function to define macros for the entire ESP-IDF project. This method is recommended for function-like macros that might not be universally supported by all compilers when using target_compile_definitions().

```cmake
add_definitions("-DFALLBACK_DNS_SERVER_ADDRESS(addr)=\"IP_ADDR4((addr), 8,8,8,8)\"")
```

--------------------------------

### Define Macros with CMake in ESP-IDF

Source: https://docs.espressif.com/projects/esp-idf/en/master/projects/esp-idf/en/stable/esp32/api-guides/lwip

This snippet demonstrates how to define preprocessor macros for lwIP using CMake's target_compile_definitions() function in ESP-IDF. It's suitable for simple definitions but may have limitations with function-like macros. Ensure lwIP component is correctly identified.

```cmake
idf_component_get_property(lwip lwip COMPONENT_LIB)
target_compile_definitions(${lwip} PRIVATE "-DETHARP_SUPPORT_VLAN=1")
```

--------------------------------

### Define Custom lwIP Hook Filename in CMake

Source: https://docs.espressif.com/projects/esp-idf/en/master/projects/esp-idf/en/stable/esp32/api-guides/lwip

This CMake snippet shows how to add a custom hook file to the ESP-IDF lwIP build process. It retrieves the lwIP component library, adds an include path to the project's main directory, and defines the custom hook filename macro `ESP_IDF_LWIP_HOOK_FILENAME`.

```cmake
idf_component_get_property(lwip lwip COMPONENT_LIB)
target_compile_options(${lwip} PRIVATE "-I${PROJECT_DIR}/main")
target_compile_definitions(${lwip} PRIVATE "-DESP_IDF_LWIP_HOOK_FILENAME=\"my_hook.h\"")

```
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