Package easyjson provides a fast and easy way to marshal/unmarshal Go structs
to/from JSON without the use of reflection. In performance tests, easyjson
outperforms the standard encoding/json
package by a factor of 4-5x, and other
JSON encoding packages by a factor of 2-3x.
easyjson aims to keep generated Go code simple enough so that it can be easily
optimized or fixed. Another goal is to provide users with the ability to
customize the generated code by providing options not available with the
standard encoding/json
package, such as generating "snake_case" names or
enabling omitempty
behavior by default.
Usage
# install
go get -u github.com/mailru/easyjson/...
# run
easyjson -all <file>.go
The above will generate <file>_easyjson.go
containing the appropriate marshaler and
unmarshaler funcs for all structs contained in <file>.go
.
Please note that easyjson requires a full Go build environment and the GOPATH
environment variable to be set. This is because easyjson code generation
invokes go run
on a temporary file (an approach to code generation borrowed
from ffjson).
Options
Usage of easyjson:
-all
generate marshaler/unmarshalers for all structs in a file
-build_tags string
build tags to add to generated file
-leave_temps
do not delete temporary files
-no_std_marshalers
don't generate MarshalJSON/UnmarshalJSON funcs
-noformat
do not run 'gofmt -w' on output file
-omit_empty
omit empty fields by default
-output_filename string
specify the filename of the output
-pkg
process the whole package instead of just the given file
-snake_case
use snake_case names instead of CamelCase by default
-lower_camel_case
use lowerCamelCase instead of CamelCase by default
-stubs
only generate stubs for marshaler/unmarshaler funcs
Using -all
will generate marshalers/unmarshalers for all Go structs in the
file. If -all
is not provided, then only those structs whose preceding
comment starts with easyjson:json
will have marshalers/unmarshalers
generated. For example:
//easyjson:json
type A struct {}
Additional option notes:
-
-snake_case
tells easyjson to generate snake_case field names by default (unless overridden by a field tag). The CamelCase to snake_case conversion algorithm should work in most cases (ie, HTTPVersion will be converted to "http_version"). -
-build_tags
will add the specified build tags to generated Go sources.
Generated Marshaler/Unmarshaler Funcs
For Go struct types, easyjson generates the funcs MarshalEasyJSON
/
UnmarshalEasyJSON
for marshaling/unmarshaling JSON. In turn, these satisify
the easyjson.Marshaler
and easyjson.Unmarshaler
interfaces and when used in
conjunction with easyjson.Marshal
/ easyjson.Unmarshal
avoid unnecessary
reflection / type assertions during marshaling/unmarshaling to/from JSON for Go
structs.
easyjson also generates MarshalJSON
and UnmarshalJSON
funcs for Go struct
types compatible with the standard json.Marshaler
and json.Unmarshaler
interfaces. Please be aware that using the standard json.Marshal
/
json.Unmarshal
for marshaling/unmarshaling will incur a significant
performance penalty when compared to using easyjson.Marshal
/
easyjson.Unmarshal
.
Additionally, easyjson exposes utility funcs that use the MarshalEasyJSON
and
UnmarshalEasyJSON
for marshaling/unmarshaling to and from standard readers
and writers. For example, easyjson provides easyjson.MarshalToHTTPResponseWriter
which marshals to the standard http.ResponseWriter
. Please see the GoDoc
listing for the full listing of
utility funcs that are available.
Controlling easyjson Marshaling and Unmarshaling Behavior
Go types can provide their own MarshalEasyJSON
and UnmarshalEasyJSON
funcs
that satisify the easyjson.Marshaler
/ easyjson.Unmarshaler
interfaces.
These will be used by easyjson.Marshal
and easyjson.Unmarshal
when defined
for a Go type.
Go types can also satisify the easyjson.Optional
interface, which allows the
type to define its own omitempty
logic.
Type Wrappers
easyjson provides additional type wrappers defined in the easyjson/opt
package. These wrap the standard Go primitives and in turn satisify the
easyjson interfaces.
