# Error Handling

[中文]

## Overview

Identifying and handling run-time errors is important for developing robust applications. There can be multiple kinds of run-time errors:

- Recoverable errors:

  - Errors indicated by functions through return values (error codes)

  - C++ exceptions, thrown using `throw` keyword

- Unrecoverable (fatal) errors:

  - Failed assertions (using `assert` macro and equivalent methods, see Assertions) and `abort()` calls.

  - CPU exceptions: access to protected regions of memory, illegal instruction, etc.

  - System level checks: watchdog timeout, cache access error, stack overflow, stack smashing, heap corruption, etc.

This guide explains ESP-IDF error handling mechanisms related to recoverable errors, and provides some common error handling patterns.

For instructions on diagnosing unrecoverable errors, see Fatal Errors.

## Error Codes

The majority of ESP-IDF-specific functions use `esp_err_t` type to return error codes. `esp_err_t` is a signed integer type. Success (no error) is indicated with `ESP_OK` code, which is defined as zero.

Various ESP-IDF header files define possible error codes using preprocessor defines. Usually these defines start with `ESP_ERR_` prefix. Common error codes for generic failures (out of memory, timeout, invalid argument, etc.) are defined in `esp_err.h` file. Various components in ESP-IDF may define additional error codes for specific situations.

For the complete list of error codes, see Error Code Reference.

## Converting Error Codes to Error Messages

For each error code defined in ESP-IDF components, `esp_err_t` value can be converted to an error code name using `esp_err_to_name()` or `esp_err_to_name_r()` functions. For example, passing `0x101` to `esp_err_to_name()` will return a `ESP_ERR_NO_MEM` string. Such strings can be used in log output to make it easier to understand which error has happened.

Additionally, `esp_err_to_name_r()` function will attempt to interpret the error code as a standard POSIX error code, if no matching `ESP_ERR_` value is found. This is done using `strerror_r` function. POSIX error codes (such as `ENOENT`, `ENOMEM`) are defined in `errno.h` and are typically obtained from `errno` variable. In ESP-IDF this variable is thread-local: multiple FreeRTOS tasks have their own copies of `errno`. Functions which set `errno` only modify its value for the task they run in.

This feature is enabled by default, but can be disabled to reduce application binary size. See CONFIG_ESP_ERR_TO_NAME_LOOKUP. When this feature is disabled, `esp_err_to_name()` and `esp_err_to_name_r()` are still defined and can be called. In this case, `esp_err_to_name()` will return `UNKNOWN ERROR`, and `esp_err_to_name_r()` will return `Unknown error 0xXXXX(YYYYY)`, where `0xXXXX` and `YYYYY` are the hexadecimal and decimal representations of the error code, respectively.

## `ESP_ERROR_CHECK` Macro

`ESP_ERROR_CHECK` macro serves similar purpose as `assert`, except that it checks `esp_err_t` value rather than a `bool` condition. If the argument of `ESP_ERROR_CHECK` is not equal `ESP_OK`, then an error message is printed on the console, and `abort()` is called.

Error message will typically look like this:

    ESP_ERROR_CHECK failed: esp_err_t 0x107 (ESP_ERR_TIMEOUT) at 0x400d1fdf

    file: "/Users/user/esp/example/main/main.c" line 20
    func: app_main
    expression: sdmmc_card_init(host, &card)

    Backtrace: 0x40086e7c:0x3ffb4ff0 0x40087328:0x3ffb5010 0x400d1fdf:0x3ffb5030 0x400d0816:0x3ffb5050

Note

If ESP-IDF monitor is used, addresses in the backtrace will be converted to file names and line numbers.

- The first line mentions the error code as a hexadecimal value, and the identifier used for this error in source code. The latter depends on CONFIG_ESP_ERR_TO_NAME_LOOKUP option being set. Address in the program where error has occurred is printed as well.

- Subsequent lines show the location in the program where `ESP_ERROR_CHECK` macro was called, and the expression which was passed to the macro as an argument.

- Finally, backtrace is printed. This is part of panic handler output common to all fatal errors. See Fatal Errors for more information about the backtrace.

## `ESP_ERROR_CHECK_WITHOUT_ABORT` Macro

`ESP_ERROR_CHECK_WITHOUT_ABORT` macro serves similar purpose as `ESP_ERROR_CHECK`, except that it will not call `abort()`.

