amend the CidFromReader slice extension math

The append+make slice extension idiom works, but note that append uses
the slice's length as its base. We need to append the number of bytes
required for length to reach cidLength, not the capacity.

The added test case panicked before this change, and works now:

	--- FAIL: TestReadCidsFromBuffer (0.00s)
	panic: runtime error: slice bounds out of range [:73] with capacity 64 [recovered]
		panic: runtime error: slice bounds out of range [:73] with capacity 64

	goroutine 37 [running]:
	testing.tRunner.func1.2({0x570d60, 0xc000016438})
		testing/testing.go:1203 +0x24e
	testing.tRunner.func1()
		testing/testing.go:1206 +0x218
	panic({0x570d60, 0xc000016438})
		runtime/panic.go:1038 +0x215
	github.com/ipfs/go-cid.CidFromReader({0x5b0e20, 0xc000010900})
		github.com/ipfs/go-cid/cid.go:803 +0x75f
	github.com/ipfs/go-cid.TestReadCidsFromBuffer(0xc00014ba00)
		github.com/ipfs/go-cid/cid_test.go:710 +0x625
	testing.tRunner(0xc00014ba00, 0x58af38)
		testing/testing.go:1253 +0x102
	created by testing.(*T).Run
		testing/testing.go:1300 +0x35a
	exit status 2
	FAIL	github.com/ipfs/go-cid	0.004s

.github/workflows/automerge.yml

@@ -33,9 +33,7 @@ jobs:
   automerge:
     needs: automerge-check
     runs-on: ubuntu-latest
-    # The check for the user is redundant here, as this job depends on the automerge-check job,
+    if: ${{ needs.automerge-check.outputs.status == 'true' }}
-    # but it prevents this job from spinning up, just to be skipped shortly after.
-    if: github.event.pull_request.user.login == 'web3-bot' && needs.automerge-check.outputs.status == 'true'
     steps:
     - name: Wait on tests
       uses: lewagon/wait-on-check-action@bafe56a6863672c681c3cf671f5e10b20abf2eaa # v0.2

.github/workflows/go-check.yml

@@ -8,28 +8,17 @@ jobs:
   unit:
     runs-on: ubuntu-latest
     name: All
-    env:
-      RUNGOGENERATE: false
     steps:
       - uses: actions/checkout@v2
         with:
           submodules: recursive
       - uses: actions/setup-go@v2
         with:
-          go-version: "1.17.x"
+          go-version: "1.16.x"
-      - name: Run repo-specific setup
-        uses: ./.github/actions/go-check-setup
-        if: hashFiles('./.github/actions/go-check-setup') != ''
-      - name: Read config
-        if: hashFiles('./.github/workflows/go-check-config.json') != ''
-        run: |
-          if jq -re .gogenerate ./.github/workflows/go-check-config.json; then
-            echo "RUNGOGENERATE=true" >> $GITHUB_ENV
-          fi
       - name: Install staticcheck
-        run: go install honnef.co/go/tools/cmd/staticcheck@df71e5d0e0ed317ebf43e6e59cf919430fa4b8f2 # 2021.1.1 (v0.2.1)
+        run: go install honnef.co/go/tools/cmd/staticcheck@434f5f3816b358fe468fa83dcba62d794e7fe04b # 2021.1 (v0.2.0)
       - name: Check that go.mod is tidy
-        uses: protocol/multiple-go-modules@v1.2
+        uses: protocol/multiple-go-modules@v1.0
         with:
           run: |
             go mod tidy
@@ -48,27 +37,14 @@ jobs:
           fi
       - name: go vet
         if: ${{ success() || failure() }} # run this step even if the previous one failed
-        uses: protocol/multiple-go-modules@v1.2
+        uses: protocol/multiple-go-modules@v1.0
         with:
           run: go vet ./...
       - name: staticcheck
         if: ${{ success() || failure() }} # run this step even if the previous one failed
-        uses: protocol/multiple-go-modules@v1.2
+        uses: protocol/multiple-go-modules@v1.0
         with:
           run: |
             set -o pipefail
             staticcheck ./... | sed -e 's@\(.*\)\.go@./\1.go@g'
-      - name: go generate
-        uses: protocol/multiple-go-modules@v1.2
-        if: (success() || failure()) && env.RUNGOGENERATE == 'true'
-        with:
-          run: |
-            git clean -fd # make sure there aren't untracked files / directories
-            go generate ./...
-            # check if go generate modified or added any files
-            if ! $(git add . && git diff-index HEAD --exit-code --quiet); then
-              echo "go generated caused changes to the repository:"
-              git status --short
-              exit 1
-            fi
 

