Context Options and Parameters

Question 1

How are contexts created?

Answer 1

stream_context_create()

Question 2

How are context options set?

Answer 2

stream_context_set_option()

Question 3

How are context parameters set?

Answer 3

stream_context_set_params()

Question 4

What are the 7 context options?

Answer 4

socket, HTTP, FTP, SSL, CURL, Phar, MongoDB

Question 5

What are socket context options available for?

Answer 5

All wrappers that work over sockets, like tcp, http, and ftp.

Question 6

What are the socket context options?

Answer 6

bindto - used to specify the IP address and/or the port number that PHP will use to access the network. The syntax is ip:port for IPv4 addresses, and [ip]:port for IPv6 addresses. Setting the IP or the port to 0 will let the system choose the IP and/or port.

backlog - used to limit the number of outstanding connections in the socket’s listen queue. This is only applicable to stream_socket_server().

Question 7

Why can’t the port number for an FTP connection be specified with bindto?

Answer 7

Because FTP creates two socket connections during normal operation.

Question 8

What are the HTTP context options?

Answer 8

method, header, user_agent, content, proxy, request_fulluri, follow_location, max_redirects, protocol_version, timeout, ignore_errors

Question 9

What are the FTP context options?

Answer 9

overwrite - allow overwriting of existing files on server
resume_pos - file offset at which to begin transfer
proxy - proxy FTP request via http proxy server

Question 10

When are CURL context options available?

Answer 10

When the CURL extension was compiled using the –with-curlwrappers configure option.

Question 11

What are the CURL context options?

Answer 11

method, header, user_agent, content, proxy, max_redirects, curl_verify_ssl_host, curl_verify_ssl_peer,

Question 12

What are the Phar context options?

Answer 12

compress - one of the Phar compression constants

metadata - Phar metadata

Question 13

What parameter can be set on a context using the stream_context_set_params() function?

Answer 13

notification - a callable to be called when an event occurs on a stream.

Question 14

How do you register custom stream wrappers?

Answer 14

With the stream_wrapper_register() function.

Question 15

What URL syntax is supported to describe a wrapper?

Answer 15

Only scheme://

scheme:/ and scheme: syntaxes are not supported.

Question 16

What are the supported URL-style protocols?

Answer 16

file://, http://, ftp://, php:// (for accessing various I/O streams), zlib:// (compression streams), data://, glob://, phar://, ssh2://, rar://, ogg://, expect:// (process interaction systems)

Question 17

What is the default wrapper used with PHP?

Answer 17

file://

It represents the local filesystem.

Question 18

When using the CLI sapi, to what directory does file:// default?

Answer 18

The directory from which the script was called.

Question 19

What does the http:// stream do?

Answer 19

It allows read-only access to files/resources via HTTP 1.0, using the HTTP GET method.

Question 20

Where can you configure a user_agent string to be used with an http:// stream?

Answer 20

In your php.ini file, or in the stream context.

Question 21

Does http:// allow you to access the headers of the resource?

Answer 21

The http:// stream allows access to the body of the resource. The headers are stored in the $http_response_header variable.

Question 22

How can you determine the URL of the resource where your document came from, after all redirects have been processed?

Answer 22

You’ll need to process the series of response headers returned by the stream.

Question 23

When is HTTPS supported via the https:// stream?

Answer 23

Only when the openssl extension is enabled.

Question 24

Can you write data or copy files to an HTTP resource?

Answer 24

No. HTTP connections are read-only. Sending POST and PUT requests can be done with the help of HTTP contexts.

Question 25

If the server does not support ______, the ftp:// connection will fail.

Answer 25

passive mode ftp

Question 26

What does the ftp:// or ftps:// stream do?

Answer 26

Allows read access to existing files and creation of new files via FTP.

Question 27

Can you open files for reading and writing via the ftp:// stream?

Answer 27

No. Either reading or writing, but not both simultaneously.

Question 28

What happens if the remote file already exists on the ftp server and you attempt to open it for writing, but have not specified the context option ‘overwrite’?

Answer 28

The connection will fail.

Question 29

What do you need to do to overwrite existing files over ftp?

Answer 29

Specify the ‘overwrite’ option in the context, and open the file for writing. Alternatively, you can use the FTP extension.

Question 30

What is the ‘from’ directive in php.ini?

Answer 30

The value to be sent as the anonymous FTP password.

Question 31

What are the various php:// streams?

Answer 31

php: //stdin (read-only)
php: //stdout (write-only)
php: //stderr (write-only)
php: //input - a read-only stream that allows you to read raw data from the request body
php: //output - a write-only stream that allows you to write to the output buffer mechanism in the same way as print and echo
php: //fd - allows direct access to the given file descriptor. For example, php://fd/3 refers to file descriptor 3
php: //memory and php://temp - read/write streams that allow temporary data to be stored in a file-like wrapper
php: //filter - a kind of meta-wrapper designed to permit the application of filters to a stream at the time of opening. This is useful with all-in-one file functions such as readfile(), file(), and file_get_contents() where there is otherwise no opportunity to apply a filter to the stream prior to the contents being read.

Question 32

What is the difference between php://input and $HTTP_RAW_POST_DATA?

Answer 32

$HTTP_RAW_POST_DATA depends on special php.ini directives.

Question 33

Is php://input available with enctype=”multipart/form-data”?

Answer 33

No.

Question 34

Can a stream opened with php://input be read multiple times?

Answer 34

Prior to PHP 5.6, no.

Question 35

What is the difference between php://memory and php://temp?

Answer 35

php://memory will always store its data in memory, whereas php://temp will use a temporary file once the amount of data stored hits a predefined limit (the default is 2MB).

Question 36

How can the memory limit of php://temp be controlled?

Answer 36

By appending /maxmemory:NN, where NN is the maximum amount of data to keep in memory before using a temporary file, in bytes.

Question 37

What is php://filter?

Answer 37

It’s a kind of meta-wrapper designed to permit the application of filters to a stream at the time of opening. This is useful with all-in-one file functions such as readfile(), file(), and file_get_contents(), where there is otherwise no opportunity to apply a filter to the stream prior to the contents being read.

Question 38

Which php I/O streams support stat()?

Answer 38

php://memory and php://temp only

Question 39

What are the php://filter parameters?

Answer 39

resource - required. specifies stream to filter.
read - optional
write - optional
filter list to apply to both chains - any filter lists which are not prefixed by read= or write= will be applied to both the read and write chains as appropriate

Question 40

What is the data:// stream wrapper for?

Answer 40

It allows inclusion of small data items as “immediate” data, as if it had been included externally.

Question 41

What is the phar:// stream wrapper for?

Answer 41

PHP archives.

Question 42

Is the ssh2:// stream wrapper enabled by default?

Answer 42

No. In order to use the ssh2.*:// wrappers you must install the SSH2 extension available from PECL.

Question 43

What are the ssh2.*:// options?

Answer 43

ssh2.shell://, ssh2.exec://, ssh2.tunnel://, ssh2.ftp://, ssh2.scp://

Question 44

What is rar:// for?

Answer 44

RAR archives.

Question 45

Is the rar:// wrapper enabled by default?

Answer 45

No. You must install it from PECL.

Question 46

What is ogg:// for?

Answer 46

Audio streams.

Question 47

What is expect:// for?

Answer 47

Accessing Expect streams for automating interactive applications. The usage is expect://command