## `ESP_RETURN_ON_ERROR` Macro

`ESP_RETURN_ON_ERROR` macro checks the error code, if the error code is not equal `ESP_OK`, it prints the message and returns the error code.

## `ESP_GOTO_ON_ERROR` Macro

`ESP_GOTO_ON_ERROR` macro checks the error code, if the error code is not equal `ESP_OK`, it prints the message, sets the local variable `ret` to the code, and then exits by jumping to `goto_tag`.

## `ESP_RETURN_ON_FALSE` Macro

`ESP_RETURN_ON_FALSE` macro checks the condition, if the condition is not equal `true`, it prints the message and returns with the supplied `err_code`.

## `ESP_GOTO_ON_FALSE` Macro

`ESP_GOTO_ON_FALSE` macro checks the condition, if the condition is not equal `true`, it prints the message, sets the local variable `ret` to the supplied `err_code`, and then exits by jumping to `goto_tag`.

## `CHECK MACROS` Examples

Some examples

    static const char* TAG = "Test";

    esp_err_t test_func(void)
    {
        esp_err_t ret = ESP_OK;

        ESP_ERROR_CHECK(x);                                         // err message printed if `x` is not `ESP_OK`, and then `abort()`.
        ESP_ERROR_CHECK_WITHOUT_ABORT(x);                           // err message printed if `x` is not `ESP_OK`, without `abort()`.
        ESP_RETURN_ON_ERROR(x, TAG, "fail reason 1");               // err message printed if `x` is not `ESP_OK`, and then function returns with code `x`.
        ESP_GOTO_ON_ERROR(x, err, TAG, "fail reason 2");            // err message printed if `x` is not `ESP_OK`, `ret` is set to `x`, and then jumps to `err`.
        ESP_RETURN_ON_FALSE(a, err_code, TAG, "fail reason 3");     // err message printed if `a` is not `true`, and then function returns with code `err_code`.
        ESP_GOTO_ON_FALSE(a, err_code, err, TAG, "fail reason 4");  // err message printed if `a` is not `true`, `ret` is set to `err_code`, and then jumps to `err`.

    err:
        // clean up
        return ret;
    }

Note

If the option CONFIG_COMPILER_OPTIMIZATION_CHECKS_SILENT in Kconfig is enabled, the error message will be discarded, while the other action works as is.

The `ESP_RETURN_XX` and `ESP_GOTO_xx` macros cannot be called from ISR. While there are `xx_ISR` versions for each of them, e.g., `ESP_RETURN_ON_ERROR_ISR`, these macros could be used in ISR.

## Error Handling Patterns

1. Attempt to recover. Depending on the situation, we may try the following methods:

   > - retry the call after some time;

   > - attempt to de-initialize the driver and re-initialize it again;

   > - fix the error condition using an out-of-band mechanism (e.g reset an external peripheral which is not responding).

   > Example:

   >     esp_err_t err;
   >     do {
   >         err = sdio_slave_send_queue(addr, len, arg, timeout);
   >         // keep retrying while the sending queue is full
   >     } while (err == ESP_ERR_TIMEOUT);
   >     if (err != ESP_OK) {
   >         // handle other errors
   >     }

2. Propagate the error to the caller. In some middleware components this means that a function must exit with the same error code, making sure any resource allocations are rolled back.

   > Example:

   >     sdmmc_card_t* card = calloc(1, sizeof(sdmmc_card_t));
   >     if (card == NULL) {
   >         return ESP_ERR_NO_MEM;
   >     }
   >     esp_err_t err = sdmmc_card_init(host, &card);
   >     if (err != ESP_OK) {
   >         // Clean up
   >         free(card);
   >         // Propagate the error to the upper layer (e.g., to notify the user).
   >         // Alternatively, application can define and return custom error code.
   >         return err;
   >     }

3. Convert into unrecoverable error, for example using `ESP_ERROR_CHECK`. See ESP_ERROR_CHECK macro section for details.

   > Terminating the application in case of an error is usually undesirable behavior for middleware components, but is sometimes acceptable at application level.

   > Many ESP-IDF examples use `ESP_ERROR_CHECK` to handle errors from various APIs. This is not the best practice for applications, and is done to make example code more concise.

   > Example:

   >     ESP_ERROR_CHECK(spi_bus_initialize(host, bus_config, dma_chan));

## C++ Exceptions

See Exception Handling.

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