77 lines
3.3 KiB
Markdown
77 lines
3.3 KiB
Markdown
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# encoding/json [](https://godoc.org/github.com/segmentio/encoding/json)
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Go package offering a replacement implementation of the standard library's
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[`encoding/json`](https://golang.org/pkg/encoding/json/) package, with much
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better performance.
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## Usage
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The exported API of this package mirrors the standard library's
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[`encoding/json`](https://golang.org/pkg/encoding/json/) package, the only
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change needed to take advantage of the performance improvements is the import
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path of the `json` package, from:
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```go
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import (
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"encoding/json"
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)
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```
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to
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```go
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import (
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"github.com/segmentio/encoding/json"
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)
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```
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One way to gain higher encoding throughput is to disable HTML escaping.
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It allows the string encoding to use a much more efficient code path which
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does not require parsing UTF-8 runes most of the time.
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## Performance Improvements
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The internal implementation uses a fair amount of unsafe operations (untyped
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code, pointer arithmetic, etc...) to avoid using reflection as much as possible,
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which is often the reason why serialization code has a large CPU and memory
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footprint.
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The package aims for zero unnecessary dynamic memory allocations and hot code
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paths that are mostly free from calls into the reflect package.
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## Compatibility with encoding/json
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This package aims to be a drop-in replacement, therefore it is tested to behave
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exactly like the standard library's package. However, there are still a few
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missing features that have not been ported yet:
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- Streaming decoder, currently the `Decoder` implementation offered by the
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package does not support progressively reading values from a JSON array (unlike
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the standard library). In our experience this is a very rare use-case, if you
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need it you're better off sticking to the standard library, or spend a bit of
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time implementing it in here ;)
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Note that none of those features should result in performance degradations if
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they were implemented in the package, and we welcome contributions!
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## Trade-offs
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As one would expect, we had to make a couple of trade-offs to achieve greater
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performance than the standard library, but there were also features that we
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did not want to give away.
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Other open-source packages offering a reduced CPU and memory footprint usually
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do so by designing a different API, or require code generation (therefore adding
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complexity to the build process). These were not acceptable conditions for us,
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as we were not willing to trade off developer productivity for better runtime
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performance. To achieve this, we chose to exactly replicate the standard
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library interfaces and behavior, which meant the package implementation was the
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only area that we were able to work with. The internals of this package make
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heavy use of unsafe pointer arithmetics and other performance optimizations,
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and therefore are not as approachable as typical Go programs. Basically, we put
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a bigger burden on maintainers to achieve better runtime cost without
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sacrificing developer productivity.
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For these reasons, we also don't believe that this code should be ported upstream
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to the standard `encoding/json` package. The standard library has to remain
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readable and approachable to maximize stability and maintainability, and make
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projects like this one possible because a high quality reference implementation
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already exists.
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