diff --git a/modules/charset/charset.go b/modules/charset/charset.go
index 3000864c2e..55e183ebfc 100644
--- a/modules/charset/charset.go
+++ b/modules/charset/charset.go
@@ -14,6 +14,7 @@ import (
 
 	"code.gitea.io/gitea/modules/log"
 	"code.gitea.io/gitea/modules/setting"
+	"code.gitea.io/gitea/modules/util"
 
 	"github.com/gogs/chardet"
 	"golang.org/x/net/html/charset"
@@ -26,9 +27,9 @@ var UTF8BOM = []byte{'\xef', '\xbb', '\xbf'}
 // ToUTF8WithFallbackReader detects the encoding of content and coverts to UTF-8 reader if possible
 func ToUTF8WithFallbackReader(rd io.Reader) io.Reader {
 	var buf = make([]byte, 2048)
-	n, err := rd.Read(buf)
+	n, err := util.ReadAtMost(rd, buf)
 	if err != nil {
-		return rd
+		return io.MultiReader(bytes.NewReader(RemoveBOMIfPresent(buf[:n])), rd)
 	}
 
 	charsetLabel, err := DetectEncoding(buf[:n])
diff --git a/modules/csv/csv.go b/modules/csv/csv.go
index ee54452891..83b1a5d37b 100644
--- a/modules/csv/csv.go
+++ b/modules/csv/csv.go
@@ -30,11 +30,8 @@ func CreateReader(input io.Reader, delimiter rune) *stdcsv.Reader {
 // CreateReaderAndGuessDelimiter tries to guess the field delimiter from the content and creates a csv.Reader.
 func CreateReaderAndGuessDelimiter(rd io.Reader) (*stdcsv.Reader, error) {
 	var data = make([]byte, 1e4)
-	size, err := rd.Read(data)
+	size, err := util.ReadAtMost(rd, data)
 	if err != nil {
-		if err == io.EOF {
-			return CreateReader(bytes.NewReader([]byte{}), rune(',')), nil
-		}
 		return nil, err
 	}
 
diff --git a/modules/git/blob.go b/modules/git/blob.go
index 5831bc3735..39b28cbe26 100644
--- a/modules/git/blob.go
+++ b/modules/git/blob.go
@@ -12,6 +12,7 @@ import (
 	"io/ioutil"
 
 	"code.gitea.io/gitea/modules/typesniffer"
+	"code.gitea.io/gitea/modules/util"
 )
 
 // This file contains common functions between the gogit and !gogit variants for git Blobs
@@ -29,7 +30,7 @@ func (b *Blob) GetBlobContent() (string, error) {
 	}
 	defer dataRc.Close()
 	buf := make([]byte, 1024)
-	n, _ := dataRc.Read(buf)
+	n, _ := util.ReadAtMost(dataRc, buf)
 	buf = buf[:n]
 	return string(buf), nil
 }
diff --git a/modules/repofiles/update.go b/modules/repofiles/update.go
index ad984c465a..5b45479f3f 100644
--- a/modules/repofiles/update.go
+++ b/modules/repofiles/update.go
@@ -19,6 +19,7 @@ import (
 	repo_module "code.gitea.io/gitea/modules/repository"
 	"code.gitea.io/gitea/modules/setting"
 	"code.gitea.io/gitea/modules/structs"
+	"code.gitea.io/gitea/modules/util"
 
 	stdcharset "golang.org/x/net/html/charset"
 	"golang.org/x/text/transform"
@@ -61,7 +62,7 @@ func detectEncodingAndBOM(entry *git.TreeEntry, repo *models.Repository) (string
 	}
 	defer reader.Close()
 	buf := make([]byte, 1024)
-	n, err := reader.Read(buf)
+	n, err := util.ReadAtMost(reader, buf)
 	if err != nil {
 		// return default
 		return "UTF-8", false
@@ -84,7 +85,7 @@ func detectEncodingAndBOM(entry *git.TreeEntry, repo *models.Repository) (string
 				}
 				defer dataRc.Close()
 				buf = make([]byte, 1024)
-				n, err = dataRc.Read(buf)
+				n, err = util.ReadAtMost(dataRc, buf)
 				if err != nil {
 					// return default
 					return "UTF-8", false
diff --git a/modules/typesniffer/typesniffer.go b/modules/typesniffer/typesniffer.go
index d257b8179b..9e29b3557c 100644
--- a/modules/typesniffer/typesniffer.go
+++ b/modules/typesniffer/typesniffer.go
@@ -10,6 +10,8 @@ import (
 	"net/http"
 	"regexp"
 	"strings"
+
+	"code.gitea.io/gitea/modules/util"
 )
 
