feat: initial implementation

README.md

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+# gomockctx
+
+Go package with [gomock](https://github.com/golang/mock) helpers for matching
+[context.Context](https://pkg.go.dev/context).

go.mod

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+module github.com/romdo/gomockctx
+
+go 1.17
+
+require github.com/golang/mock v1.6.0

go.sum

@@ -0,0 +1,25 @@
+github.com/golang/mock v1.6.0 h1:ErTB+efbowRARo13NNdxyJji2egdxLGQhRaY+DUumQc=
+github.com/golang/mock v1.6.0/go.mod h1:p6yTPP+5HYm5mzsMV8JkE6ZKdX+/wYM6Hr+LicevLPs=
+github.com/yuin/goldmark v1.3.5/go.mod h1:mwnBkeHKe2W/ZEtQ+71ViKU8L12m81fl3OWwC1Zlc8k=
+golang.org/x/crypto v0.0.0-20190308221718-c2843e01d9a2/go.mod h1:djNgcEr1/C05ACkg1iLfiJU5Ep61QUkGW8qpdssI0+w=
+golang.org/x/crypto v0.0.0-20191011191535-87dc89f01550/go.mod h1:yigFU9vqHzYiE8UmvKecakEJjdnWj3jj499lnFckfCI=
+golang.org/x/mod v0.4.2/go.mod h1:s0Qsj1ACt9ePp/hMypM3fl4fZqREWJwdYDEqhRiZZUA=
+golang.org/x/net v0.0.0-20190404232315-eb5bcb51f2a3/go.mod h1:t9HGtf8HONx5eT2rtn7q6eTqICYqUVnKs3thJo3Qplg=
+golang.org/x/net v0.0.0-20190620200207-3b0461eec859/go.mod h1:z5CRVTTTmAJ677TzLLGU+0bjPO0LkuOLi4/5GtJWs/s=
+golang.org/x/net v0.0.0-20210405180319-a5a99cb37ef4/go.mod h1:p54w0d4576C0XHj96bSt6lcn1PtDYWL6XObtHCRCNQM=
+golang.org/x/sync v0.0.0-20190423024810-112230192c58/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
+golang.org/x/sync v0.0.0-20210220032951-036812b2e83c/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
+golang.org/x/sys v0.0.0-20190215142949-d0b11bdaac8a/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
+golang.org/x/sys v0.0.0-20190412213103-97732733099d/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
+golang.org/x/sys v0.0.0-20201119102817-f84b799fce68/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
+golang.org/x/sys v0.0.0-20210330210617-4fbd30eecc44/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
+golang.org/x/sys v0.0.0-20210510120138-977fb7262007/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
+golang.org/x/term v0.0.0-20201126162022-7de9c90e9dd1/go.mod h1:bj7SfCRtBDWHUb9snDiAeCFNEtKQo2Wmx5Cou7ajbmo=
+golang.org/x/text v0.3.0/go.mod h1:NqM8EUOU14njkJ3fqMW+pc6Ldnwhi/IjpwHt7yyuwOQ=
+golang.org/x/text v0.3.3/go.mod h1:5Zoc/QRtKVWzQhOtBMvqHzDpF6irO9z98xDceosuGiQ=
+golang.org/x/tools v0.0.0-20180917221912-90fa682c2a6e/go.mod h1:n7NCudcB/nEzxVGmLbDWY5pfWTLqBcC2KZ6jyYvM4mQ=
+golang.org/x/tools v0.0.0-20191119224855-298f0cb1881e/go.mod h1:b+2E5dAYhXwXZwtnZ6UAqBI28+e2cm9otk0dWdXHAEo=
+golang.org/x/tools v0.1.1/go.mod h1:o0xws9oXOQQZyjljx8fwUC0k7L1pTE6eaCbjGeHmOkk=
+golang.org/x/xerrors v0.0.0-20190717185122-a985d3407aa7/go.mod h1:I/5z698sn9Ka8TeJc9MKroUUfqBBauWjQqLJ2OPfmY0=
+golang.org/x/xerrors v0.0.0-20191011141410-1b5146add898/go.mod h1:I/5z698sn9Ka8TeJc9MKroUUfqBBauWjQqLJ2OPfmY0=
+golang.org/x/xerrors v0.0.0-20200804184101-5ec99f83aff1/go.mod h1:I/5z698sn9Ka8TeJc9MKroUUfqBBauWjQqLJ2OPfmY0=

