feat: add ErrNotFound

storage/benchmarks/go.mod

@@ -16,12 +16,25 @@ require (
 	github.com/alexbrainman/goissue34681 v0.0.0-20191006012335-3fc7a47baff5 // indirect
 	github.com/gogo/protobuf v1.3.2 // indirect
 	github.com/google/uuid v1.3.0 // indirect
+	github.com/ipfs/go-cid v0.4.1 // indirect
 	github.com/ipfs/go-datastore v0.6.0 // indirect
 	github.com/ipfs/go-log v1.0.3 // indirect
 	github.com/ipfs/go-log/v2 v2.0.3 // indirect
 	github.com/jbenet/goprocess v0.1.4 // indirect
+	github.com/klauspost/cpuid/v2 v2.0.9 // indirect
+	github.com/minio/sha256-simd v1.0.0 // indirect
+	github.com/mr-tron/base58 v1.2.0 // indirect
+	github.com/multiformats/go-base32 v0.0.3 // indirect
+	github.com/multiformats/go-base36 v0.1.0 // indirect
+	github.com/multiformats/go-multibase v0.0.3 // indirect
+	github.com/multiformats/go-multihash v0.2.2 // indirect
+	github.com/multiformats/go-varint v0.0.6 // indirect
 	github.com/opentracing/opentracing-go v1.1.0 // indirect
+	github.com/spaolacci/murmur3 v1.1.0 // indirect
 	go.uber.org/atomic v1.6.0 // indirect
 	go.uber.org/multierr v1.5.0 // indirect
 	go.uber.org/zap v1.10.0 // indirect
+	golang.org/x/crypto v0.1.0 // indirect
+	golang.org/x/sys v0.1.0 // indirect
+	lukechampine.com/blake3 v1.1.6 // indirect
 )

