I consider this a good compromise between all async (that works but is pretty complex and honestly a bit useless) and nothing async that is not the most optimal way to deal with things as reqwest and egg-mode are async by nature

src/lib.rs

@@ -1,17 +1,13 @@
 // std
 use std::{
-    path::Path,
     borrow::Cow,
     collections::HashMap,
-    io::{stdin, copy},
+    io::stdin,
     fmt,
-    fs::{read_to_string, write, create_dir_all, File, remove_file},
+    fs::{read_to_string, write},
     error::Error,
 };
 
-// futures
-use futures::executor::block_on;
-
 // toml
 use serde::Deserialize;
 
@@ -36,11 +32,20 @@ use elefren::{
 };
 
 // reqwest
-use reqwest::Client;
+use reqwest::Url;
+
+// tokio
+use tokio::{
+    io::copy,
+    fs::{File, create_dir_all, remove_file},
+};
 
 // htmlescape
 use htmlescape::decode_html;
 
+// log
+use log::{info, warn, error, debug};
+
 /**********
  * Generic usage functions
 ***********/
@@ -52,18 +57,19 @@ fn read_state(s: &str) -> Option<u64> {
     let state = read_to_string(s);
 
     if let Ok(s) = state {
+        debug!("Last Tweet ID (from file): {}", &s);
         return s.parse::<u64>().ok();
     }
 
     None
 }
 
-/// Write last treated tweet id to a file
+/// Writes last treated tweet id to a file
 fn write_state(f: &str, s: u64) -> Result<(), std::io::Error> {
     write(f, format!("{}", s))
 }
 
-/// Get twitter oauth2 token
+/// Gets twitter oauth2 token
 fn get_oauth2_token(config: &Config) -> Token {
     let con_token = KeyPair::new(String::from(&config.twitter.consumer_key), String::from(&config.twitter.consumer_secret));
     let access_token = KeyPair::new(String::from(&config.twitter.access_key), String::from(&config.twitter.access_secret));
@@ -74,17 +80,17 @@ fn get_oauth2_token(config: &Config) -> Token {
     }
 }
 
-/// Get twitter user timeline
-fn get_user_timeline(config: &Config, token: Token, lid: Option<u64>) -> Result<Vec<Tweet>, Box<dyn Error>> {
+/// Gets twitter user timeline
+async fn get_user_timeline(config: &Config, token: Token, lid: Option<u64>) -> Result<Vec<Tweet>, Box<dyn Error>> {
     // fix the page size to 200 as it is the maximum Twitter authorizes
-    let (_timeline, feed) = block_on(user_timeline(UserID::from(String::from(&config.twitter.username)), true, false, &token)
+    let (_timeline, feed) = user_timeline(UserID::from(String::from(&config.twitter.username)), true, false, &token)
                 .with_page_size(200)
-                .older(lid))?;
+                .older(lid).await?;
 
     Ok(feed.to_vec())
 }
 
-/// decode urls from UrlEntities
+/// Decodes urls from UrlEntities
 fn decode_urls(urls: &Vec<UrlEntity>) -> HashMap<String, String> {
     let mut decoded_urls = HashMap::new();
 
@@ -98,6 +104,8 @@ fn decode_urls(urls: &Vec<UrlEntity>) -> HashMap<String, String> {
     decoded_urls
 }
 
+/// Decodes the Twitter mention to something that will make sense once Twitter has joined the
+/// Fediverse
 fn twitter_mentions(ums: &Vec<MentionEntity>) -> HashMap<String, String> {
     let mut decoded_mentions = HashMap::new();
 
@@ -108,24 +116,24 @@ fn twitter_mentions(ums: &Vec<MentionEntity>) -> HashMap<String, String> {
     decoded_mentions
 }
 