 // Use at most this many bytes to determine Content Type.
@@ -86,8 +88,8 @@ func DetectContentType(data []byte) SniffedType {
 // DetectContentTypeFromReader guesses the content type contained in the reader.
 func DetectContentTypeFromReader(r io.Reader) (SniffedType, error) {
 	buf := make([]byte, sniffLen)
-	n, err := r.Read(buf)
-	if err != nil && err != io.EOF {
+	n, err := util.ReadAtMost(r, buf)
+	if err != nil {
 		return SniffedType{}, fmt.Errorf("DetectContentTypeFromReader io error: %w", err)
 	}
 	buf = buf[:n]
diff --git a/modules/util/io.go b/modules/util/io.go
new file mode 100644
index 0000000000..b467c0ac8a
--- /dev/null
+++ b/modules/util/io.go
@@ -0,0 +1,20 @@
+// Copyright 2021 The Gitea Authors. All rights reserved.
+// Use of this source code is governed by a MIT-style
+// license that can be found in the LICENSE file.
+
+package util
+
+import (
+	"io"
+)
+
+// ReadAtMost reads at most len(buf) bytes from r into buf.
+// It returns the number of bytes copied. n is only less then len(buf) if r provides fewer bytes.
+// If EOF occurs while reading, err will be nil.
+func ReadAtMost(r io.Reader, buf []byte) (n int, err error) {
+	n, err = io.ReadFull(r, buf)
+	if err == io.EOF || err == io.ErrUnexpectedEOF {
+		err = nil
+	}
+	return
+}
diff --git a/routers/common/repo.go b/routers/common/repo.go
index 8d33fb07fb..e5b1a0493a 100644
--- a/routers/common/repo.go
+++ b/routers/common/repo.go
@@ -18,6 +18,7 @@ import (
 	"code.gitea.io/gitea/modules/log"
 	"code.gitea.io/gitea/modules/setting"
 	"code.gitea.io/gitea/modules/typesniffer"
+	"code.gitea.io/gitea/modules/util"
 )
 
 // ServeBlob download a git.Blob
@@ -42,8 +43,8 @@ func ServeBlob(ctx *context.Context, blob *git.Blob) error {
 // ServeData download file from io.Reader
 func ServeData(ctx *context.Context, name string, size int64, reader io.Reader) error {
 	buf := make([]byte, 1024)
-	n, err := reader.Read(buf)
-	if err != nil && err != io.EOF {
+	n, err := util.ReadAtMost(reader, buf)
+	if err != nil {
 		return err
 	}
 	if n >= 0 {
diff --git a/routers/web/repo/attachment.go b/routers/web/repo/attachment.go
index 5becbea271..a32bc3e140 100644
--- a/routers/web/repo/attachment.go
+++ b/routers/web/repo/attachment.go
@@ -15,6 +15,7 @@ import (
 	"code.gitea.io/gitea/modules/setting"
 	"code.gitea.io/gitea/modules/storage"
 	"code.gitea.io/gitea/modules/upload"
+	"code.gitea.io/gitea/modules/util"
 	"code.gitea.io/gitea/routers/common"
 )
 
@@ -43,10 +44,8 @@ func uploadAttachment(ctx *context.Context, allowedTypes string) {
 	defer file.Close()
 
 	buf := make([]byte, 1024)
-	n, _ := file.Read(buf)
-	if n > 0 {
-		buf = buf[:n]
-	}
+	n, _ := util.ReadAtMost(file, buf)
+	buf = buf[:n]
 
 	err = upload.Verify(buf, header.Filename, allowedTypes)
 	if err != nil {
diff --git a/routers/web/repo/editor.go b/routers/web/repo/editor.go
index 0f978c7b01..f7a8778344 100644
--- a/routers/web/repo/editor.go
+++ b/routers/web/repo/editor.go
@@ -114,7 +114,7 @@ func editFile(ctx *context.Context, isNewFile bool) {
 		ctx.Data["FileName"] = blob.Name()
 
 		buf := make([]byte, 1024)
-		n, _ := dataRc.Read(buf)
+		n, _ := util.ReadAtMost(dataRc, buf)
 		buf = buf[:n]
 