storage/benchmarks/go.sum

@@ -12,6 +12,8 @@ github.com/google/renameio v0.1.0/go.mod h1:KWCgfxg9yswjAJkECMjeO8J8rahYeXnNhOm4
 github.com/google/uuid v1.1.1/go.mod h1:TIyPZe4MgqvfeYDBFedMoGGpEw/LqOeaOT+nhxU+yHo=
 github.com/google/uuid v1.3.0 h1:t6JiXgmwXMjEs8VusXIJk2BXHsn+wx8BZdTaoZ5fu7I=
 github.com/google/uuid v1.3.0/go.mod h1:TIyPZe4MgqvfeYDBFedMoGGpEw/LqOeaOT+nhxU+yHo=
+github.com/ipfs/go-cid v0.4.1 h1:A/T3qGvxi4kpKWWcPC/PgbvDA2bjVLO7n4UeVwnbs/s=
+github.com/ipfs/go-cid v0.4.1/go.mod h1:uQHwDeX4c6CtyrFwdqyhpNcxVewur1M7l7fNU7LKwZk=
 github.com/ipfs/go-datastore v0.5.0/go.mod h1:9zhEApYMTl17C8YDp7JmU7sQZi2/wqiYh73hakZ90Bk=
 github.com/ipfs/go-datastore v0.6.0 h1:JKyz+Gvz1QEZw0LsX1IBn+JFCJQH4SJVFtM4uWU0Myk=
 github.com/ipfs/go-datastore v0.6.0/go.mod h1:rt5M3nNbSO/8q1t4LNkLyUwRs8HupMeN/8O4Vn9YAT8=
@@ -30,12 +32,30 @@ github.com/jbenet/goprocess v0.1.4/go.mod h1:5yspPrukOVuOLORacaBi858NqyClJPQxYZl
 github.com/kisielk/errcheck v1.1.0/go.mod h1:EZBBE59ingxPouuu3KfxchcWSUPOHkagtvWXihfKN4Q=
 github.com/kisielk/errcheck v1.5.0/go.mod h1:pFxgyoBC7bSaBwPgfKdkLd5X25qrDl4LWUI2bnpBCr8=
 github.com/kisielk/gotool v1.0.0/go.mod h1:XhKaO+MFFWcvkIS/tQcRk01m1F5IRFswLeQ+oQHNcck=
+github.com/klauspost/cpuid/v2 v2.0.4/go.mod h1:FInQzS24/EEf25PyTYn52gqo7WaD8xa0213Md/qVLRg=
+github.com/klauspost/cpuid/v2 v2.0.9 h1:lgaqFMSdTdQYdZ04uHyN2d/eKdOMyi2YLSvlQIBFYa4=
+github.com/klauspost/cpuid/v2 v2.0.9/go.mod h1:FInQzS24/EEf25PyTYn52gqo7WaD8xa0213Md/qVLRg=
 github.com/kr/pretty v0.1.0/go.mod h1:dAy3ld7l9f0ibDNOQOHHMYYIIbhfbHSm3C4ZsoJORNo=
 github.com/kr/pretty v0.2.0/go.mod h1:ipq/a2n7PKx3OHsz4KJII5eveXtPO4qwEXGdVfWzfnI=
 github.com/kr/pretty v0.3.1 h1:flRD4NNwYAUpkphVc1HcthR4KEIFJ65n8Mw5qdRn3LE=
 github.com/kr/pty v1.1.1/go.mod h1:pFQYn66WHrOpPYNljwOMqo10TkYh1fy3cYio2l3bCsQ=
 github.com/kr/text v0.1.0/go.mod h1:4Jbv+DJW3UT/LiOwJeYQe1efqtUx/iVham/4vfdArNI=
 github.com/kr/text v0.2.0 h1:5Nx0Ya0ZqY2ygV366QzturHI13Jq95ApcVaJBhpS+AY=
+github.com/minio/sha256-simd v1.0.0 h1:v1ta+49hkWZyvaKwrQB8elexRqm6Y0aMLjCNsrYxo6g=
+github.com/minio/sha256-simd v1.0.0/go.mod h1:OuYzVNI5vcoYIAmbIvHPl3N3jUzVedXbKy5RFepssQM=
+github.com/mr-tron/base58 v1.1.0/go.mod h1:xcD2VGqlgYjBdcBLw+TuYLr8afG+Hj8g2eTVqeSzSU8=
+github.com/mr-tron/base58 v1.2.0 h1:T/HDJBh4ZCPbU39/+c3rRvE0uKBQlU27+QI8LJ4t64o=
+github.com/mr-tron/base58 v1.2.0/go.mod h1:BinMc/sQntlIE1frQmRFPUoPA1Zkr8VRgBdjWI2mNwc=
+github.com/multiformats/go-base32 v0.0.3 h1:tw5+NhuwaOjJCC5Pp82QuXbrmLzWg7uxlMFp8Nq/kkI=
+github.com/multiformats/go-base32 v0.0.3/go.mod h1:pLiuGC8y0QR3Ue4Zug5UzK9LjgbkL8NSQj0zQ5Nz/AA=
+github.com/multiformats/go-base36 v0.1.0 h1:JR6TyF7JjGd3m6FbLU2cOxhC0Li8z8dLNGQ89tUg4F4=
+github.com/multiformats/go-base36 v0.1.0/go.mod h1:kFGE83c6s80PklsHO9sRn2NCoffoRdUUOENyW/Vv6sM=
+github.com/multiformats/go-multibase v0.0.3 h1:l/B6bJDQjvQ5G52jw4QGSYeOTZoAwIO77RblWplfIqk=
+github.com/multiformats/go-multibase v0.0.3/go.mod h1:5+1R4eQrT3PkYZ24C3W2Ue2tPwIdYQD509ZjSb5y9Oc=
+github.com/multiformats/go-multihash v0.2.2 h1:Uu7LWs/PmWby1gkj1S1DXx3zyd3aVabA4FiMKn/2tAc=
+github.com/multiformats/go-multihash v0.2.2/go.mod h1:dXgKXCXjBzdscBLk9JkjINiEsCKRVch90MdaGiKsvSM=
