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Improve return type of base64_decode() #4492

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47 changes: 29 additions & 18 deletions src/Type/Php/Base64DecodeDynamicFunctionReturnTypeExtension.php
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Original file line number Diff line number Diff line change
Expand Up @@ -6,13 +6,15 @@
use PHPStan\Analyser\Scope;
use PHPStan\DependencyInjection\AutowiredService;
use PHPStan\Reflection\FunctionReflection;
use PHPStan\TrinaryLogic;
use PHPStan\Type\BenevolentUnionType;
use PHPStan\Type\Constant\ConstantBooleanType;
use PHPStan\Type\Constant\ConstantStringType;
use PHPStan\Type\DynamicFunctionReturnTypeExtension;
use PHPStan\Type\MixedType;
use PHPStan\Type\StringType;
use PHPStan\Type\Type;
use PHPStan\Type\UnionType;
use function base64_decode;

#[AutowiredService]
final class Base64DecodeDynamicFunctionReturnTypeExtension implements DynamicFunctionReturnTypeExtension
Expand All @@ -30,32 +32,41 @@ public function getTypeFromFunctionCall(
): Type
{
$args = $functionCall->getArgs();
if (!isset($args[1])) {
if (!isset($args[0])) {
return new StringType();
}

$argType = $scope->getType($args[1]->value);

if ($argType instanceof MixedType) {
return new BenevolentUnionType([new StringType(), new ConstantBooleanType(false)]);
$stringArgNode = $args[0]->value;
$constantStrings = $scope->getType($stringArgNode)->getConstantStrings();
if ($constantStrings !== []) {
$isValidBase64 = TrinaryLogic::lazyExtremeIdentity(
$constantStrings,
static function (ConstantStringType $constantString): TrinaryLogic {
$isValid = base64_decode($constantString->getValue(), true) !== false;
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@staabm staabm Jan 27, 2026 •
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base64-decoding any string from within the codebase could skyrocket memory needed by phpstan analysis.

e.g. some codebases contain multi-megabyte base64 representations of images

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@ondrejmirtes ondrejmirtes Jan 27, 2026

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Yeah, I'm inclining not doing this at all.

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@jlherren jlherren Jan 27, 2026

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Would a length-limit help?

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@ondrejmirtes ondrejmirtes Feb 10, 2026

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I'm really not sure why would we want to decode literal strings passed to this method at all.

return TrinaryLogic::createFromBoolean($isValid);
},
);
} else {
$isValidBase64 = TrinaryLogic::createMaybe();
}

$isTrueType = $argType->isTrue();
$isFalseType = $argType->isFalse();
$compareTypes = $isTrueType->compareTo($isFalseType);
if ($compareTypes === $isTrueType) {
return new UnionType([new StringType(), new ConstantBooleanType(false)]);
if (isset($functionCall->getArgs()[1])) {
$strictArgNode = $functionCall->getArgs()[1]->value;
$isStrict = $scope->getType($strictArgNode)->toBoolean()->toTrinaryLogic();
} else {
$isStrict = TrinaryLogic::createNo();
}
if ($compareTypes === $isFalseType) {

if ($isStrict->no() || $isValidBase64->yes()) {
return new StringType();
}

// second argument could be interpreted as true
if (!$isTrueType->no()) {
return new UnionType([new StringType(), new ConstantBooleanType(false)]);
if ($isStrict->yes() && $isValidBase64->no()) {
return new ConstantBooleanType(false);
}

return new StringType();
if ($isStrict->maybe() && $isValidBase64->maybe()) {
return new BenevolentUnionType([new StringType(), new ConstantBooleanType(false)]);
}
return new UnionType([new StringType(), new ConstantBooleanType(false)]);
}

}
11 changes: 6 additions & 5 deletions tests/PHPStan/Analyser/data/functions.php
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Original file line number Diff line number Diff line change
Expand Up @@ -78,11 +78,12 @@
$fileObject = new \SplFileObject(__FILE__);
$fileObjectStat = $fileObject->fstat();

$base64DecodeWithoutStrict = base64_decode('');
$base64DecodeWithStrictDisabled = base64_decode('', false);
$base64DecodeWithStrictEnabled = base64_decode('', true);
$base64DecodeDefault = base64_decode('', null);
$base64DecodeBenevolent = base64_decode('', $undefined);
$string = (string)time();
$base64DecodeWithoutStrict = base64_decode($string);
$base64DecodeWithStrictDisabled = base64_decode($string, false);
$base64DecodeWithStrictEnabled = base64_decode($string, true);
$base64DecodeDefault = base64_decode($string, null);
$base64DecodeBenevolent = base64_decode($string, $undefined);


//str_word_count
Expand Down
16 changes: 16 additions & 0 deletions tests/PHPStan/Analyser/nsrt/base64_decode.php
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Expand Up @@ -11,11 +11,27 @@ public function nonStrictMode(string $string): void
{
assertType('string', base64_decode($string));
assertType('string', base64_decode($string, false));
assertType('string', base64_decode($string, 0));
assertType('string', base64_decode('UEhQU3Rhbg==', false));
assertType('string', base64_decode('!!!', false));
}

public function strictMode(string $string): void
{
assertType('string|false', base64_decode($string, true));
assertType('string|false', base64_decode($string, 1));
assertType('string', base64_decode(mt_rand() ? 'UEhQU3Rhbg==' : 'cm9ja3Mh', true));
assertType('string|false', base64_decode(mt_rand() ? 'UEhQU3Rhbg==' : '!!!', true));
assertType('false', base64_decode(mt_rand() ? '!' : '!!!', true));
}

public function mixedMode(string $string): void
{
assertType('(string|false)', base64_decode($string, unknown()));
assertType('(string|false)', base64_decode($string, mt_rand(0, 1) === 1));
assertType('(string|false)', base64_decode($string, mt_rand(0, 1)));
assertType('string', base64_decode('UEhQU3Rhbg==', mt_rand(0, 1) === 1));
assertType('string|false', base64_decode('!!!', mt_rand(0, 1) === 1));
}

}
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