Merge branch 'master' into 7454-azure-custom-data

[arvados.git] / services / keepstore / collision.go

diff --git a/services/keepstore/collision.go b/services/keepstore/collision.go
index be26514a00ce6ae9092bf12981f5f55818a083f1..a4af563729b3cf0e72686a2913fd3664e497e24d 100644 (file)
--- a/services/keepstore/collision.go
+++ b/services/keepstore/collision.go
@@ -1,6 +1,7 @@
 package main
 
 import (
+       "bytes"
        "crypto/md5"
        "fmt"
        "io"
@@ -47,3 +48,37 @@ func collisionOrCorrupt(expectMD5 string, buf1, buf2 []byte, rdr io.Reader) erro
        }
        return <-outcome
 }
+
+func compareReaderWithBuf(rdr io.Reader, expect []byte, hash string) error {
+       bufLen := 1 << 20
+       if bufLen > len(expect) && len(expect) > 0 {
+               // No need for bufLen to be longer than
+               // expect, except that len(buf)==0 would
+               // prevent us from handling empty readers the
+               // same way as non-empty readers: reading 0
+               // bytes at a time never reaches EOF.
+               bufLen = len(expect)
+       }
+       buf := make([]byte, bufLen)
+       cmp := expect
+
+       // Loop invariants: all data read so far matched what
+       // we expected, and the first N bytes of cmp are
+       // expected to equal the next N bytes read from
+       // rdr.
+       for {
+               n, err := rdr.Read(buf)
+               if n > len(cmp) || bytes.Compare(cmp[:n], buf[:n]) != 0 {
+                       return collisionOrCorrupt(hash, expect[:len(expect)-len(cmp)], buf[:n], rdr)
+               }
+               cmp = cmp[n:]
+               if err == io.EOF {
+                       if len(cmp) != 0 {
+                               return collisionOrCorrupt(hash, expect[:len(expect)-len(cmp)], nil, nil)
+                       }
+                       return nil
+               } else if err != nil {
+                       return err
+               }
+       }
+}