PHP: rfc:stream_errors

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====== PHP RFC: Stream Error Handling Improvements ======
  * Version: 1.0
  * Date: 2025-11-18
  * Author: Jakub Zelenka, bukka@php.net
  * Status: Under Discussion

===== Introduction =====

PHP's stream error handling has historically been inconsistent across different stream wrappers and operations. Errors
are reported through various mechanisms - some use warnings, others use notices, and the error messages often lack
structure or context. This makes it difficult to:

  * Handle errors programmatically without relying on error handlers
  * Distinguish between different types of errors
  * Retrieve error information after operations complete
  * Build robust applications that need fine-grained error control

This RFC proposes a unified error handling system for PHP streams that provides:

  * **Consistent error reporting** across all stream wrappers
  * **Multiple error modes** - traditional warnings, exceptions, or silent mode
  * **Structured error storage** - retrieve detailed error information programmatically
  * **Custom error handlers** - error callback support
  * **Semantic error codes** - well-defined codes for different error conditions

===== Proposal =====

This proposal introduces a comprehensive error handling system for PHP streams through new context options, a dedicated
exception class, error codes, and a function to retrieve stored errors.

==== Stream Error Context Options ====

Three new context options are added under the root `stream` field to control error handling behavior:

=== error_mode ===

Controls how errors are reported. Accepts one of the following constants:

  * **STREAM_ERROR_MODE_ERROR** (default) - Use standard PHP error reporting (warnings/notices)
  * **STREAM_ERROR_MODE_EXCEPTION** - Throw StreamException for terminal errors
  * **STREAM_ERROR_MODE_SILENT** - Suppress all error output

Terminal errors are those that prevent an operation from completing (e.g., file not found, permission denied).
Non-terminal errors are warnings or notices that don't stop execution (e.g., buffer truncation).

In exception mode, only terminal errors throw exceptions. Non-terminal errors are still stored (if error_store permits)
but don't interrupt execution.

=== error_store ===

Controls which errors are stored for later retrieval via `stream_get_errors()`. Accepts one of:

  * **STREAM_ERROR_STORE_AUTO** (default) - Automatically decide based on error_mode:
    * With ERROR mode: stores none
    * With EXCEPTION mode: stores non-terminal errors
    * With SILENT mode: stores all errors
  * **STREAM_ERROR_STORE_NONE** - Don't store any errors
  * **STREAM_ERROR_STORE_NON_TERMINAL** - Store only non-terminal errors
  * **STREAM_ERROR_STORE_TERMINAL** - Store only terminal errors
  * **STREAM_ERROR_STORE_ALL** - Store all errors

Stored errors can be retrieved using `stream_get_errors()` with either a stream resource (for stream-specific errors)
or wrapper name (for wrapper-level errors).

=== error_handler ===

Optional callback to receive error notifications. The callback signature is:

<code php>
function(string $wrapper, ?resource $stream, int $code, string $message, ?string $param): void
</code>

Parameters:
  * **$wrapper** - The wrapper name (e.g., "file", "http", "PHP")
  * **$stream** - The stream resource if available, null for wrapper-level errors
  * **$code** - One of the STREAM_ERROR_CODE_* constants
  * **$message** - Human-readable error message
  * **$param** - Additional context (typically filename or URL)

The error handler is called regardless of the error_mode setting, allowing custom logging or handling logic.

==== API ====

=== stream_get_errors Function ===

<code php>
<?php

/**
 * Retrieve stored stream errors
 * 
 * Retrieves errors that have been stored according to the error_store context option.
 * Errors can be retrieved for a specific stream, a specific wrapper, or all wrappers.
 * 
 * @param resource|string|null $subject Optional filter:
 *   - resource: Returns errors for the specific stream
 *   - string: Returns errors for the specified wrapper name
 *   - null: Returns errors for all wrappers
 * 
 * @return array Array of error arrays, each containing:
 *   - 'message' (string): The error message
 *   - 'code' (int): STREAM_ERROR_CODE_* constant
 *   - 'severity' (int): PHP error level (E_WARNING, E_NOTICE, etc.)
 *   - 'terminal' (bool): Whether this is a terminal error
 *   - 'wrapper' (string): Wrapper name
 *   - 'param' (string|null): Additional context if available
 *   - 'docref' (string|null): Documentation reference if available
 * 
 * @throws TypeError If $subject is not a resource, string, or null
 */
function stream_get_errors($subject = null): array {}

