### [apps-discuss] Review of draft-ietf-appsawg-file-scheme

Dave Crocker <dhc2@dcrocker.net> Tue, 12 April 2016 19:30 UTC

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Review of: The file URI Scheme
I-D: draft-ietf-appsawg-file-scheme-05

(I see that a -06 version was released today.  Based on a quick
scan of differences from the -05 version, I do not see their
affecting the review.)

Reviewer:  D. Crocker
Date:      12 April 2016

This review was performed in my role as document shepherd.

The review was originally written last November but unfortunately I lost
track of it and apologize for the delay.

I should also comment that I've just consulted a number of others who
have been involved in discussions about the draft and hope that they
will response to this review, on the mailing list.

Summary:

The specification seeks to detail the file: URI scheme, which
"identifies a file on a particular file system", and replaces RFC 1738.

The document has been housed within the Apps Area WG, but has received
little substantive comment -- somewhere in the range of 5-8 people, with
small bursts of activity. Although at least some have tended to be
supportive, there have been notable exceptions. Worse, significant
issues that were raised were not obviously resolved on the list.  (I
looked at postings by others, immediately after the author's postings,
to see whether there were statements of agreement that an issue had been
resolved, and did not generally see them, concerning those substantive
issues.)

The draft began as an individual effort, in June 2013, went through many
revisions, and was adopted by AppsAWG in January 2015, and has had a
number of revisions.  I note a 9/26/2014 (pre-AppsAWG) comment from
Daniel Stenberg:

"I would rather have a new spec straighten up and tighten the
language somewhat so that we can get a stricter interpretation of
how a file:// is supposed to work."

which, in spite of the many document revisions, unfortunately matches my
own assessment of the current draft.

I also note a 9/15/2015 (post-AppsAWG adoption) comment from Mark
Nottingham, on behalf of the W3C TAG:

Regarding the use of file:// URIs on the web, there are a few
issues that need to be resolved for interoperability:

1. How does file:// fit into the web's origin model?

2. How does retrieval of file:// URIs fit into
[Fetch](https://fetch.spec.whatwg.org/) and/or the [URL
standard](https://url.spec.whatwg.org)?

This document does not address any of these issues, so we
encourage the APPSAWG to consider addressing these.

One point of process discussion about the draft was to distinguish
between documenting current practice, versus specifying enhancements.
Another was to distinguish between use of the construct locally (within
a user's own system) versus globally, across the public Web.  Again,
neither matter appears to be resolved clearly within the draft, and I
can't tell tell clearly which goals the draft targets, even with the
Abstract text:

"It attempts to define a common core which is intended to
interoperate across the broad spectrum of existing
implementations, while at the same time documenting other current
practices."

These two goals entail a classic choice in development of a
specification that deals with existing practice.  Clarity between the
two goals and careful precision about which is being served, is essential.

A file: construct should be of significant utility to the Internet
community.  So it warrants careful community review and extensive
indication of active support.  That is, there ought to be a basis for
assessing the likelihood of implementation and use.  As of now, this is
not possible.

In technical terms, document seems to suffer some confusion about its
role as a format specification, versus as a protocol specification.  I
believe this issue is basic and important.  It needs to be resolved.

For a specification involving such a potentially and presumably
important capability, I think significant community support should be
required... unless the spec is to be offered as Experimental, which is
the most I'm inclined to recommend at this point...

Details:

> Applications Area Working Group                                M. Kerwin
> Internet-Draft                                                       QUT
> Obsoletes: 1738 (if approved)                           December 1, 2015

I believe it merely updates it.  It essentially replaces only Section
3.10 of that RFC.

> Intended status: Standards Track
> Expires: June 3, 2016
>
>
>                           The file URI Scheme
>                    draft-ietf-appsawg-file-scheme-05
>
> Abstract
>
>    This document specifies the "file" Uniform Resource Identifier (URI)
>    scheme, obsoleting the definition in RFC 1738.
>
>    It attempts to define a common core which is intended to interoperate

attempts to define -> defines

also: common core of what? I think the answer is a common core of object
storage naming convention, but whatever is correct, it should be made
explicit here.

>    across the broad spectrum of existing implementations, while at the
>    same time documenting other current practices.

implementations of ... URI-based file system accessing mechanisms?

