Add content-based mime-type detection

data/README.md

@@ -6,3 +6,7 @@
 # lru
 
 An LRU implementation. Accessors available for the first item, last item, list of all keys, count, fullness, membership checks, explicit drops, and popping the oldest in a loop. You can also set a callback for when items are dropped and dump the current contents of the LRU.
+
+# mimetype
+
+Convenience function for determining a mime-type from an `io.Reader`.

data/mime.go

@@ -0,0 +1,41 @@
+package ridata
+
+import (
+	"io"
+
+	"net/http"
+
+	"github.com/dsoprea/go-logging"
+)
+
+const (
+	MimetypeLeadBytes = 512
+)
+
+// GetMimetypeFromContent uses net/http to map from magic-bytes to mime-type.
+func GetMimetypeFromContent(r io.Reader, fileSize int) (mimetype string, err error) {
+	defer func() {
+		if state := recover(); state != nil {
+			err = log.Wrap(state.(error))
+		}
+	}()
+
+	// TODO(dustin): !! Add test.
+
+	leadCount := MimetypeLeadBytes
+	if fileSize > 0 && fileSize < leadCount {
+		leadCount = fileSize
+	}
+
+	buffer := make([]byte, leadCount)
+
+	n, err := io.ReadFull(r, buffer)
+	log.PanicIf(err)
+
+	buffer = buffer[:n]
+
+	// Always returns a valid mime-type.
+	contentType := http.DetectContentType(buffer)
+
+	return contentType, nil
+}

data/mime_test.go

@@ -0,0 +1,63 @@
+package ridata
+
+import (
+    "bytes"
+    "testing"
+
+    "encoding/hex"
+
+    "github.com/dsoprea/go-logging"
+    "github.com/dsoprea/go-utility/filesystem"
+)
+
+func TestGetMimetypeFromContent(t *testing.T) {
+    raw := "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"
+
+    buffer, err := hex.DecodeString(raw)
+    log.PanicIf(err)
+
+    b := bytes.NewBuffer(buffer)
+
+    mimetype, err := GetMimetypeFromContent(b, 0)
+    log.PanicIf(err)
+
+    if mimetype != "image/jpeg" {
+        t.Fatalf("Mime-type not correct: [%s]", mimetype)
+    }
+}
+
+func TestGetMimetypeFromContent__ShortData_Error(t *testing.T) {
+    raw := "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"
+
+    buffer, err := hex.DecodeString(raw)
+    log.PanicIf(err)
+
+    buffer = buffer[:256]
+
+    b := rifs.NewSeekableBufferWithBytes(buffer)
+
+    _, err = GetMimetypeFromContent(b, 0)
+    if err == nil {
+        t.Fatalf("Expected error for not enough data.")
+    } else if err.Error() != "unexpected EOF" {
+        log.Panic(err)
+    }
+}
+
+func TestGetMimetypeFromContent__ShortData_Success(t *testing.T) {
+    raw := "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"
+
+    buffer, err := hex.DecodeString(raw)
+    log.PanicIf(err)
+
+    buffer = buffer[:256]
+
+    b := rifs.NewSeekableBufferWithBytes(buffer)
+
+    mimetype, err := GetMimetypeFromContent(b, len(buffer))
+    log.PanicIf(err)
+
+    if mimetype != "image/jpeg" {
+        t.Fatalf("Mime-type not correct: [%s]", mimetype)
+    }
+}