Re: [go-nuts] Having difficulty converting []byte to float
After talking with a coworker it seems that "grep" returns a \n after its
output. That was the bugger keeping my initial efforts from working. Grep
was meant for "human consumption". I will need to look into buffio and
scanner as Tamas suggested.
On Friday, May 18, 2018 at 11:06:46 AM UTC-4, John Fox wrote:
>
> Drilling down farther for the heck of it
>
> os/exec/exec.go
> func (c *Cmd) Output() ([]byte, error) { if c.Stdout != nil {
>
> return nil, errors.New("exec: Stdout already set")
>
> }
>
> var stdout bytes.Buffer
>
> c.Stdout = &stdout
>
> captureErr := c.Stderr == nil
>
> if captureErr {
>
> c.Stderr = &prefixSuffixSaver{N: 32 << 10}
>
> }
>
> err := c.Run()
>
> if err != nil && captureErr {
>
> if ee, ok := err.(*ExitError); ok {
>
> ee.Stderr = c.Stderr.(*prefixSuffixSaver).Bytes()
>
> }
>
> }
>
> return stdout.Bytes(), err
>
> }
>
>
> stdout.Bytes() = bytes.Buffer.Bytes()
> bytes/buffer.go
>
> // Bytes returns a slice of length b.Len() holding the unread portion of the
> buffer.// The slice is valid for use only until the next buffer modification
> (that is,// only until the next call to a method like Read, Write, Reset, or
> Truncate).// The slice aliases the buffer content at least until the next
> buffer modification,// so immediate changes to the slice will affect the
> result of future reads.
> func (b *Buffer) Bytes() []byte { return b.buf[b.off:] }
>
> // A Buffer is a variable-sized buffer of bytes with Read and Write
> methods.// The zero value for Buffer is an empty buffer ready to use.
> type Buffer struct {
> buf []byte // contents are the bytes buf[off : len(buf)]
> off int // read at &buf[off], write at &buf[len(buf)]
> bootstrap [64]byte // memory to hold first slice; helps small buffers
> avoid allocation.
> lastRead readOp // last read operation, so that Unread* can work
> correctly.
> // FIXME: it would be advisable to align Buffer to cachelines to avoid
> false
> // sharing.
> }
>
> I am still not sure where the "10" or '\n' came from, but I know enough to
> get the program working. I am really enjoying getting to learn this language
> and excited for all that I can get it to do, even if it comes with the
> expected frustrations and head against wall banging.
>
>
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Re: [go-nuts] Having difficulty converting []byte to float
After talking with a coworker it seems that "grep" returns a \n after its
output. That was the bugger keeping my initial efforts from working.
On Friday, May 18, 2018 at 11:06:46 AM UTC-4, John Fox wrote:
>
> Drilling down farther for the heck of it
>
> os/exec/exec.go
> func (c *Cmd) Output() ([]byte, error) { if c.Stdout != nil {
>
> return nil, errors.New("exec: Stdout already set")
>
> }
>
> var stdout bytes.Buffer
>
> c.Stdout = &stdout
>
> captureErr := c.Stderr == nil
>
> if captureErr {
>
> c.Stderr = &prefixSuffixSaver{N: 32 << 10}
>
> }
>
> err := c.Run()
>
> if err != nil && captureErr {
>
> if ee, ok := err.(*ExitError); ok {
>
> ee.Stderr = c.Stderr.(*prefixSuffixSaver).Bytes()
>
> }
>
> }
>
> return stdout.Bytes(), err
>
> }
>
>
> stdout.Bytes() = bytes.Buffer.Bytes()
> bytes/buffer.go
>
> // Bytes returns a slice of length b.Len() holding the unread portion of the
> buffer.// The slice is valid for use only until the next buffer modification
> (that is,// only until the next call to a method like Read, Write, Reset, or
> Truncate).// The slice aliases the buffer content at least until the next
> buffer modification,// so immediate changes to the slice will affect the
> result of future reads.
> func (b *Buffer) Bytes() []byte { return b.buf[b.off:] }
>
> // A Buffer is a variable-sized buffer of bytes with Read and Write
> methods.// The zero value for Buffer is an empty buffer ready to use.
> type Buffer struct {
> buf []byte // contents are the bytes buf[off : len(buf)]
> off int // read at &buf[off], write at &buf[len(buf)]
> bootstrap [64]byte // memory to hold first slice; helps small buffers
> avoid allocation.