>
> Note to Readers (To be removed by the RFC Editor)
>
>    This draft should be discussed on the IETF Applications Area Working
>    Group discussion list <apps-discuss@ietf.org>.
>
> Status of This Memo
>
>    This Internet-Draft is submitted in full conformance with the
>    provisions of BCP 78 and BCP 79.
>
>    Internet-Drafts are working documents of the Internet Engineering
>    Task Force (IETF).  Note that other groups may also distribute
>    working documents as Internet-Drafts.  The list of current Internet-
>    Drafts is at http://datatracker.ietf.org/drafts/current/.
>
>    Internet-Drafts are draft documents valid for a maximum of six months
>    and may be updated, replaced, or obsoleted by other documents at any
>    time.  It is inappropriate to use Internet-Drafts as reference
>    material or to cite them other than as "work in progress."
>
>    This Internet-Draft will expire on June 3, 2016.
>
>
>    Copyright (c) 2015 IETF Trust and the persons identified as the
>
>    This document is subject to BCP 78 and the IETF Trust's Legal
>    Provisions Relating to IETF Documents
>
>
>
> Kerwin                    Expires June 3, 2016                  [Page 1]
>
> Internet-Draft                 file-scheme                 December 2015
>
>
>    (http://trustee.ietf.org/license-info) in effect on the date of
>    publication of this document.  Please review these documents
>    carefully, as they describe your rights and restrictions with respect
>    to this document.  Code Components extracted from this document must
>    include Simplified BSD License text as described in Section 4.e of
>    the Trust Legal Provisions and are provided without warranty as
>    described in the Simplified BSD License.
>
>
>    1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
>      1.1.  History . . . . . . . . . . . . . . . . . . . . . . . . .   3
>      1.2.  Similar Technologies  . . . . . . . . . . . . . . . . . .   3
>      1.3.  Notational Conventions  . . . . . . . . . . . . . . . . .   4
>    2.  Syntax  . . . . . . . . . . . . . . . . . . . . . . . . . . .   4
>    3.  Operations on file URIs . . . . . . . . . . . . . . . . . . .   5
>      3.1.  Translating Local File Path to file URI . . . . . . . . .   5
>      3.2.  Translating Non-local File Path to file URI . . . . . . .   6
>      3.3.  Incompatible File Paths . . . . . . . . . . . . . . . . .   7
>        3.3.1.  Win32 Namespaces  . . . . . . . . . . . . . . . . . .   7
>    4.  Encoding  . . . . . . . . . . . . . . . . . . . . . . . . . .   7
>    5.  Origins . . . . . . . . . . . . . . . . . . . . . . . . . . .   7
>    6.  Security Considerations . . . . . . . . . . . . . . . . . . .   8
>    7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   8
>    8.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   9
>    9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   9
>      9.1.  Normative References  . . . . . . . . . . . . . . . . . .   9
>      9.2.  Informative References  . . . . . . . . . . . . . . . . .  10
>    Appendix A.  Example URIs . . . . . . . . . . . . . . . . . . . .  12
>    Appendix B.  System-specific Operations . . . . . . . . . . . . .  12
>      B.1.  POSIX Systems . . . . . . . . . . . . . . . . . . . . . .  12
>      B.2.  DOS- and Windows-Like Systems . . . . . . . . . . . . . .  12
>      B.3.  Mac OS X Systems  . . . . . . . . . . . . . . . . . . . .  13
>      B.4.  OpenVMS Files-11 Systems  . . . . . . . . . . . . . . . .  13
>    Appendix C.  Nonstandard Syntax Variations  . . . . . . . . . . .  13
>      C.1.  DOS and Windows Drive Letters . . . . . . . . . . . . . .  13
>        C.1.1.  Relative Paths  . . . . . . . . . . . . . . . . . . .  14
>        C.1.2.  Vertical Bar Character  . . . . . . . . . . . . . . .  14
>      C.2.  UNC Strings . . . . . . . . . . . . . . . . . . . . . . .  15
>      C.3.  UNC Paths . . . . . . . . . . . . . . . . . . . . . . . .  15
>      C.4.  Backslash as Separator  . . . . . . . . . . . . . . . . .  16
>    Appendix D.  Example of IRI vs Percent-Encoded URI  . . . . . . .  17
>    Appendix E.  UNC Syntax . . . . . . . . . . . . . . . . . . . . .  18
>    Appendix F.  Collected Rules  . . . . . . . . . . . . . . . . . .  19
>    Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  20
>
>
>
>
>
>
> Kerwin                    Expires June 3, 2016                  [Page 2]
>
> Internet-Draft                 file-scheme                 December 2015
>
>
> 1.  Introduction
>
>    A file URI identifies a file on a particular file system.  It can be
>    used in discussions about the file, and if other conditions are met
>    it can be dereferenced to directly access the file.