The easyjson/opt
type wrappers are useful when needing to distinguish between
a missing value and/or when needing to specifying a default value. Type
wrappers allow easyjson to avoid additional pointers and heap allocations and
can significantly increase performance when used properly.
Memory Pooling
easyjson uses a buffer pool that allocates data in increasing chunks from 128
to 32768 bytes. Chunks of 512 bytes and larger will be reused with the help of
sync.Pool
. The maximum size of a chunk is bounded to reduce redundant memory
allocation and to allow larger reusable buffers.
easyjson's custom allocation buffer pool is defined in the easyjson/buffer
package, and the default behavior pool behavior can be modified (if necessary)
through a call to buffer.Init()
prior to any marshaling or unmarshaling.
Please see the GoDoc listing
for more information.
Issues, Notes, and Limitations
-
easyjson is still early in its development. As such, there are likely to be bugs and missing features when compared to
encoding/json
. In the case of a missing feature or bug, please create a GitHub issue. Pull requests are welcome! -
Unlike
encoding/json
, object keys are case-sensitive. Case-insensitive matching is not currently provided due to the significant performance hit when doing case-insensitive key matching. In the future, case-insensitive object key matching may be provided via an option to the generator. -
easyjson makes use of
unsafe
, which simplifies the code and provides significant performance benefits by allowing no-copy conversion from[]byte
tostring
. That said,unsafe
is used only when unmarshaling and parsing JSON, and anyunsafe
operations / memory allocations done will be safely deallocated by easyjson. Set the build tageasyjson_nounsafe
to compile it withoutunsafe
. -
easyjson is compatible with Google App Engine. The
appengine
build tag (set by App Engine's environment) will automatically disable the use ofunsafe
, which is not allowed in App Engine's Standard Environment. Note that the use with App Engine is still experimental. -
Floats are formatted using the default precision from Go's
strconv
package. As such, easyjson will not correctly handle high precision floats when marshaling/unmarshaling JSON. Note, however, that there are very few/limited uses where this behavior is not sufficient for general use. That said, a different package may be needed if precise marshaling/unmarshaling of high precision floats to/from JSON is required. -
While unmarshaling, the JSON parser does the minimal amount of work needed to skip over unmatching parens, and as such full validation is not done for the entire JSON value being unmarshaled/parsed.
-
Currently there is no true streaming support for encoding/decoding as typically for many uses/protocols the final, marshaled length of the JSON needs to be known prior to sending the data. Currently this is not possible with easyjson's architecture.
Benchmarks
Most benchmarks were done using the example 13kB example JSON (9k after eliminating whitespace). This example is similar to real-world data, is well-structured, and contains a healthy variety of different types, making it ideal for JSON serialization benchmarks.
Note:
-
For small request benchmarks, an 80 byte portion of the above example was used.
-
For large request marshaling benchmarks, a struct containing 50 regular samples was used, making a ~500kB output JSON.
-
Benchmarks are showing the results of easyjson's default behaviour, which makes use of
unsafe
.
Benchmarks are available in the repository and can be run by invoking make
.
easyjson vs. encoding/json
easyjson is roughly 5-6 times faster than the standard encoding/json
for
unmarshaling, and 3-4 times faster for non-concurrent marshaling. Concurrent
marshaling is 6-7x faster if marshaling to a writer.
easyjson vs. ffjson
easyjson uses the same approach for JSON marshaling as ffjson, but takes a significantly different approach to lexing and parsing JSON during unmarshaling. This means easyjson is roughly 2-3x faster for unmarshaling and 1.5-2x faster for non-concurrent unmarshaling.
As of this writing, ffjson
seems to have issues when used concurrently:
specifically, large request pooling hurts ffjson
's performance and causes
scalability issues. These issues with ffjson
can likely be fixed, but as of
writing remain outstanding/known issues with ffjson
.
easyjson and ffjson
have similar performance for small requests, however
easyjson outperforms ffjson
by roughly 2-5x times for large requests when
used with a writer.
easyjson vs. go/codec
go/codec provides compile-time helpers for JSON generation. In this case, helpers do not work like marshalers as they are encoding-independent.
easyjson is generally 2x faster than go/codec
for non-concurrent benchmarks
and about 3x faster for concurrent encoding (without marshaling to a writer).