 		// Only some file types are editable online as text.
@@ -747,7 +747,7 @@ func UploadFileToServer(ctx *context.Context) {
 	defer file.Close()
 
 	buf := make([]byte, 1024)
-	n, _ := file.Read(buf)
+	n, _ := util.ReadAtMost(file, buf)
 	if n > 0 {
 		buf = buf[:n]
 	}
diff --git a/routers/web/repo/lfs.go b/routers/web/repo/lfs.go
index 173ffb773f..937d623e5a 100644
--- a/routers/web/repo/lfs.go
+++ b/routers/web/repo/lfs.go
@@ -26,6 +26,7 @@ import (
 	"code.gitea.io/gitea/modules/setting"
 	"code.gitea.io/gitea/modules/storage"
 	"code.gitea.io/gitea/modules/typesniffer"
+	"code.gitea.io/gitea/modules/util"
 )
 
 const (
@@ -272,7 +273,7 @@ func LFSFileGet(ctx *context.Context) {
 	}
 	defer dataRc.Close()
 	buf := make([]byte, 1024)
-	n, err := dataRc.Read(buf)
+	n, err := util.ReadAtMost(dataRc, buf)
 	if err != nil {
 		ctx.ServerError("Data", err)
 		return
@@ -297,10 +298,10 @@ func LFSFileGet(ctx *context.Context) {
 			break
 		}
 
-		buf := charset.ToUTF8WithFallbackReader(io.MultiReader(bytes.NewReader(buf), dataRc))
+		rd := charset.ToUTF8WithFallbackReader(io.MultiReader(bytes.NewReader(buf), dataRc))
 
 		// Building code view blocks with line number on server side.
-		fileContent, _ := ioutil.ReadAll(buf)
+		fileContent, _ := ioutil.ReadAll(rd)
 
 		var output bytes.Buffer
 		lines := strings.Split(string(fileContent), "\n")
diff --git a/routers/web/repo/view.go b/routers/web/repo/view.go
index 2be81d7485..64b97a91ab 100644
--- a/routers/web/repo/view.go
+++ b/routers/web/repo/view.go
@@ -31,6 +31,7 @@ import (
 	"code.gitea.io/gitea/modules/setting"
 	"code.gitea.io/gitea/modules/structs"
 	"code.gitea.io/gitea/modules/typesniffer"
+	"code.gitea.io/gitea/modules/util"
 )
 
 const (
@@ -264,7 +265,7 @@ func renderDirectory(ctx *context.Context, treeLink string) {
 		defer dataRc.Close()
 
 		buf := make([]byte, 1024)
-		n, _ := dataRc.Read(buf)
+		n, _ := util.ReadAtMost(dataRc, buf)
 		buf = buf[:n]
 
 		st := typesniffer.DetectContentType(buf)
@@ -299,7 +300,7 @@ func renderDirectory(ctx *context.Context, treeLink string) {
 					defer dataRc.Close()
 
 					buf = make([]byte, 1024)
-					n, err = dataRc.Read(buf)
+					n, err = util.ReadAtMost(dataRc, buf)
 					if err != nil {
 						ctx.ServerError("Data", err)
 						return
@@ -413,7 +414,7 @@ func renderFile(ctx *context.Context, entry *git.TreeEntry, treeLink, rawLink st
 	ctx.Data["RawFileLink"] = rawLink + "/" + ctx.Repo.TreePath
 
 	buf := make([]byte, 1024)
-	n, _ := dataRc.Read(buf)
+	n, _ := util.ReadAtMost(dataRc, buf)
 	buf = buf[:n]
 
 	st := typesniffer.DetectContentType(buf)
@@ -445,10 +446,8 @@ func renderFile(ctx *context.Context, entry *git.TreeEntry, treeLink, rawLink st
 				defer dataRc.Close()
 
 				buf = make([]byte, 1024)
-				n, err = dataRc.Read(buf)
-				// Error EOF don't mean there is an error, it just means we read to
-				// the end
-				if err != nil && err != io.EOF {
+				n, err = util.ReadAtMost(dataRc, buf)
+				if err != nil {
 					ctx.ServerError("Data", err)
 					return
 				}