Guess mime type based on path

Try to determine the mime type of a file first based on its path, then
based on its content.

The previous behavior (looking only at the file content) inferred a
mime type of `text/xml` for `.svg` files (instead of `image/svg+xml`)
which prevented them from being shown when embedded e.g. in a markdown
document.

radicle-httpd/Cargo.lock

@@ -1468,6 +1468,16 @@ version = "0.3.17"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "6877bb514081ee2a7ff5ef9de3281f14a4dd4bceac4c09388074a6b5df8a139a"
 
+[[package]]
+name = "mime_guess"
+version = "2.0.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f7c44f8e672c00fe5308fa235f821cb4198414e1c77935c1ab6948d3fd78550e"
+dependencies = [
+ "mime",
+ "unicase",
+]
+
 [[package]]
 name = "miniz_oxide"
 version = "0.7.4"
@@ -2019,6 +2029,7 @@ dependencies = [
  "infer",
  "lexopt",
  "lru",
+ "mime_guess",
  "nonempty 0.12.0",
  "pretty_assertions",
  "radicle",
@@ -2941,6 +2952,12 @@ version = "1.17.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "42ff0bf0c66b8238c6f3b578df37d0b7848e55df8577b3f74f92a69acceeb825"
 
+[[package]]
+name = "unicase"
+version = "2.8.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "75b844d17643ee918803943289730bec8aac480150456169e647ed0b576ba539"
+
 [[package]]
 name = "unicode-display-width"
 version = "0.3.0"

radicle-httpd/Cargo.toml

@@ -30,6 +30,7 @@ hyper = { version = "1.6.0", default-features = false }
 infer = { version = "0.19.0" }
 lexopt = { version = "0.3.1" }
 lru = { version = "0.16.0" }
+mime_guess = { version = "2.0.5" }
 nonempty = { version = "0.12.0", features = ["serialize"] }
 radicle = { version = "0.18.0" }
 radicle-surf = { version = "0.22.0", default-features = false, features = ["serde"] }

radicle-httpd/src/raw.rs

@@ -74,7 +74,7 @@ async fn file_by_commit_handler(
     let repo: Repository = repo.backend.into();
     let blob = repo.blob(sha, &path)?;
 
-    blob_response(blob)
+    blob_response(blob, &path)
 }
 
 async fn archive_by_refname_handler(
@@ -173,22 +173,24 @@ async fn file_by_canonical_head_handler(
     let repo: Repository = repo.backend.into();
     let blob = repo.blob(sha, &path)?;
 
-    blob_response(blob)
+    blob_response(blob, &path)
 }
 
-fn blob_response(blob: Blob<BlobRef>) -> Result<(StatusCode, HeaderMap, Vec<u8>), Error> {
+fn blob_response(
+    blob: Blob<BlobRef>,
+    path: &str,
+) -> Result<(StatusCode, HeaderMap, Vec<u8>), Error> {
     let mut response_headers = HeaderMap::new();
     if blob.size() > MAX_BLOB_SIZE {
         return Ok::<_, Error>((StatusCode::PAYLOAD_TOO_LARGE, response_headers, vec![]));
     }
 
-    let content = blob.content();
-    let mime = infer::get(content).map(|i| i.mime_type().to_string());
+    let mime = mime_guess::from_path(path)
+        .first_raw()
+        .or_else(|| infer::get(blob.content()).map(|i| i.mime_type()))
+        .unwrap_or("application/octet-stream");
 
-    response_headers.insert(
-        header::CONTENT_TYPE,
-        HeaderValue::from_str(&mime.unwrap_or("application/octet-stream".to_string()))?,
-    );
+    response_headers.insert(header::CONTENT_TYPE, HeaderValue::from_str(mime)?);
 
     Ok::<_, Error>((StatusCode::OK, response_headers, blob.content().to_owned()))
 }