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IO-475: Fix UNC path prefix validation in FilenameUtils #825

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IO-475: Fix UNC path prefix validation in FilenameUtils #825

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ba525f1
[IO-745] Fix FilenameUtils#getPrefixLength for UNC paths without trai…
MiriamCohenDev Jan 21, 2026
318c919
[IO-745] Fix FilenameUtilsTest Adding and modifying tests to match th…
MiriamCohenDev Jan 21, 2026
64038e1
IO-475: Address all review comments from Grigory
MiriamCohenDev Jan 26, 2026
cc47983
Merge remote-tracking branch 'upstream/master' into IO-475-fix-unc-pr…
MiriamCohenDev Feb 2, 2026
860bc20
Fix Checkstyle violations and address review comments
MiriamCohenDev Feb 2, 2026
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21 changes: 16 additions & 5 deletions src/main/java/org/apache/commons/io/FilenameUtils.java
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Original file line number Diff line number Diff line change
Expand Up @@ -930,15 +930,25 @@ public static int getPrefixLength(final String fileName) {
if (!isSeparator(ch0) || !isSeparator(ch1)) {
return isSeparator(ch0) ? 1 : 0;
}
// UNC path: //hostname or //hostname/...
int posUnix = fileName.indexOf(UNIX_NAME_SEPARATOR, 2);
int posWin = fileName.indexOf(WINDOWS_NAME_SEPARATOR, 2);
if (posUnix == NOT_FOUND && posWin == NOT_FOUND || posUnix == 2 || posWin == 2) {

if (posUnix == 2 || posWin == 2) {
return NOT_FOUND;
}
posUnix = posUnix == NOT_FOUND ? posWin : posUnix;
posWin = posWin == NOT_FOUND ? posUnix : posWin;
final int pos = Math.min(posUnix, posWin) + 1;
final String hostnamePart = fileName.substring(2, pos - 1);
final int pos;
final String hostnamePart;
if (posUnix == NOT_FOUND && posWin == NOT_FOUND) {
pos = fileName.length();
hostnamePart = fileName.substring(2);
} else {
posUnix = posUnix == NOT_FOUND ? posWin : posUnix;
posWin = posWin == NOT_FOUND ? posUnix : posWin;
pos = Math.min(posUnix, posWin) + 1;
hostnamePart = fileName.substring(2, pos - 1);
}

return isValidHostName(hostnamePart) ? pos : NOT_FOUND;
}

Expand Down Expand Up @@ -1683,3 +1693,4 @@ public FilenameUtils() {
// empty
}
}

25 changes: 16 additions & 9 deletions src/test/java/org/apache/commons/io/FilenameUtilsTest.java
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Original file line number Diff line number Diff line change
Expand Up @@ -192,7 +192,7 @@ void testEqualsNormalized() {
void testEqualsNormalizedError_IO_128() {
assertFalse(FilenameUtils.equalsNormalizedOnSystem("//file.txt", "file.txt"));
assertFalse(FilenameUtils.equalsNormalizedOnSystem("file.txt", "//file.txt"));
assertFalse(FilenameUtils.equalsNormalizedOnSystem("//file.txt", "//file.txt"));
assertTrue(FilenameUtils.equalsNormalizedOnSystem("//file.txt", "//file.txt"));
}

@Test
Expand Down Expand Up @@ -275,7 +275,7 @@ void testGetFullPath() {
assertNull(FilenameUtils.getFullPath("1:"));
assertNull(FilenameUtils.getFullPath("1:a"));
assertNull(FilenameUtils.getFullPath("///a/b/c.txt"));
assertNull(FilenameUtils.getFullPath("//a"));
assertEquals("//a", FilenameUtils.getFullPath("//a"));

assertEquals("", FilenameUtils.getFullPath(""));

Expand Down Expand Up @@ -317,7 +317,7 @@ void testGetFullPathNoEndSeparator() {
assertNull(FilenameUtils.getFullPathNoEndSeparator("1:"));
assertNull(FilenameUtils.getFullPathNoEndSeparator("1:a"));
assertNull(FilenameUtils.getFullPathNoEndSeparator("///a/b/c.txt"));
assertNull(FilenameUtils.getFullPathNoEndSeparator("//a"));
assertEquals("//a", FilenameUtils.getFullPathNoEndSeparator("//a"));

assertEquals("", FilenameUtils.getFullPathNoEndSeparator(""));

