• Daniel Martí's avatar
    encoding/json: encode struct field names ahead of time · 2d3599e5
    Daniel Martí authored
    Struct field names are static, so we can run HTMLEscape on them when
    building each struct type encoder. Then, when running the struct
    encoder, we can select either the original or the escaped field name to
    write directly.
    
    When the encoder is not escaping HTML, using the original string works
    because neither Go struct field names nor JSON tags allow any characters
    that would need to be escaped, like '"', '\\', or '\n'.
    
    When the encoder is escaping HTML, the only difference is that '<', '>',
    and '&' are allowed via JSON struct field tags, hence why we use
    HTMLEscape to properly escape them.
    
    All of the above lets us encode field names with a simple if/else and
    WriteString calls, which are considerably simpler and faster than
    encoding an arbitrary string.
    
    While at it, also include the quotes and colon in these strings, to
    avoid three WriteByte calls in the loop hot path.
    
    Also added a few tests, to ensure that the behavior in these edge cases
    is not broken. The output of the tests is the same if this optimization
    is reverted.
    
    name           old time/op    new time/op    delta
    CodeEncoder-4    7.12ms ± 0%    6.14ms ± 0%  -13.85%  (p=0.004 n=6+5)
    
    name           old speed      new speed      delta
    CodeEncoder-4   272MB/s ± 0%   316MB/s ± 0%  +16.08%  (p=0.004 n=6+5)
    
    name           old alloc/op   new alloc/op   delta
    CodeEncoder-4    91.9kB ± 0%    93.2kB ± 0%   +1.43%  (p=0.002 n=6+6)
    
    name           old allocs/op  new allocs/op  delta
    CodeEncoder-4      0.00           0.00          ~     (all equal)
    
    Updates #5683.
    
    Change-Id: I6f6a340d0de4670799ce38cf95b2092822d2e3ef
    Reviewed-on: https://go-review.googlesource.com/122460
    Run-TryBot: Daniel Martí <mvdan@mvdan.cc>
    TryBot-Result: Gobot Gobot <gobot@golang.org>
    Reviewed-by: 's avatarBrad Fitzpatrick <bradfitz@golang.org>
    2d3599e5
encode_test.go 23.5 KB