json: configurable numeric decoding (#137)

* json: stylistic improvements, better code reuse

Initial benchmark results show this change
to be approximately performance-neutral.

* bump tested Go versions to just 1.20 and 1.21
* json: add ParseFlags values UseInt64, UseUint64, UseBigInt
* json: use atomic.Pointer

.github/workflows/benchmark.yml

@@ -1,61 +1,63 @@
+---
 name: Benchmark
 
-on:
-- pull_request
+"on":
+  - pull_request
 
 jobs:
   benchmark:
     strategy:
       matrix:
         ref:
-        - master
-        - ${{ github.sha }}
+          - master
+          - ${{ github.sha }}
 
     runs-on: ubuntu-latest
 
     steps:
-    - name: Steup Go
-      uses: actions/setup-go@v2
-      with:
-        go-version: 1.17
-
-    - name: Checkout
-      uses: actions/checkout@v2
-      with:
-        ref: ${{ matrix.ref }}
-
-    - name: Run Benchmarks
-      run: go test -v -run '^$' -bench '(Marshal|Unmarshal)$/codeResponse' -benchmem -benchtime 3s -cpu 1 -count 5 ./json | tee bench.txt
-
-    - name: Upload Benchmarks
-      uses: actions/upload-artifact@v2
-      with:
-        name: ${{ matrix.ref }}
-        path: bench.txt
+      - name: Setup Go
+        uses: actions/setup-go@v2
+        with:
+          go-version: "1.21"
+
+      - name: Checkout
+        uses: actions/checkout@v2
+        with:
+          ref: ${{ matrix.ref }}
+
+      - name: Run Benchmarks
+        # Without 6 iterations, benchstat will claim statistical insignificance.
+        run: go test -v -run '^$' -bench '(Marshal|Unmarshal)$/codeResponse' -benchmem -benchtime 3s -cpu 1 -count 6 ./json | tee bench.txt
+
+      - name: Upload Benchmarks
+        uses: actions/upload-artifact@v2
+        with:
+          name: ${{ matrix.ref }}
+          path: bench.txt
 
   benchstat:
     needs: [benchmark]
     runs-on: ubuntu-latest
 
     steps:
-    - name: Steup Go
-      uses: actions/setup-go@v2
-      with:
-        go-version: 1.17
-
-    - name: Setup Benchstat
-      run: go install golang.org/x/perf/cmd/benchstat@latest
-
-    - name: Download Benchmark Results
-      uses: actions/download-artifact@v2
-      with:
-        path: .
-
-    - name: Run Benchstat
-      run: benchstat ./master/bench.txt ./${{ github.sha }}/bench.txt | tee benchstat.txt
-
-    - name: Upload Benchstat Results
-      uses: actions/upload-artifact@v2
-      with:
-        name: benchstat
-        path: benchstat.txt
+      - name: Steup Go
+        uses: actions/setup-go@v2
+        with:
+          go-version: "1.21"
+
+      - name: Setup Benchstat
+        run: go install golang.org/x/perf/cmd/benchstat@latest
+
+      - name: Download Benchmark Results
+        uses: actions/download-artifact@v2
+        with:
+          path: .
+
+      - name: Run Benchstat
+        run: benchstat ./master/bench.txt ./${{ github.sha }}/bench.txt | tee benchstat.txt
+
+      - name: Upload Benchstat Results
+        uses: actions/upload-artifact@v2
+        with:
+          name: benchstat
+          path: benchstat.txt

.github/workflows/test.yml

@@ -1,30 +1,29 @@
+---
 name: Test
 
-on:
-- pull_request
+"on":
+  - pull_request
 
 jobs:
   test:
     strategy:
       matrix:
         go:
-        - 1.14
-        - 1.15
-        - 1.16
-        - 1.17
+          - "1.20"
+          - "1.21"
 
     runs-on: ubuntu-latest
 
     steps:
-    - uses: actions/checkout@v2
+      - uses: actions/checkout@v2
 
-    - name: Setup Go ${{ matrix.go }}
-      uses: actions/setup-go@v2
-      with:
-        go-version: ${{ matrix.go }}
+      - name: Setup Go ${{ matrix.go }}
+        uses: actions/setup-go@v2
+        with:
+          go-version: ${{ matrix.go }}
 
-    - name: Download Dependencies
-      run: go mod download
+      - name: Download Dependencies
+        run: go mod download
 
-    - name: Run Tests
-      run: make test
+      - name: Run Tests
+        run: make test

Makefile

@@ -1,6 +1,6 @@
 .PHONY: test bench-simple clean update-golang-test fuzz fuzz-json
 
