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# Civetweb API Reference
### `mg_read( conn, buf, len );`
### Parameters
| Parameter | Type | Description |
| :--- | :--- | :--- |
|**`conn`**|`struct mg_connection *`| A pointer referencing the connection |
|**`buf`**|`void *`| A pointer to the location where the received data can be stored |
|**`len`**|`size_t`| The maximum number of bytes to be stored in the buffer |
### Return Value
| Type | Description |
| :--- | :--- |
|`int`| The number of read bytes, or a status indication |
### Description
The function `mg_read()` receives data over an existing connection. The data is handled as binary and is stored in a buffer whose address has been provided as a parameter. The function returns the number of read bytes when successful, the value **0** when the connection has been closed by peer and a negative value when no more data could be read from the connection.
### Example
```
#define RECV_BUF_SIZE 1 << 20
size_t read_data(struct mg_connection* conn,
uint8_t* buff,
size_t buff_len) {
size_t read_len = 0;
while (read_len < buff_len) {
size_t sz_to_read = std::min<size_t>(RECV_BUF_SIZE, buff_len - read_len);
int this_read = mg_read(conn, buff + read_len, sz_to_read);
if (this_read < 0) {
std::cerr << "[error] Failed to read data" << std::endl;
break;
} else {
read_len += size_t(this_read);
if (this_read > 0) {
std::cout << "[debug] Received " << this_read << " more bytes" << std::endl;
}
}
}
return read_len;
}
```
### See Also
* [`mg_printf();`](mg_printf.md)
* [`mg_write();`](mg_write.md)
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