?>
</code>

=== StreamException Class ===

<code php>
<?php

/**
 * Exception thrown by stream operations in STREAM_ERROR_MODE_EXCEPTION mode
 * 
 * This exception is thrown for terminal errors when a stream context is configured
 * with error_mode set to STREAM_ERROR_MODE_EXCEPTION. It provides structured access
 * to error details including the wrapper name and optional parameter.
 */
class StreamException extends Exception
{
    /**
     * Get the parameter associated with the error
     * 
     * Returns additional context about the error, typically a filename or URL.
     * 
     * @return string|null The parameter or null if not available
     */
    public function getParam(): ?string {}
    
    /**
     * Get the wrapper that generated the error
     * 
     * Returns the name of the stream wrapper that encountered the error.
     * 
     * @return string The wrapper name (e.g., "file", "http", "ftp")
     */
    public function getWrapperName(): string {}
}

?>
</code>

=== Error Mode Constants ===

<code php>
<?php

/**
 * Use standard PHP error reporting (warnings, notices)
 * This is the default mode and maintains backward compatibility.
 */
const STREAM_ERROR_MODE_ERROR = 0;

/**
 * Throw StreamException for terminal errors
 * Non-terminal errors are still reported according to error_store setting.
 */
const STREAM_ERROR_MODE_EXCEPTION = 1;

/**
 * Suppress all error output
 * Errors can still be stored and retrieved programmatically.
 */
const STREAM_ERROR_MODE_SILENT = 2;

?>
</code>

=== Error Store Constants ===

<code php>
<?php

/**
 * Automatically decide storage based on error_mode
 * - ERROR mode: stores none
 * - EXCEPTION mode: stores non-terminal errors
 * - SILENT mode: stores all errors
 */
const STREAM_ERROR_STORE_AUTO = 0;

/**
 * Don't store any errors
 */
const STREAM_ERROR_STORE_NONE = 1;

/**
 * Store only non-terminal errors
 */
const STREAM_ERROR_STORE_NON_TERMINAL = 2;

/**
 * Store only terminal errors
 */
const STREAM_ERROR_STORE_TERMINAL = 3;

/**
 * Store all errors (both terminal and non-terminal)
 */
const STREAM_ERROR_STORE_ALL = 4;

?>
</code>

=== Error Code Constants ===

Error codes are organized by operation category to make error handling more intuitive:

<code php>
<?php

// General errors
const STREAM_ERROR_CODE_NONE = 0;
const STREAM_ERROR_CODE_GENERIC = 1;

// I/O operation errors (10-29)
const STREAM_ERROR_CODE_READ_FAILED = 10;
const STREAM_ERROR_CODE_WRITE_FAILED = 11;
const STREAM_ERROR_CODE_SEEK_FAILED = 12;
const STREAM_ERROR_CODE_SEEK_NOT_SUPPORTED = 13;
const STREAM_ERROR_CODE_FLUSH_FAILED = 14;
const STREAM_ERROR_CODE_TRUNCATE_FAILED = 15;
const STREAM_ERROR_CODE_CONNECT_FAILED = 16;
const STREAM_ERROR_CODE_BIND_FAILED = 17;
const STREAM_ERROR_CODE_LISTEN_FAILED = 18;
const STREAM_ERROR_CODE_NOT_WRITABLE = 19;
const STREAM_ERROR_CODE_NOT_READABLE = 20;

