1<?php
2
3declare(strict_types=1);
4
5namespace GuzzleHttp\Psr7;
6
7use Psr\Http\Message\StreamInterface;
8
9/**
10 * Decorator used to return only a subset of a stream.
11 */
12final class LimitStream implements StreamInterface
13{
14    use StreamDecoratorTrait;
15
16    /** @var int Offset to start reading from */
17    private $offset;
18
19    /** @var int Limit the number of bytes that can be read */
20    private $limit;
21
22    /** @var StreamInterface */
23    private $stream;
24
25    /**
26     * @param StreamInterface $stream Stream to wrap
27     * @param int             $limit  Total number of bytes to allow to be read
28     *                                from the stream. Pass -1 for no limit.
29     * @param int             $offset Position to seek to before reading (only
30     *                                works on seekable streams).
31     */
32    public function __construct(
33        StreamInterface $stream,
34        int $limit = -1,
35        int $offset = 0
36    ) {
37        $this->stream = $stream;
38        $this->setLimit($limit);
39        $this->setOffset($offset);
40    }
41
42    public function eof(): bool
43    {
44        // Always return true if the underlying stream is EOF
45        if ($this->stream->eof()) {
46            return true;
47        }
48
49        // No limit and the underlying stream is not at EOF
50        if ($this->limit === -1) {
51            return false;
52        }
53
54        return $this->stream->tell() >= $this->offset + $this->limit;
55    }
56
57    /**
58     * Returns the size of the limited subset of data
59     */
60    public function getSize(): ?int
61    {
62        if (null === ($length = $this->stream->getSize())) {
63            return null;
64        } elseif ($this->limit === -1) {
65            return $length - $this->offset;
66        } else {
67            return min($this->limit, $length - $this->offset);
68        }
69    }
70
71    /**
72     * Allow for a bounded seek on the read limited stream
73     */
74    public function seek($offset, $whence = SEEK_SET): void
75    {
76        if ($whence !== SEEK_SET || $offset < 0) {
77            throw new \RuntimeException(sprintf(
78                'Cannot seek to offset %s with whence %s',
79                $offset,
80                $whence
81            ));
82        }
83
84        $offset += $this->offset;
85
86        if ($this->limit !== -1) {
87            if ($offset > $this->offset + $this->limit) {
88                $offset = $this->offset + $this->limit;
89            }
90        }
91
92        $this->stream->seek($offset);
93    }
94
95    /**
96     * Give a relative tell()
97     */
98    public function tell(): int
99    {
100        return $this->stream->tell() - $this->offset;
101    }
102
103    /**
104     * Set the offset to start limiting from
105     *
106     * @param int $offset Offset to seek to and begin byte limiting from
107     *
108     * @throws \RuntimeException if the stream cannot be seeked.
109     */
110    public function setOffset(int $offset): void
111    {
112        $current = $this->stream->tell();
113
114        if ($current !== $offset) {
115            // If the stream cannot seek to the offset position, then read to it
116            if ($this->stream->isSeekable()) {
117                $this->stream->seek($offset);
118            } elseif ($current > $offset) {
119                throw new \RuntimeException("Could not seek to stream offset $offset");
120            } else {
121                $this->stream->read($offset - $current);
122            }
123        }
124
125        $this->offset = $offset;
126    }
127
128    /**
129     * Set the limit of bytes that the decorator allows to be read from the
130     * stream.
131     *
132     * @param int $limit Number of bytes to allow to be read from the stream.
133     *                   Use -1 for no limit.
134     */
135    public function setLimit(int $limit): void
136    {
137        $this->limit = $limit;
138    }
139
140    public function read($length): string
141    {
142        if ($this->limit === -1) {
143            return $this->stream->read($length);
144        }
145
146        // Check if the current position is less than the total allowed
147        // bytes + original offset
148        $remaining = ($this->offset + $this->limit) - $this->stream->tell();
149        if ($remaining > 0) {
150            // Only return the amount of requested data, ensuring that the byte
151            // limit is not exceeded
152            return $this->stream->read(min($remaining, $length));
153        }
154
155        return '';
156    }
157}
158