feat: Update client capability flags

Adjust client capability flags based on server support.
Add a new field to manage explicitly disabled flags.

- client/auth.go: Improve logic for adjusting client capability flags
- client/conn.go: Add field to manage explicitly disabled flags

Author: masahide

client/auth.go

@@ -211,15 +211,8 @@ func (c *Conn) writeAuthHandshake() error {
 	capability := mysql.CLIENT_PROTOCOL_41 | mysql.CLIENT_SECURE_CONNECTION |
 		mysql.CLIENT_LONG_PASSWORD | mysql.CLIENT_TRANSACTIONS | mysql.CLIENT_PLUGIN_AUTH
 	// Adjust client capability flags based on server support
-	// ---- Inherit capabilities that the server has and the user has NOT explicitly denied ----
-	inherit := c.capability & ^c.dcaps             // Server-side capabilities minus explicit denies
-	capability |= inherit & mysql.CLIENT_LONG_FLAG // Existing
-	// ---- Handling of CLIENT_QUERY_ATTRIBUTES ----
-	if c.ccaps&mysql.CLIENT_QUERY_ATTRIBUTES != 0 { // Explicitly ON
-		capability |= mysql.CLIENT_QUERY_ATTRIBUTES
-	} else if inherit&mysql.CLIENT_QUERY_ATTRIBUTES != 0 { // Server has it and no denial
-		capability |= mysql.CLIENT_QUERY_ATTRIBUTES
-	}
+	capability |= c.capability & mysql.CLIENT_LONG_FLAG
+	capability |= c.capability & mysql.CLIENT_QUERY_ATTRIBUTES
 	// Adjust client capability flags on specific client requests
 	// Only flags that would make any sense setting and aren't handled elsewhere
 	// in the library are supported here
@@ -229,6 +222,8 @@ func (c *Conn) writeAuthHandshake() error {
 		c.ccaps&mysql.CLIENT_COMPRESS | c.ccaps&mysql.CLIENT_ZSTD_COMPRESSION_ALGORITHM |
 		c.ccaps&mysql.CLIENT_LOCAL_FILES
 
+	capability &^= c.clientExplicitOffCaps
+
 	// To enable TLS / SSL
 	if c.tlsConfig != nil {
 		capability |= mysql.CLIENT_SSL
@@ -368,7 +363,5 @@ func (c *Conn) writeAuthHandshake() error {
 		data[pos] = 0x03
 	}
 
-	c.capability = capability // update capability to the one we sent
-
 	return c.WritePacket(data)
 }

client/conn.go

@@ -45,7 +45,8 @@ type Conn struct {
 	capability uint32
 	// client-set capabilities only
 	ccaps uint32
-	dcaps uint32 // disabled capabilities
+	// Flags explicitly disabled via SetCapability/UnsetCapability
+	clientExplicitOffCaps uint32
 
 	attributes map[string]string
 
@@ -237,14 +238,14 @@ func (c *Conn) Ping() error {
 
 // SetCapability enables the use of a specific capability
 func (c *Conn) SetCapability(cap uint32) {
-	c.dcaps &^= cap
 	c.ccaps |= cap
+	c.clientExplicitOffCaps &^= cap
 }
 
 // UnsetCapability disables the use of a specific capability
 func (c *Conn) UnsetCapability(cap uint32) {
 	c.ccaps &^= cap
-	c.dcaps |= cap
+	c.clientExplicitOffCaps |= cap
 }
 
 // HasCapability returns true if the connection has the specific capability