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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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23 changes: 18 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 @@ -16,6 +16,7 @@
*/
package org.apache.commons.io;

import java.io.Console;
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import java.io.File;
import java.util.ArrayDeque;
import java.util.ArrayList;
Expand Down Expand Up @@ -930,15 +931,27 @@ public static int getPrefixLength(final String fileName) {
if (!isSeparator(ch0) || !isSeparator(ch1)) {
return isSeparator(ch0) ? 1 : 0;
}

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// 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);
int pos;
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
33 changes: 18 additions & 15 deletions src/test/java/org/apache/commons/io/FilenameUtilsTest.java
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Expand Up @@ -70,31 +70,31 @@ public void setUp() throws Exception {
+ " as the parent directory does not exist");
}
try (BufferedOutputStream output3 =
new BufferedOutputStream(Files.newOutputStream(testFile1))) {
new BufferedOutputStream(Files.newOutputStream(testFile1))) {
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TestUtils.generateTestData(output3, testFile1Size);
}
if (!Files.exists(testFile2.getParent())) {
throw new IOException("Cannot create file " + testFile2
+ " as the parent directory does not exist");
}
try (BufferedOutputStream output2 =
new BufferedOutputStream(Files.newOutputStream(testFile2))) {
new BufferedOutputStream(Files.newOutputStream(testFile2))) {
TestUtils.generateTestData(output2, testFile2Size);
}
if (!Files.exists(testFile1.getParent())) {
throw new IOException("Cannot create file " + testFile1
+ " as the parent directory does not exist");
}
try (BufferedOutputStream output1 =
new BufferedOutputStream(Files.newOutputStream(testFile1))) {
new BufferedOutputStream(Files.newOutputStream(testFile1))) {
TestUtils.generateTestData(output1, testFile1Size);
}
if (!Files.exists(testFile2.getParent())) {
throw new IOException("Cannot create file " + testFile2
+ " as the parent directory does not exist");
}
try (BufferedOutputStream output =
new BufferedOutputStream(Files.newOutputStream(testFile2))) {
new BufferedOutputStream(Files.newOutputStream(testFile2))) {
TestUtils.generateTestData(output, testFile2Size);
}
}
Expand Down Expand Up @@ -192,7 +192,6 @@ 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"));
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}

@Test
Expand Down Expand Up @@ -275,7 +274,6 @@ void testGetFullPath() {
assertNull(FilenameUtils.getFullPath("1:"));
assertNull(FilenameUtils.getFullPath("1:a"));
assertNull(FilenameUtils.getFullPath("///a/b/c.txt"));
assertNull(FilenameUtils.getFullPath("//a"));
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assertEquals("", FilenameUtils.getFullPath(""));

Expand All @@ -288,6 +286,7 @@ void testGetFullPath() {

assertEquals("C:/", FilenameUtils.getFullPath("C:/"));
assertEquals("//server/", FilenameUtils.getFullPath("//server/"));
assertEquals("//server", FilenameUtils.getFullPath("//server"));
assertEquals("~/", FilenameUtils.getFullPath("~"));
assertEquals("~/", FilenameUtils.getFullPath("~/"));
assertEquals("~user/", FilenameUtils.getFullPath("~user"));
Expand Down Expand Up @@ -317,7 +316,6 @@ void testGetFullPathNoEndSeparator() {
assertNull(FilenameUtils.getFullPathNoEndSeparator("1:"));
assertNull(FilenameUtils.getFullPathNoEndSeparator("1:a"));
assertNull(FilenameUtils.getFullPathNoEndSeparator("///a/b/c.txt"));
assertNull(FilenameUtils.getFullPathNoEndSeparator("//a"));
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assertEquals("", FilenameUtils.getFullPathNoEndSeparator(""));

