I have this message received from an IRC server
:shiplu!shiplu#example.com PRIVMSG &channel :bot: Poor baby!\r\n
Here PRIVMSG is command. The rest part at the right is &channel :bot: Poor baby!
Now what is the last parameter? :bot: Poor baby! or Poor baby!
On the RFC2810 Section 2.3.1 It written that
nospcrlfcl = %x01-09 / %x0B-0C / %x0E-1F / %x21-39 / %x3B-FF
; any octet except NUL, CR, LF, " " and ":"
middle = nospcrlfcl *( ":" / nospcrlfcl )
trailing = *( ":" / " " / nospcrlfcl )
Now if :bot: Poor baby! is the last parameter how can it contain any colon? nospcrlfcl is defined not to contain any colon. If Poor baby! is the last parameter how can :bot: become middle?
The trailing (last) parameter is flagged with a colon and may contain spaces. Middle parameters may not contain spaces, and may not start with a colon.
So &channel is a "middle" and bot: Poor baby! (without the leading colon) is "trailing".
Related
I have customer input that may include letters, digits or spaces. For instance:
local customer_input = 'I need 2 tomatoes';
or
local customer_input = 'I need two tomatoes';
However, due to the nature of my application, I may get #, *, #, etc, in the customer_input string. I want to remove any non alphanumeric characters but the space.
I tried with these:
customer_input , _ = customer_input:gsub("%W%S+", "");
This one drops everything but the first word in the phrase.
or
customer_input , _ = customer_input:gsub("%W%S", "");
This one actually drops the space and the first letter of each word.
So, I know I am doing it wrong but I am not really sure how to match alphanumeric + space. I am sure this must be simple but I have not been able to figure it out.
Thanks very much for any help!
You may use
customer_input , _ = customer_input:gsub("[^%w%s]+", "");
See the Lua demo online
Pattern details
[^ - start of a negated character class that matches any char but:
%w - an alphanumeric
%s - a whitespace
]+ - 1 or more times.
For example I quite often see this URL come up.
https://ghbtns.com/github-btn.html?user=example&repo=card&type=watch&count=true
Is the & meant to be & or should/can it be left as &?
& is for encoding the ampersand in HTML.
For example, in a hyperlink:
…
(Note that this only changes the link, not the URL. The URL is still /github-btn.html?user=example&repo=card&type=watch&count=true.)
While you may encode every & (that is part of the content) with & in HTML, you are only required to encode ambiguous ampersands.
From rfc3986:
Reserved Characters
URIs include components and subcomponents that are delimited by characters in the "reserved" set. These characters are called "reserved" because they may (or may not) be defined as delimiters by the generic syntax, by each scheme-specific syntax, or by the implementation-specific syntax of a URI's dereferencing algorithm.
...
reserved = gen-delims / sub-delims
gen-delims = ":" / "/" / "?" / "#" / "[" / "]" / "#"
sub-delims = "!" / "$" / "&" / "'" / "(" / ")"
/ "*" / "+" / "," / ";" / "="
The purpose of reserved characters is to provide a set of delimiting
characters that are distinguishable from other data within a URI. URIs
that differ in the replacement of a reserved character with its
corresponding percent-encoded octet are not equivalent.
Percent-encoding a reserved character, or decoding a percent-encoded
octet that corresponds to a reserved character, will change how the
URI is interpreted by most applications.
...
URI producing applications should percent-encode data octets that
correspond to characters in the reserved set unless these characters
are specifically allowed by the URI scheme to represent data in that
component. If a reserved character is found in a URI component and
no delimiting role is known for that character, then it must be
interpreted as representing the data octet corresponding to that
character's encoding in US-ASCII.
So & within a URL should be encoded if it's part of the value and has no delimiting role.Here's simple PHP code fragment using urlencode() function:
<?php
$query_string = 'foo=' . urlencode($foo) . '&bar=' . urlencode($bar);
echo '<a href="mycgi?' . htmlentities($query_string) . '">';
?>
After viewing this previous SO question regarding percent encoding, I'm curious as to which styles of encodings are correct - the Wikipedia article on percent encoding alludes to using + instead of %20 for spaces, while still having an application/x-www-urlencoded content type.
This leads me to think the + vs. %20 behavior depends on which part of the URL is being encoded. What differences are preferred for path segments vs. query strings? Details and references for this specification would be greatly appreciated.