// File system operation errors (30-69)
const STREAM_ERROR_CODE_DISABLED = 30;
const STREAM_ERROR_CODE_NOT_FOUND = 31;
const STREAM_ERROR_CODE_PERMISSION_DENIED = 32;
const STREAM_ERROR_CODE_ALREADY_EXISTS = 33;
const STREAM_ERROR_CODE_INVALID_PATH = 34;
const STREAM_ERROR_CODE_PATH_TOO_LONG = 35;
const STREAM_ERROR_CODE_OPEN_FAILED = 36;
const STREAM_ERROR_CODE_CREATE_FAILED = 37;
const STREAM_ERROR_CODE_DUP_FAILED = 38;
const STREAM_ERROR_CODE_UNLINK_FAILED = 39;
const STREAM_ERROR_CODE_RENAME_FAILED = 40;
const STREAM_ERROR_CODE_MKDIR_FAILED = 41;
const STREAM_ERROR_CODE_RMDIR_FAILED = 42;
const STREAM_ERROR_CODE_STAT_FAILED = 43;
const STREAM_ERROR_CODE_META_FAILED = 44;
const STREAM_ERROR_CODE_CHMOD_FAILED = 45;
const STREAM_ERROR_CODE_CHOWN_FAILED = 46;
const STREAM_ERROR_CODE_COPY_FAILED = 47;
const STREAM_ERROR_CODE_TOUCH_FAILED = 48;
const STREAM_ERROR_CODE_INVALID_MODE = 49;
const STREAM_ERROR_CODE_INVALID_META = 50;
const STREAM_ERROR_CODE_MODE_NOT_SUPPORTED = 51;
const STREAM_ERROR_CODE_READONLY = 52;
const STREAM_ERROR_CODE_RECURSION_DETECTED = 53;

// Wrapper/protocol errors (70-89)
const STREAM_ERROR_CODE_NOT_IMPLEMENTED = 70;
const STREAM_ERROR_CODE_NO_OPENER = 71;
const STREAM_ERROR_CODE_PERSISTENT_NOT_SUPPORTED = 72;
const STREAM_ERROR_CODE_WRAPPER_NOT_FOUND = 73;
const STREAM_ERROR_CODE_WRAPPER_DISABLED = 74;
const STREAM_ERROR_CODE_PROTOCOL_UNSUPPORTED = 75;
const STREAM_ERROR_CODE_WRAPPER_REGISTRATION_FAILED = 76;
const STREAM_ERROR_CODE_WRAPPER_UNREGISTRATION_FAILED = 77;
const STREAM_ERROR_CODE_WRAPPER_RESTORATION_FAILED = 78;

// Filter errors (90-99)
const STREAM_ERROR_CODE_FILTER_NOT_FOUND = 90;
const STREAM_ERROR_CODE_FILTER_FAILED = 91;

// Cast/conversion errors (100-109)
const STREAM_ERROR_CODE_CAST_FAILED = 100;
const STREAM_ERROR_CODE_CAST_NOT_SUPPORTED = 101;
const STREAM_ERROR_CODE_MAKE_SEEKABLE_FAILED = 102;
const STREAM_ERROR_CODE_BUFFERED_DATA_LOST = 103;

// Network/socket errors (110-129)
const STREAM_ERROR_CODE_NETWORK_SEND_FAILED = 110;
const STREAM_ERROR_CODE_NETWORK_RECV_FAILED = 111;
const STREAM_ERROR_CODE_SSL_NOT_SUPPORTED = 112;
const STREAM_ERROR_CODE_RESUMPTION_FAILED = 113;
const STREAM_ERROR_CODE_SOCKET_PATH_TOO_LONG = 114;
const STREAM_ERROR_CODE_OOB_NOT_SUPPORTED = 115;
const STREAM_ERROR_CODE_PROTOCOL_ERROR = 116;
const STREAM_ERROR_CODE_INVALID_URL = 117;
const STREAM_ERROR_CODE_INVALID_RESPONSE = 118;
const STREAM_ERROR_CODE_INVALID_HEADER = 119;
const STREAM_ERROR_CODE_INVALID_PARAM = 120;
const STREAM_ERROR_CODE_REDIRECT_LIMIT = 121;
const STREAM_ERROR_CODE_AUTH_FAILED = 122;

