diff --git a/build.pl b/build.pl
index 1e0cf3122..8919168d7 100755
--- a/build.pl
+++ b/build.pl
@@ -329,6 +329,7 @@ TARGET: lib/go/camli/blobserver/localdisk
 TARGET: lib/go/camli/client
 TARGET: lib/go/camli/httputil
 TARGET: lib/go/camli/jsonsign
+TARGET: lib/go/camli/magic
 TARGET: lib/go/camli/misc/httprange
 TARGET: lib/go/camli/mysqlindexer
     - ext:github.com/Philio/GoMySQL
diff --git a/lib/go/camli/magic/magic.go b/lib/go/camli/magic/magic.go
new file mode 100644
index 000000000..3758f81d9
--- /dev/null
+++ b/lib/go/camli/magic/magic.go
@@ -0,0 +1,44 @@
+/*
+Copyright 2011 Google Inc.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+nYou may obtain a copy of the License at
+
+     http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package magic
+
+import (
+	"bytes"
+)
+
+type prefixEntry struct {
+	prefix []byte
+	mtype  string
+}
+
+var prefixTable = []prefixEntry{
+	{[]byte("\xff\xd8\xff\xe1"), "image/jpeg"},
+	{[]byte("\xff\xd8\xff\xe0"), "image/jpeg"},
+	{[]byte{137, 'P', 'N', 'G', '\r', '\n', 26, 10}, "image/png"},
+}
+
+// Returns the emptry string if unknown.
+func MimeType(hdr []byte) string {
+	hlen := len(hdr)
+	for _, pte := range prefixTable {
+		plen := len(pte.prefix)
+		if hlen > plen && bytes.Equal(hdr[:plen], pte.prefix) {
+			return pte.mtype
+		}
+	}
+	return ""
+}
diff --git a/lib/go/camli/mysqlindexer/receive.go b/lib/go/camli/mysqlindexer/receive.go
index 6081c1bbb..54996a4ba 100644
--- a/lib/go/camli/mysqlindexer/receive.go
+++ b/lib/go/camli/mysqlindexer/receive.go
@@ -19,9 +19,9 @@ package mysqlindexer
 import (
 	"camli/blobref"
 	"camli/blobserver"
+	"camli/magic"
 	"camli/schema"
 
-	"bytes"
 	"io"
 	"json"
 	"log"
@@ -55,17 +55,6 @@ func (sn *blobSniffer) IsTruncated() bool {
 	return sn.written > maxSniffSize
 }
 
-type prefixEntry struct {
-	prefix []byte
-	mtype  string
-}
-
-var prefixTable = []prefixEntry{
-	{[]byte("\xff\xd8\xff\xe1"), "image/jpeg"},
-	{[]byte("\xff\xd8\xff\xe0"), "image/jpeg"},
-	{[]byte{137, 'P', 'N', 'G', '\r', '\n', 26, 10}, "image/png"},
-}
-
 // returns content type (string) or nil if unknown
 func (sn *blobSniffer) MimeType() interface{} {
 	if sn.mimeType != nil {
@@ -75,21 +64,17 @@ func (sn *blobSniffer) MimeType() interface{} {
 }
 
 func (sn *blobSniffer) Parse() {
-	hlen := len(sn.header)
-	for _, pte := range prefixTable {
-		plen := len(pte.prefix)
-		if hlen > plen && bytes.Equal(sn.header[:plen], pte.prefix) {
-			sn.mimeType = &pte.mtype
-		}
-	}
-
 	// Try to parse it as JSON
+	// TODO: move this into the magic library?  Is the magic library Camli-specific
+	// or to be upstreamed elsewhere?
 	if sn.bufferIsCamliJson() {
 		str := "application/json; camliType=" + sn.camli.Type
 		sn.mimeType = &str
 	}
 
-	return
+	if mime := magic.MimeType(sn.header); mime != "" {
+		sn.mimeType = &mime
+	}
 }
 
 func (sn *blobSniffer) bufferIsCamliJson() bool {