more tests + small refactoring (no more App struct)

app/http/http.go

@@ -0,0 +1,86 @@
+// Package http provides functions for detecting a request or a file content type.
+package http
+
+import (
+	"fmt"
+	"net/http"
+	"os"
+	"strings"
+)
+
+// ContentType is a string which represents a content type.
+type ContentType string
+
+const (
+	// PDFContentType represents... the PDF content type.
+	PDFContentType ContentType = "application/pdf"
+	// HTMLContentType represents... the HTML content type.
+	HTMLContentType ContentType = "text/html"
+	// OctetStreamContentType represents... the octet stream content type.
+	OctetStreamContentType ContentType = "application/octet-stream"
+	// ZipContentType represents... the zip content type.
+	ZipContentType ContentType = "application/zip"
+	// MultipartFormDataContentType represents... the multipart form data content type.
+	MultipartFormDataContentType ContentType = "multipart/form-data"
+)
+
+type notAuthorizedContentTypeError struct{}
+
+func (e *notAuthorizedContentTypeError) Error() string {
+	return fmt.Sprintf("Accepted values for 'Content-Type': %s, %s", OctetStreamContentType, MultipartFormDataContentType)
+}
+
+// FindAuthorizedContentType tries to return a content type according to a request header.
+// If no authorized content type found, throws an error.
+func FindAuthorizedContentType(h http.Header) (ContentType, error) {
+	ct := findContentType(h.Get("Content-Type"), HTMLContentType, OctetStreamContentType, MultipartFormDataContentType)
+	if ct == "" {
+		return "", &notAuthorizedContentTypeError{}
+	}
+
+	return ct, nil
+}
+
+type notAuthorizedFileContentTypeError struct{}
+
+func (e *notAuthorizedFileContentTypeError) Error() string {
+	return fmt.Sprintf("Unable to detect a file content type")
+}
+
+// SniffContentType tries to detect the content type of a file.
+// If no authorized content type found, throws an error.
+func SniffContentType(f *os.File) (ContentType, error) {
+	// only the first 512 bytes are used to sniff the content type.
+	buffer := make([]byte, 512)
+	n, err := f.Read(buffer)
+	if err != nil {
+		return "", err
+	}
+
+	// resets the read pointer.
+	f.Seek(0, 0)
+
+	// using n if size of buffer < 512 bytes.
+	ct := findContentType(http.DetectContentType(buffer[:n]), PDFContentType, HTMLContentType, OctetStreamContentType, ZipContentType)
+	if ct == "" {
+		return "", &notAuthorizedFileContentTypeError{}
+	}
+
+	return ct, nil
+}
+
+// findContentType parses a string representing a content type and tries to find
+// one of the given content types.
+func findContentType(contentType string, contentTypes ...ContentType) ContentType {
+	for _, ct := range contentTypes {
+		if i := strings.IndexRune(contentType, ';'); i != -1 {
+			contentType = contentType[0:i]
+		}
+
+		if contentType == string(ct) {
+			return ct
+		}
+	}
+
+	return ""
+}