Note: I assume that non-alphanumeric characters will be encoded via UTF-8, in that each octet for a character becomes a %XX string. Correct me if I am wrong here (for instance latin-1 instead of utf-8), but I am more interested in the differences between the encodings of different parts of a URL.
This leads me to think the + vs. %20 behavior depends on which part of the URL is being encoded.
Not only does it depend on the particular URL component, but it also depends on the circumstances in which that component is populated with data.
The use of '+' for encoding space characters is specific to the application/x-www-form-urlencoded format, which applies to webform data that is being submitted in an HTTP request. It does not apply to a URL itself.
The application/x-www-form-urlencoded format is formally defined by W3C in the HTML specifications. Here is the definition from HTML 4.01:
Section 17.13.3 Processing form data, Step four: Submit the encoded form data set
This specification does not specify all valid submission methods or content types that may be used with forms. However, HTML 4 user agents must support the established conventions in the following cases:
• If the method is "get" and the action is an HTTP URI, the user agent takes the value of action, appends a `?' to it, then appends the form data set, encoded using the "application/x-www-form-urlencoded" content type. The user agent then traverses the link to this URI. In this scenario, form data are restricted to ASCII codes.
• If the method is "post" and the action is an HTTP URI, the user agent conducts an HTTP "post" transaction using the value of the action attribute and a message created according to the content type specified by the enctype attribute.
Section 17.13.4 Form content types, application/x-www-form-urlencoded
This is the default content type. Forms submitted with this content type must be encoded as follows:
1.Control names and values are escaped. Space characters are replaced by '+', and then reserved characters are escaped as described in [RFC1738], section 2.2: Non-alphanumeric characters are replaced by '%HH', a percent sign and two hexadecimal digits representing the ASCII code of the character. Line breaks are represented as "CR LF" pairs (i.e., '%0D%0A').
2.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 '&'.
The corresponding HTML5 definitions (Section 4.10.22.3 Form submission algorithm and Section 4.10.22.6 URL-encoded form data) are way more refined and detailed, but for purposes of this discussion, the jist is roughly the same.
So, in the situation where the webform data is submitted via an HTTP GET request instead of a POST request, the webform data is encoded using application/x-www-form-urlencoded and placed as-is in the URL query component.
Per RFC 3986: Uniform Resource Identifier (URI): Generic Syntax:
URI producing applications should percent-encode data octets that correspond to characters in the reserved set unless these characters are specifically allowed by the URI scheme to represent data in that component.
'+' is a reserved character:
reserved = gen-delims / sub-delims
gen-delims = ":" / "/" / "?" / "#" / "[" / "]" / "#"
sub-delims = "!" / "$" / "&" / "'" / "(" / ")"
/ "*" / "+" / "," / ";" / "="
The query component explicitly allows unencoded '+' characters, as it allows characters from sub-delims:
unreserved = ALPHA / DIGIT / "-" / "." / "_" / "~"
pct-encoded = "%" HEXDIG HEXDIG
pchar = unreserved / pct-encoded / sub-delims / ":" / "#"
query = *( pchar / "/" / "?" )
So, in the context of a webform submission, spaces are encoded using '+' prior to then being put as-is into the query component. This is allowed by the URL syntax, since the encoded form of application/x-www-form-urlencoded is compatible with the definition of the query component.
So, for example: http://server/script?field=hello+world
However, outside of a webform submission, putting a space character directly into the query component requires the use of pct-encoded, since ' ' is not included in either unreserved or sub-delims, and is not explicitly allowed by the query definition.
So, for example: http://server/script?hello%20world
Similar rules also apply to the path component, due to its use of pchar:
path = path-abempty ; begins with "/" or is empty
/ path-absolute ; begins with "/" but not "//"
/ path-noscheme ; begins with a non-colon segment
/ path-rootless ; begins with a segment
/ path-empty ; zero characters
path-abempty = *( "/" segment )
path-absolute = "/" [ segment-nz *( "/" segment ) ]
path-noscheme = segment-nz-nc *( "/" segment )
path-rootless = segment-nz *( "/" segment )
path-empty = 0<pchar>
segment = *pchar
segment-nz = 1*pchar
segment-nz-nc = 1*( unreserved / pct-encoded / sub-delims / "#" )
; non-zero-length segment without any colon ":"
So, although path does allow for unencoded sub-delims characters, a '+' character gets treated as-is, not as an encoded space. application/x-www-form-urlencoded is not used with the path component, so a space character has to be encoded as %20 due to the definitions of pchar and segment-nz-nc.