-/// Retrieve a single media from a tweet and store it in a temporary file
-fn get_tweet_media(m: &MediaEntity, t: &str) -> Result<String, Box<dyn Error>> {
+/// Retrieves a single media from a tweet and store it in a temporary file
+async fn get_tweet_media(m: &MediaEntity, t: &str) -> Result<String, Box<dyn Error>> {
     match m.media_type {
         MediaType::Photo => {
-            return cache_media(&m.media_url_https, t);
+            return cache_media(&m.media_url_https, t).await;
         },
         _ => {
             match &m.video_info {
                 Some(v) => {
                     for variant in &v.variants {
                         if variant.content_type == "video/mp4" {
-                            return cache_media(&variant.url, t);
+                            return cache_media(&variant.url, t).await;
                         }
                     }
-                    return Err(Box::new(ScootalooError::new(format!("Media Type for {} is video but no mp4 file URL is available", &m.url).as_str())));
+                    return Err(ScootalooError::new(&format!("Media Type for {} is video but no mp4 file URL is available", &m.url)).into());
                 },
                 None => {
-                    return Err(Box::new(ScootalooError::new(format!("Media Type for {} is video but does not contain any video_info", &m.url).as_str())));
+                    return Err(ScootalooError::new(&format!("Media Type for {} is video but does not contain any video_info", &m.url)).into());
                 },
             }
         },
@@ -135,7 +143,7 @@ fn get_tweet_media(m: &MediaEntity, t: &str) -> Result<String, Box<dyn Error>> {
 /*
  * Those functions are related to the Mastodon side of things
  */
-/// Get Mastodon Data
+/// Gets Mastodon Data
 fn get_mastodon_token(masto: &MastodonConfig) -> Mastodon {
     let data = Data {
         base: Cow::from(String::from(&masto.base)),
@@ -148,7 +156,7 @@ fn get_mastodon_token(masto: &MastodonConfig) -> Mastodon {
     Mastodon::from(data)
 }
 
-/// build toot text from tweet
+/// Builds toot text from tweet
 fn build_basic_status(tweet: &Tweet) -> Result<String, Box<dyn Error>> {
     let mut toot = String::from(&tweet.text);
 
@@ -174,31 +182,26 @@ fn build_basic_status(tweet: &Tweet) -> Result<String, Box<dyn Error>> {
 /*
  * Generic private functions
  */
-fn cache_media(u: &str, t: &str) -> Result<String, Box<dyn Error>> {
+/// Gets and caches Twitter Media inside the determined temp dir
+async fn cache_media(u: &str, t: &str) -> Result<String, Box<dyn Error>> {
     // create dir
-    if !Path::new(t).is_dir() {
-        create_dir_all(t)?;
-    }
+    create_dir_all(t).await?;
 
     // get file
-    let client = Client::new();
-    let mut response = client.get(u).send()?;
+    let mut response = reqwest::get(u).await?;
 
     // create local file
-    let dest_filename = match response.url()
-                    .path_segments()
-                    .and_then(|segments| segments.last()) {
-                        Some(r) => r,
-                        None => {
-                            return Err(Box::new(ScootalooError::new(format!("Cannot determine the destination filename for {}", u).as_str())));
-                        },
-                    };
+    let url = Url::parse(u)?;
+    let dest_filename = url.path_segments().ok_or_else(|| ScootalooError::new(&format!("Cannot determine the destination filename for {}", u)))?
+                    .last().ok_or_else(|| ScootalooError::new(&format!("Cannot determine the destination filename for {}", u)))?;
 
     let dest_filepath = format!("{}/{}", t, dest_filename);
 
-    let mut dest_file = File::create(&dest_filepath)?;
+    let mut dest_file = File::create(&dest_filepath).await?;
 
-    copy(&mut response, &mut dest_file)?;
+    while let Some(chunk) = response.chunk().await? {
+        copy(&mut &*chunk, &mut dest_file).await?;
+    }
 
     Ok(dest_filepath)
 }
@@ -284,7 +287,7 @@ pub fn parse_toml(toml_file: &str) -> Config {
 
 /// Generic register function
 /// As this function is supposed to be run only once, it will panic for every error it encounters
-/// Most of this function is a direct copy/paste of the official `mammut` crate
+/// Most of this function is a direct copy/paste of the official `elefren` crate
 pub fn register(host: &str) {
     let mut builder = App::builder();
     builder.client_name(Cow::from(String::from(env!("CARGO_PKG_NAME"))))
@@ -312,7 +315,8 @@ pub fn register(host: &str) {
 }
 