Since this is a specification, and it has intended for wide use, there
should be some sort of basic definition of what a file system is.
Nothing fancy. And by way of priming the pump:

...on a particular file system, which is an object stored in a
structured naming-and-accessing environment on a host. The URI can be
used...

>
>    The file URI scheme is not coupled with a specific protocol, nor with
>    a specific media type.  See Section 3 for a discussion of operations
>    that can be performed on a file URI.

I think these defined operations are not really performed 'on' the
file URI, but rather are used to create or apply the URI.

Also:

media type. -> media type [rfc6838].

>    This document defines a syntax that is compatible with most extant
>    implementations, while attempting to push towards a stricter subset
>    of "ideal" constructs.  In many cases it simultaneously acknowledges
>    and deprecates some less common or outdated constructs.

*** ideal?

How does it 'acknowledge' such constructs?

>
> 1.1.  History
>
>    The file URI scheme was first defined in [RFC1630], which, being an
>    informational RFC, does not specify an Internet standard.  The

My personal preference is for documents to refrain from referring to
their standards status or the status of other documents. "Status" is an
ephemeral attribute that should be external to the details of a
specification, IMO.

That is, make the discussion be in terms of the technical and
operational issues, not the standards status.

>    definition was standardised in [RFC1738], and the scheme was
>    registered with the Internet Assigned Numbers Authority (IANA);

IANA registration is a side-effect of the specs and typically isn't
called out this way, I believe.

>    however that definition omitted certain language included by the
>    former that clarified aspects such as:

... by former that...   missing word?

>
>    o  the use of slashes to denote boundaries between directory levels
>       of a hierarchical file system; and
>
>    o  the requirement that client software convert the file URI into a
>       file name in the local file name conventions.

*** Hmmm. A requirement like that moves this from being a URI
specification to being a file protocol specification...

>
>    The Internet draft [I-D.hoffman-file-uri] was written in an effort to
>    keep the file URI scheme on standards track when [RFC1738] was made
>    obsolete, but that draft expired in 2005.  It enumerated concerns
>    arising from the various, often conflicting implementations of the
>    scheme.  It serves as the spiritual predecessor of this document.
>
>    Additionally the WHATWG defines a living URL standard [WHATWG-URL],
>    which includes algorithms for interpreting file URIs (as URLs).

How does it relate to the current draft?  At the least, doesn't it
instead belong in the next 'Similar Technologies' section?

>
> 1.2.  Similar Technologies
>
>    The Universal Naming Convention (UNC) [MS-DTYP] defines a string
>    format that can perform a similar role to the file URI scheme in
>    describing the location of files.  A UNC filespace selector string
>    has three parts: host, share, and path; see Appendix E.  This
>    document describes but does not specify a means of translating
>    between UNC filespace selector strings and file URIs in Appendix C.2.

"describes but does not specify" seems an odd distinction.  Not exactly
sure what it means.

>
>
>
> Kerwin                    Expires June 3, 2016                  [Page 3]
>
> Internet-Draft                 file-scheme                 December 2015
>
>
> 1.3.  Notational Conventions
>
>    The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
>    "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
>    document are to be interpreted as described in [RFC2119].
>
>    Throughout this document the term "local" is used to describe files
>    that can be accessed directly through the local file system.  It is
>    important to note that a local file may not be physically located on
>    the local machine, for example if a networked file system is
>    transparently mounted into the local file system.

I'm not exactly sure what 'accessed directly' means, in the modern world
of file systems.  Unfortunately, this is cast as a major point of
concern in the document.  How is 'directly' different from 'no authority
value is specified'?