+github.com/multiformats/go-varint v0.0.6 h1:gk85QWKxh3TazbLxED/NlDVv8+q+ReFJk7Y2W/KhfNY=
+github.com/multiformats/go-varint v0.0.6/go.mod h1:3Ls8CIEsrijN6+B7PbrXRPxHRPuXSrVKRY101jdMZYE=
 github.com/opentracing/opentracing-go v1.1.0 h1:pWlfV3Bxv7k65HYwkikxat0+s3pV4bsqf19k25Ur8rU=
 github.com/opentracing/opentracing-go v1.1.0/go.mod h1:UkNAQd3GIcIGf0SeVgPpRdFStlNbqXla1AfSYxPUl2o=
 github.com/pkg/errors v0.8.1 h1:iURUrRGxPUNPdy5/HRSm+Yj6okJ6UtLINN0Q9M4+h3I=
@@ -44,6 +64,8 @@ github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZb
 github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
 github.com/rogpeppe/go-internal v1.3.0/go.mod h1:M8bDsm7K2OlrFYOpmOWEs/qY81heoFRclV5y23lUDJ4=
 github.com/rogpeppe/go-internal v1.9.0 h1:73kH8U+JUqXU8lRuOHeVHaa/SZPifC7BkcraZVejAe8=
+github.com/spaolacci/murmur3 v1.1.0 h1:7c1g84S4BPRrfL5Xrdp6fOJ206sU9y293DDHaoy0bLI=
+github.com/spaolacci/murmur3 v1.1.0/go.mod h1:JwIasOWyU6f++ZhiEuf87xNszmSA2myDM2Kzu9HwQUA=
 github.com/stretchr/objx v0.1.0/go.mod h1:HFkY916IF+rwdDfMAkV7OtwuqBVzrE8GR6GFx+wExME=
 github.com/stretchr/testify v1.3.0/go.mod h1:M5WIy9Dh21IEIfnGCwXGc5bZfKNJtfHm1UVUgZn+9EI=
 github.com/stretchr/testify v1.4.0 h1:2E4SXV/wtOkTonXsotYi4li6zVWxYlZuYNCXe9XRJyk=
@@ -64,6 +86,8 @@ golang.org/x/crypto v0.0.0-20190308221718-c2843e01d9a2/go.mod h1:djNgcEr1/C05ACk
 golang.org/x/crypto v0.0.0-20190510104115-cbcb75029529/go.mod h1:yigFU9vqHzYiE8UmvKecakEJjdnWj3jj499lnFckfCI=
 golang.org/x/crypto v0.0.0-20191011191535-87dc89f01550/go.mod h1:yigFU9vqHzYiE8UmvKecakEJjdnWj3jj499lnFckfCI=
 golang.org/x/crypto v0.0.0-20200622213623-75b288015ac9/go.mod h1:LzIPMQfyMNhhGPhUkYOs5KpL4U8rLKemX1yGLhDgUto=
+golang.org/x/crypto v0.1.0 h1:MDRAIl0xIo9Io2xV565hzXHw3zVseKrJKodhohM5CjU=
+golang.org/x/crypto v0.1.0/go.mod h1:RecgLatLF4+eUMCP1PoPZQb+cVrJcOPbHkTkbkB9sbw=
 golang.org/x/lint v0.0.0-20190930215403-16217165b5de h1:5hukYrvBGR8/eNkX5mdUezrA6JiaEZDtJb9Ei+1LlBs=
 golang.org/x/lint v0.0.0-20190930215403-16217165b5de/go.mod h1:6SW0HCj/g11FgYtHlgUYUwCkIfeOF89ocIRzGO/8vkc=
 golang.org/x/mod v0.0.0-20190513183733-4bf6d317e70e/go.mod h1:mXi4GBBbnImb6dmsKGUJ2LatrhH/nqhxcFungHvyanc=
@@ -81,6 +105,8 @@ golang.org/x/sync v0.0.0-20201020160332-67f06af15bc9/go.mod h1:RxMgew5VJxzue5/jJ
 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 v0.0.0-20200930185726-fdedc70b468f/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
+golang.org/x/sys v0.1.0 h1:kunALQeHf1/185U1i0GOB/fy1IPRDDpuoOOqRReG57U=
+golang.org/x/sys v0.1.0/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
 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 v0.0.0-20180221164845-07fd8470d635/go.mod h1:n7NCudcB/nEzxVGmLbDWY5pfWTLqBcC2KZ6jyYvM4mQ=
@@ -107,3 +133,5 @@ gopkg.in/yaml.v2 v2.2.2/go.mod h1:hI93XBmqTisBFMUTm0b8Fm+jr3Dg1NNxqwp+5A1VGuI=
 gopkg.in/yaml.v2 v2.4.0 h1:D8xgwECY7CYvx+Y2n4sBz93Jn9JRvxdiyyo8CTfuKaY=
 honnef.co/go/tools v0.0.1-2019.2.3 h1:3JgtbtFHMiCmsznwGVTUWbgGov+pVqnlf1dEJTNAXeM=
 honnef.co/go/tools v0.0.1-2019.2.3/go.mod h1:a3bituU0lyd329TUQxRnasdCoJDkEUEAqEt0JzvZhAg=
+lukechampine.com/blake3 v1.1.6 h1:H3cROdztr7RCfoaTpGZFQsrqvweFLrqS73j7L7cmR5c=
+lukechampine.com/blake3 v1.1.6/go.mod h1:tkKEOtDkNtklkXtLNEOGNq5tcV90tJiA1vAA12R78LA=