// Encoding/decoding errors (130-139)
const STREAM_ERROR_CODE_ARCHIVING_FAILED = 130;
const STREAM_ERROR_CODE_ENCODING_FAILED = 131;
const STREAM_ERROR_CODE_DECODING_FAILED = 132;
const STREAM_ERROR_CODE_INVALID_FORMAT = 133;

// Resource/allocation errors (140-149)
const STREAM_ERROR_CODE_ALLOCATION_FAILED = 140;
const STREAM_ERROR_CODE_TEMPORARY_FILE_FAILED = 141;

// Locking errors (150-159)
const STREAM_ERROR_CODE_LOCK_FAILED = 150;
const STREAM_ERROR_CODE_LOCK_NOT_SUPPORTED = 151;

// Userspace stream errors (160-169)
const STREAM_ERROR_CODE_USERSPACE_NOT_IMPLEMENTED = 160;
const STREAM_ERROR_CODE_USERSPACE_INVALID_RETURN = 161;
const STREAM_ERROR_CODE_USERSPACE_CALL_FAILED = 162;

?>
</code>

==== Stream vs Wrapper Errors ====

The error handling system distinguishes between two types of errors:

**Stream Errors** are associated with a specific stream resource and are stored in the stream itself. These errors can be retrieved by passing the stream resource to `stream_get_errors()`.

**Wrapper Errors** occur during wrapper operations that don't result in a stream (e.g., failed `fopen()` attempts, `unlink()`, `rename()`). These are stored globally per wrapper name and can be retrieved by passing the wrapper name to `stream_get_errors()` or by calling it with no arguments to get all wrapper errors.

This separation allows precise error tracking:
- Stream errors: `stream_get_errors($stream)`
- Specific wrapper errors: `stream_get_errors('file')`
- All wrapper errors: `stream_get_errors()`

==== Logged Errors ====

PHP's stream system has an existing mechanism for "logged errors" that are accumulated during certain operations and
displayed together (e.g., when `fopen()` fails). This RFC keeps this functionality but the error displaying is done
through the new error handling so the context options work here as well.

==== Usage Examples ====

=== Exception Mode ===

<code php>
<?php

$context = stream_context_create([
    'stream' => [
        'error_mode' => STREAM_ERROR_MODE_EXCEPTION,
    ]
]);

try {
    $stream = fopen('/nonexistent/file.txt', 'r', false, $context);
} catch (StreamException $e) {
    echo "Error: " . $e->getMessage() . "\n";
    echo "Code: " . $e->getCode() . "\n";
    echo "Wrapper: " . $e->getWrapperName() . "\n";
    echo "File: " . $e->getParam() . "\n";
}

?>
</code>

=== Silent Mode with Error Storage ===

<code php>
<?php

$context = stream_context_create([
    'stream' => [
        'error_mode' => STREAM_ERROR_MODE_SILENT,
        'error_store' => STREAM_ERROR_STORE_ALL,
    ]
]);

$stream = @fopen('http://example.com/nonexistent', 'r', false, $context);

if ($stream === false) {
    $errors = stream_get_errors('http');
    
    foreach ($errors as $error) {
        echo "Error {$error['code']}: {$error['message']}\n";
        
        if ($error['code'] === STREAM_ERROR_CODE_NOT_FOUND) {
            echo "Resource not found, using fallback...\n";
            // Handle 404 specifically
        }
    }
}

?>
</code>

=== Custom Error Handler ===

<code php>
<?php

$errorLog = [];

$context = stream_context_create([
    'stream' => [
        'error_mode' => STREAM_ERROR_MODE_SILENT,
        'error_handler' => function($wrapper, $stream, $code, $message, $param) use (&$errorLog) {
            $errorLog[] = [
                'timestamp' => time(),
                'wrapper' => $wrapper,
                'code' => $code,
                'message' => $message,
                'param' => $param,
            ];
        }
    ]
]);

