Part of my application relies on a HTTP client which is based on the Win32 API.
Each HTTP query is initiated with calls to WinHttpOpenRequest like
std::wstring method = L"POST";
std::wstring path = L"/foo/bar%baz";
WinHttpOpenRequest(
m_connectionHandler,
method.c_str(),
path.c_str(),
NULL,
WINHTTP_NO_REFERER,
WINHTTP_DEFAULT_ACCEPT_TYPES,
WINHTTP_FLAG_SECURE);
Until now, I was relying on the default behavior of WinHttpOpenRequest for properly percent encode the query.
I just discovered that the literal character % was left unescaped by default and that I must pass WINHTTP_FLAG_ESCAPE_PERCENT as additional flag.
I do not really get why this API encodes every reserved characters correctly except for the percent character itself. Are there any pragmatic reasons behind this choice? And can I safely use this additionnal flag, or are there any pitfalls I cannot see?
The only reason I can imagine is to avoid a double percent encoding with the default behavior, i.e I would already percent encoded my query, and the WinHttpOpenRequest cannot guess whether the percent characters it reads are the result of a percent encoding or not.
% It can also be used as an escape character, for example, you cannot print out '%' just with printf("%") but printf("%%").
If you block escape function of the %, As what does IInspectable say, You will not be able to use the escape function like %20, And other more: %2B, %2F, %3F, %3D, %21...
Description on msdn document, Flag WINHTTP_FLAG_ESCAPE_PERCENT means
The string passed in for pwszObjectName is converted from an LPCWSTR
to an LPSTR. All unsafe characters are converted to an escape sequence
including the percent symbol.
But ,by default,
all unsafe characters except the percent symbol are
converted to an escape sequence.
I have code which lists keys using ListObjectsPages->Contents->Key and copies those keys using CopyObject. This works in general but for some keys it's complaining NoSuchKey: The specified key does not exist. The set of keys it's complaining about include keys with +.
ListObjectsPages returns key "foo+bar".
CopyObject on "foo+bar" gives the NoSuchKey error.
CopyObject on "foo bar" (unescaped) gives the NoSuchKey error.
Oddly, if I use the CLI: aws s3 cp on "foo+bar", the copy works. But I can't use the CLI. I need to use the sdk.
I'm using v1.8.11
As Rayfen mentioned, the plus characters could be the result of space replacement.
Update:
Everything was hashed out here https://github.com/aws/aws-sdk-go/issues/1438. Rayfen was right about needing to QueryEscape. I'm going to award the only current answer with the bounty since it adds useful information, but not select it as correct.
The object key and metadata document is clear:
The following character sets are generally safe for use in key names:
Alphanumeric characters [0-9a-zA-Z]
Special characters !, -, _, ., *, ', (, and )
Not only + would be converted into space with, but, from the section "Characters That Might Require Special Handling" of the same page, ':' should also be converted back from space, which QueryUnescape does not do (it only convert space back to +).
Check if your keys include other special characters to be handled with care, like : (also replaced by space), # or = (replaced by ;), or , and ?.
Check in particular if the key obtained from QueryUnescape has a + instead of a ':' in the original key: that could be a space incorrectly "unescaped".
This details what was happening: https://github.com/aws/aws-sdk-go/issues/1438
The main issue was that CopySource needs to be url-encoded and not the Key field, which was surprising to me. (I was url-encoding both.)
The other issue was that I was using path.Join which strips out trailing \. This is a problem because s3 keys can have trailing \ - which represents a sort of folder.
Which characters make a URL invalid?
Are these valid URLs?
example.com/file[/].html
http://example.com/file[/].html
In general URIs as defined by RFC 3986 (see Section 2: Characters) may contain any of the following 84 characters:
ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789-._~:/?#[]#!$&'()*+,;=
Note that this list doesn't state where in the URI these characters may occur.
Any other character needs to be encoded with the percent-encoding (%hh). Each part of the URI has further restrictions about what characters need to be represented by an percent-encoded word.
The '[' and ']' in this example are "unwise" characters but still legal. If the '/' in the []'s is meant to be part of file name then it is invalid since '/' is reserved and should be properly encoded:
http://example.com/file[/].html
To add some clarification and directly address the question above, there are several classes of characters that cause problems for URLs and URIs.
There are some characters that are disallowed and should never appear in a URL/URI, reserved characters (described below), and other characters that may cause problems in some cases, but are marked as "unwise" or "unsafe". Explanations for why the characters are restricted are clearly spelled out in RFC-1738 (URLs) and RFC-2396 (URIs). Note the newer RFC-3986 (update to RFC-1738) defines the construction of what characters are allowed in a given context but the older spec offers a simpler and more general description of which characters are not allowed with the following rules.
