bootstrap: improve error recovery flags to curl

alternative to rust-lang#128459

fixes rust-lang#110178

src/bootstrap/bootstrap.py

@@ -79,6 +79,8 @@ def get(base, url, path, checksums, verbose=False):
                 eprint("removing", temp_path)
             os.unlink(temp_path)
 
+def curl_version():
+    return re.match("^curl ([0-9]+\\.[0-9]+)", run(["curl", "-V"]))[1]
 
 def download(path, url, probably_big, verbose):
     for _ in range(4):
@@ -107,11 +109,15 @@ def _download(path, url, probably_big, verbose, exception):
         # If curl is not present on Win32, we should not sys.exit
         #   but raise `CalledProcessError` or `OSError` instead
         require(["curl", "--version"], exception=platform_is_win32())
-        run(["curl", option,
+        extra_flags = []
+        if curl_version() > 7.70:
+            extra_flags = [ "--retry-all-errors" ]
+        run(["curl", option] + extra_flags + [
             "-L", # Follow redirect.
             "-y", "30", "-Y", "10",    # timeout if speed is < 10 bytes/sec for > 30 seconds
             "--connect-timeout", "30",  # timeout if cannot connect within 30 seconds
             "-o", path,
+            "--continue-at", "-",
             "--retry", "3", "-SRf", url],
             verbose=verbose,
             exception=True, # Will raise RuntimeError on failure

src/bootstrap/src/core/download.rs

@@ -21,6 +21,15 @@ fn try_run(config: &Config, cmd: &mut Command) -> Result<(), ()> {
     config.try_run(cmd)
 }
 
+fn curl_version() -> f32 {
+    let mut curl = Command::new("curl");
+    curl.arg("-V");
+    let Ok(out) = curl.output() else { return 0.0 };
+    let out = out.stdout;
+    let Some(i) = out[5..].iter().position(|&x| x == b' ') else { return 0.0 };
+    std::str::from_utf8(&out[5..i + 5]).unwrap().parse().unwrap_or(0.0)
+}
+
 /// Generic helpers that are useful anywhere in bootstrap.
 impl Config {
     pub fn is_verbose(&self) -> bool {
@@ -219,6 +228,8 @@ impl Config {
             "30", // timeout if cannot connect within 30 seconds
             "-o",
             tempfile.to_str().unwrap(),
+            "--continue-at",
+            "-",
             "--retry",
             "3",
             "-SRf",
@@ -229,6 +240,10 @@ impl Config {
         } else {
             curl.arg("--progress-bar");
         }
+        // --retry-all-errors was added in 7.71.0, don't use it if curl is old.
+        if curl_version() > 7.70 {
+            curl.arg("--retry-all-errors");
+        }
         curl.arg(url);
         if !self.check_run(&mut curl) {
             if self.build.contains("windows-msvc") {