storage/memstore/memstore.go

@@ -3,8 +3,9 @@ package memstore
 import (
 	"bytes"
 	"context"
-	"fmt"
 	"io"
+
+	"github.com/ipld/go-ipld-prime/storage"
 )
 
 // Store is a simple in-memory storage.
@@ -56,7 +57,7 @@ func (store *Store) Get(ctx context.Context, key string) ([]byte, error) {
 	store.beInitialized()
 	content, exists := store.Bag[key]
 	if !exists {
-		return nil, fmt.Errorf("404") // FIXME this needs a standard error type
+		return nil, storage.NewErrNotFoundForKey(key)
 	}
 	cpy := make([]byte, len(content))
 	copy(cpy, content)
@@ -82,7 +83,7 @@ func (store *Store) Put(ctx context.Context, key string, content []byte) error {
 func (store *Store) GetStream(ctx context.Context, key string) (io.ReadCloser, error) {
 	content, exists := store.Bag[key]
 	if !exists {
-		return nil, fmt.Errorf("404") // FIXME this needs a standard error type
+		return nil, storage.NewErrNotFoundForKey(key)
 	}
 	return noopCloser{bytes.NewReader(content)}, nil
 }
@@ -91,7 +92,7 @@ func (store *Store) GetStream(ctx context.Context, key string) (io.ReadCloser, e
 func (store *Store) Peek(ctx context.Context, key string) ([]byte, io.Closer, error) {
 	content, exists := store.Bag[key]
 	if !exists {
-		return nil, nil, fmt.Errorf("404") // FIXME this needs a standard error type
+		return nil, nil, storage.NewErrNotFoundForKey(key)
 	}
 	return content, noopCloser{nil}, nil
 }