> lastRead readOp // last read operation, so that Unread* can work
> correctly.
> // FIXME: it would be advisable to align Buffer to cachelines to avoid
> false
> // sharing.
> }
>
> I am still not sure where the "10" or '\n' came from, but I know enough to
> get the program working. I am really enjoying getting to learn this language
> and excited for all that I can get it to do, even if it comes with the
> expected frustrations and head against wall banging.
>
>
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Re: [go-nuts] Having difficulty converting []byte to float
Drilling down farther for the heck of it
os/exec/exec.go
func (c *Cmd) Output() ([]byte, error) { if c.Stdout != nil {
return nil, errors.New("exec: Stdout already set")
}
var stdout bytes.Buffer
c.Stdout = &stdout
captureErr := c.Stderr == nil
if captureErr {
c.Stderr = &prefixSuffixSaver{N: 32 << 10}
}
err := c.Run()
if err != nil && captureErr {
if ee, ok := err.(*ExitError); ok {
ee.Stderr = c.Stderr.(*prefixSuffixSaver).Bytes()
}
}
return stdout.Bytes(), err
}
stdout.Bytes() = bytes.Buffer.Bytes()
bytes/buffer.go
// Bytes returns a slice of length b.Len() holding the unread portion of the
buffer.// The slice is valid for use only until the next buffer modification
(that is,// only until the next call to a method like Read, Write, Reset, or
Truncate).// The slice aliases the buffer content at least until the next
buffer modification,// so immediate changes to the slice will affect the result
of future reads.
func (b *Buffer) Bytes() []byte { return b.buf[b.off:] }
// A Buffer is a variable-sized buffer of bytes with Read and Write methods.//
The zero value for Buffer is an empty buffer ready to use.
type Buffer struct {
buf []byte // contents are the bytes buf[off : len(buf)]
off int // read at &buf[off], write at &buf[len(buf)]
bootstrap [64]byte // memory to hold first slice; helps small buffers
avoid allocation.
lastRead readOp // last read operation, so that Unread* can work
correctly.
// FIXME: it would be advisable to align Buffer to cachelines to avoid
false
// sharing.
}
I am still not sure where the "10" or '\n' came from, but I know enough to get
the program working. I am really enjoying getting to learn this language and
excited for all that I can get it to do, even if it comes with the expected
frustrations and head against wall banging.
--
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Re: [go-nuts] Having difficulty converting []byte to float
Thank you both for the quick responses. I looked in to https://github.com/lovoo/ipmi_exporter yesterday and saw the TrimSpace used as well, but I am still not sure what is adding the '\n' to the commands's Output(). Tamas, I will have to look into thebuff IO, even if I am not using this for production use (home lab), I'd still like to know what you mean behind it (though I think I have a basic understanding). Jesse, what you state matches up with what I was reading in the packages. Thank you for helping to clarify and explain it. I should have recalled how Todd McLeod kept referring to the ASCII wiki/table to see what the bytes referenced. Thank you two again! I should be able to get it working today and I will update my github with the working, custom Prometheus metric exporter for FreeNAS. -- You received this message because you are subscribed to the Google Groups "golang-nuts" group. To unsubscribe from this group and stop receiving emails from it, send an email to golang-nuts+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
Re: [go-nuts] Having difficulty converting []byte to float
On Fri, May 18, 2018 at 12:26 PM, wrote: > Hello all. I am creating a custom exporter for FreeNAS > https://github.com/Maelos/freenas_exporter and am stuck on the conversion of > the string of bytes provided by the commands output to a float. Here is my > code, what I have tried, and my results: > > What I have tried and results (commented so you can try and see each > https://play.golang.org/p/sevfk7Nt2w4 > Attempt 1 = binary.LittleEndian.Uint64([]bytes) to math.Float64frombits You've got a 2 byte slice, but you need 8 bytes. You're getting an 'index out of range' because you need a slice of 8 bytes. > Attempt 3 = Bytes to bytes.Reader to binary.Read(slice of bytes, > binary.LittleEndian, floatVariableToFill) to