Fix ReadAt with offset==EOF (#51)

* Fix ReadAt with offset==EOF

Fix a problem when a `ReadAt` requests a read at the offset that in plaintext corresponds exactly to a block starting at the EOF.

We forward to where the block *would* be, thereby we never read the previous block header, and therefore do not get the "final" marker set

We fix by reading (and skipping) the previous block if a request starts exactly at a block boundary to pick up the "final" marker.

We calculate `t`, to be the number of full blocks to skip and `k` to be the number of bytes to skip before the response starts:

```
	t := offset / int64(maxPayloadSize)
	k := offset % int64(maxPayloadSize)
```

We add the following if we start at a block boundary after the first block:

```
	if offset > 0 && k == 0 {
		k = maxPayloadSize
		t--
	}
```

This will read the previous block to read the "final" flag and skip its content.

.github/workflows/codeql.yml

@@ -0,0 +1,47 @@
+name: "Code scanning - action"
+
+on:
+  push:
+  pull_request:
+  schedule:
+    - cron: '0 19 * * 0'
+
+jobs:
+  CodeQL-Build:
+
+    # CodeQL runs on ubuntu-latest and windows-latest
+    runs-on: ubuntu-latest
+
+    steps:
+    - name: Checkout repository
+      uses: actions/checkout@v2
+      with:
+        # We must fetch at least the immediate parents so that if this is
+        # a pull request then we can checkout the head.
+        fetch-depth: 2
+
+    # Initializes the CodeQL tools for scanning.
+    - name: Initialize CodeQL
+      uses: github/codeql-action/init@v2
+      # Override language selection by uncommenting this and choosing your languages
+      # with:
+      #   languages: go, javascript, csharp, python, cpp, java
+
+    # Autobuild attempts to build any compiled languages  (C/C++, C#, or Java).
+    # If this step fails, then you should remove it and run the build manually (see below)
+    - name: Autobuild
+      uses: github/codeql-action/autobuild@v2
+
+    # ℹ️ Command-line programs to run using the OS shell.
+    # 📚 https://git.io/JvXDl
+
+    # ✏️ If the Autobuild fails above, remove it and uncomment the following three lines
+    #    and modify them (or add more) to build your code if your project
+    #    uses a compiled language
+
+    #- run: |
+    #   make bootstrap
+    #   make release
+
+    - name: Perform CodeQL Analysis
+      uses: github/codeql-action/analyze@v2

.github/workflows/go.yml

@@ -10,48 +10,57 @@ on:
 
 jobs:
   build:
-    name: Build Go ${{ matrix.go-version }}
+    name: Lint ${{ matrix.go-version }}
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        go-version: [1.15.x, 1.16.x]
+        go-version: [1.20.x]
     steps:
     - name: Set up Go ${{ matrix.go-version }}
-      uses: actions/setup-go@v1
+      uses: actions/setup-go@v2
       with:
         go-version: ${{ matrix.go-version }}
       id: go
 
     - name: Check out code into the Go module directory
-      uses: actions/checkout@v1
+      uses: actions/checkout@v2
 
-    - name: Build
-      env:
-        GO111MODULE: on
+    - name: go vet
+      run: go vet ./...
+
+    - name: go fmt
+      run: diff <(gofmt -d .) <(printf "")
+
+    - name: golangci-lint
       run: |
-         curl -sfL https://raw.githubusercontent.com/golangci/golangci-lint/master/install.sh | sh -s -- -b $(go env GOPATH)/bin v1.33.0
-         $(go env GOPATH)/bin/golangci-lint run --config ./.golangci.yml
-         go vet ./...
+        curl -sfL https://raw.githubusercontent.com/golangci/golangci-lint/master/install.sh | sh -s -- -b $(go env GOPATH)/bin v1.51.2
+        $(go env GOPATH)/bin/golangci-lint run --config ./.golangci.yml
+
   test:
     name: Testing Go ${{ matrix.go-version }} on ${{ matrix.os }}
     runs-on: ${{ matrix.os }}
     strategy:
       matrix:
-        go-version: [1.16.x]
+        go-version: [1.18.x, 1.19.x, 1.20.x]
         os: [ubuntu-latest, windows-latest, macos-latest]
     steps:
     - name: Set up Go ${{ matrix.go-version }} on ${{ matrix.os }}
-      uses: actions/setup-go@v1
+      uses: actions/setup-go@v2
       with:
         go-version: ${{ matrix.go-version }}
       id: go
 
     - name: Check out code into the Go module directory
-      uses: actions/checkout@v1
+      uses: actions/checkout@v2
 
     - name: Test on ${{ matrix.os }}
       env:
         GO111MODULE: on
       run: |
          go test ./...
 
+    - name: Test on race ${{ matrix.os }}
+      env:
+        GO111MODULE: on
+      run: |
+        go test -race ./...