Expand All @@ -330,6 +328,7 @@ 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 @@ -408,12 +407,12 @@ void testGetPath() {
assertNull(FilenameUtils.getPath("1:"));
assertNull(FilenameUtils.getPath("1:a"));
assertNull(FilenameUtils.getPath("///a/b/c.txt"));
assertNull(FilenameUtils.getPath("//a"));
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assertEquals("", FilenameUtils.getPath(""));
assertEquals("", FilenameUtils.getPath(DRIVE_C));
assertEquals("", FilenameUtils.getPath("C:/"));
assertEquals("", FilenameUtils.getPath("//server/"));
assertEquals("",FilenameUtils.getPath("//server"));
assertEquals("", FilenameUtils.getPath("~"));
assertEquals("", FilenameUtils.getPath("~/"));
assertEquals("", FilenameUtils.getPath("~user"));
Expand Down Expand Up @@ -450,12 +449,12 @@ void testGetPathNoEndSeparator() {
assertNull(FilenameUtils.getPathNoEndSeparator("1:"));
assertNull(FilenameUtils.getPathNoEndSeparator("1:a"));
assertNull(FilenameUtils.getPathNoEndSeparator("///a/b/c.txt"));
assertNull(FilenameUtils.getPathNoEndSeparator("//a"));
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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 +483,6 @@ void testGetPrefix() {
assertNull(FilenameUtils.getPrefix("1:"));
assertNull(FilenameUtils.getPrefix("1:a"));
assertNull(FilenameUtils.getPrefix("\\\\\\a\\b\\c.txt"));
assertNull(FilenameUtils.getPrefix("\\\\a"));
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assertEquals("", FilenameUtils.getPrefix(""));
assertEquals("\\", FilenameUtils.getPrefix("\\"));
Expand All @@ -498,6 +496,7 @@ 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 All @@ -507,6 +506,7 @@ void testGetPrefix() {
assertEquals("\\", FilenameUtils.getPrefix("\\a\\b\\c.txt"));
assertEquals("C:\\", FilenameUtils.getPrefix("C:\\a\\b\\c.txt"));
assertEquals("\\\\server\\", FilenameUtils.getPrefix("\\\\server\\a\\b\\c.txt"));
assertEquals("\\\\a", FilenameUtils.getPrefix("\\\\a"));

assertEquals("", FilenameUtils.getPrefix("a/b/c.txt"));
assertEquals("/", FilenameUtils.getPrefix("/a/b/c.txt"));
Expand Down Expand Up @@ -534,7 +534,6 @@ 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"));
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assertEquals(0, FilenameUtils.getPrefixLength(""));
assertEquals(1, FilenameUtils.getPrefixLength("\\"));
Expand All @@ -548,6 +547,7 @@ 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 All @@ -558,6 +558,7 @@ void testGetPrefixLength() {
assertEquals(2, FilenameUtils.getPrefixLength("C:a\\b\\c.txt"));
assertEquals(3, FilenameUtils.getPrefixLength("C:\\a\\b\\c.txt"));
assertEquals(9, FilenameUtils.getPrefixLength("\\\\server\\a\\b\\c.txt"));
assertEquals(3, FilenameUtils.getPrefixLength( "\\\\a"));

assertEquals(0, FilenameUtils.getPrefixLength("a/b/c.txt"));
assertEquals(1, FilenameUtils.getPrefixLength("/a/b/c.txt"));
Expand Down Expand Up @@ -775,8 +776,8 @@ void testNormalize() {
assertNull(FilenameUtils.normalize("1:"));
assertNull(FilenameUtils.normalize("1:a"));
assertNull(FilenameUtils.normalize("\\\\\\a\\b\\c.txt"));
assertNull(FilenameUtils.normalize("\\\\a"));
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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"));
assertEquals(DRIVE_C + SEP + "a" + SEP + "b" + SEP + "c.txt", FilenameUtils.normalize("C:\\a\\b/c.txt"));
Expand Down Expand Up @@ -915,13 +916,14 @@ 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"));
assertEquals(SEP + SEP + "1::" + SEP + "a" + SEP + "b" + SEP + "c.txt", FilenameUtils.normalize("\\\\1::\\a\\b\\c.txt"));
assertEquals(SEP + SEP + "server.example.org" + SEP + "a" + SEP + "b" + SEP + "c.txt", FilenameUtils.normalize("\\\\server.example.org\\a\\b\\c.txt"));
assertEquals(SEP + SEP + "server.sub.example.org" + SEP + "a" + SEP + "b" + SEP + "c.txt",
FilenameUtils.normalize("\\\\server.sub.example.org\\a\\b\\c.txt"));
FilenameUtils.normalize("\\\\server.sub.example.org\\a\\b\\c.txt"));
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assertEquals(SEP + SEP + "server." + SEP + "a" + SEP + "b" + SEP + "c.txt", FilenameUtils.normalize("\\\\server.\\a\\b\\c.txt"));
assertEquals(SEP + SEP + "1::127.0.0.1" + SEP + "a" + SEP + "b" + SEP + "c.txt", FilenameUtils.normalize("\\\\1::127.0.0.1\\a\\b\\c.txt"));

Expand Down Expand Up @@ -986,8 +988,8 @@ void testNormalizeNoEndSeparator() {
assertNull(FilenameUtils.normalizeNoEndSeparator("1:"));
assertNull(FilenameUtils.normalizeNoEndSeparator("1:a"));
assertNull(FilenameUtils.normalizeNoEndSeparator("\\\\\\a\\b\\c.txt"));
assertNull(FilenameUtils.normalizeNoEndSeparator("\\\\a"));
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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"));
assertEquals(DRIVE_C + SEP + "a" + SEP + "b" + SEP + "c.txt", FilenameUtils.normalizeNoEndSeparator("C:\\a\\b/c.txt"));
Expand Down Expand Up @@ -1127,6 +1129,7 @@ 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 +1211,4 @@ 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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