feat: improve file extension detection

If a file extension is explicitly specified in the upload name, it is
always used directly. Detection of common file extension combinations is
also performed. Currently, only ".tar.gz" and ".tar.xz" are detected. If
you would like to add support for more common combinations, please open
an issue or pull request.

If no file extension is explicitly specified, jaf falls back to MIME
type detection via the github.com/gabriel-vasile/mimetype library.

extdetect/extension_detection.go

@@ -0,0 +1,56 @@
+package extdetect
+
+import (
+	"strings"
+
+	"github.com/gabriel-vasile/mimetype"
+)
+
+var knownCombinations []string = []string{
+	".tar.gz",
+	".tar.xz",
+}
+
+func BuildFileExtension(fileData []byte, name string) string {
+	// First, check whether any file ending has been specified manually
+	curExtIdx := strings.LastIndex(name, ".")
+
+	if curExtIdx == -1 {
+		// No file ending specified in name, use MIME type detection
+		return mimetype.Detect(fileData).Extension()
+	}
+
+	// Otherwise, some file extension was manually specified and we will use that. First, check
+	// whether this is an "easy" case of file extension, i.e., a name where there is only one "."
+	// character and we can treat what's after it as the file extension.
+	nextExtIdx := strings.LastIndex(name[:curExtIdx], ".")
+	if nextExtIdx == -1 {
+		// Just one ".", so an easy case
+		return name[curExtIdx:]
+	}
+
+	// There are multiple "." in the name. Look for known extension combinations (e.g., ".tar.gz",
+	// ".tar.xz") and use that if found.
+	// XXX: This could be done more efficiently (at least in theory) with some suffix tree structure
+	//      but for the few known combinations we have, it would likely be slower on real-world
+	//      computer architectures.
+	stillBuilding := true
+	for stillBuilding {
+		stillBuilding = false
+		for _, comb := range knownCombinations {
+			if !strings.HasPrefix(comb, name[nextExtIdx:]) {
+				continue
+			}
+
+			stillBuilding = true
+			curExtIdx = nextExtIdx
+			nextExtIdx = strings.LastIndex(name[:curExtIdx], ".")
+			if nextExtIdx == -1 {
+				// No more extension candidates -> return current state of the builder
+				return name[curExtIdx:]
+			}
+		}
+	}
+
+	return name[curExtIdx:]
+}

extdetect/extension_detection_test.go

@@ -0,0 +1,65 @@
+package extdetect
+
+import (
+	"os"
+	"testing"
+)
+
+func TestDetectedExtensions(t *testing.T) {
+	const fixturePath = "../fixtures/gps.png"
+
+	type tType struct {
+		name           string
+		fileData       []byte
+		expectedOutput string
+	}
+
+	pngFile, err := os.ReadFile(fixturePath)
+	if err != nil {
+		t.Fatalf("Could not open \"%s\" which is required for the test. Error: %s", fixturePath,
+			err)
+	}
+
+	tests := []tType{
+		{ // extension is detected correctly from file when not specified explicitly
+			name:           "foo",
+			fileData:       pngFile,
+			expectedOutput: ".png",
+		},
+		{
+			name:           "foo.txt",
+			expectedOutput: ".txt",
+		},
+		{ // simple extension that's the last part of a known combination is detected correctly
+			name:           "foo.gz",
+			expectedOutput: ".gz",
+		},
+		{ // simple extension that's the first part of a known combination is detected correctly
+			name:           "foo.tar",
+			expectedOutput: ".tar",
+		},
+		{ // combined extension is detected correctly
+			name:           "foo.tar.gz",
+			expectedOutput: ".tar.gz",
+		},
+		{
+			name:           "foo.tar.xz",
+			expectedOutput: ".tar.xz",
+		},
+		{ // combined extension that is NOT known only returns the last part
+			name:           "foo.jpg.zip",
+			expectedOutput: ".zip",
+		},
+		{ // combined extension is detected correctly even with many "." in the name
+			name:           "foo.jpg.zip.tar.gz",
+			expectedOutput: ".tar.gz",
+		},
+	}
+
+	for _, test := range tests {
+		output := BuildFileExtension(test.fileData, test.name)
+		if output != test.expectedOutput {
+			t.Fatalf("got output '%s', expected '%s'", output, test.expectedOutput)
+		}
+	}
+}