Expand All @@ -330,6 +330,7 @@ void testGetFullPathNoEndSeparator() {

assertEquals("C:/", FilenameUtils.getFullPathNoEndSeparator("C:/"));
assertEquals("//server/", FilenameUtils.getFullPathNoEndSeparator("//server/"));
assertEquals("//server", FilenameUtils.getFullPathNoEndSeparator("//server"));
assertEquals("~", FilenameUtils.getFullPathNoEndSeparator("~"));
assertEquals("~/", FilenameUtils.getFullPathNoEndSeparator("~/"));
assertEquals("~user", FilenameUtils.getFullPathNoEndSeparator("~user"));
Expand Down Expand Up @@ -408,7 +409,7 @@ void testGetPath() {
assertNull(FilenameUtils.getPath("1:"));
assertNull(FilenameUtils.getPath("1:a"));
assertNull(FilenameUtils.getPath("///a/b/c.txt"));
assertNull(FilenameUtils.getPath("//a"));
assertEquals("", FilenameUtils.getPath("//a"));

assertEquals("", FilenameUtils.getPath(""));
assertEquals("", FilenameUtils.getPath(DRIVE_C));
Expand Down Expand Up @@ -450,12 +451,13 @@ void testGetPathNoEndSeparator() {
assertNull(FilenameUtils.getPathNoEndSeparator("1:"));
assertNull(FilenameUtils.getPathNoEndSeparator("1:a"));
assertNull(FilenameUtils.getPathNoEndSeparator("///a/b/c.txt"));
assertNull(FilenameUtils.getPathNoEndSeparator("//a"));
assertEquals("", FilenameUtils.getPathNoEndSeparator("//a"));

assertEquals("", FilenameUtils.getPathNoEndSeparator(""));
assertEquals("", FilenameUtils.getPathNoEndSeparator(DRIVE_C));
assertEquals("", FilenameUtils.getPathNoEndSeparator("C:/"));
assertEquals("", FilenameUtils.getPathNoEndSeparator("//server/"));
assertEquals("", FilenameUtils.getPathNoEndSeparator("//server"));
assertEquals("", FilenameUtils.getPathNoEndSeparator("~"));
assertEquals("", FilenameUtils.getPathNoEndSeparator("~/"));
assertEquals("", FilenameUtils.getPathNoEndSeparator("~user"));
Expand Down Expand Up @@ -484,7 +486,7 @@ void testGetPrefix() {
assertNull(FilenameUtils.getPrefix("1:"));
assertNull(FilenameUtils.getPrefix("1:a"));
assertNull(FilenameUtils.getPrefix("\\\\\\a\\b\\c.txt"));
assertNull(FilenameUtils.getPrefix("\\\\a"));
assertEquals("\\\\a", FilenameUtils.getPrefix("\\\\a"));

assertEquals("", FilenameUtils.getPrefix(""));
assertEquals("\\", FilenameUtils.getPrefix("\\"));
Expand All @@ -498,6 +500,7 @@ void testGetPrefix() {

assertEquals("C:\\", FilenameUtils.getPrefix("C:\\"));
assertEquals("//server/", FilenameUtils.getPrefix("//server/"));
assertEquals("//server", FilenameUtils.getPrefix("//server"));
assertEquals("~/", FilenameUtils.getPrefix("~"));
assertEquals("~/", FilenameUtils.getPrefix("~/"));
assertEquals("~user/", FilenameUtils.getPrefix("~user"));
Expand Down Expand Up @@ -534,7 +537,7 @@ void testGetPrefixLength() {
assertEquals(-1, FilenameUtils.getPrefixLength("1:"));
assertEquals(-1, FilenameUtils.getPrefixLength("1:a"));
assertEquals(-1, FilenameUtils.getPrefixLength("\\\\\\a\\b\\c.txt"));
assertEquals(-1, FilenameUtils.getPrefixLength("\\\\a"));
assertEquals(3, FilenameUtils.getPrefixLength("\\\\a"));