> 2.  Syntax
>
>    The file URI syntax is defined here in Augmented Backus-Naur Form
>    (ABNF) [RFC5234], including the core ABNF syntax rule "ALPHA" defined
>    by that specification, and importing the "userinfo", "host" and
>    "path-absolute" rules from [RFC3986] (as updated by [RFC6874].)

Possibly cleaner:

[RFC5234]. Imported rules:

From [RFC5234]: ALPHA

From [RFC3986], [RFC6874]: userinfo, host, authority,
path-absolute

>    The core syntax in [RFC3986] includes "path" and "authority"
>    components, for each of which only a subset is used in the definition
>    of the file URI scheme.  The relevant subset of "path" is "path-
>    absolute", and the subset of "authority" is "file-auth", given below.
>
>    Please note Appendix C that lists some other commonly seen but
>    nonstandard variations.
>
>       file-URI       = file-scheme ":" file-hier-part
>
>       file-scheme    = "file"
>
>       file-hier-part = "//" auth-path
>                      / local-path
>
>       auth-path      = [ file-auth ] path-absolute
>
>       local-path     = path-absolute
>
>       file-auth      = [ userinfo "@" ] host

Syntax problem:

If auth-path has no file-auth, since it's optional, then both the
auth-path and local-path of file-hier-part reduce to path-absolute.
Methinks that's creates a parsing ambiguity?

Hmmm. I'm also not sure whether stylistic nuance and exact compatibility
with the meta-specification documents this is based on are worth

I believe this could derive more smoothly from section 3 of RFC3986,
with something like:

URI        = scheme ":" hier-part    ; from RFC 3986

scheme     = "file"

hier-part  = "//"
( authority
/ local-path )

(The parens are to make the binding of the alternatives visually
unambiguous. Relying on formal, implicit binding rules can create tricky
usability errors. The hier-part rule in RFC 3986 might be an example:
Concatenation is has tighter binding than alternatives, in ABNF, but the
labeling in RFC3986 could imply a different parsing. Presumably the
authors of RFC 3986 got the BNF correct, but I'm guessing a random
reader could easily get it wrong... )

>    The syntax definition above is different from those given in
>    [RFC1630] and [RFC1738] as it is derived from the generic syntax of
>    [RFC3986], which post-dates all previous specifications.

all previous -> the previous file URI

>    As a special case, the "file-auth" rule can match the string
>    "localhost" or the empty string; either value is interpreted as "the
>    machine from which the URI is being interpreted," exactly as if no
>    authority was present.  To maximise compatibility with previous

'as if no authority" was present.'  Probably should be 'were' present,
but more significantly 'authority' is not defined.

This is a reason to re-use the ABNF rulenames from RFC 3986, when you
are importing them, but modify the <element> portion to suit the file
including going down a different line of resolution on this issue, in
his 2 November 1:42pm posting. However the issue here is resolved, the
main point is that the text needs to be consistent and clear in its
language. It seems that the current text does not fully resolve the
points he raised.)

Since file-auth is shown as optional, that handles the empty string
already and doesn't need a comment.

Offhand, I wonder whether the details of the "As special case" paragraph
can (and should) instead be reflected directly in the ABNF?

> Kerwin                    Expires June 3, 2016                  [Page 4]
>
> Internet-Draft                 file-scheme                 December 2015
>
>
>    specifications, implementations MAY choose to include an empty "file-
>    auth".
>
>    Systems exhibit different levels of case-sensitivity.  Unless the
>    file system is known to be case-insensitive, implementations MUST
>    maintain the case of file and directory names when translating file
>    URIs to and from the local system's representation of file paths, and
>    any systems or devices that transport file URIs MUST NOT alter the
>    case of file URIs they transport.

This is protocol language, not URI format/semantics language.

I believe that the needs of this spec are served by something along the
lines of:

Some systems have case-sensitive file naming and some do not.  Hence
the  file scheme supports case sensitivity, in order to retain the case
as given. Any transport-related handling of the file URI scheme MUST
retain the case as given. Any mapping to or from a case-insensitive form
is soley the responsibility of the implementation processing the file
URI on behalf of the referenced file system.

