Easy function to call to fetch the primary email address of a user in Rust.

fetch_github_primary_email.rs

// Example usage:
//     let github_email = fetch_github_primary_email(&some_access_token)?;
// 
// Cargo.toml:
// .. 
// [dependencies]
// rocket = "0.3.11"
// curl = "0.4"
// serde = "1.0"
// serde_json = "1.0"
// ..


extern crate curl;
extern crate serde;
extern crate serde_json;

use curl::easy::{Easy, List};

const GITHUB_V3_API: &str = "https://api.github.com";
const CONTENT_TYPE_JSON: &str = "application/json";
const GITHUB_APP_NAME: &str = "Example-App";

// handles any Error Result and converts to a 500 error in Rocket (for use within a Rocket Web Application).
// CHANGEME to return any other type of useful error
macro_rules! error_to_500 {
    ($x:expr) => {
        match $x {
            Err(err) => {
                eprintln!("{}", err.to_string());
                return Err(rocket::http::Status::InternalServerError);
            }
            Ok(_) => (),
        }
    };
}

fn github_v3_query(access_token: &str, endpoint: &str) -> Result<String, Status> {
    let mut easy = Easy::new();
    match easy.url(&format!("{}{}", GITHUB_V3_API, endpoint)) {
        Err(err) => {
            eprintln!("{}", err.to_string());
            return Err(rocket::http::Status::InternalServerError);
        }
        Ok(_) => (),
    };

    let mut headers = List::new();
    error_to_500!(headers.append(&format!("User-Agent: {}", GITHUB_APP_NAME)));
    error_to_500!(headers.append(&format!("Authorization: token {}", access_token)));
    error_to_500!(headers.append(&format!("Accept: {}", CONTENT_TYPE_JSON)));
    error_to_500!(easy.http_headers(headers));

    let mut data = Vec::new();
    {
        let mut transfer = easy.transfer();
        error_to_500!(transfer.write_function(|new_data| {
            data.extend_from_slice(new_data);
            Ok(new_data.len())
        }));
        error_to_500!(transfer.perform());
    }

    let http_status_response = easy.response_code();
    error_to_500!(http_status_response);
    let response_code = http_status_response.unwrap();
    if response_code != 200 {
        eprintln!(
            "Github V3 API returned {} : {}",
            response_code,
            String::from_utf8_lossy(data.as_slice())
        );
        return Err(rocket::http::Status::InternalServerError);
    }

    Ok(String::from_utf8_lossy(data.as_slice()).to_string())
}

fn fetch_github_primary_email(access_token: &str) -> Result<String, Status> {
    let github_emails_str = github_v3_query(access_token, &"/user/emails")?;
    let email_parse_result = serde_json::from_str(&github_emails_str);
    error_to_500!(email_parse_result);
    let github_emails: Vec<serde_json::Value> = email_parse_result.unwrap();
    let mut github_primary_email = String::from("");
    for x in github_emails {
        if x["primary"].is_boolean() && x["primary"].as_bool().unwrap() {
            let parsed_email = x["email"].as_str();
            github_primary_email = match parsed_email {
                None => {
                    eprintln!("Did not find a string during json decoding email from GitHub");
                    return Err(rocket::http::Status::InternalServerError);
                }
                Some(t) => t.to_string(),
            };
            break;
        }
    }
    Ok(github_primary_email)
}