go.mod

@@ -7,6 +7,7 @@ require (
 	github.com/dsoprea/go-jpeg-image-structure/v2 v2.0.0-20210512043942-b434301c6836
 	github.com/dsoprea/go-logging v0.0.0-20200710184922-b02d349568dd
 	github.com/dsoprea/go-png-image-structure/v2 v2.0.0-20210512210324-29b889a6093d
+	github.com/gabriel-vasile/mimetype v1.4.1
 	github.com/go-errors/errors v1.1.1
 	golang.org/x/exp v0.0.0-20220722155223-a9213eeb770e
 )
@@ -17,6 +18,6 @@ require (
 	github.com/dsoprea/go-utility/v2 v2.0.0-20200717064901-2fccff4aa15e // indirect
 	github.com/go-xmlfmt/xmlfmt v0.0.0-20191208150333-d5b6f63a941b // indirect
 	github.com/golang/geo v0.0.0-20200319012246-673a6f80352d // indirect
-	golang.org/x/net v0.0.0-20200707034311-ab3426394381 // indirect
+	golang.org/x/net v0.0.0-20220624214902-1bab6f366d9e // indirect
 	gopkg.in/yaml.v2 v2.3.0 // indirect
 )

go.sum

@@ -18,6 +18,8 @@ github.com/dsoprea/go-png-image-structure/v2 v2.0.0-20210512210324-29b889a6093d/
 github.com/dsoprea/go-utility v0.0.0-20200711062821-fab8125e9bdf/go.mod h1:95+K3z2L0mqsVYd6yveIv1lmtT3tcQQ3dVakPySffW8=
 github.com/dsoprea/go-utility/v2 v2.0.0-20200717064901-2fccff4aa15e h1:IxIbA7VbCNrwumIYjDoMOdf4KOSkMC6NJE4s8oRbE7E=
 github.com/dsoprea/go-utility/v2 v2.0.0-20200717064901-2fccff4aa15e/go.mod h1:uAzdkPTub5Y9yQwXe8W4m2XuP0tK4a9Q/dantD0+uaU=
+github.com/gabriel-vasile/mimetype v1.4.1 h1:TRWk7se+TOjCYgRth7+1/OYLNiRNIotknkFtf/dnN7Q=
+github.com/gabriel-vasile/mimetype v1.4.1/go.mod h1:05Vi0w3Y9c/lNvJOdmIwvrrAhX3rYhfQQCaf9VJcv7M=
 github.com/go-errors/errors v1.0.1/go.mod h1:f4zRHt4oKfwPJE5k8C9vpYG+aDHdBFUsgrm6/TyX73Q=
 github.com/go-errors/errors v1.0.2/go.mod h1:psDX2osz5VnTOnFWbDeWwS7yejl+uV3FEWEp4lssFEs=
 github.com/go-errors/errors v1.1.1 h1:ljK/pL5ltg3qoN+OtN6yCv9HWSfMwxSx90GJCZQxYNg=
@@ -38,12 +40,18 @@ golang.org/x/net v0.0.0-20200320220750-118fecf932d8/go.mod h1:z5CRVTTTmAJ677TzLL
 golang.org/x/net v0.0.0-20200501053045-e0ff5e5a1de5/go.mod h1:qpuaurCH72eLCgpAm/N6yyVIVM9cpaDIP3A8BGJEC5A=
 golang.org/x/net v0.0.0-20200513185701-a91f0712d120/go.mod h1:qpuaurCH72eLCgpAm/N6yyVIVM9cpaDIP3A8BGJEC5A=
 golang.org/x/net v0.0.0-20200520182314-0ba52f642ac2/go.mod h1:qpuaurCH72eLCgpAm/N6yyVIVM9cpaDIP3A8BGJEC5A=
-golang.org/x/net v0.0.0-20200707034311-ab3426394381 h1:VXak5I6aEWmAXeQjA+QSZzlgNrpq9mjcfDemuexIKsU=
 golang.org/x/net v0.0.0-20200707034311-ab3426394381/go.mod h1:/O7V0waA8r7cgGh81Ro3o1hOxt32SMVPicZroKQ2sZA=
+golang.org/x/net v0.0.0-20220624214902-1bab6f366d9e h1:TsQ7F31D3bUCLeqPT0u+yjp1guoArKaNKmCr22PYgTQ=
+golang.org/x/net v0.0.0-20220624214902-1bab6f366d9e/go.mod h1:XRhObCWvk6IyKnWLug+ECip1KBveYUHfp+8e9klMJ9c=
 golang.org/x/sys v0.0.0-20190215142949-d0b11bdaac8a/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
 golang.org/x/sys v0.0.0-20190412213103-97732733099d/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
 golang.org/x/sys v0.0.0-20200323222414-85ca7c5b95cd/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
+golang.org/x/sys v0.0.0-20210615035016-665e8c7367d1/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
+golang.org/x/sys v0.0.0-20220520151302-bc2c85ada10a/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
+golang.org/x/term v0.0.0-20210927222741-03fcf44c2211/go.mod h1:jbD1KX2456YbFQfuXm/mYQcufACuNUgVhRMnK/tPxf8=
 golang.org/x/text v0.3.0/go.mod h1:NqM8EUOU14njkJ3fqMW+pc6Ldnwhi/IjpwHt7yyuwOQ=
+golang.org/x/text v0.3.7/go.mod h1:u+2+/6zg+i71rQMx5EYifcz6MCKuco9NR6JIITiCfzQ=
+golang.org/x/tools v0.0.0-20180917221912-90fa682c2a6e/go.mod h1:n7NCudcB/nEzxVGmLbDWY5pfWTLqBcC2KZ6jyYvM4mQ=
 gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405 h1:yhCVgyC4o1eVCa2tZl7eS0r+SDo693bJlVdllGtEeKM=
 gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
 gopkg.in/yaml.v2 v2.2.7/go.mod h1:hI93XBmqTisBFMUTm0b8Fm+jr3Dg1NNxqwp+5A1VGuI=