>
> 3.  Operations on file URIs

Use of normative language in this section is inappropriate.  It does not
provide protocol details and provides essentially no semantics.

>    Implementations that provide dereferencing ooperations on file URIs

ooperations -> operations

>    SHOULD, at a minimum, provide a read-like operation to return the
>    contents of a file located by a file URI.  Additional operations MAY
>    be provided, such as writing to, creating, and deleting files.  See
>    the POSIX file and directory operations [POSIX] for examples of
>    standardized operations that can be performed on files.

What is the practical benefit of giving the reader superficial tutorial

>    File URIs can also be translated to and from other, similar
>    constructs, such as local file paths or UNC strings.

I don't know what this means.  And how is this sentence useful?

>    A file URI can be dependably dereferenced or translated to a local
>    file path only if it is local.  A file URI is considered "local" if
>    it has a blank or no authority, or the authority is the special
>    string "localhost".
>
>    This specification neither defines nor forbids a mechanism for
>    accessing non-local files.  See SMB [MS-SMB], NFS [RFC7530], NCP
>    [NOVELL] for examples of protocols that can be used to access files
>    over a network.  Also see Appendix C.2 for a discussion on
>    translating non-local file URIs to and from UNC stings.
>
> 3.1.  Translating Local File Path to file URI
>
>    Below is an algorithmic description of the process used to convert a
>    file path to a URI; see Section 4.
>
>    1.  Resolve the file path to its fully qualified absolute form.

What does this mean?  Where is it defined?

>
>    2.  Initialise the URI with the "file:" scheme identifier.
>
>    3.  If including an empty authority field, append the "//" sigil to
>        the URI.

sigil ???  pretty stylized vocabulary...

What about the alternative of including a /non-empty/ authority field?

>    4.  Append a slash character "/" to the URI, to signify the path
>        root.>

>    5.  For each directory in the path after the root:
>
>        1.  Transform the directory name to a path segment ([RFC3986],
>            Section 3.3) as per Section 2 of [RFC3986].

I think that Section 2 does not specify how to do a transform, although
yes, it does make reference to doing one.  Rather, it specifies encoding
rules.  The details of how to do a transform are left to the implementer.

Hence I believe the above should be something like:

1. Transform the directory name to a path segment (RFC3986],
Section 3.3]) to conform to the encoding rules of Section 2 of
[RFC3986].  The specific rules for mapping between a file system name
and a file scheme URI are outside the scope of this specification.

>        2.  Append the transformed segment and a delimiting slash
>            character "/" to the URI.
>
>    6.  If the path includes a file name:
>
>        1.  Transform the file name to a path segment as above.
>
>        2.  Append the transformed segment to the URI.

A slash is required at the end of a directory, even if there is no file
name?

> Differences from RFC 1738

Seems like this belongs elsewhere in the document, like maybe an
appendix.  It is irrelevant except as an historical note.

>    In [RFC1738] a file URL always started with the token "file://",
>    followed by an (optionally blank) authority and a "/".  That "/" was
>    not considered part of the path.  This implies that the correct
>    encoding for a file path in a UNIX-like environment would have been:
>
>         token     + authority + slash + path
>       = "file://" + ""        + "/"   + "/path/to/file.txt"
>       = "file:////path/to/file.txt"
>
>    However that construct was never observed in practice, and in fact
>    would have collided with the eventual encoding of UNC strings in URIs
>    described in Appendix C.3.
>
> 3.2.  Translating Non-local File Path to file URI
>
>    Translating a non-local file path, including a UNC string, to a file
>    URI follows the same basic algorithm as for local files, above,
>    except that the authority MUST refer to the network-accesible node
>    that hosts the file.

