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Write long characteristic #83

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Write long characteristic #83

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353a574
added WriteLongCharacteristic and fixed bugs in PrepareWrite and Exec…
Feb 10, 2021
344ea03
Merge branch 'master' into write-long-characteristic
Jul 12, 2021
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3 changes: 3 additions & 0 deletions client.go
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Original file line number Diff line number Diff line change
Expand Up @@ -40,6 +40,9 @@ type Client interface {
// WriteCharacteristic writes a characteristic value to a server. [Vol 3, Part G, 4.9.3]
WriteCharacteristic(c *Characteristic, value []byte, noRsp bool) error

// WriteLongCharacteristic writes a characteristic value that is longer than the MTU to a server. [Vol 3, Part F, 3.4.6]
WriteLongCharacteristic(c *Characteristic, value []byte) error

// ReadDescriptor reads a characteristic descriptor from a server. [Vol 3, Part G, 4.12.1]
ReadDescriptor(d *Descriptor) ([]byte, error)

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5 changes: 5 additions & 0 deletions darwin/client.go
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Expand Up @@ -256,6 +256,11 @@ func (cln *Client) WriteCharacteristic(c *ble.Characteristic, b []byte, noRsp bo
return nil
}

// WriteLongCharacteristic writes a characteristic value that is longer than the MTU to a server. [Vol 3, Part F, 3.4.6]
func (cln *Client) WriteLongCharacteristic(c *ble.Characteristic, b []byte) error {
panic("not implemented")
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Rather than panic, this should return an error. Forcing a panic upon a calling program is bit jarring for the caller to deal with.

}

// ReadDescriptor reads a characteristic descriptor from a server. [Vol 3, Part G, 4.12.1]
func (cln *Client) ReadDescriptor(d *ble.Descriptor) ([]byte, error) {
cbdsc, err := cln.pc.findCbDsc(d)
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3 changes: 2 additions & 1 deletion linux/att/client.go
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Expand Up @@ -422,6 +422,7 @@ func (c *Client) PrepareWrite(handle uint16, offset uint16, value []byte) (uint1
req.SetAttributeOpcode()
req.SetAttributeHandle(handle)
req.SetValueOffset(offset)
req.SetPartAttributeValue(value)

b, err := c.sendReq(req)
if err != nil {
Expand Down Expand Up @@ -452,7 +453,7 @@ func (c *Client) ExecuteWrite(flags uint8) error {
txBuf := <-c.chTxBuf
defer func() { c.chTxBuf <- txBuf }()

req := ExecuteWriteRequest(txBuf[:1])
req := ExecuteWriteRequest(txBuf[:2])
req.SetAttributeOpcode()
req.SetFlags(flags)

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27 changes: 27 additions & 0 deletions linux/gatt/client.go
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Expand Up @@ -252,6 +252,26 @@ func (p *Client) WriteCharacteristic(c *ble.Characteristic, v []byte, noRsp bool
return p.ac.Write(c.ValueHandle, v)
}

// WriteLongCharacteristic writes a characteristic value that is longer than the MTU to a server. [Vol 3, Part F, 3.4.6]
func (p *Client) WriteLongCharacteristic(c *ble.Characteristic, v []byte) error {
p.Lock()
defer p.Unlock()

offset := 0
prepareWriteLength := 0

for offset < len(v) {
prepareWriteLength = MinInt( len(v) - offset, p.conn.TxMTU()-5 )
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Adding a function here adds a bit of complexity when an if would suffice. Since MinInt isn't used anywhere else, I don't see that it adds much value at this time. Additionally, I'd have to go review the spec to see recall why 5 is subtracted from the MTU here. I suspect it is overhead related. Please add a const which clarifies the reason for the subtraction.

Suggestion:

maxLength := p.conn.TxMTU() - 5

for offset < len(v) {
    length := len(v) - offset
    if length > maxLength {
        length = maxLength
    }

    value := v[offset:offset+length]
    ...

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You could also avoid having to track offset just by advancing v:

maxLength := p.conn.TxMTU() - 5
for len(v) > 0 {
    length := len(v)
    if length > maxLength {
        length = maxLength
    }
    ...
    v = v[length:]
}

value := v[offset:offset+prepareWriteLength]
if _, _, _, err := p.ac.PrepareWrite(c.ValueHandle, uint16(offset), value ); err != nil {
return err
}
offset += prepareWriteLength
}

return p.ac.ExecuteWrite(0x01) // flags: 0x00=cancel all, 0x01=write all
}

// ReadDescriptor reads a characteristic descriptor from a server. [Vol 3, Part G, 4.12.1]
func (p *Client) ReadDescriptor(d *ble.Descriptor) ([]byte, error) {
p.Lock()
Expand Down Expand Up @@ -401,3 +421,10 @@ type sub struct {
nHandler ble.NotificationHandler
iHandler ble.NotificationHandler
}

func MinInt( a int, b int) int {
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If you are ok with my suggestion above, this function can be removed.

if a < b {
return a
}
return b
}