fix(download): use preferred extensions map for platform-stable MIME lookups

mime.ExtensionsByType returns extensions in alphabetical order from the
system MIME database, which varies by platform and Go version (e.g.
.ehtml before .html for text/html). Add a preferredExtensions map for
common MIME types to always return the canonical extension.

commit: 2cb614b9eb1eed1017cce97b5e7966350a5c9b0b
author: brice · 8mo ago · 2026-02-12 18:28 UTC
parent: 87e495c
signature: GPG VerifiedCD88F9E564E0102646FB6077A1A07C7C7C3E349D · arch-gpg Verified for the committer email

2 files · +21 -1

M internal/domain/download/filename.go +20 -0


@@ -46,6 +46,22 @@ func SanitizeFilenameWithExtension(name, mimeType string) string {
46	46		return clean
47	47		}
48	48
	49	+	// preferredExtensions maps MIME types whose stdlib extension list is
	50	+	// platform-dependent (alphabetical order) to the canonical extension.
	51	+	// Without this, mime.ExtensionsByType("text/html") may return ".ehtml"
	52	+	// instead of ".html" depending on the system MIME database.
	53	+	var preferredExtensions = map[string]string{
	54	+	"text/html": ".html",
	55	+	"text/plain": ".txt",
	56	+	"text/xml": ".xml",
	57	+	"application/xhtml+xml": ".xhtml",
	58	+	"image/jpeg": ".jpg",
	59	+	"image/svg+xml": ".svg",
	60	+	"audio/mpeg": ".mp3",
	61	+	"video/mp4": ".mp4",
	62	+	"application/octet-stream": ".bin",
	63	+	}
	64	+
49	65		// GetExtensionFromMimeType returns a file extension for a given MIME type.
50	66		// Returns empty string if MIME type is unknown or empty.
51	67		// Handles MIME types with parameters (e.g., "application/pdf; charset=binary").

@@ -61,6 +77,10 @@ func GetExtensionFromMimeType(mimeType string) string {
61	77		return ""
62	78		}
63	79
	80	+	if ext, ok := preferredExtensions[mediaType]; ok {
	81	+	return ext
	82	+	}
	83	+
64	84		exts, err := mime.ExtensionsByType(mediaType)
65	85		if err != nil \|\| len(exts) == 0 {
66	86		return ""


@@ -46,6 +46,22 @@ func SanitizeFilenameWithExtension(name, mimeType string) string {
46	return clean	46		return clean
47	}	47		}
48		48
		49	+	// preferredExtensions maps MIME types whose stdlib extension list is
		50	+	// platform-dependent (alphabetical order) to the canonical extension.
		51	+	// Without this, mime.ExtensionsByType("text/html") may return ".ehtml"
		52	+	// instead of ".html" depending on the system MIME database.
		53	+	var preferredExtensions = map[string]string{
		54	+	"text/html": ".html",
		55	+	"text/plain": ".txt",
		56	+	"text/xml": ".xml",
		57	+	"application/xhtml+xml": ".xhtml",
		58	+	"image/jpeg": ".jpg",
		59	+	"image/svg+xml": ".svg",
		60	+	"audio/mpeg": ".mp3",
		61	+	"video/mp4": ".mp4",
		62	+	"application/octet-stream": ".bin",
		63	+	}
		64	+
49	// GetExtensionFromMimeType returns a file extension for a given MIME type.	65		// GetExtensionFromMimeType returns a file extension for a given MIME type.
50	// Returns empty string if MIME type is unknown or empty.	66		// Returns empty string if MIME type is unknown or empty.
51	// Handles MIME types with parameters (e.g., "application/pdf; charset=binary").	67		// Handles MIME types with parameters (e.g., "application/pdf; charset=binary").

@@ -61,6 +77,10 @@ func GetExtensionFromMimeType(mimeType string) string {
61	return ""	77		return ""
62	}	78		}
63		79
		80	+	if ext, ok := preferredExtensions[mediaType]; ok {
		81	+	return ext
		82	+	}
		83	+
64	exts, err := mime.ExtensionsByType(mediaType)	84		exts, err := mime.ExtensionsByType(mediaType)
65	if err != nil \|\| len(exts) == 0 {	85		if err != nil \|\| len(exts) == 0 {
66	return ""	86		return ""

M internal/domain/download/filename_test.go +1 -1


@@ -147,7 +147,7 @@ func TestGetExtensionFromMimeType(t *testing.T) {
147	147		{
148	148		name: "text html with charset",
149	149		input: "text/html; charset=utf-8",
150		-	expected: ".htm",
	150	+	expected: ".html",
151	151		},
152	152		{
153	153		name: "mime type with multiple params",


@@ -147,7 +147,7 @@ func TestGetExtensionFromMimeType(t *testing.T) {
147		{	147		{
148		name: "text html with charset",	148		name: "text html with charset",
149		input: "text/html; charset=utf-8",	149		input: "text/html; charset=utf-8",
150	-	expected: ".htm",	150	+	expected: ".html",
151		},	151		},
152		{	152		{
153		name: "mime type with multiple params",	153		name: "mime type with multiple params",