network: Adaptive timeout (#7410)

* server can start when no network for local dev

* fixed superfluous response.WriteHeader call" warning

* adaptive based on last write time

* more doc

* refactoring

weed/util/net_timeout.go

@@ -1,13 +1,24 @@
 package util
 
 import (
-	"github.com/seaweedfs/seaweedfs/weed/glog"
 	"net"
 	"time"
 
+	"github.com/seaweedfs/seaweedfs/weed/glog"
+
 	"github.com/seaweedfs/seaweedfs/weed/stats"
 )
 
+const (
+	// minThroughputBytesPerSecond defines the minimum expected throughput (4KB/s)
+	// Used to calculate timeout scaling based on data transferred
+	minThroughputBytesPerSecond = 4000
+	
+	// graceTimeCapMultiplier caps the grace period for slow clients at 3x base timeout
+	// This prevents indefinite connections while allowing time for server-side chunk fetches
+	graceTimeCapMultiplier = 3
+)
+
 // Listener wraps a net.Listener, and gives a place to store the timeout
 // parameters. On Accept, it will wrap the net.Conn with our own Conn for us.
 type Listener struct {
@@ -39,11 +50,28 @@ type Conn struct {
 	isClosed     bool
 	bytesRead    int64
 	bytesWritten int64
+	lastWrite    time.Time
+}
+
+// calculateBytesPerTimeout calculates the expected number of bytes that should
+// be transferred during one timeout period, based on the minimum throughput.
+// Returns at least 1 to prevent division by zero.
+func calculateBytesPerTimeout(timeout time.Duration) int64 {
+	bytesPerTimeout := int64(float64(minThroughputBytesPerSecond) * timeout.Seconds())
+	if bytesPerTimeout <= 0 {
+		return 1 // Prevent division by zero
+	}
+	return bytesPerTimeout
 }
 
 func (c *Conn) Read(b []byte) (count int, e error) {
 	if c.ReadTimeout != 0 {
-		err := c.Conn.SetReadDeadline(time.Now().Add(c.ReadTimeout * time.Duration(c.bytesRead/40000+1)))
+		// Calculate expected bytes per timeout period based on minimum throughput (4KB/s)
+		// Example: with ReadTimeout=30s, bytesPerTimeout = 4000 * 30 = 120KB
+		// After reading 1MB: multiplier = 1,000,000/120,000 + 1 ≈ 9, deadline = 30s * 9 = 270s
+		bytesPerTimeout := calculateBytesPerTimeout(c.ReadTimeout)
+		timeoutMultiplier := time.Duration(c.bytesRead/bytesPerTimeout + 1)
+		err := c.Conn.SetReadDeadline(time.Now().Add(c.ReadTimeout * timeoutMultiplier))
 		if err != nil {
 			return 0, err
 		}
@@ -58,8 +86,42 @@ func (c *Conn) Read(b []byte) (count int, e error) {
 
 func (c *Conn) Write(b []byte) (count int, e error) {
 	if c.WriteTimeout != 0 {
-		// minimum 4KB/s
-		err := c.Conn.SetWriteDeadline(time.Now().Add(c.WriteTimeout * time.Duration(c.bytesWritten/40000+1)))
+		now := time.Now()
+		// Calculate timeout with two components:
+		// 1. Base timeout scaled by cumulative data (minimum throughput of 4KB/s)
+		// 2. Additional grace period if there was a gap since last write (for chunk fetch delays)
+		
+		// Calculate expected bytes per timeout period based on minimum throughput (4KB/s)
+		// Example: with WriteTimeout=30s, bytesPerTimeout = 4000 * 30 = 120KB
+		// After writing 1MB: multiplier = 1,000,000/120,000 + 1 ≈ 9, baseTimeout = 30s * 9 = 270s
+		bytesPerTimeout := calculateBytesPerTimeout(c.WriteTimeout)
+		timeoutMultiplier := time.Duration(c.bytesWritten/bytesPerTimeout + 1)
+		baseTimeout := c.WriteTimeout * timeoutMultiplier
+		
+		// If it's been a while since last write, add grace time for server-side chunk fetches
+		// But cap it to avoid keeping slow clients connected indefinitely
+		// 
+		// The comparison uses unscaled WriteTimeout intentionally: triggers grace when idle time
+		// exceeds base timeout, independent of throughput scaling.
+		if !c.lastWrite.IsZero() {
+			timeSinceLastWrite := now.Sub(c.lastWrite)
+			if timeSinceLastWrite > c.WriteTimeout {
+				// Add grace time capped at graceTimeCapMultiplier * scaled timeout.
+				// This allows total deadline up to 4x scaled timeout for server-side delays.
+				//
+				// Example: WriteTimeout=30s, 1MB written (multiplier≈9), baseTimeout=270s
+				// If 400s gap occurs fetching chunks: graceTime capped at 270s*3=810s
+				// Final deadline: 270s + 810s = 1080s (~18min) to accommodate slow storage
+				// But if only 50s gap: graceTime = 50s, final deadline = 270s + 50s = 320s
+				graceTime := timeSinceLastWrite
+				if graceTime > baseTimeout*graceTimeCapMultiplier {
+					graceTime = baseTimeout * graceTimeCapMultiplier
+				}
+				baseTimeout += graceTime
+			}
+		}
+		
+		err := c.Conn.SetWriteDeadline(now.Add(baseTimeout))
 		if err != nil {
 			return 0, err
 		}
@@ -68,6 +130,7 @@ func (c *Conn) Write(b []byte) (count int, e error) {
 	if e == nil {
 		stats.BytesOut(int64(count))
 		c.bytesWritten += int64(count)
+		c.lastWrite = time.Now()
 	}
 	return
 }