accesible  -> accessible

>    For example, in a clustered OpenVMS Files-11 system the authority
>    would contain the node name.  Where the original node reference
>    includes a username and password in an access control string, they
>    MAY be transcribed into the userinfo field of the authority
>    ([RFC3986], Section 3.2.1), security considerations (Section 6)
>    notwithstanding.
>
>    See Appendix C.2 for an explicit handling of UNC strings.
>
>
>
>
>
>
>
> Kerwin                    Expires June 3, 2016                  [Page 6]
>
> Internet-Draft                 file-scheme                 December 2015
>
>
> 3.3.  Incompatible File Paths
>
>    Some conventional file path formats are known to be incompatible with
>    the file URI scheme.
>
> 3.3.1.  Win32 Namespaces
>
>    The Microsoft Windows API defines Win32 Namespaces [Win32-Namespaces]
>    for interacting with files and devices using Windows API functions.
>    These namespaced paths are prefixed by "\\?\" for Win32 File
>    Namespaces and "\\.\" for Win32 Device Namespaces.  There is also a
>    special case for UNC file paths in Win32 File Namespaces, referred to
>    as "Long UNC", using the prefix "\\?\UNC\".
>
>    This specification does not define a mechanism for translating
>    namespaced paths to or from file URIs.

No it doesn't, although it contains some language that almost seems to.
The language needs to be removed, in favor of the above simple sentence.

Further, language about 'incompatibility' is a commentary that belongs
in the Introduction or some other place outside the main spec.  It's an
important discussion point, but it's not part of the spec.

>
> 4.  Encoding
>
>    To avoid ambiguity, a file URI SHOULD be transported as an
>    Internationalized Resource Identifier (IRI) [RFC3987], or as a URI
>    with non-ASCII characters encoded according to the UTF-8 character
>    encoding [STD63] and percent-encoded as needed ([RFC3986],
>    Section 2.5).
>
>    The encoding of a file URI depends on the file system that stores the

I'm not sure this sentence is correct.  It's a natural assumption but
arguably one can lay any encoding convention on top of any data store.

>    identified file.  If the file system uses a known non-Unicode
>    character encoding, the path SHOULD be converted to a sequence of
>    characters from the Universal Character Set [ISO10646] normalized
>    according to Normalization Form C (NFC) [UTR15], before being
>    translated to a file URI, and conversely a file URI SHOULD be
>    converted back to the file system's native encoding when
>    dereferencing or translating to a file path.
>
>       Note that many modern file systems encode directory and file names
>       as arbitrary sequences of octets.  In those cases, the
>       representation as an encoded string often depends on the user's
>       localization settings, or defaults to UTF-8 [STD63].
>
>    When the file system's encoding is not known the file URI SHOULD be
>    transported as an Internationalized Resource Identifier (IRI)
>    [RFC3987] to avoid ambiguity.  See Appendix D for examples.

I'm inclined to think that this section either needs to be far more
complete -- and I'm not recommending it do that -- or it merely needs to
caution implementers to make sure that file scheme URI storage needs to
be idempotent with the original, interoperable form.

>
> 5.  Origins
>
>    As per [RFC6454], Section 4, when determining the origin of a file
>    URI implementations MAY return an implementation-defined value.

Now we are back to protocol, rather than basic representation. But it
seems minimal in detail and utility.
>
>
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>
>    Historically, user agents have granted content from the file URI
>    scheme a tremendous amount of privilege.  However, granting all local
>    files such wide privileges can lead to privilege escalation attacks.
>    Some user agents have had success granting local files directory-
>    based privileges, but this approach has not been widely adopted.
>    Other user agents use globally unique identifiers for each file URI,
>    which is the most secure option.

This paragraph belongs in the next, Security Considerations section.
Without the protocol-ish paragraph before it.

>
> 6.  Security Considerations
>
>    There are many security considerations for URI schemes discussed in
>    [RFC3986].
>
>    File access and the granting of privileges for specific operations
>    are complex topics, and the use of file URIs can complicate the
>    security model in effect for file privileges.  Software using file
>    URIs MUST NOT grant greater access than would be available for other
>    file access methods.

This sort of normative statement has no real meaning, and certainly none
without explanation.  At base, the reader cannot tell was satisfies the
normative statement and what does not.