 /// This is where the magic happens
-pub fn run(config: Config) {
+#[tokio::main]
+pub async fn run(config: Config) {
     // retrieve the last tweet ID for the username
     let last_tweet_id = read_state(&config.scootaloo.last_tweet_path);
 
@@ -323,13 +327,13 @@ pub fn run(config: Config) {
     let mastodon = get_mastodon_token(&config.mastodon);
 
     // get user timeline feed (Vec<tweet>)
-    let mut feed = get_user_timeline(&config, token, last_tweet_id).unwrap_or_else(|e|
+    let mut feed = get_user_timeline(&config, token, last_tweet_id).await.unwrap_or_else(|e|
         panic!("Something went wrong when trying to retrieve {}’s timeline: {}", &config.twitter.username, e)
     );
 
     // empty feed -> exiting
     if feed.is_empty() {
-        println!("Nothing to retrieve since last time, exiting…");
+        info!("Nothing to retrieve since last time, exiting…");
         return;
     }
 
@@ -338,9 +342,11 @@ pub fn run(config: Config) {
 
     for tweet in &feed {
         // determine if the tweet is part of a thread (response to self) or a standard response
+        debug!("Treating Tweet {} inside feed", tweet.id);
         if let Some(r) =  &tweet.in_reply_to_screen_name {
                 if &r.to_lowercase() != &config.twitter.username.to_lowercase() {
                     // we are responding not threading
+                    info!("Tweet is a direct response, skipping");
                     continue;
                 }
         };
@@ -349,7 +355,7 @@ pub fn run(config: Config) {
         let mut status_text = match build_basic_status(tweet) {
             Ok(t) => t,
             Err(e) => {
-                println!("Could not create status from tweet {}: {}", tweet.id ,e);
+                error!("Could not create status from tweet {}: {}", tweet.id ,e);
                 continue;
             },
         };
@@ -359,39 +365,38 @@ pub fn run(config: Config) {
         // reupload the attachments if any
         if let Some(m) = &tweet.extended_entities {
             for media in &m.media {
-                let local_tweet_media_path = match get_tweet_media(&media, &config.scootaloo.cache_path) {
+                let local_tweet_media_path = match get_tweet_media(&media, &config.scootaloo.cache_path).await {
                     Ok(m) => m,
                     Err(e) => {
-                        println!("Cannot get tweet media for {}: {}", &media.url, e);
+                        warn!("Cannot get tweet media for {}: {}", &media.url, e);
                         continue;
                     },
                 };
 
                 let mastodon_media_ids = match mastodon.media(Cow::from(String::from(&local_tweet_media_path))) {
                     Ok(m) => {
-                        remove_file(&local_tweet_media_path).unwrap_or_else(|e|
-                            println!("Attachment for {} has been upload, but I’m unable to remove the existing file: {}", &local_tweet_media_path, e)
+                        remove_file(&local_tweet_media_path).await.unwrap_or_else(|e|
+                            warn!("Attachment {} has been uploaded but I’m unable to remove the existing file: {}", &local_tweet_media_path, e)
                         );
                         m.id
                     },
                     Err(e) => {
-                        println!("Cannot attach media {} to Mastodon Instance: {}", &local_tweet_media_path, e);
+                        error!("Attachment {} cannot be uploaded to Mastodon Instance: {}", &local_tweet_media_path, e);
                         continue;
                     }
                 };
-
                 status_medias.push(mastodon_media_ids);
-
                 // last step, removing the reference to the media from with the toot’s text
                 status_text = status_text.replace(&media.url, "");
             }
         }
 
+        debug!("Building corresponding Mastodon status");
         let status = StatusBuilder::new()
             .status(&status_text)
             .media_ids(status_medias)
             .build()
-            .expect(format!("Cannot build status with text {}", &status_text).as_str());
+            .expect(&format!("Cannot build status with text {}", &status_text));
 
         // publish status
         mastodon.new_status(status).unwrap();