feat(services/autumn): download and preview files

crates/core/files/src/lib.rs

@@ -1,3 +1,78 @@
-// pub fn
+use std::io::Write;
 
-pub fn decrypt(data: &mut [u8]) {}
+use aes_gcm::{aead::AeadMutInPlace, Aes256Gcm, Key, KeyInit, Nonce};
+use revolt_config::{config, FilesS3};
+use revolt_result::{create_error, Result};
+
+use aws_sdk_s3::{
+    config::{Credentials, Region},
+    Client, Config,
+};
+
+use base64::prelude::*;
+
+/// Create an S3 client
+pub fn create_client(s3_config: FilesS3) -> Client {
+    let provider_name = "my-creds";
+    let creds = Credentials::new(
+        s3_config.access_key_id,
+        s3_config.secret_access_key,
+        None,
+        None,
+        provider_name,
+    );
+
+    let config = Config::builder()
+        .region(Region::new(s3_config.region))
+        .endpoint_url(s3_config.endpoint)
+        .credentials_provider(creds)
+        .build();
+
+    Client::from_conf(config)
+}
+
+/// Create an AES-256-GCM cipher
+pub fn create_cipher(key: &str) -> Aes256Gcm {
+    let key = &BASE64_STANDARD.decode(key).unwrap()[..];
+    let key: &Key<Aes256Gcm> = key.into();
+    Aes256Gcm::new(key)
+}
+
+/// Fetch a file from S3 (and decrypt it)
+pub async fn fetch_from_s3(bucket_id: &str, path: &str, nonce: &str) -> Result<Vec<u8>> {
+    let config = config().await;
+    let client = create_client(config.files.s3);
+
+    // Send a request for the file
+    let mut obj = client
+        .get_object()
+        .bucket(bucket_id)
+        .key(path)
+        .send()
+        .await
+        .inspect_err(|err| {
+            revolt_config::capture_error(err);
+        })
+        .map_err(|_| create_error!(InternalError))?;
+
+    // Read the file from remote
+    let mut buf = vec![];
+    while let Some(bytes) = obj.body.next().await {
+        let data = bytes.map_err(|_| create_error!(InternalError))?;
+        buf.write_all(&data)
+            .map_err(|_| create_error!(InternalError))?;
+        // is there a more efficient way to do this?
+        // we just want the Vec<u8>
+    }
+
+    // Recover nonce as bytes
+    let nonce = &BASE64_STANDARD.decode(nonce).unwrap()[..];
+    let nonce: &Nonce<typenum::consts::U12> = nonce.into();
+
+    // Decrypt the file
+    create_cipher(&config.files.encryption_key)
+        .decrypt_in_place(nonce, b"", &mut buf)
+        .map_err(|_| create_error!(InternalError))?;
+
+    Ok(buf)
+}