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Chapter 24

HypertextTransfer Protocol

(HTTP)

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CONTENTSCONTENTS

• HTTP TRANSACTION• REQUEST MESSAGE• RESPONSE MESSAGE• HEADER• EXAMPLES• SOME OTHER FEATURES

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HTTP uses the services of HTTP uses the services of TCP on well-known port 80.TCP on well-known port 80.

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HTTPTRANSACTION

24.124.1

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Figure 24-1

HTTP transaction

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Figure 24-2

Message categories

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24.224.2

REQUESTMESSAGE

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Figure 25-3

Request message

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Figure 24-4

Request line

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Figure 24-5

URL

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RESPONSEMESSAGE

24.324.3

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Figure 24-6

Response message

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Figure 24-7

Status line

Status code: Same format as FTP responses (three digits)

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HEADER

24.424.4

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Figure 24-8

Header format

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Figure 24-9 Headers

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EXAMPLES

24.524.5

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Example 1Example 1

This example retrieves a document. We use the GET method to retrieve an image with the path /usr/bin/image1.

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Figure 24-10 Example 1

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Example 2Example 2

This example retrieves information about a document. We use the HEAD method to retrieve information about an HTML document (see Chapter 25)

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Figure 24-11

Example 2

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Example 3Example 3

In this example, the client wants to send input data to the server. We use the POST method.

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Figure 24-12

Example 3

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SOME OTHER FEATURES

24.624.6

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HTTP version 1.1 HTTP version 1.1 specifies a persistent specifies a persistent connection by default.connection by default.