storage/notfound.go

@@ -0,0 +1,101 @@
+package storage
+
+import (
+	"errors"
+
+	"github.com/ipfs/go-cid"
+)
+
+// ErrNotFound is a 404, but for block storage systems. It is returned when
+// a block is not found. The Cid property may be cid.Undef if the NotFound error
+// was not created with a specific CID (e.g. when using a non-CID key in a
+// storage Get operation).
+//
+// ErrNotFound implements `interface{NotFound() bool}`, which makes it roughly
+// compatible with the legacy github.com/ipfs/go-ipld-format#ErrNotFound.
+// The IsNotFound() function here will test for this and therefore be compatible
+// with this ErrNotFound, and the legacy ErrNotFound. The same is not true for
+// the legacy github.com/ipfs/go-ipld-format#IsNotFound.
+//
+// errors.Is() should be preferred as the standard Go way to test for errors;
+// however due to the move of the legacy ErrNotFound to this package, it may
+// not report correctly where older block storage packages emit the legacy
+// ErrNotFound. The IsNotFound() function provides a maximally compatible
+// matching function that should be able to determine whether an ErrNotFound,
+// either new or legacy, exists within a wrapped error chain.
+type ErrNotFound struct {
+	Cid cid.Cid
+}
+
+// NewErrNotFound is a convenience factory that creates a new ErrNotFound error
+// from a CID.
+func NewErrNotFound(c cid.Cid) ErrNotFound {
+	return ErrNotFound{Cid: c}
+}
+
+// NewErrNotFound is a convenience factory that creates a new ErrNotFound error
+// from a key. If the key is a CID#KeyString(), then it will be cast to a CID,
+// otherwise the Cid of the ErrNotFound will be cid.Undef.
+func NewErrNotFoundForKey(key string) ErrNotFound {
+	if c, err := cid.Cast([]byte(key)); err == nil {
+		return ErrNotFound{Cid: c}
+	}
+	return ErrNotFound{Cid: cid.Undef}
+}
+
+func (e ErrNotFound) Error() string {
+	if e.Cid == cid.Undef {
+		return "ipld: could not find node"
+	}
+	return "ipld: could not find " + e.Cid.String()
+}
+
+// NotFound always returns true, and is used to feature-test for ErrNotFound
+// errors.
+func (e ErrNotFound) NotFound() bool {
+	return true
+}
+
+// Is allows errors.Is to work with this error type. It is compatible with the
+// legacy github.com/ipfs/go-ipld-format#ErrNotFound, and other related error
+// types as it uses a feature-test on the NotFound() method.
+//
+// It is important to note that because errors.Is() performs a reverse match,
+// whereby the Is() of the error being checked is called on the target,
+// the legacy ErrNotFound#Is will perform a strict type match, which will fail
+// where the original error is of the legacy type. Where compatibility is
+// required across multiple block storage systems that may return legacy error
+// types, use the IsNotFound() function instead.
+func (e ErrNotFound) Is(err error) bool {
+	if v, ok := err.(interface{ NotFound() bool }); ok && v.NotFound() {
+		return v.NotFound()
+	}
+	return false
+}
+
+var enf = ErrNotFound{}
+
+// IsNotFound returns true if the error is a ErrNotFound, or compatible with an
+// ErrNotFound, or wraps such an error. Compatibility is determined by the
+// type implementing the NotFound() method which returns true.
+// It is compatible with the legacy github.com/ipfs/go-ipld-format#ErrNotFound,
+// and other related error types.
+//
+// This is NOT the same as errors.Is(err, storage.ErrNotFound{}) which relies on
+// the Is() of the original err rather than the target. IsNotFound() uses the
+// Is() of storage.ErrNotFound to perform the check. The difference being that
+// the err being checked doesn't need to have a feature-testing Is() method for
+// this to succeed, it only needs to have a NotFound() method that returns true.
+//
+// Prefer this method for maximal compatibility, including wrapped errors, that
+// implement the minimal interface{ NotFound() true }.
+func IsNotFound(err error) bool {
+	for {
+		if enf.Is(err) {
+			return true
+		}
+		if err = errors.Unwrap(err); err == nil {
+			return false
+		}
+	}
+}

