Add golang.py for Go release downloads

Mirror Go release tarballs and installers from go.dev. The script uses
the official go.dev/dl/?mode=json&include=all listing as the index and
downloads files from dl.google.com/go via curl with atomic .tmp + rename.

Compared to the previously common rsync upstream rsync.mirrors.ustc.edu.cn::golang/
this is a direct from-origin sync that does not depend on another mirror.

Used by NJU mirror's golang job (~646G, 8118 files).

Author: yaoge123

golang.py

@@ -0,0 +1,125 @@
+#!/usr/bin/env python3
+"""Golang mirror sync script.
+
+Fetches version list from go.dev API and downloads all files from dl.google.com/go/.
+Cleans up stale files that are no longer in the version list.
+"""
+import json
+import os
+import sys
+import subprocess
+import hashlib
+
+WORKDIR = os.environ.get("TUNASYNC_WORKING_DIR", "/data/mirrors/golang")
+BASE_URL = "https://dl.google.com/go/"
+API_URL = "https://go.dev/dl/?mode=json&include=all"
+
+
+def fetch_versions():
+    """Fetch version list from go.dev API."""
+    print("Fetching version list from go.dev...")
+    try:
+        result = subprocess.run(
+            ["curl", "-s", "-m", "60", API_URL],
+            capture_output=True, text=True, timeout=90
+        )
+        data = json.loads(result.stdout)
+    except Exception as e:
+        print(f"Error: failed to fetch version list: {e}")
+        sys.exit(1)
+
+    files = {}
+    for v in data:
+        for f in v.get("files", []):
+            filename = f["filename"]
+            sha256 = f.get("sha256", "")
+            files[filename] = {
+                "url": BASE_URL + filename,
+                "sha256": sha256,
+            }
+    return files
+
+
+def download_file(filename, url, filepath):
+    """Download a file if not present or size mismatch."""
+    tmpfile = filepath + ".tmp"
+    try:
+        result = subprocess.run(
+            ["curl", "-s", "-L", "-m", "600", "-o", tmpfile, url],
+            timeout=630
+        )
+        if result.returncode == 0:
+            os.rename(tmpfile, filepath)
+            return True
+        else:
+            if os.path.exists(tmpfile):
+                os.remove(tmpfile)
+            return False
+    except Exception:
+        if os.path.exists(tmpfile):
+            os.remove(tmpfile)
+        return False
+
+
+def get_remote_size(url):
+    """Get remote file size via HEAD request."""
+    try:
+        result = subprocess.run(
+            ["curl", "-sI", "-m", "10", url],
+            capture_output=True, text=True, timeout=15
+        )
+        for line in result.stdout.splitlines():
+            if line.lower().startswith("content-length:"):
+                return int(line.split(":", 1)[1].strip())
+    except Exception:
+        pass
+    return None
+
+
+def main():
+    os.makedirs(WORKDIR, exist_ok=True)
+    os.chdir(WORKDIR)
+
+    expected = fetch_versions()
+    print(f"Total files to sync: {len(expected)}")
+
+    downloaded = 0
+    skipped = 0
+    errors = 0
+
+    for filename, info in expected.items():
+        filepath = os.path.join(WORKDIR, filename)
+        url = info["url"]
+
+        # Check if file exists and has correct size
+        if os.path.isfile(filepath):
+            remote_size = get_remote_size(url)
+            if remote_size is not None:
+                local_size = os.path.getsize(filepath)
+                if local_size == remote_size:
+                    skipped += 1
+                    continue
+
+        print(f"Downloading {filename}...")
+        if download_file(filename, url, filepath):
+            downloaded += 1
+        else:
+            errors += 1
+            print(f"ERROR: failed to download {filename}")
+
+    print(f"Done. Downloaded: {downloaded}, Skipped: {skipped}, Errors: {errors}")
+
+    # Clean up stale files
+    print("Cleaning up stale files...")
+    stale = 0
+    for fname in os.listdir(WORKDIR):
+        fpath = os.path.join(WORKDIR, fname)
+        if os.path.isfile(fpath) and fname not in expected:
+            print(f"Removing stale file: {fname}")
+            os.remove(fpath)
+            stale += 1
+    print(f"Removed {stale} stale files.")
+
+
+if __name__ == "__main__":
+    main()