uploadhandler.go

@@ -7,9 +7,9 @@ import (
 	"math/rand"
 	"net/http"
 	"os"
-	"strings"
 
 	"github.com/leon-richardt/jaf/exifscrubber"
+	"github.com/leon-richardt/jaf/extdetect"
 )
 
 type uploadHandler struct {
@@ -65,8 +65,7 @@ func (handler *uploadHandler) ServeHTTP(w http.ResponseWriter, r *http.Request)
 		}
 	}
 
-	_, fileExtension := splitFileName(header.Filename)
+	link, err := generateLink(handler, fileData[:], header.Filename)
-	link, err := generateLink(handler, fileData[:], fileExtension)
 	if err != nil {
 		http.Error(w, "could not save file: "+err.Error(), http.StatusInternalServerError)
 		log.Println("    could not save file: " + err.Error())
@@ -80,13 +79,15 @@ func (handler *uploadHandler) ServeHTTP(w http.ResponseWriter, r *http.Request)
 // Generates a valid link to uploadFile with the specified file extension.
 // Returns the link or an error in case of failure.
 // Does not close the passed file pointer.
-func generateLink(handler *uploadHandler, fileData []byte, fileExtension string) (string, error) {
+func generateLink(handler *uploadHandler, fileData []byte, fileName string) (string, error) {
+	ext := extdetect.BuildFileExtension(fileData, fileName)
+
 	// Find an unused file name
 	var fullFileName string
 	var savePath string
 	for {
 		fileStem := createRandomFileName(handler.config.LinkLength)
-		fullFileName = fileStem + fileExtension
+		fullFileName = fileStem + ext
 		savePath = handler.config.FileDir + fullFileName
 
 		if !fileExists(savePath) {
@@ -125,14 +126,3 @@ func createRandomFileName(length int) string {
 
 	return string(chars)
 }
-
-func splitFileName(name string) (string, string) {
-	extIndex := strings.LastIndex(name, ".")
-
-	if extIndex == -1 {
-		// No dot at all
-		return name, ""
-	}
-
-	return name[:extIndex], name[extIndex:]
-}