Fix hardcoded http scheme and add panic recovery

Address CodeRabbit review #3512114811:

1. **Major: Fix hardcoded http:// scheme in Location URLs**
   - Location URLs always used http:// regardless of client connection
   - HTTPS clients got http:// URLs (incorrect)
   - Fixed: Detect scheme from request
   - Check X-Forwarded-Proto header (for proxies) first
   - Check r.TLS != nil for direct HTTPS
   - Fallback to http for plain connections
   - Applied to all 4 CompleteMultipartUploadResult locations

2. **Major: Add panic recovery to discovery goroutine**
   - Long-running background goroutine could crash entire process
   - Panic in refreshFilerList would terminate program
   - Fixed: Add defer recover() with error logging
   - Goroutine failures now logged, not fatal

3. **Note: Close() idempotency already implemented**
   - Review flagged as duplicate issue
   - Already fixed in commit 3d7a65c7e
   - sync.Once (closeDiscoveryOnce) prevents double-close panic
   - Safe to call Close() multiple times

Changes:
- filer_multipart.go:
  - Add getRequestScheme() helper function
  - Update all 4 Location URLs to use dynamic scheme
  - Format: scheme://host/bucket/key (was: http://...)

- filer_client.go:
  - Add panic recovery to discoverFilers()
  - Log panics instead of crashing

Benefits:
- Correct scheme (https/http) in Location URLs
- Works behind proxies (X-Forwarded-Proto)
- No process crashes from discovery failures
- Production-hardened background goroutine
- Proper AWS S3 API compliance

weed/s3api/filer_multipart.go

@@ -43,6 +43,20 @@ type InitiateMultipartUploadResult struct {
 	s3.CreateMultipartUploadOutput
 }
 
+// getRequestScheme determines the URL scheme (http or https) from the request
+// Checks X-Forwarded-Proto header first (for proxies), then TLS state
+func getRequestScheme(r *http.Request) string {
+	// Check X-Forwarded-Proto header for proxied requests
+	if proto := r.Header.Get("X-Forwarded-Proto"); proto != "" {
+		return proto
+	}
+	// Check if connection is TLS
+	if r.TLS != nil {
+		return "https"
+	}
+	return "http"
+}
+
 func (s3a *S3ApiServer) createMultipartUpload(r *http.Request, input *s3.CreateMultipartUploadInput) (output *InitiateMultipartUploadResult, code s3err.ErrorCode) {
 
 	glog.V(2).Infof("createMultipartUpload input %v", input)
@@ -185,9 +199,9 @@ func (s3a *S3ApiServer) completeMultipartUpload(r *http.Request, input *s3.Compl
 		if entry, _ := s3a.getEntry(dirName, entryName); entry != nil && entry.Extended != nil {
 			if uploadId, ok := entry.Extended[s3_constants.SeaweedFSUploadId]; ok && *input.UploadId == string(uploadId) {
 				// Location uses the S3 endpoint that the client connected to
-				// Format: http://s3-endpoint/bucket/object (following AWS S3 API)
+				// Format: scheme://s3-endpoint/bucket/object (following AWS S3 API)
 				return &CompleteMultipartUploadResult{
-                                        Location: aws.String(fmt.Sprintf("http://%s/%s/%s", r.Host, url.PathEscape(*input.Bucket), urlPathEscape(*input.Key))),
+                                        Location: aws.String(fmt.Sprintf("%s://%s/%s/%s", getRequestScheme(r), r.Host, url.PathEscape(*input.Bucket), urlPathEscape(*input.Key))),
 					Bucket:   input.Bucket,
 					ETag:     aws.String("\"" + filer.ETagChunks(entry.GetChunks()) + "\""),
 					Key:      objectKey(input.Key),
@@ -404,7 +418,7 @@ func (s3a *S3ApiServer) completeMultipartUpload(r *http.Request, input *s3.Compl
 		// The latest version information is tracked in the .versions directory metadata
 
 		output = &CompleteMultipartUploadResult{
-			Location:  aws.String(fmt.Sprintf("http://%s/%s/%s", r.Host, url.PathEscape(*input.Bucket), urlPathEscape(*input.Key))),
+			Location:  aws.String(fmt.Sprintf("%s://%s/%s/%s", getRequestScheme(r), r.Host, url.PathEscape(*input.Bucket), urlPathEscape(*input.Key))),
 			Bucket:    input.Bucket,
 			ETag:      aws.String("\"" + filer.ETagChunks(finalParts) + "\""),
 			Key:       objectKey(input.Key),
@@ -457,7 +471,7 @@ func (s3a *S3ApiServer) completeMultipartUpload(r *http.Request, input *s3.Compl
 
 		// Note: Suspended versioning should NOT return VersionId field according to AWS S3 spec
 		output = &CompleteMultipartUploadResult{
-			Location: aws.String(fmt.Sprintf("http://%s/%s/%s", r.Host, url.PathEscape(*input.Bucket), urlPathEscape(*input.Key))),
+			Location: aws.String(fmt.Sprintf("%s://%s/%s/%s", getRequestScheme(r), r.Host, url.PathEscape(*input.Bucket), urlPathEscape(*input.Key))),
 			Bucket:   input.Bucket,
 			ETag:     aws.String("\"" + filer.ETagChunks(finalParts) + "\""),
 			Key:      objectKey(input.Key),
@@ -514,7 +528,7 @@ func (s3a *S3ApiServer) completeMultipartUpload(r *http.Request, input *s3.Compl
 
 		// For non-versioned buckets, return response without VersionId
 		output = &CompleteMultipartUploadResult{
-			Location: aws.String(fmt.Sprintf("http://%s/%s/%s", r.Host, url.PathEscape(*input.Bucket), urlPathEscape(*input.Key))),
+			Location: aws.String(fmt.Sprintf("%s://%s/%s/%s", getRequestScheme(r), r.Host, url.PathEscape(*input.Bucket), urlPathEscape(*input.Key))),
 			Bucket:   input.Bucket,
 			ETag:     aws.String("\"" + filer.ETagChunks(finalParts) + "\""),
 			Key:      objectKey(input.Key),

weed/wdclient/filer_client.go

@@ -218,6 +218,12 @@ func (fc *FilerClient) Close() {
 // discoverFilers periodically queries the master to discover filers in the same group
 // and updates the filer list. This runs in a background goroutine.
 func (fc *FilerClient) discoverFilers() {
+	defer func() {
+		if r := recover(); r != nil {
+			glog.Errorf("FilerClient: panic in filer discovery goroutine for group '%s': %v", fc.filerGroup, r)
+		}
+	}()
+	
 	// Do an initial discovery
 	fc.refreshFilerList()