Now, regarding the charset used to encode characters -
For a webform submission, that charset is dictated by rules defined in the webform encoding algorithm (more so in HTML5 than HTML4) used to prepare the webform data prior to inserting it into the URL. In a nutshell, the HTML can specify an accept-charset attribute or hidden _charset_ field directly in the <form> itself, otherwise the charset is typically the charset used by the parent HTML.
However, outside of a webform submission, there is no formal standard for which charset is used to encode non-ascii characters in a URL component (the IRI syntax, on the other hand, requires UTF-8 especially when converting an IRI into an URI/URL). Outside of IRI, it is up to particular URI schemes to dictate their charsets (the HTTP scheme does not), otherwise the server decides which charset it wants to use. Most schemes/servers use UTF-8 nowadays, but there are still some servers/schemes that use other charsets, typically based on the server's locale (Latin1, Shift-JIS, etc). There have been attempts to add charset reporting directly in the URL and/or in HTTP (such as Deterministic URI Encoding
), but those are not commonly used.
Is it actually safe/valid to use multidimensional array synthax in the URL query string?
http://example.com?abc[]=123&abc[]=456
It seems to work in every browser and I always thought it was OK to use, but accodring to a comment in this article it is not: http://www.456bereastreet.com/archive/201008/what_characters_are_allowed_unencoded_in_query_strings/#comment4
I would like to hear a second opinion.
The answer is not simple.
The following is extracted from section 3.2.2 of RFC 3986 :
A host identified by an Internet Protocol literal address, version 6
[RFC3513] or later, is distinguished by enclosing the IP literal
within square brackets ("[" and "]"). This is the only place where
square bracket characters are allowed in the URI syntax.
This seems to answer the question by flatly stating that square brackets are not allowed anywhere else in the URI. But there is a difference between a square bracket character and a percent encoded square bracket character.
The following is extracted from the beginning of section 3 of RFC 3986 :
Syntax Components
The generic URI syntax consists of a hierarchical sequence of
components referred to as the scheme, authority, path, query, and
fragment.
URI = scheme ":" hier-part [ "?" query ] [ "#" fragment ]
So the "query" is a component of the "URI".
The following is extracted from section 2.2 of RFC 3986 :
2.2. Reserved Characters
URIs include components and subcomponents that are delimited by
characters in the "reserved" set. These characters are called
"reserved" because they may (or may not) be defined as delimiters by
the generic syntax, by each scheme-specific syntax, or by the
implementation-specific syntax of a URI's dereferencing algorithm.
If data for a URI component would conflict with a reserved
character's purpose as a delimiter, then the conflicting data must
be percent-encoded before the URI is formed.
reserved = gen-delims / sub-delims
gen-delims = ":" / "/" / "?" / "#" / "[" / "]" / "#"
sub-delims = "!" / "$" / "&" / "'" / "(" / ")"
/ "*" / "+" / "," / ";" / "="
So square brackets may appear in a query string, but only if they are percent encoded. Unless they aren't, to be explained further down in section 2.2 :
URI producing applications should percent-encode data octets that
correspond to characters in the reserved set unless these characters
are specifically allowed by the URI scheme to represent data in that
component. If a reserved character is found in a URI component and
no delimiting role is known for that character, then it must be
interpreted as representing the data octet corresponding to that
character's encoding in US-ASCII.
So because square brackets are only allowed in the "host" subcomponent, they "should" be percent encoded in other components and subcomponents, and in this case in the "query" component, unless RFC 3986 explicitly allows unencoded square brackets to represent data in the query component, which is does not.
However, if a "URI producing application" fails to do what it "should" do, by leaving square brackets unencoded in the query, then readers of the URI are not to reject the URI outright. Instead, the square brackets are to be considered as belonging to the data of the query component, since they are not used as delimiters in that component.
This is why, for example, it is not a violation of RFC 3986 when PHP accepts both unencoded and percent encoded square brackets as valid characters in a query string, and even assigns to them a special purpose. However, it would appear that authors who try to take advantage of this loophole by not percent encoding square brackets are in violation of RFC 3986.