Excluded US-ASCII Characters disallowed within the URI syntax:
control = <US-ASCII coded characters 00-1F and 7F hexadecimal>
space = <US-ASCII coded character 20 hexadecimal>
delims = "<" | ">" | "#" | "%" | <">
The character "#" is excluded because it is used to delimit a URI from a fragment identifier. The percent character "%" is excluded because it is used for the encoding of escaped characters. In other words, the "#" and "%" are reserved characters that must be used in a specific context.
List of unwise characters are allowed but may cause problems:
unwise = "{" | "}" | "|" | "\" | "^" | "[" | "]" | "`"
Characters that are reserved within a query component and/or have special meaning within a URI/URL:
reserved = ";" | "/" | "?" | ":" | "#" | "&" | "=" | "+" | "$" | ","
The "reserved" syntax class above refers to those characters that are allowed within a URI, but which may not be allowed within a particular component of the generic URI syntax. Characters in the "reserved" set are not reserved in all contexts. The hostname, for example, can contain an optional username so it could be something like ftp://user#hostname/ where the '#' character has special meaning.
Here is an example of a URL that has invalid and unwise characters (e.g. '$', '[', ']') and should be properly encoded:
http://mw1.google.com/mw-earth-vectordb/kml-samples/gp/seattle/gigapxl/$[level]/r$[y]_c$[x].jpg
Some of the character restrictions for URIs and URLs are programming language-dependent. For example, the '|' (0x7C) character although only marked as "unwise" in the URI spec will throw a URISyntaxException in the Java java.net.URI constructor so a URL like http://api.google.com/q?exp=a|b is not allowed and must be encoded instead as http://api.google.com/q?exp=a%7Cb if using Java with a URI object instance.
Most of the existing answers here are impractical because they totally ignore the real-world usage of addresses like:
https://en.wikipedia.org/wiki/Möbius_strip or
https://zh.wikipedia.org/wiki/Wikipedia:关于中文维基百科/en.
First, a digression into terminology. What are these addresses? Are they valid URLs?
Historically, the answer was "no". According to RFC 3986, from 2005, such addresses are not URIs (and therefore not URLs, since URLs are a type of URIs). Per the terminology of 2005 IETF standards, we should properly call them IRIs (Internationalized Resource Identifiers), as defined in RFC 3987, which are technically not URIs but can be converted to URIs simply by percent-encoding all non-ASCII characters in the IRI.
Per modern spec, the answer is "yes". The WHATWG Living Standard simply classifies everything that would previously be called "URIs" or "IRIs" as "URLs". This aligns the specced terminology with how normal people who haven't read the spec use the word "URL", which was one of the spec's goals.
What characters are allowed under the WHATWG Living Standard?
Per this newer meaning of "URL", what characters are allowed? In many parts of the URL, such as the query string and path, we're allowed to use arbitrary "URL units", which are
URL code points and percent-encoded bytes.
What are "URL code points"?
The URL code points are ASCII alphanumeric, U+0021 (!), U+0024 ($), U+0026 (&), U+0027 ('), U+0028 LEFT PARENTHESIS, U+0029 RIGHT PARENTHESIS, U+002A (*), U+002B (+), U+002C (,), U+002D (-), U+002E (.), U+002F (/), U+003A (:), U+003B (;), U+003D (=), U+003F (?), U+0040 (#), U+005F (_), U+007E (~), and code points in the range U+00A0 to U+10FFFD, inclusive, excluding surrogates and noncharacters.
(Note that the list of "URL code points" doesn't include %, but that %s are allowed in "URL code units" if they're part of a percent-encoding sequence.)
The only place I can spot where the spec permits the use of any character that's not in this set is in the host, where IPv6 addresses are enclosed in [ and ] characters. Everywhere else in the URL, either URL units are allowed or some even more restrictive set of characters.
What characters were allowed under the old RFCs?
For the sake of history, and since it's not explored fully elsewhere in the answers here, let's examine was allowed under the older pair of specs.
First of all, we have two types of RFC 3986 reserved characters:
:/?#[]#, which are part of the generic syntax for a URI defined in RFC 3986
!$&'()*+,;=, which aren't part of the RFC's generic syntax, but are reserved for use as syntactic components of particular URI schemes. For instance, semicolons and commas are used as part of the syntax of data URIs, and & and = are used as part of the ubiquitous ?foo=bar&qux=baz format in query strings (which isn't specified by RFC 3986).
Any of the reserved characters above can be legally used in a URI without encoding, either to serve their syntactic purpose or just as literal characters in data in some places where such use could not be misinterpreted as the character serving its syntactic purpose. (For example, although / has syntactic meaning in a URL, you can use it unencoded in a query string, because it doesn't have meaning in a query string.)
RFC 3986 also specifies some unreserved characters, which can always be used simply to represent data without any encoding:
abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789-._~
Finally, the % character itself is allowed for percent-encodings.
