StreamOpenFailureUnchecked

warning native on by default

Group: Probable bugs

Detect fopen result passed to a stream-only operation without excluding false.

Example

<?php
function bad($path) { $h = fopen($path, 'rb'); fread($h, 12); }

Reported:

• line 2: Check that the stream opened successfully.

Detection

Follow each producer reaching a local read, including results written on an earlier loop turn or before a backward jump. A check of an earlier result does not check a later replacement; a check repeated before every consumption does. Ignore producers belonging to other result contracts when selecting an unchecked result.

• Report fopen result passed to a stream-only operation without excluding false.
• Resolve builtin calls and named arguments before checking the contract. Project-local callees are considered only when their bodies or immutable summaries establish the required facts. The default is enabled, with positive proof required.
• For flow-dependent conditions, require a reachable source-to-use path with no intervening invalidation. Unknown calls, ambiguous aliases, recursion or analysis-budget exhaustion cannot establish definite facts.

Exceptions (no report)

• Strict/truthy success guards, terminating error branches, proven wrappers and overwritten identities are excluded.
• Because fopen yields a stream resource or false, any condition on the same reaching handle that separates the two outcomes is a guard, not only a strict comparison. Recognized conditions: the bare variable (truthiness), empty(), is_resource(), is_bool(), strict or loose comparison of any of these with a true/false literal on either side, their negation with !, a conjunct of &&/and that holds, a disjunct of ||/or that fails, and a plain assignment of the fopen call itself used as the condition (if ($h = fopen(...)), if (($h = fopen(...)) !== false)).
• A guard applies when it dominates the use: the use is in the branch of an if/elseif/else or ternary the condition selects, in the body of a while loop whose condition is the guard, in the right operand of a short-circuit operator whose left operand is the condition, or after an earlier statement of the same statement list that is either an if whose body always leaves (return, throw, exit, break, continue, goto) or an expression statement that only completes on success: $h = fopen(...) or die();, $h === false and throw ...;, $h ?: throw ...;. The guarded variable must still hold the same fopen result at the use; a reassignment between guard and use voids the guard.
• Not treated as guards: assert() (it can be compiled out), a comparison stored in another variable, switch (true)/match (true) arms, an error branch that only calls a function or method without leaving syntactically, and a preceding stream call on the same handle.
• When several producer paths join, a path crossing an explicit error-handler registration is left unknown if the bounded local scan cannot establish ordinary warning behavior. This abstains from following that producer; it does not prove the handle is valid. A direct restore or a direct handler that only returns false can permit tracking until unsupported intervening effects occur. A different unguarded opening remains reportable when its own path is unaffected. Single-producer behavior is unchanged.
• Unresolved targets, incomplete required facts, suppressed findings and PHP versions lacking the referenced API or language feature produce no report. User declarations shadowing builtin names are not builtin contracts.
• A value the shared flow analysis proves is not the failure value at the use is never reported, whatever form the proof takes: a test in an enclosing branch, loop condition or short-circuit operand, an early exit, a statement that leaves on the failing outcome ($v !== false or exit;, $v or throw …;, $v ?: throw …;), a failing branch that ends in a call that never returns (a callee declared never, or a function or a final or private method every path of which throws or exits), a test stored in a boolean and tested later while neither the boolean nor the tested variable has been written, and, on PHP 8.0 and later outside any try with a catch, a builtin call that returned after receiving the value for a parameter that only accepts arrays, objects or callables: such a call throws a TypeError for false. A switch (true) case is read like the condition of an if/elseif chain; in a switch on the variable itself with constant labels, the cases after a false or null label and the default hold a value that is neither, as does a true case. Positions PHP may skip prove nothing: the right side of ??=, the arguments of a null-safe call and anything chained after ?->. A null-safe call to a never-returning method does not end the path, and f(...) creates a closure without calling f. An arm of match (true) is read like a switch (true) case; an arm that throws, exits or calls a function that never returns takes no part in what holds after the match. | and & between two tests are read like || and && for the outcome that fixes both operands (a false |, a true &), and a strict in_array($v, [...], true) over literals that include neither false nor null excludes both where it holds. goto jumps are followed, including a jump out of a try or catch block, which runs the finally blocks it leaves on its way. Where a goto label is written before the use, and after the place where its scope first names the checked variable, a variable that can hold the same value, or code that may write any variable (extract, compact, get_defined_vars, parse_str given one argument, a variable variable, $GLOBALS, eval, an included file), a jump can land between a guard and the use: only what the flow analysis establishes counts there, and a guard recognized by where it is written proves nothing. Two variables can hold the same value when one is written from the other by a plain assignment, an assignment by reference or ??=, when a foreach takes one out of the other, or through a chain of those; in the value assigned, the receiver and the arguments of a call, the operands of an operator other than ??, the variables a string embeds and an element key do not count, and a statement that only reads (echo $prefix . $parts['host'];) ties nothing. A parameter is named from the start of the function, and a checked expression that reads $this or no variable counts every label before it. In a scope the flow analysis does not follow (one that evaluates or includes code, which may write any variable) a guarded use after such a label is therefore reported. A generator is followed: while it is suspended at a yield, the code that consumes it may write only what an unknown call may write, and, when the generator returns by reference, the variable it yields. A label written before all of that, such as a retry: label ahead of the try that produces and checks the value, changes nothing, whatever else the function reads beside the checked value; at file level every label written before the use counts. What was established of a static local holds until the next call, or code that runs without a call being written (an object converted to text, a magic property or offset access, the destructor of an object a variable held when it is given another value), that may enter the function again and assign the variable. A call of PHP's own counts as such when it may run code of the project: it is given a callback other than the name of a PHP function that only computes on text and numbers and raises no warning whatever text it is given (a closed list: strlen, trim, intval and the like, not hexdec, abs or chr, which warn about text that is no number), an object it may convert, a class name it loads (method_exists($name, 'm'), is_callable('A::b'), defined('A::B'), class_alias($name, 'B'), new ReflectionClass($name), $arrayObject->setIteratorClass($name)), a class to construct ($statement->fetchObject('Row')) or a filter that one of PHP's own FILTER_… constants does not name, which may be the one that calls back, or it runs what was registered earlier (an error, session or output-buffer handler, the callbacks of a cURL transfer or an XML parser, an iterator wrapped in another, a filter added to a stream). A warning that a PHP function raises by itself when called directly (hex2bin given an odd number of digits, a file that cannot be read) is not counted, although the error handler of the project receives it. This limits every guard form of this specification, not only the ones the flow analysis reads.

Fix

No automatic fix: choosing fallback versus failure belongs to the caller.

PHP versions

Apply only on PHP versions supporting the referenced APIs and syntax (within PHP 5.3–8.5). Builtin behavior and argument contracts follow the configured PHP version. Extension-specific calls require resolved extension API symbols; do not treat same-named application functions as extension calls.

Options

None. Enable or disable this rule through normal rule configuration.

Configure

In custos.json:

{
  "rules": {
    "StreamOpenFailureUnchecked": {
      "enabled": false
    }
  }
}

Suppress

Before the statement or declaration (or the first statement of the file):

// @custos-ignore StreamOpenFailureUnchecked