According to RFC 3986, the Query component of an URL has the following grammar:
*( pchar / "/" / "?" )
From appendix A of the same RFC:
pchar = unreserved / pct-encoded / sub-delims / ":" / "#"
[...]
pct-encoded = "%" HEXDIG HEXDIG
unreserved = ALPHA / DIGIT / "-" / "." / "_" / "~"
[...]
sub-delims = "!" / "$" / "&" / "'" / "(" / ")"
/ "*" / "+" / "," / ";" / "="
My interpretation of this is that anything that isn't:
ALPHA / DIGIT / "-" / "." / "_" / "~" /
"!" / "$" / "&" / "'" / "(" / ")" /
"*" / "+" / "," / ";" / "=" / ":" / "#"
...should be pct-encoded, i.e percent-encoded. Thus [ and ] should be percent-encoded to follow RFC 3986.
David N. Jafferian's answer is fantastic. I just want to add a couple updates and practical notes:
For many years, every browser has left square brackets in query strings unencoded when submitting the request to the server. (Source: https://bugzilla.mozilla.org/show_bug.cgi?id=1152455#c6). As such, I imagine a huge portion of the web has come to rely on this behavior, which makes it extremely unlikely to change.
My reading of the WHATWG URL standard which, at least for web purposes, can be seen as superseding RFC 3986, is that it codifies this behavior of not encoding [ and ] in query strings.
Edit: Based on the comments and other answers, a more correct reading of the WHATWG URL standard is that unencoded [/] are invalid, but also should be tolerated when received/parsed and, once parsed that way, should even be re-serialized without encoding.
I'd ideally like to comment on Ethan's answer really, but don't have sufficient reputation to do it.
I'm not sure that the relevant part of the WHATWG URL standard is being referenced here. I think the correct part might be in the definition of a valid URL-query string, which it describes as being composed of URL units that themselves are formed from URL code points and percent-encoded bytes. Square brackets are listed within URL code points and thus fall into the percent-encoded bytes category.
Thus, in answer to the original question, multidimensional array syntax (i.e. using square brackets to represent array indexing) within the query part of the URL is valid, provided the square brackets are percent encoded (as %5B for [ and %5D for ]).
My understanding that square brackets are not first-class citizens anyway. Here is the quote:
https://www.rfc-editor.org/rfc/rfc1738
Other characters are unsafe because gateways and other transport
agents are known to sometimes modify such characters. These
characters are "{", "}", "|", "", "^", "~", "[", "]", and "`".
I always had a temptation to go for that sort of query when I had to pass an array, but I steered away from it. The reason being:
It is not cleared defined in RFC.
Different languages may interpret it differently.
You have a couple of options to pass an array:
Encode the string representation of the array(JSON may be?)
Have parameters like "val1=blah&val2=blah&.." or something like that.
And if you are sure about the language you are using, you can (safely) go for the kind of query string you have (Just that you need to %-encode [] also).
I have an application that takes all the parameters in the url like this: /category/subcategory/sub-subcategory. I want to be able to give out extra parameters at the end of the URL, like page-2/order-desc. This would make the whole URL into cat/subcat/sub-subcat{delimiting-character}page-2/order-desc.
My question is: what characters could I use as {delimiting-character}. I tend to prefer ":" as I know for sure it will never appear anyplace else but I don't know if it would be standard compliant or at least if it will not give me problems in the future.
As I recall vimeo used something like this: vimeo.com/video:{code} but they seem to have changed this.
You can use alphanumeric, plus the special characters "$-_.+!*'(),"
More info here: http://www.ietf.org/rfc/rfc1738.txt
Also, take note not to exceed 2000 characters in url
The most recent URI spec is RFC 3986; see the ABNF for details on what characters are allowed in which parts for the URI.
The format for an absolute path part is:
path-absolute = "/" [ segment-nz *( "/" segment ) ]
segment = *pchar
segment-nz = 1*pchar
pchar = unreserved / pct-encoded / sub-delims / ":" / "#"
pct-encoded = "%" HEXDIG HEXDIG
unreserved = ALPHA / DIGIT / "-" / "." / "_" / "~"
sub-delims = "!" / "$" / "&" / "'" / "(" / ")"
/ "*" / "+" / "," / ";" / "="
See http://www.ietf.org/rfc/rfc1738.txt
Basically, you are allowed all aphanumerics as well as $ - _ . + ! * ' ( ) ,
If you use dash or underscore, remember that a dash is read by Google as a hyphen, so does not alter how your URL is categorized. An underscore is counted as a character, and can mess up your SEO.
Ex: dash-use = dash use (2 words);
underscore_use = underscore_use (1 word)
You could use a dash or an underscore (these are used frequently). You could use any character you want to but for example, spaces turn into %20 in the url so they don't look too-nice.