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snapshot: read meta.json correctly. #5193

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merged 2 commits into from
Jan 8, 2019
Merged

snapshot: read meta.json correctly. #5193

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91aa911
snapshot: read meta.json correctly.
hanshasselberg Jan 6, 2019
b65679f
add explanation why we no longer use json.Decode.
hanshasselberg Jan 7, 2019
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8 changes: 6 additions & 2 deletions snapshot/archive.go
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Original file line number Diff line number Diff line change
Expand Up @@ -18,6 +18,7 @@ import (
"fmt"
"hash"
"io"
"io/ioutil"
"time"

"github.com/hashicorp/raft"
Expand Down Expand Up @@ -193,8 +194,11 @@ func read(in io.Reader, metadata *raft.SnapshotMeta, snap io.Writer) error {

switch hdr.Name {
case "meta.json":
dec := json.NewDecoder(io.TeeReader(archive, metaHash))
if err := dec.Decode(&metadata); err != nil {
buf, err := ioutil.ReadAll(io.TeeReader(archive, metaHash))
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I think it's worth commenting on why this is needed. The root cause seems to be something like:

// json.Decode will stop reading as soon as the initial JSON element (the object) is closed 
// (i.e. at the closing brace) which means the final newline, if any, is not read and so is not 
// delivered to `metaHash`. This means that the hash calculated is not the same as the
// one in SHA256SUMS which was calculated over the raw bytes in the file. By explicitly 
// reading the whole thing first we ensure that we calculate the hash over the exact
// same bytes regardless of whitespace.

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Good point, I will add a comment!

if err != nil {
return fmt.Errorf("failed to read snapshot metadata: %v", err)
}
if err := json.Unmarshal(buf, &metadata); err != nil {
return fmt.Errorf("failed to decode snapshot metadata: %v", err)
}

Expand Down
19 changes: 19 additions & 0 deletions snapshot/archive_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -63,6 +63,25 @@ func TestArchive(t *testing.T) {
}
}

func TestArchive_GoodData(t *testing.T) {
paths := []string{
"../test/snapshot/spaces-meta.tar",
}
for i, p := range paths {
f, err := os.Open(p)
if err != nil {
t.Fatalf("err: %v", err)
}
defer f.Close()

var metadata raft.SnapshotMeta
err = read(f, &metadata, ioutil.Discard)
if err != nil {
t.Fatalf("case %d: should've read the snapshot, but didn't: %v", i, err)
}
}
}

func TestArchive_BadData(t *testing.T) {
cases := []struct {
Name string
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Binary file added test/snapshot/spaces-meta.tar
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