gomockctx.go

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+// Package gomockctx contains gomock helpers for matching context.Context
+// objects.
+package gomockctx
+
+import (
+	"context"
+	"fmt"
+	"reflect"
+
+	"github.com/golang/mock/gomock"
+)
+
+type (
+	contextKey   string
+	contextValue string
+)
+
+var ctxKey contextKey = "gomockctx context ID"
+
+func newCtxID() contextValue {
+	id, err := randString(64)
+	if err != nil {
+		panic(err)
+	}
+
+	return contextValue(id)
+}
+
+func value(ctx context.Context) contextValue {
+	var value contextValue
+	v := ctx.Value(ctxKey)
+	if s, ok := v.(contextValue); ok {
+		value = s
+	}
+
+	return value
+}
+
+// New returns a context as a child of the given parent, and with a randomized
+// gomockctx ID value set, making it a gomockctx context. This can then be used
+// with Is to get a gomock Matcher which returns true for the context from New,
+// or any child contexts of it.
+//
+// If crypto/rand returns an error, this will panic trying to generate the
+// gomockctx ID. In practise though, crypto/rand should never return a error.
+func New(parent context.Context) context.Context {
+	return context.WithValue(parent, ctxKey, newCtxID())
+}
+
+// Is accepts a context with a gomockctx ID value (as returned from New), and
+// returns a gomock.Matcher which returns true for the given context, of any
+// child contexts of it.
+//
+// If ctx was not returned from New, the resulting matcher will ALWAYS return
+// false.
+func Is(ctx context.Context) gomock.Matcher {
+	return WithValue(ctxKey, value(ctx))
+}
+
+// WithValue creates a generic gomock context matcher which returns true for any
+// context which has the specified key/value.
+func WithValue(key interface{}, value interface{}) gomock.Matcher {
+	return &contextMatcher{
+		key:   key,
+		value: value,
+	}
+}
+
+// ID returns the gomockctx ID value in the given context, or a empty string if
+// it not a gomockctx context.
+func ID(ctx context.Context) string {
+	return string(value(ctx))
+}
+
+type contextMatcher struct {
+	key   interface{}
+	value interface{}
+}
+
+var _ gomock.Matcher = &contextMatcher{}
+
+func (e *contextMatcher) Matches(x interface{}) bool {
+	ctx, ok := x.(context.Context)
+	if !ok {
+		return false
+	}
+
+	return reflect.DeepEqual(e.value, ctx.Value(e.key))
+}
+
+func (e *contextMatcher) String() string {
+	return fmt.Sprintf(`context with "%+v" = "%+v"`, e.key, e.value)
+}

rand.go

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+package gomockctx
+
+import (
+	"crypto/rand"
+	"math/big"
+)
+
+const alphabet = "ABCDEFGHIJKLMNOPQRSTUVWXYZ" +
+	"abcdefghijklmnopqrstuvwxyz" +
+	"0123456789"
+
+// randString returns a cryptographically secure random string of alphanumeric
+// characters of n length.
+//
+// Borrowed from github.com/jimeh/rands package.
+func randString(n int) (string, error) {
+	l := big.NewInt(int64(len(alphabet)))
+	b := make([]byte, n)
+	for i := 0; i < n; i++ {
+		index, err := rand.Int(rand.Reader, l)
+		if err != nil {
+			return "", err
+		}
+		b[i] = alphabet[index.Int64()]
+	}
+
+	return string(b), nil
+}