error check You've got 2 bytes in your bytes.Reader and you're trying to read 8 bytes from it, this is why you get an error. A float64 is 8 bytes so you need at least 8 bytes in your bytes.Reader. > Attempt 2 = bytes to string, String to float (strconv) You are parsing the string "2\n" which isn't a string representation of a float. So that's not going to work. The fact that these bytes are ascii characters means that your other attempts don't make a lot of sense. The ascii value for the character '2' is 50 so even if your other attempts worked you'd get a float with 50 instead of the 2 you're expecting. If you do f, err := strconv.ParseFloat(strings.TrimSpace(string(text)), 64) you'll trim off the invalid '\n' and you'll just have a '2' that will parse correctly. -- You received this message because you are subscribed to the Google Groups "golang-nuts" group. To unsubscribe from this group and stop receiving emails from it, send an email to golang-nuts+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
[go-nuts] Having difficulty converting []byte to float
The input is string, so use strconv.ParseFloat, or ParseInt (will there be non-integer number of cpus?) Just trim the LF with strings.TrimSpace. For production use, leave out the grep and bash, read the output lines directly with bufio.Scanner. -- You received this message because you are subscribed to the Google Groups "golang-nuts" group. To unsubscribe from this group and stop receiving emails from it, send an email to golang-nuts+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
[go-nuts] Having difficulty converting []byte to float
Hello all. I am creating a custom exporter for
FreeNAS https://github.com/Maelos/freenas_exporter and am stuck on the
conversion of the string of bytes provided by the commands output to a
float. Here is my code, what I have tried, and my results:
What I have tried and results (commented so you can try and see each
https://play.golang.org/p/sevfk7Nt2w4
Attempt 1 = binary.LittleEndian.Uint64([]bytes) to math.Float64frombits
Attempt 2 = bytes to string, String to float (strconv)
Attempt 3 = Bytes to bytes.Reader to binary.Read(slice of bytes,
binary.LittleEndian, floatVariableToFill) to error check
Please let me know what more I can provide. I will keep hacking away at it
tomorrow, but hoping I can get this done soon. Full go play write up below:
package main
import (
//You may need to edit these in or out depending upon the attempt
"bytes"
"encoding/binary"
"fmt"
//"strconv"
//"math"
)
func main() {
// I have been able to test this part and I do get a return of "[50 10]"
which is correct (converts string "2" for 2 CPUs). The exact statement may
be a bit different.
// I am running the script on the latest FreeNAS whic his built from
11.1STABLE FreeBSD. I have Go installed and am building the files on the
shell
//numCPUCmd := exec.Command("bash", "-c","/usr/local/bin/ipmitool -I
lanplus -H ipmiAddress -U ipmiUser -f /root/ipmi_password sdr elist all |
grep -c -i \"cpu.*temp\"")
//numCPUBytes, _ := numCPUCmd.Output() //returns a slice of bytes and an
error
// ATTEMPT 1
var flty float64
sob := []byte{50, 10}
fmt.Printf("\n%T %v\n\n", sob, sob)
buf := bytes.NewReader(sob)
err := binary.Read(buf, binary.LittleEndian, &flty)
if err != nil {
fmt.Println("binary.Read failed:", err)
}
fmt.Println(flty)
/*Result
[]uint8 [50 10]
binary.Read failed: unexpected EOF
0
*/
//ATTEMPT 2
/*
var f float64
text := []byte{50, 10} // A decimal value represented as Latin-1 text
f, err := strconv.ParseFloat(string(text), 64)
if err != nil {
panic(err)
}
fmt.Println(f)
*/
/*Result
panic: strconv.ParseFloat: parsing "2\n": invalid syntax
goroutine 1 [running]:
main.main()
/tmp/sandbox657430918/main.go:44 +0x160
*/
//ATTEMPT3
/*
sob := []byte{50, 10}
bits := binary.LittleEndian.Uint64(sob)
fmt.Printf("\n\n%T %v\n\n", bits, bits)
flty := math.Float64frombits(bits)
fmt.Printf("\n\n%T %v\n\n", flty, flty)
inty := int(flty)
fmt.Printf("\n\n%T %v\n\n", inty, inty)
*/
/* Result
panic: runtime error: index out of range
goroutine 1 [running]:
encoding/binary.binary.littleEndian.Uint64(...)
/usr/local/go/src/encoding/binary/binary.go:76
main.main()
/tmp/sandbox742704811/main.go:62 +0x20
*/
}
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