.golangci.yml

@@ -12,14 +12,12 @@ linters:
     - goimports
     - misspell
     - govet
-    - golint
     - ineffassign
     - gosimple
-    - deadcode
     - unused
-    - structcheck
     - prealloc
     - unconvert
+    - revive
 
 issues:
   exclude-use-default: false

cmd/ncrypt/main.go

@@ -19,10 +19,10 @@
 //
 // Usage: ncrypt [FLAGS] [ARGUMENTS...]
 //
-//    -cipher string   Specify cipher - default: platform depended
-//    -d               Decrypt
-//    -list            List supported algorithms
-//    -p      string   Specify the password - default: prompt for password
+//	-cipher string   Specify cipher - default: platform depended
+//	-d               Decrypt
+//	-list            List supported algorithms
+//	-p      string   Specify the password - default: prompt for password
 //
 // Examples:
 //

go.mod

@@ -1,8 +1,10 @@
 module github.com/minio/sio
 
 require (
-	golang.org/x/crypto v0.0.0-20190513172903-22d7a77e9e5f
-	golang.org/x/sys v0.0.0-20190412213103-97732733099d
+	golang.org/x/crypto v0.6.0
+	golang.org/x/sys v0.5.0
 )
 
-go 1.13
+require golang.org/x/term v0.5.0 // indirect
+
+go 1.18

go.sum

@@ -1,8 +1,6 @@
-golang.org/x/crypto v0.0.0-20190308221718-c2843e01d9a2/go.mod h1:djNgcEr1/C05ACkg1iLfiJU5Ep61QUkGW8qpdssI0+w=
-golang.org/x/crypto v0.0.0-20190513172903-22d7a77e9e5f h1:R423Cnkcp5JABoeemiGEPlt9tHXFfw5kvc0yqlxRPWo=
-golang.org/x/crypto v0.0.0-20190513172903-22d7a77e9e5f/go.mod h1:yigFU9vqHzYiE8UmvKecakEJjdnWj3jj499lnFckfCI=
-golang.org/x/net v0.0.0-20190404232315-eb5bcb51f2a3/go.mod h1:t9HGtf8HONx5eT2rtn7q6eTqICYqUVnKs3thJo3Qplg=
-golang.org/x/sys v0.0.0-20190215142949-d0b11bdaac8a/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
-golang.org/x/sys v0.0.0-20190412213103-97732733099d h1:+R4KGOnez64A81RvjARKc4UT5/tI9ujCIVX+P5KiHuI=
-golang.org/x/sys v0.0.0-20190412213103-97732733099d/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
-golang.org/x/text v0.3.0/go.mod h1:NqM8EUOU14njkJ3fqMW+pc6Ldnwhi/IjpwHt7yyuwOQ=
+golang.org/x/crypto v0.6.0 h1:qfktjS5LUO+fFKeJXZ+ikTRijMmljikvG68fpMMruSc=
+golang.org/x/crypto v0.6.0/go.mod h1:OFC/31mSvZgRz0V1QTNCzfAI1aIRzbiufJtkMIlEp58=
+golang.org/x/sys v0.5.0 h1:MUK/U/4lj1t1oPg0HfuXDN/Z1wv31ZJ/YcPiGccS4DU=
+golang.org/x/sys v0.5.0/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
+golang.org/x/term v0.5.0 h1:n2a8QNdAb0sZNpU9R1ALUXBbY+w51fCQDN+7EdxNBsY=
+golang.org/x/term v0.5.0/go.mod h1:jMB1sMXY+tzblOD4FWmEbocvup2/aLOaQEp7JmGp78k=

reader-v1.go

@@ -17,7 +17,6 @@ package sio
 import (
 	"errors"
 	"io"
-	"io/ioutil"
 )
 
 type encReaderV10 struct {
@@ -237,7 +236,7 @@ func (r *decReaderAtV10) ReadAt(p []byte, offset int64) (n int, err error) {
 	}
 	decReader.SeqNum = uint32(t)
 	if k := offset % int64(maxPayloadSize); k > 0 {
-		if _, err := io.CopyN(ioutil.Discard, &decReader, k); err != nil {
+		if _, err := io.CopyN(io.Discard, &decReader, k); err != nil {
 			return 0, err
 		}
 	}

reader-v2.go

@@ -17,7 +17,6 @@ package sio
 import (
 	"errors"
 	"io"
-	"io/ioutil"
 	"sync"
 )
 
@@ -291,6 +290,11 @@ func (r *decReaderAtV20) ReadAt(p []byte, offset int64) (n int, err error) {
 	if t+1 > (1<<32)-1 {
 		return 0, errUnexpectedSize
 	}
+	k := offset % int64(maxPayloadSize)
+	if offset > 0 && k == 0 {
+		k = maxPayloadSize
+		t--
+	}
 
 	decReader := decReaderV20{
 		authDecV20: r.ad,
@@ -300,8 +304,8 @@ func (r *decReaderAtV20) ReadAt(p []byte, offset int64) (n int, err error) {
 	}
 	defer decReader.recycle()
 	decReader.SeqNum = uint32(t)
-	if k := offset % int64(maxPayloadSize); k > 0 {
-		if _, err := io.CopyN(ioutil.Discard, &decReader, k); err != nil {
+	if k > 0 {
+		if _, err := io.CopyN(io.Discard, &decReader, k); err != nil {
 			return 0, err
 		}
 	}