In an attempt to measure marshaling performance of go/codec
(as opposed to
allocations/memcpy/writer interface invocations), a benchmark was done with
resetting length of a byte slice rather than resetting the whole slice to nil.
However, the optimization in this exact form may not be applicable in practice,
since the memory is not freed between marshaling operations.
easyjson vs 'ujson' python module
ujson is using C code for parsing, so it is interesting to see how plain golang compares to that. It is imporant to note that the resulting object for python is slower to access, since the library parses JSON object into dictionaries.
easyjson is slightly faster for unmarshaling and 2-3x faster than ujson
for
marshaling.
Benchmark Results
ffjson
results are from February 4th, 2016, using the latest ffjson
and go1.6.
go/codec
results are from March 4th, 2016, using the latest go/codec
and go1.6.
Unmarshaling
lib | json size | MB/s | allocs/op | B/op |
---|---|---|---|---|
standard | regular | 22 | 218 | 10229 |
standard | small | 9.7 | 14 | 720 |
easyjson | regular | 125 | 128 | 9794 |
easyjson | small | 67 | 3 | 128 |
ffjson | regular | 66 | 141 | 9985 |
ffjson | small | 17.6 | 10 | 488 |
codec | regular | 55 | 434 | 19299 |
codec | small | 29 | 7 | 336 |
ujson | regular | 103 | N/A | N/A |
Marshaling, one goroutine.
lib | json size | MB/s | allocs/op | B/op |
---|---|---|---|---|
standard | regular | 75 | 9 | 23256 |
standard | small | 32 | 3 | 328 |
standard | large | 80 | 17 | 1.2M |
easyjson | regular | 213 | 9 | 10260 |
easyjson* | regular | 263 | 8 | 742 |
easyjson | small | 125 | 1 | 128 |
easyjson | large | 212 | 33 | 490k |
easyjson* | large | 262 | 25 | 2879 |
ffjson | regular | 122 | 153 | 21340 |
ffjson** | regular | 146 | 152 | 4897 |
ffjson | small | 36 | 5 | 384 |
ffjson** | small | 64 | 4 | 128 |
ffjson | large | 134 | 7317 | 818k |
ffjson** | large | 125 | 7320 | 827k |
codec | regular | 80 | 17 | 33601 |
codec*** | regular | 108 | 9 | 1153 |
codec | small | 42 | 3 | 304 |
codec*** | small | 56 | 1 | 48 |
codec | large | 73 | 483 | 2.5M |
codec*** | large | 103 | 451 | 66007 |
ujson | regular | 92 | N/A | N/A |
* marshaling to a writer,
** using ffjson.Pool()
,
*** reusing output slice instead of resetting it to nil
Marshaling, concurrent.
lib | json size | MB/s | allocs/op | B/op |
---|---|---|---|---|
standard | regular | 252 | 9 | 23257 |
standard | small | 124 | 3 | 328 |
standard | large | 289 | 17 | 1.2M |
easyjson | regular | 792 | 9 | 10597 |
easyjson* | regular | 1748 | 8 | 779 |
easyjson | small | 333 | 1 | 128 |
easyjson | large | 718 | 36 | 548k |
easyjson* | large | 2134 | 25 | 4957 |
ffjson | regular | 301 | 153 | 21629 |
ffjson** | regular | 707 | 152 | 5148 |
ffjson | small | 62 | 5 | 384 |
ffjson** | small | 282 | 4 | 128 |
ffjson | large | 438 | 7330 | 1.0M |
ffjson** | large | 131 | 7319 | 820k |
codec | regular | 183 | 17 | 33603 |
codec*** | regular | 671 | 9 | 1157 |
codec | small | 147 | 3 | 304 |
codec*** | small | 299 | 1 | 48 |
codec | large | 190 | 483 | 2.5M |
codec*** | large | 752 | 451 | 77574 |
* marshaling to a writer,
** using ffjson.Pool()
,
*** reusing output slice instead of resetting it to nil