// Attempt multiple file operations
$files = ['file1.txt', 'file2.txt', 'file3.txt'];

foreach ($files as $file) {
    $stream = fopen($file, 'r', false, $context);
    if ($stream !== false) {
        fclose($stream);
    }
}

// Review all errors that occurred
foreach ($errorLog as $entry) {
    echo "[{$entry['timestamp']}] {$entry['wrapper']}: {$entry['message']}\n";
}

?>
</code>

=== Retrieving Stream-Specific Errors ===

<code php>
<?php

$context = stream_context_create([
    'stream' => [
        'error_mode' => STREAM_ERROR_MODE_SILENT,
        'error_store' => STREAM_ERROR_STORE_ALL,
    ]
]);

$stream = fopen('php://temp', 'r+', false, $context);

// Perform operations that may generate errors
fwrite($stream, 'test data');
fseek($stream, -100, SEEK_SET); // This may generate a non-terminal error

// Get errors specific to this stream
$errors = stream_get_errors($stream);

foreach ($errors as $error) {
    if (!$error['terminal']) {
        echo "Warning: {$error['message']}\n";
    }
}

fclose($stream);

?>
</code>

=== Setting Default Context ===

You can set default error handling for functions that don't accept a context parameter using `stream_context_set_default()`:

<code php>
<?php

stream_context_set_default([
    'stream' => [
        'error_mode' => STREAM_ERROR_MODE_EXCEPTION,
    ]
]);

// Now all stream operations use exception mode by default
try {
    $contents = file_get_contents('/nonexistent/file.txt');
} catch (StreamException $e) {
    echo "Failed to read file: " . $e->getMessage() . "\n";
}

// Or using silent mode for specific operations
$silentContext = stream_context_create([
    'stream' => [
        'error_mode' => STREAM_ERROR_MODE_SILENT,
    ]
]);

if (file_get_contents('/another/file.txt', false, $silentContext) === false) {
    $errors = stream_get_errors('file');
    // Handle errors programmatically
}

?>
</code>

===== Backward Incompatible Changes =====

This RFC only adds new functionality and does not modify existing behavior except small changes noted below.

There is one case of error that was incorrectly reported and such warning got dropped. There might be a few extra
warnings that were supposed to be hidden. Those are more fixes however.

Another potentially minor BC break in passing context for opening stream to the new stream. This was done only for
some wrapper (mainly the network related ones). This should be actually expected for all streams but for some reason it
wasn't the case. So such change seems to make sense. However, if this becomes a problem, there is a way to make it
limited to errors or selected options so the impact can be eliminated if needed.

===== Proposed PHP Version(s) =====

PHP 8.6

===== Future Scope =====

This proposal establishes a foundation for future enhancements:

  * **Additional error codes** - As new stream operations and wrappers are added
  * **Error code ranges** - Reserved ranges for extensions to define custom error codes

===== Proposed Voting Choices =====

As per the voting RFC, a yes/no vote with a 2/3 majority is needed for this proposal to be accepted.

<doodle title="Should the Stream Error Handling Improvements be added to PHP core?" auth="bukka" voteType="single" closed="true">
   * Yes
   * No
</doodle>

The vote started on 2025-XX-XX at XX:XX UTC and ends on 2025-XX-XX at XX:XX UTC.

===== Patches and Tests =====

A working implementation is at https://github.com/php/php-src/pull/20524

===== Implementation =====

After the project is implemented, this section will contain:
  - the version(s) it was merged to
  - a link to the git commit(s)

===== References =====

  * PHP Stream Documentation: https://www.php.net/manual/en/book.stream.php
  * Stream Context Options: https://www.php.net/manual/en/context.php
  * Error Handling in PHP: https://www.php.net/manual/en/language.errors.php

===== Changelog =====

  * 1.0 - Initial version
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