Go - Decoding Data with a Customized Binary Format to Structs

Problem: You want to decode the customized binary format back to structs.

Solution: Use the encoding/binary package to take data from the binary format and reconstruct structs from it.

func   main ()   { 
      var   data   Meter 
      file ,   err   :=   os . Open ( "bindata" ) 
      if   err   !=   nil   { 
          log . Println ( "Cannot  read  file:" ,   err ) 
      } 
      err   =   binary . Read ( file ,   binary . BigEndian ,   & data ) 
      if   err   !=   nil   { 
          log . Println ( "Cannot  read  binary:" ,   err ) 
      } 
}

Start with creating a struct to contain your data. Instead of Write you use Read , passing the reader to it, the byte order, and the struct instance you want to store data. This will read the bytes from the file and write them to the struct.

Here’s how you can do it manually, instead of using a one - liner like Read :

func   main ()   { 
      var   data   Meter   =   Meter {} 
      file ,   err   :=   os . Open ( "data.bin" ) 
      if   err   !=   nil   { 
          log . Println ( "Cannot  read  file:" ,   err ) 
      } 
      buf   :=   make ([] byte ,   24 ) 
      file . Read ( buf ) 
     defer   file . Close () 

      data . Id   =   binary . BigEndian . Uint32 ( buf [: 4 ]) 
      data . Voltage   =   math . Float32frombits ( binary . BigEndian . Uint32 ( buf [ 4 : 8 ])) 
      data . Current   =   math . Float32frombits ( binary . BigEndian . Uint32 ( buf [ 8 : 12 ])) 
      data . Energy   =   binary . BigEndian . Uint32 ( buf [ 12 : 16 ]) 
      data . Timestamp   =   binary . BigEndian . Uint64 ( buf [ 16 :]) 
      fmt . Println ( data ) 
}

As expected, the single function decoding takes longer than with gob, but the performance is fast when you manually decode the data into structs. It’s a bit more tedious to code, but the performance is there if you need it.