Fix race condition

If we download first time url, it will create cache file and keep updating
it until download complete.
Race condition exist, when second request for same file comes, and it will
pickup incomplete file.

Signed-off-by: Denys Fedoryshchenko <denys.f@collabora.com>

Author: nuclearcat

src/azure.rs

@@ -199,6 +199,7 @@ async fn get_file_from_blob(filename: String) -> ReceivedFile {
         }
         Err(e) => {
             eprintln!("Error getting blob URL: {:?}", e);
+            return received_file;
         }
     }
     // append SAS token to blob URL
@@ -210,8 +211,26 @@ async fn get_file_from_blob(filename: String) -> ReceivedFile {
     let cache_filename_headers = format!("cache/{}.headers", digest.to_hex_lowercase());
     // check if cache file exists
     if std::path::Path::new(&cache_filename).exists() {
+        // check if headers file exists, and if not wait up to 300 seconds
+        // This is to avoid race condition, when we start to download file, but it is not yet completed
+        // and second request to same file downloads incomplete file
+        let mut headers_file_exists = false;
+        for seconds in 0..300 {
+            if std::path::Path::new(&cache_filename_headers).exists() {
+                headers_file_exists = true;
+                break;
+            }
+            std::thread::sleep(std::time::Duration::from_millis(1000));
+            println!("Waiting for headers file {} to exist: {} seconds", cache_filename_headers, seconds);
+        }
+
+        if !headers_file_exists {
+            eprintln!("Headers file {} does not exist", cache_filename_headers);
+            return received_file;
+        }
         //println!("Cache file {} exists", cache_filename);
         // is cached file non-zero length?
+        // is cached file non-zero length?
         let metadata = std::fs::metadata(&cache_filename).unwrap();
         if metadata.len() > 0 {
             //println!("Cache file {} is non-zero length", cache_filename);
@@ -229,6 +248,7 @@ async fn get_file_from_blob(filename: String) -> ReceivedFile {
                         "Error deleting cached file {}: {:?}",
                         cache_filename_headers, e
                     );
+                    return received_file;
                 }
             }
             match std::fs::remove_file(&cache_filename_headers) {
@@ -238,6 +258,7 @@ async fn get_file_from_blob(filename: String) -> ReceivedFile {
                         "Error deleting cached file {}: {:?}",
                         cache_filename_headers, e
                     );
+                    return received_file;
                 }
             }
         }
@@ -259,14 +280,14 @@ async fn get_file_from_blob(filename: String) -> ReceivedFile {
                 eprintln!("Error getting blob: {:?}", response.status());
                 return received_file;
             }
-            save_headers_to_file(cache_filename_headers, response.headers().clone());
             received_file.headers = response.headers().clone();
+            let resp_headers = response.headers().clone();
             let body = response.bytes().await.unwrap();
             // just write all to cache file
             let mut f = File::create(&cache_filename).unwrap();
             f.write_all(&body).unwrap();
             // write headers
-
+            save_headers_to_file(cache_filename_headers, resp_headers);
             received_file.cached_filename = cache_filename;
             received_file.valid = true;
         }