assertEquals(0, FilenameUtils.getPrefixLength(""));
assertEquals(1, FilenameUtils.getPrefixLength("\\"));
Expand All @@ -548,6 +551,7 @@ void testGetPrefixLength() {

assertEquals(3, FilenameUtils.getPrefixLength("C:\\"));
assertEquals(9, FilenameUtils.getPrefixLength("//server/"));
assertEquals(8, FilenameUtils.getPrefixLength("//server"));
assertEquals(2, FilenameUtils.getPrefixLength("~"));
assertEquals(2, FilenameUtils.getPrefixLength("~/"));
assertEquals(6, FilenameUtils.getPrefixLength("~user"));
Expand Down Expand Up @@ -775,7 +779,7 @@ void testNormalize() {
assertNull(FilenameUtils.normalize("1:"));
assertNull(FilenameUtils.normalize("1:a"));
assertNull(FilenameUtils.normalize("\\\\\\a\\b\\c.txt"));
assertNull(FilenameUtils.normalize("\\\\a"));
assertEquals(SEP + SEP + "a", FilenameUtils.normalize("\\\\a"));

assertEquals("a" + SEP + "b" + SEP + "c.txt", FilenameUtils.normalize("a\\b/c.txt"));
assertEquals("" + SEP + "a" + SEP + "b" + SEP + "c.txt", FilenameUtils.normalize("\\a\\b/c.txt"));
Expand Down Expand Up @@ -915,6 +919,7 @@ void testNormalize() {
assertNull(FilenameUtils.normalize("//server/../a"));
assertNull(FilenameUtils.normalize("//server/.."));
assertEquals(SEP + SEP + "server" + SEP + "", FilenameUtils.normalize("//server/"));
assertEquals(SEP + SEP + "server", FilenameUtils.normalize("//server"));

assertEquals(SEP + SEP + "127.0.0.1" + SEP + "a" + SEP + "b" + SEP + "c.txt", FilenameUtils.normalize("\\\\127.0.0.1\\a\\b\\c.txt"));
assertEquals(SEP + SEP + "::1" + SEP + "a" + SEP + "b" + SEP + "c.txt", FilenameUtils.normalize("\\\\::1\\a\\b\\c.txt"));
Expand Down Expand Up @@ -986,7 +991,7 @@ void testNormalizeNoEndSeparator() {
assertNull(FilenameUtils.normalizeNoEndSeparator("1:"));
assertNull(FilenameUtils.normalizeNoEndSeparator("1:a"));
assertNull(FilenameUtils.normalizeNoEndSeparator("\\\\\\a\\b\\c.txt"));
assertNull(FilenameUtils.normalizeNoEndSeparator("\\\\a"));
assertEquals(SEP + SEP + "a", FilenameUtils.normalizeNoEndSeparator("\\\\a"));

assertEquals("a" + SEP + "b" + SEP + "c.txt", FilenameUtils.normalizeNoEndSeparator("a\\b/c.txt"));
assertEquals("" + SEP + "a" + SEP + "b" + SEP + "c.txt", FilenameUtils.normalizeNoEndSeparator("\\a\\b/c.txt"));
Expand Down Expand Up @@ -1127,6 +1132,7 @@ void testNormalizeNoEndSeparator() {
assertNull(FilenameUtils.normalizeNoEndSeparator("//server/../a"));
assertNull(FilenameUtils.normalizeNoEndSeparator("//server/.."));
assertEquals(SEP + SEP + "server" + SEP + "", FilenameUtils.normalizeNoEndSeparator("//server/"));
assertEquals(SEP + SEP + "server", FilenameUtils.normalizeNoEndSeparator("//server"));
}

@Test
Expand Down Expand Up @@ -1208,4 +1214,5 @@ void testSeparatorsToWindows() {
assertEquals("\\a\\b\\c", FilenameUtils.separatorsToWindows("/a/b/c"));
assertEquals("D:\\a\\b\\c", FilenameUtils.separatorsToWindows("D:/a/b/c"));
}

}
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