That leaves only the following ASCII characters that are forbidden from appearing in a URL:
The control characters (chars 0-1F and 7F), including new line, tab, and carriage return.
"<>^`{|}
Every other character from ASCII can legally feature in a URL.
Then RFC 3987 extends that set of unreserved characters with the following unicode character ranges:
%xA0-D7FF / %xF900-FDCF / %xFDF0-FFEF
/ %x10000-1FFFD / %x20000-2FFFD / %x30000-3FFFD
/ %x40000-4FFFD / %x50000-5FFFD / %x60000-6FFFD
/ %x70000-7FFFD / %x80000-8FFFD / %x90000-9FFFD
/ %xA0000-AFFFD / %xB0000-BFFFD / %xC0000-CFFFD
/ %xD0000-DFFFD / %xE1000-EFFFD
These block choices from the old spec seem bizarre and arbitrary given the latest Unicode block definitions; this is probably because the blocks have been added to in the decade since RFC 3987 was written.
Finally, it's perhaps worth noting that simply knowing which characters can legally appear in a URL isn't sufficient to recognise whether some given string is a legal URL or not, since some characters are only legal in particular parts of the URL. For example, the reserved characters [ and ] are legal as part of an IPv6 literal host in a URL like http://[1080::8:800:200C:417A]/foo but aren't legal in any other context, so the OP's example of http://example.com/file[/].html is illegal.
In your supplementary question you asked if www.example.com/file[/].html is a valid URL.
That URL isn't valid because a URL is a type of URI and a valid URI must have a scheme like http: (see RFC 3986).
If you meant to ask if http://www.example.com/file[/].html is a valid URL then the answer is still no because the square bracket characters aren't valid there.
The square bracket characters are reserved for URLs in this format: http://[2001:db8:85a3::8a2e:370:7334]/foo/bar (i.e. an IPv6 literal instead of a host name)
It's worth reading RFC 3986 carefully if you want to understand the issue fully.
All valid characters that can be used in a URI (a URL is a type of URI) are defined in RFC 3986.
All other characters can be used in a URL provided that they are "URL Encoded" first. This involves changing the invalid character for specific "codes" (usually in the form of the percent symbol (%) followed by a hexadecimal number).
This link, HTML URL Encoding Reference, contains a list of the encodings for invalid characters.
Several of Unicode character ranges are valid HTML5, although it might still not be a good idea to use them.
E.g., href docs say http://www.w3.org/TR/html5/links.html#attr-hyperlink-href:
The href attribute on a and area elements must have a value that is a valid URL potentially surrounded by spaces.
Then the definition of "valid URL" points to http://url.spec.whatwg.org/, which says it aims to:
Align RFC 3986 and RFC 3987 with contemporary implementations and obsolete them in the process.
That document defines URL code points as:
ASCII alphanumeric, "!", "$", "&", "'", "(", ")", "*", "+", ",", "-", ".", "/", ":", ";", "=", "?", "#", "_", "~", and code points in the ranges U+00A0 to U+D7FF, U+E000 to U+FDCF, U+FDF0 to U+FFFD, U+10000 to U+1FFFD, U+20000 to U+2FFFD, U+30000 to U+3FFFD, U+40000 to U+4FFFD, U+50000 to U+5FFFD, U+60000 to U+6FFFD, U+70000 to U+7FFFD, U+80000 to U+8FFFD, U+90000 to U+9FFFD, U+A0000 to U+AFFFD, U+B0000 to U+BFFFD, U+C0000 to U+CFFFD, U+D0000 to U+DFFFD, U+E1000 to U+EFFFD, U+F0000 to U+FFFFD, U+100000 to U+10FFFD.
The term "URL code points" is then used in the statement:
If c is not a URL code point and not "%", parse error.
in a several parts of the parsing algorithm, including the schema, authority, relative path, query and fragment states: so basically the entire URL.
Also, the validator http://validator.w3.org/ passes for URLs like "你好", and does not pass for URLs with characters like spaces "a b"
Of course, as mentioned by Stephen C, it is not just about characters but also about context: you have to understand the entire algorithm. But since class "URL code points" is used on key points of the algorithm, it that gives a good idea of what you can use or not.
See also: Unicode characters in URLs
I needed to select characters to split URLs in a string, so I decided to create a list of characters which could not be found in the URL by myself:
>>> allowed = "-_.~!*'();:#&=+$,/?%#[]?#ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789"
>>> from string import printable
>>> ''.join(set(printable).difference(set(allowed)))
'`" <\x0b\n\r\x0c\\\t{^}|>'
So, the possible choices are the newline, tab, space, backslash and "<>{}^|. I guess I'll go with the space or newline. :)
I am implementing an old HTTP (0.9, 1.0, 1.1) request and response reader/writer. The request URI is the most problematic place.
