3 URI Codec: Encoding and Decoding URIs

package: base

The net/uri-codec module provides utilities for encoding and decoding strings using the URI encoding rules given in RFC 2396 [RFC2396], and to encode and decode name/value pairs using the application/x-www-form-urlencoded mimetype given in the HTML 4.0 specification. There are minor differences between the two encodings.

The URI encoding allows a few characters to be represented as-is: a through z, A through Z, 0-9, -, _, ., !, ~, *, ', ( and ). The remaining characters are encoded as %‹xx›, where ‹xx› is the two-character hex representation of the integer value of the character (where the mapping character–integer is determined by US-ASCII if the integer is less than 128).

The encoding, in line with RFC 2396’s recommendation, represents a character as-is, if possible. The decoding allows any characters to be represented by their hex values, and allows characters to be incorrectly represented as-is. The library provides “unreserved” encoders that encode !, *, ', (, and ) using their hex representation, which is not recommended by RFC 2396 but avoids problems with some contexts.

The rules for the application/x-www-form-urlencoded mimetype given in the HTML 4.0 spec are:

Control names and values are escaped. Space characters are replaced by +, and then reserved characters are escaped as described in RFC 1738, section 2.2: Non-alphanumeric characters are replaced by %‹xx› representing the ASCII code of the character. Line breaks are represented as CRLF pairs: %0D%0A. Note that RFC 2396 supersedes RFC 1738 [RFC1738].
The control names/values are listed in the order they appear in the document. The name is separated from the value by = and name/value pairs are separated from each other by either ; or &. When encoding, ; is used as the separator by default. When decoding, both ; and & are parsed as separators by default.

These application/x-www-form-urlencoded rules differs slightly from the straight encoding in RFC 2396 in that + is allowed, and it represents a space. The net/uri-codec library follows this convention, encoding a space as + and decoding + as a space. In addition, since there appear to be some broken decoders on the web, the library also encodes !, ~, ', (, and ) using their hex representation, which is the same choice as made by the Java’s URLEncoder.

3.1 Functions

procedure
(uri-encode str) → string?
str : string?

Encode a string using the URI encoding rules.

procedure
(uri-decode str) → string?
str : string?

Decode a string using the URI decoding rules.

procedure
(uri-path-segment-encode str) → string?
str : string?

Encodes a string according to the rules in [RFC3986] for path segments.

procedure
(uri-path-segment-decode str) → string?
str : string?

Decodes a string according to the rules in [RFC3986] for path segments.

procedure
(uri-userinfo-encode str) → string?
str : string?

Encodes a string according to the rules in [RFC3986] for the userinfo field.

procedure
(uri-userinfo-decode str) → string?
str : string?

Decodes a string according to the rules in [RFC3986] for the userinfo field.

procedure
(uri-unreserved-encode str) → string?
str : string?

Encodes a string according to the rules in [RFC3986](section 2.3) for the unreserved characters.

procedure
(uri-unreserved-decode str) → string?
str : string?

Decodes a string according to the rules in [RFC3986](section 2.3) for the unreserved characters.

procedure
(uri-path-segment-unreserved-encode str) → string?
str : string?

Encodes a string according to the rules in [RFC3986] for path segments, but also encodes characters that uri-unreserved-encode encodes and that uri-encode does not.

procedure
(uri-path-segment-unreserved-decode str) → string?
str : string?

Decodes a string according to the rules in [RFC3986] for path segments.

procedure
(form-urlencoded-encode str) → string?
str : string?

Encode a string using the application/x-www-form-urlencoded encoding rules. The result string contains no non-ASCII characters.

procedure
(form-urlencoded-decode str) → string?
str : string?

Decode a string encoded using the application/x-www-form-urlencoded encoding rules.

procedure
(alist->form-urlencoded alist) → string?
alist : (listof (cons/c symbol? (or/c false/c string?)))

Encode an association list using the application/x-www-form-urlencoded encoding rules.

The current-alist-separator-mode parameter determines the separator used in the result.

procedure
(form-urlencoded->alist str)
→ (listof (cons/c symbol? (or/c false/c string?)))
str : string

Decode a string encoded using the application/x-www-form-urlencoded encoding rules into an association list. All keys are case-folded for conversion to symbols.

