mount: improve read throughput by enabling parallel HTTP connections

This addresses issue #7504 where a single weed mount FUSE instance does
not fully utilize node network bandwidth when reading large files.

The root cause is that HTTP GET streaming reads were getting serialized
even with multiple concurrent goroutines, due to:

1. HTTP/2 multiplexing all requests over a single TCP connection
2. The streaming loop using a 64KB intermediate buffer with extra copies

Changes:

http/client: Enable truly parallel connections
- Set ForceAttemptHTTP2: false to disable HTTP/2 multiplexing
- Set MaxConnsPerHost: 0 (unlimited) to allow parallel connections per host
- This lets multiple goroutines use separate TCP connections to the same
  volume server

filer/stream: Add direct-to-buffer fast path
- For full, uncompressed, unencrypted chunks, use RetriedFetchChunkData
  to read directly into the destination buffer
- This skips the 64KB staged streaming loop and avoids an extra memory copy
- Falls back to streaming path on partial fill or error

These changes should improve bandwidth utilization when reading large files
through a single mount instance.

Ref: #7504

weed/filer/stream.go

@@ -374,6 +374,24 @@ func (c *ChunkStreamReader) fetchChunkToBuffer(chunkView *ChunkView) error {
 		glog.V(1).Infof("operation LookupFileId %s failed, err: %v", chunkView.FileId, err)
 		return err
 	}
+
+	// Fast path: for full, plain chunks, read directly into a single buffer to avoid
+	// the streaming loop (which stages 64KB at a time and adds an extra copy).
+	if chunkView.CipherKey == nil && !chunkView.IsGzipped && chunkView.IsFullChunk() {
+		buf := make([]byte, chunkView.ViewSize)
+		n, fetchErr := util_http.RetriedFetchChunkData(context.Background(), buf, urlStrings, nil, false, true, chunkView.OffsetInChunk, chunkView.FileId)
+		if fetchErr == nil && n == len(buf) {
+			c.buffer = buf
+			c.bufferOffset = chunkView.ViewOffset
+			c.chunk = chunkView.FileId
+			return nil
+		}
+		// Fall back to the streaming path on partial fill or error
+		if fetchErr != nil {
+			glog.V(1).Infof("read %s direct failed, err: %v, falling back to stream", chunkView.FileId, fetchErr)
+		}
+	}
+
 	var buffer bytes.Buffer
 	var shouldRetry bool
 	jwt := JwtForVolumeServer(chunkView.FileId)

weed/util/http/client/http_client.go

@@ -130,7 +130,10 @@ func NewHttpClient(clientName ClientName, opts ...HttpClientOpt) (*HTTPClient, e
 	httpClient.Transport = &http.Transport{
 		MaxIdleConns:        1024,
 		MaxIdleConnsPerHost: 1024,
-		TLSClientConfig:     tlsConfig,
+		// Allow truly parallel per-host connections and avoid HTTP/2 multiplexing
+		MaxConnsPerHost:   0,     // unlimited
+		ForceAttemptHTTP2: false, // disable HTTP/2 to avoid implicit single-connection multiplexing
+		TLSClientConfig:   tlsConfig,
 	}
 	httpClient.Client = &http.Client{
 		Transport: httpClient.Transport,