You can't just use RFC 1738, 2396 or 3986 as it is. There are many old HTTP clients and servers that allow more characters. So I've made research based on accidentally published web server access logs: "GET URI HTTP/1.0" 200.
I've found that the following non-standard characters are often used in URIs:
\ { } < > | ` ^ "
These characters were described in RFC 1738 as unsafe.
If you want to be compatible with all old HTTP clients and servers - you have to allow these characters in the request URI.
Please read more information about this research in oghttp-request-collector.
This is not really an answer to your question, but validating URLs is really a serious p.i.t.a. You're probably just better off validating the domain name and leave query part of the URL be. That is my experience.
You could also resort to pinging the URL and seeing if it results in a valid response, but that might be too much for such a simple task.
Regular expressions to detect URLs are abundant, google it :)
I can't comment on the above answers, but wanted to emphasize the point (in another answer) that allowed characters aren't allowed everywhere. For example, domain names can't have underscores, so http://test_url.com is invalid.
From the source (emphasis added when needed):
Unsafe:
Characters can be unsafe for a number of reasons. The space character is unsafe because significant spaces may disappear and insignificant spaces may be introduced when URLs are transcribed or typeset or subjected to the treatment of word-processing programs.
The characters "<" and ">" are unsafe because they are used as the
delimiters around URLs in free text; the quote mark (""") is used to
delimit URLs in some systems. The character "#" is unsafe and should
always be encoded because it is used in World Wide Web and in other
systems to delimit a URL from a fragment/anchor identifier that might
follow it. The character "%" is unsafe because it is used for
encodings of other characters. Other characters are unsafe because
gateways and other transport agents are known to sometimes modify such
characters. These characters are "{", "}", "|", "", "^", "~", "[",
"]", and "`".
All unsafe characters must always be encoded within a URL. For
example, the character "#" must be encoded within URLs even in systems
that do not normally deal with fragment or anchor identifiers, so that
if the URL is copied into another system that does use them, it will
not be necessary to change the URL encoding.
Source
I came up with a couple of regular expressions for PHP that will convert URLs in text to anchor tags. (First it converts all www. URLs to http://, and then converts all URLs with https?:// to a href=... HTML links
$string = preg_replace('/(https?:\/\/)([!#$&-;=?\-\[\]_a-z~%]+)/sim', '$2', preg_replace('/(\s)((www\.)([!#$&-;=?\-\[\]_a-z~%]+))/sim', '$1http://$2', $string) );
I'm looking for a character to use a filename delimiter (I'm storing multiple filenames in a plaintext string). Windows seems not to allow :, ?, *, <, >, ", |, / and \ in filenames. Obviously, \ and / can't be used, since they mean something within a path. Is there any reason why any of those others shouldn't be used? I'm just thinking that, similar to / or \, those other disallowed characters may have special meaning that I shouldn't assume won't be in path names. Of those other 7 characters, are any definitely safe or definitely unsafe to use for this purpose?
The characters : and " are also used in paths. Colon is the drive unit delimiter, and quotation marks are used when spaces are part of a folder or file name.
The charactes * and ? are used as wildcards when searching for files.
The characters < and > are used for redirecting an application's input and output to and from a file.
The character | is used for piping output from one application into input of another application.
I would choose the pipe character for separating file names. It's not used in paths, and its shape has a natural separation quality to it.
An alternative could be to use XML in the string. There is a bit of overhead and some characters need encoding, but the advantage is that it can handle any characters and the format is self explanatory and well defined.
Windows uses the semicolon as a filename delimiter: ;. look at the PATH environment variable, it is filled with ; between path elements.
(Also, in Python, the os.path.pathsep returns ";", while it expands to ":" on Unix)
I have used * in the past. The reason for portability to Linux/Unix. True, technically it can be used on those fileysystems too. In practice, all common OSes use it as a wildcard, thus it's quite uncommon in filenames. Also, people are not surprised if programs do break when you put a * in a filename.
Why dont you use any character with ALT key combination like ‡ (Alt + 0135) as delimiter ?
It is actually possible to create files programmatically with every possible character except \. (At least, this was true at one time and it's possible that Windows has changed its policy since.) Naturally, files containing certain characters will be harder to work with than others.
What were you using to determine which characters Windows allows?
Update: The set of characters allowed by Windows is also be determined by the underlying filesystem, and other factors. There is a blog entry on MSDN that explains this in more detail.
If all you need is the appearance of a colon, and will be creating it programatically, why not make use of a UTF-8 character that just looks like a colon?
My first choice would be the Modifier Letter (U+A789), as it is a typical RTL character and appears a lot like a colon. It is what I use when I need a full DateTime in the filename, such as file_2017-05-04_16꞉45꞉22_clientNo.jpg
I would stay away from characters like the Hebrew Punctuation Sof Pasuq (U+05C3), as it is a LTR character and may mess with how a system aligns the file name itself.