The current-alist-separator-mode parameter determines the way that separators are parsed in the input.

parameter
(current-alist-separator-mode)
→ (one-of/c 'amp 'semi 'amp-or-semi 'semi-or-amp)
(current-alist-separator-mode mode) → void?
mode : (one-of/c 'amp 'semi 'amp-or-semi 'semi-or-amp)

A parameter that determines the separator used/recognized between associations in form-urlencoded->alist, alist->form-urlencoded, url->string, and string->url.

The default value is 'amp-or-semi, which means that both & and ; are treated as separators when parsing, and & is used as a separator when encoding. The 'semi-or-amp mode is similar, but ; is used when encoding. The other modes use/recognize only one of the separators.

Examples:

> (define ex '((x . "foo") (y . "bar") (z . "baz")))
> (current-alist-separator-mode 'amp) ; try 'amp...
> (form-urlencoded->alist "x=foo&y=bar&z=baz")
'((x . "foo") (y . "bar") (z . "baz"))
> (form-urlencoded->alist "x=foo;y=bar;z=baz")
'((x . "foo;y=bar;z=baz"))
> (alist->form-urlencoded ex)
"x=foo&y=bar&z=baz"
> (current-alist-separator-mode 'semi) ; try 'semi...
> (form-urlencoded->alist "x=foo;y=bar;z=baz")
'((x . "foo") (y . "bar") (z . "baz"))
> (form-urlencoded->alist "x=foo&y=bar&z=baz")
'((x . "foo&y=bar&z=baz"))
> (alist->form-urlencoded ex)
"x=foo;y=bar;z=baz"
> (current-alist-separator-mode 'amp-or-semi) ; try 'amp-or-semi...
> (form-urlencoded->alist "x=foo&y=bar&z=baz")
'((x . "foo") (y . "bar") (z . "baz"))
> (form-urlencoded->alist "x=foo;y=bar;z=baz")
'((x . "foo") (y . "bar") (z . "baz"))
> (alist->form-urlencoded ex)
"x=foo&y=bar&z=baz"
> (current-alist-separator-mode 'semi-or-amp) ; try 'semi-or-amp...
> (form-urlencoded->alist "x=foo&y=bar&z=baz")
'((x . "foo") (y . "bar") (z . "baz"))
> (form-urlencoded->alist "x=foo;y=bar;z=baz")
'((x . "foo") (y . "bar") (z . "baz"))
> (alist->form-urlencoded ex)
"x=foo;y=bar;z=baz"

3.2 URI Codec Unit

uri-codec@ and uri-codec^ are deprecated. They exist for backward-compatibility and will likely be removed in the future. New code should use the net/uri-codec module.

(require net/uri-codec-unit)

package: compatibility-lib

value
uri-codec@ : unit?

Imports nothing, exports uri-codec^.

3.3 URI Codec Signature

(require net/uri-codec-sig)

package: compatibility-lib

signature
uri-codec^ : signature

Includes everything exported by the net/uri-codec module except uri-path-segment-unreserved-encode and uri-path-segment-unreserved-decode.

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1	HTTP Client
2	URLs and HTTP
3	URI Codec: Encoding and Decoding URIs
4	FTP: Client
5	Send URL: Opening a Web Browser
6	SMTP: Sending E-Mail
7	sendmail: Sending E-Mail
8	Headers: Parsing and Constructing
9	Header Field Encoding
10	IMAP: Reading Mail
11	POP3: Reading Mail
12	MIME: Decoding Internet Data
13	Base 64: Encoding and Decoding
14	Quoted-Printable: Encoding and Decoding
15	DNS: Domain Name Service Queries
16	NNTP: Newsgroup Protocol
17	TCP: Unit and Signature
18	TCP Redirect: tcp^ via Channels
19	SSL Unit: tcp^ via SSL
20	CGI Scripts
21	Cookie: Legacy HTTP Client Storage
22	Git Repository Checkout
	Bibliography
	Index