storage/notfound_test.go

@@ -0,0 +1,105 @@
+package storage_test
+
+import (
+	"errors"
+	"fmt"
+	"testing"
+
+	"github.com/ipfs/go-cid"
+	"github.com/ipld/go-ipld-prime/storage"
+)
+
+func TestNotFound(t *testing.T) {
+	nf := storage.ErrNotFound{}
+	if !storage.IsNotFound(nf) {
+		t.Fatal("expected ErrNotFound to be a NotFound error")
+	}
+	if !errors.Is(nf, storage.ErrNotFound{}) {
+		t.Fatal("expected ErrNotFound to be a NotFound error")
+	}
+	if nf.Error() != "ipld: could not find node" {
+		t.Fatal("unexpected error message")
+	}
+
+	nf = storage.NewErrNotFound(cid.MustParse("bafybeigdyrzt5sfp7udm7hu76uh7y26nf3efuylqabf3oclgtqy55fbzdi"))
+	if !storage.IsNotFound(nf) {
+		t.Fatal("expected ErrNotFound to be a NotFound error")
+	}
+	if !errors.Is(nf, storage.ErrNotFound{}) {
+		t.Fatal("expected ErrNotFound to be a NotFound error")
+	}
+	if nf.Error() != "ipld: could not find bafybeigdyrzt5sfp7udm7hu76uh7y26nf3efuylqabf3oclgtqy55fbzdi" {
+		t.Fatal("unexpected error message")
+	}
+
+	wrappedNf := fmt.Errorf("wrapped outer: %w", fmt.Errorf("wrapped inner: %w", nf))
+	if !storage.IsNotFound(wrappedNf) {
+		t.Fatal("expected wrapped ErrNotFound to be a NotFound error")
+	}
+	if !errors.Is(wrappedNf, storage.ErrNotFound{}) {
+		t.Fatal("expected wrapped ErrNotFound to be a NotFound error")
+	}
+
+	fmt.Println("WeirdNotFoundErr")
+	wnf := weirdNotFoundError{}
+	if !storage.IsNotFound(wnf) {
+		t.Fatal("expected weirdNotFoundError to be a NotFound error")
+	}
+	if !errors.Is(wnf, storage.ErrNotFound{}) {
+		t.Fatal("expected weirdNotFoundError to be a NotFound error")
+	}
+
+	// a weirder case, this one implements `NotFound()` but it returns false; but
+	// it also implements the same Is() that will claim it's a not-found, so
+	// it should work one way around, but not the other, when it's being asked
+	// whether an error is or not
+	wnnf := weirdNotNotFoundError{}
+	if storage.IsNotFound(wnnf) {
+		// this shouldn't be true because we test NotFound()==true
+		t.Fatal("expected weirdNotNotFoundError to NOT be a NotFound error")
+	}
+	if !errors.Is(wnnf, storage.ErrNotFound{}) {
+		// this should be true, because weirdNotNotFoundError.Is() performs the
+		// check on storage.ErrNotFound{}.NotFound() which does return true.
+		t.Fatal("expected weirdNotNotFoundError to be a NotFound error")
+	}
+	if errors.Is(nf, weirdNotNotFoundError{}) {
+		// switch them around and we get the same result as storage.IsNotFound, but
+		// won't work with wrapped weirdNotNotFoundError errors.
+		t.Fatal("expected weirdNotNotFoundError to NOT be a NotFound error")
+	}
+}
+
+type weirdNotFoundError struct{}
+
+func (weirdNotFoundError) NotFound() bool {
+	return true
+}
+
+func (weirdNotFoundError) Is(err error) bool {
+	if v, ok := err.(interface{ NotFound() bool }); ok && v.NotFound() {
+		return v.NotFound()
+	}
+	return false
+}
+
+func (weirdNotFoundError) Error() string {
+	return "weird not found error"
+}
+
+type weirdNotNotFoundError struct{}
+
+func (weirdNotNotFoundError) NotFound() bool {
+	return false
+}
+
+func (weirdNotNotFoundError) Is(err error) bool {
+	if v, ok := err.(interface{ NotFound() bool }); ok && v.NotFound() {
+		return v.NotFound()
+	}
+	return false
+}
+
+func (weirdNotNotFoundError) Error() string {
+	return "weird not NOT found error"
+}