.github/workflows/go-test.yml

@@ -10,9 +10,7 @@ jobs:
       fail-fast: false
       matrix:
         os: [ "ubuntu", "windows", "macos" ]
-        go: [ "1.16.x", "1.17.x" ]
+        go: [ "1.15.x", "1.16.x" ]
-    env:
-      COVERAGES: ""
     runs-on: ${{ matrix.os }}-latest
     name: ${{ matrix.os}} (go ${{ matrix.go }})
     steps:
@@ -26,30 +24,24 @@ jobs:
         run: |
           go version
           go env
-      - name: Run repo-specific setup
-        uses: ./.github/actions/go-test-setup
-        if: hashFiles('./.github/actions/go-test-setup') != ''
       - name: Run tests
-        uses: protocol/multiple-go-modules@v1.2
+        uses: protocol/multiple-go-modules@v1.0
         with:
-          run: go test -v -coverprofile module-coverage.txt ./...
+          run: go test -v -coverprofile coverage.txt ./...
       - name: Run tests (32 bit)
         if: ${{ matrix.os != 'macos' }} # can't run 32 bit tests on OSX.
-        uses: protocol/multiple-go-modules@v1.2
+        uses: protocol/multiple-go-modules@v1.0
         env:
           GOARCH: 386
         with:
           run: go test -v ./...
       - name: Run tests with race detector
         if: ${{ matrix.os == 'ubuntu' }} # speed things up. Windows and OSX VMs are slow
-        uses: protocol/multiple-go-modules@v1.2
+        uses: protocol/multiple-go-modules@v1.0
         with:
           run: go test -v -race ./...
-      - name: Collect coverage files
-        shell: bash
-        run: echo "COVERAGES=$(find . -type f -name 'module-coverage.txt' | tr -s '\n' ',' | sed 's/,$//')" >> $GITHUB_ENV
       - name: Upload coverage to Codecov
-        uses: codecov/codecov-action@51d810878be5422784e86451c0e7c14e5860ec47 # v2.0.2
+        uses: codecov/codecov-action@a1ed4b322b4b38cb846afb5a0ebfa17086917d27 # v1.5.0
         with:
-          files: '${{ env.COVERAGES }}'
+          file: coverage.txt
           env_vars: OS=${{ matrix.os }}, GO=${{ matrix.go }}

cid.go

@@ -22,7 +22,6 @@ package cid
 import (
 	"bytes"
 	"encoding"
-	"encoding/binary"
 	"encoding/json"
 	"errors"
 	"fmt"
@@ -174,24 +173,16 @@ func NewCidV0(mhash mh.Multihash) Cid {
 // Panics if the multihash is invalid.
 func NewCidV1(codecType uint64, mhash mh.Multihash) Cid {
 	hashlen := len(mhash)
-
+	// two 8 bytes (max) numbers plus hash
-	// Two 8 bytes (max) numbers plus hash.
+	buf := make([]byte, 1+varint.UvarintSize(codecType)+hashlen)
-	// We use strings.Builder to only allocate once.
+	n := varint.PutUvarint(buf, 1)
-	var b strings.Builder
+	n += varint.PutUvarint(buf[n:], codecType)
-	b.Grow(1 + varint.UvarintSize(codecType) + hashlen)
+	cn := copy(buf[n:], mhash)
-
-	b.WriteByte(1)
-
-	var buf [binary.MaxVarintLen64]byte
-	n := varint.PutUvarint(buf[:], codecType)
-	b.Write(buf[:n])
-
-	cn, _ := b.Write(mhash)
 	if cn != hashlen {
 		panic("copy hash length is inconsistent")
 	}
 
-	return Cid{b.String()}
+	return Cid{string(buf[:n+hashlen])}
 }
 
 var (

cid_fuzz.go

@@ -1,4 +1,3 @@
-//go:build gofuzz
 // +build gofuzz
 
 package cid

go.mod

@@ -7,4 +7,4 @@ require (
 	golang.org/x/crypto v0.0.0-20210506145944-38f3c27a63bf // indirect
 )
 
-go 1.16
+go 1.15