perf: request compressed responses for the release index

CHANGELOG.md

@@ -1,3 +1,7 @@
+# Unreleased
+
+- Request compressed responses when querying the release index, shrinking the transfer from ~3.7MB to ~150KB.
+
 # 4.2.4 - 2026-08-25
 
 - `elan install`/`elan toolchain install` now report an already-installed toolchain as such and exit with code 0 instead of failing with `'...' is already installed`.

src/download/src/lib.rs

@@ -139,6 +139,12 @@ pub mod curl {
                 .follow_location(true)
                 .chain_err(|| "failed to set follow redirects")?;
 
+            // The handle is shared with `fetch_url`, which asks for compressed responses; make
+            // sure we get the file's raw bytes here so that content length and resuming work.
+            handle
+                .accept_encoding("identity")
+                .chain_err(|| "failed to set accept encoding")?;
+
             if resume_from > 0 {
                 handle
                     .resume_from(resume_from)

src/elan-utils/src/utils.rs

@@ -530,6 +530,8 @@ pub fn fetch_url(url: &str) -> Result<String> {
         let mut handle = handle.borrow_mut();
         handle.url(url).unwrap();
         handle.follow_location(true).unwrap();
+        // request transparent compression; the release index in particular is ~25x smaller gzipped
+        handle.accept_encoding("").unwrap();
         let mut transfer = handle.transfer();
         transfer
             .write_function(|new_data| {