markdown 使用Reqwest和dotenv #rust的Rust客户端

Posted 2021-05-05

# Rust Client using Reqwest

```rust
extern crate dotenv;
    extern crate hyper;

    use http::header::{HeaderName, HeaderValue};
    use reqwest::{Client, Method, Url};

    fn get_env_vars() -> (HeaderName, HeaderValue, Url) {
        // use dotenv to pull the values from .env
        let cmc_api_key = dotenv::var("CMC_API_KEY").expect("CMC_API_KEY not found");
        let cmc_api_endpoint = dotenv::var("CMC_API_ENDPOINT").expect("CMC_API_ENDPOINT not found");
        let cmc_header_name = dotenv::var("CMC_HEADER_NAME").expect("CMC_HEADER_NAME not found");

        // parse and unwrap the values
        let header_name = cmc_header_name.parse::<HeaderName>().unwrap();
        let header_value = cmc_api_key.parse::<HeaderValue>().unwrap();
        let url: Url = cmc_api_endpoint.parse().unwrap();

        // return a tuple of the values
        (header_name, header_value, url)
    }

    fn fetch_cmc_data(name: HeaderName, value: HeaderValue, url: Url) -> reqwest::Response {
        let client = Client::new();

        let request = client
            .request(Method::GET, url)
            .header(name, value)
            .build()
            .unwrap();

        client.execute(request).unwrap()
    }

    fn main() {
        let (header_name, header_value, url) = get_env_vars();
        let mut response = fetch_cmc_data(header_name, header_value, url);

        println!("{:?}", response.text());
    }
```

This is a Rust client using the libraries `reqwest` and `dotenv` . It calls an API endpoint at coinmarketcap.com and returns a list of cryptocurrencies, the first 60+ lines are found at the bottom of this post.

1. starting from `fn main()`, a tuple of the `header_name`, `header_value`, and `url` are returned from `get_env_vars()`
2. `get_env_vars()` pulls the values from a `.env` file in the same directory
    - `CMC_API_KEY` - a [coinmarketcap.com](http://coinmarketcap.com) API key. Get yours at: {link here}
    - `CMC_API_ENDPOINT` - [https://pro-api.coinmarketcap.com/v1/cryptocurrency/listings/latest](https://pro-api.coinmarketcap.com/v1/cryptocurrency/listings/latest)
    - `CMC_HEADER_NAME` - which is `"X-CMC_PRO_API_KEY"`
3. the contents of the tuple are passed into `fn fetch_cmc_data()` , which then returns `reqwest::Response` into `mut response` .
    - a `reqwest::Client` is instantiated first
    - a `reqwest::RequestBuilder` receives the `url` in `request()` , and the header name and value are passed into `header()`
    - `.build()` and `.unwrap()` are called immediately to create a `reqwest::Request`
    - `client` now executes the `request`, and calls `unwrap()` , but you should handle a client error here
4. `text()` output from `mut response` is fed into a printing function. Boom!

### Response

This is the first part of the response from the above client request:

```
{
    "status":  {
        "timestamp":  "2019-02-16T08: 28: 15.822Z",
        "error_code":  0,
        "error_message":  null,
        "elapsed":  14,
        "credit_count":  1    
    },
    "data":  [
        {
            "id":  1,
            "name":  "Bitcoin",
            "symbol":  "BTC",
            "slug":  "bitcoin",
            "circulating_supply":  17540550,
            "total_supply":  17540550,
            "max_supply":  21000000,
            "date_added":  "2013-04-28T00: 00: 00.000Z",
            "num_market_pairs":  6653,
            "tags":  [
                "mineable"            
            ],
            "platform":  null,
                "cmc_rank":  1,
                "last_updated":  "2019-02-16T08: 27: 28.000Z",
                "quote":  {
                    "USD":  {
                            "price":  3635.49176252,
                            "volume_24h":  6060386037.82371,
                            "percent_change_1h":  0.0488409,
                            "percent_change_24h":  0.14031,
                            "percent_change_7d":  -0.810947,
                            "market_cap":  63768525035.07019,
                            "last_updated":  "2019-02-16T08: 27: 28.000Z"                
                    }            
                }        
        },
        {
                "id":  1027,
                "name":  "Ethereum",
                "symbol":  "ETH",
                "slug":  "ethereum",
                "circulating_supply":  104879559.8741,
                "total_supply":  104879559.8741,
                "max_supply":  null,
                "date_added":  "2015-08-07T00: 00: 00.000Z",
                "num_market_pairs":  4759,
                "tags":  [
                    "mineable"            
                ],
                "platform":  null,
                "cmc_rank":  2,
                "last_updated":  "2019-02-16T08: 27: 19.000Z",
                "quote":  {
                    "USD":  {
                            "price":  123.164946188,
                            "volume_24h":  2964473039.45236,
                            "percent_change_1h":  0.0820388,
                            "percent_change_24h":  0.194405,
                            "percent_change_7d":  3.483,
                            "market_cap":  12917485348.11465,
                            "last_updated":  "2019-02-16T08: 27: 19.000Z"                
                    }            
                }        
        },
...
```