-golang.version ?= 1.15.2
+golang.version ?= 1.21
 golang.tmp.root := /tmp/golang$(golang.version)
 golang.tmp.json.root := $(golang.tmp.root)/go-go$(golang.version)/src/encoding/json
 golang.test.files := $(wildcard json/golang_*_test.go)
@@ -10,7 +10,7 @@ go-fuzz-build := ${GOPATH}/bin/go-fuzz-build
 go-fuzz-corpus := ${GOPATH}/src/github.com/dvyukov/go-fuzz-corpus
 go-fuzz-dep := ${GOPATH}/src/github.com/dvyukov/go-fuzz/go-fuzz-dep
 
-test: test-ascii test-json test-json-bugs test-json-1.17 test-proto test-iso8601 test-thrift test-purego
+test: test-ascii test-json test-json-bugs test-proto test-iso8601 test-thrift test-purego
 
 test-ascii:
 	go test -cover -race ./ascii
@@ -21,9 +21,6 @@ test-json:
 test-json-bugs:
 	go test -race ./json/bugs/...
 
-test-json-1.17:
-	go test -cover -race -tags go1.17 ./json
-
 test-proto:
 	go test -cover -race ./proto
 

go.mod

@@ -1,5 +1,7 @@
 module github.com/segmentio/encoding
 
-go 1.14
+go 1.18
 
 require github.com/segmentio/asm v1.1.3
+
+require golang.org/x/sys v0.0.0-20211110154304-99a53858aa08 // indirect

json/codec.go

@@ -4,6 +4,7 @@ import (
 	"encoding"
 	"encoding/json"
 	"fmt"
+	"math/big"
 	"reflect"
 	"sort"
 	"strconv"
@@ -49,19 +50,21 @@ type decodeFunc func(decoder, []byte, unsafe.Pointer) ([]byte, error)
 type emptyFunc func(unsafe.Pointer) bool
 type sortFunc func([]reflect.Value)
 
-var (
-	// Eventually consistent cache mapping go types to dynamically generated
-	// codecs.
-	//
-	// Note: using a uintptr as key instead of reflect.Type shaved ~15ns off of
-	// the ~30ns Marhsal/Unmarshal functions which were dominated by the map
-	// lookup time for simple types like bool, int, etc..
-	cache unsafe.Pointer // map[unsafe.Pointer]codec
-)
+// Eventually consistent cache mapping go types to dynamically generated
+// codecs.
+//
+// Note: using a uintptr as key instead of reflect.Type shaved ~15ns off of
+// the ~30ns Marhsal/Unmarshal functions which were dominated by the map
+// lookup time for simple types like bool, int, etc..
+var cache atomic.Pointer[map[unsafe.Pointer]codec]
 
 func cacheLoad() map[unsafe.Pointer]codec {
-	p := atomic.LoadPointer(&cache)
-	return *(*map[unsafe.Pointer]codec)(unsafe.Pointer(&p))
+	p := cache.Load()
+	if p == nil {
+		return nil
+	}
+
+	return *p
 }
 
 func cacheStore(typ reflect.Type, cod codec, oldCodecs map[unsafe.Pointer]codec) {
@@ -72,7 +75,7 @@ func cacheStore(typ reflect.Type, cod codec, oldCodecs map[unsafe.Pointer]codec)
 		newCodecs[t] = c
 	}
 
-	atomic.StorePointer(&cache, *(*unsafe.Pointer)(unsafe.Pointer(&newCodecs)))
+	cache.Store(&newCodecs)
 }
 
 func typeid(t reflect.Type) unsafe.Pointer {
@@ -838,6 +841,7 @@ func constructInlineValueEncodeFunc(encode encodeFunc) encodeFunc {
 // compiles down to zero instructions.
 // USE CAREFULLY!
 // This was copied from the runtime; see issues 23382 and 7921.
+//
 //go:nosplit
 func noescape(p unsafe.Pointer) unsafe.Pointer {
 	x := uintptr(p)
@@ -1078,6 +1082,7 @@ var (
 	float32Type = reflect.TypeOf(float32(0))
 	float64Type = reflect.TypeOf(float64(0))
 
+	bigIntType     = reflect.TypeOf(new(big.Int))
 	numberType     = reflect.TypeOf(json.Number(""))
 	stringType     = reflect.TypeOf("")
 	stringsType    = reflect.TypeOf([]string(nil))
@@ -1104,6 +1109,8 @@ var (
 	jsonUnmarshalerType = reflect.TypeOf((*Unmarshaler)(nil)).Elem()
 	textMarshalerType   = reflect.TypeOf((*encoding.TextMarshaler)(nil)).Elem()
 	textUnmarshalerType = reflect.TypeOf((*encoding.TextUnmarshaler)(nil)).Elem()
+
+	bigIntDecoder = constructJSONUnmarshalerDecodeFunc(bigIntType, false)
 )
 
 // =============================================================================