>    File systems typically assign an operational meaning to special
>    characters, such as the "/", "\", ":", "[", and "]" characters, and
>    to special device names like ".", "..", "...", "aux", "lpt", etc.  In
>    some cases, merely testing for the existence of such a name will
>    cause the operating system to pause or invoke unrelated system calls,
>    leading to significant security concerns regarding denial of service
>    and unintended data transfer.  It would be impossible for this
>    specification to list all such significant characters and device
>    names.  Implementers MUST research the reserved names and characters
>    for the types of storage device that may be attached to their
>    application and restrict the use of data obtained from URI components
>    accordingly.
>
>    Additionally, as discussed in the HP OpenVMS Systems Documentation
>    <http://h71000.www7.hp.com/doc/84final/ba554_90015/ch03s09.html>
>    "access control strings include sufficient information to allow
>    someone to break in to the remote account, [therefore] they create
>    serious security exposure."  In a similar vein, the presence of a
>    [RFC3986].  As such, the userinfo field of a file URI, if present,
>    MUST NOT contain a password.

Is there really no stable, published document that says something similar?

> 7.  IANA Considerations
>
>    This document defines the following URI scheme, so the "Permanent URI
>    Schemes" registry has been updated accordingly.  This registration
>    complies with [BCP35].
>
>    Scheme name:
>
>
>
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>
>
>       file
>
>    Status:
>       permanent
>
>    Applications/protocols that use this scheme name:
>       Commonly used in hypertext documents to refer to files without
>       depending on network access.  Supported by major browsers.
>
>       Windows API (PathCreateFromUrl, UrlCreateFromPath).
>
>       Perl LWP.
>
>    Contact:
>       Matthew Kerwin <matthew.kerwin@qut.edu.au>
>
>    Change Controller:
>       This scheme is registered under the IETF tree.  As such, the IETF
>       maintains change control.
>
> 8.  Acknowledgements
>
>    This specification is derived from [RFC1738], [RFC3986], and
>    [I-D.hoffman-file-uri] (expired); the acknowledgements in those
>    documents still apply.
>
>    Additional thanks to Dave Risney, author of the informative IE Blog
>    article <http://blogs.msdn.com/b/ie/archive/2006/12/06/file-uris-in-
>    windows.aspx>, and Dave Thaler for their comments and suggestions.
>
> 9.  References
>
> 9.1.  Normative References
>
>    [BCP35]    Thaler, D., Ed., Hansen, T., and T. Hardie, "Guidelines
>               and Registration Procedures for URI Schemes", BCP 35,
>               RFC 7595, DOI 10.17487/RFC7595, June 2015,
>               <http://www.rfc-editor.org/info/bcp35>.
>
>    [ISO10646]
>               International Organization for Standardization,
>               "Information Technology - Universal Multiple-Octet Coded
>               Character Set (UCS)", ISO/IEC 10646:2003, December 2003.
>
>    [RFC1035]  Mockapetris, P., "Domain names - implementation and
>               specification", STD 13, RFC 1035, DOI 10.17487/RFC1035,
>               November 1987, <http://www.rfc-editor.org/info/rfc1035>.
>
>
>
>
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>
>
>    [RFC1123]  Braden, R., Ed., "Requirements for Internet Hosts -
>               Application and Support", STD 3, RFC 1123,
>               DOI 10.17487/RFC1123, October 1989,
>               <http://www.rfc-editor.org/info/rfc1123>.
>
>    [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
>               Requirement Levels", BCP 14, RFC 2119,
>               DOI 10.17487/RFC2119, March 1997,
>               <http://www.rfc-editor.org/info/rfc2119>.
>
>    [RFC3986]  Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
>               Resource Identifier (URI): Generic Syntax", STD 66,
>               RFC 3986, DOI 10.17487/RFC3986, January 2005,
>               <http://www.rfc-editor.org/info/rfc3986>.
>
>    [RFC3987]  Duerst, M. and M. Suignard, "Internationalized Resource
>               Identifiers (IRIs)", RFC 3987, DOI 10.17487/RFC3987,
>               January 2005, <http://www.rfc-editor.org/info/rfc3987>.
>
>    [RFC4291]  Hinden, R. and S. Deering, "IP Version 6 Addressing
>               Architecture", RFC 4291, DOI 10.17487/RFC4291, February
>               2006, <http://www.rfc-editor.org/info/rfc4291>.
>
>    [RFC5234]  Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
>               Specifications: ABNF", STD 68, RFC 5234,
>               DOI 10.17487/RFC5234, January 2008,
>               <http://www.rfc-editor.org/info/rfc5234>.
>
>    [RFC6874]  Carpenter, B., Cheshire, S., and R. Hinden, "Representing
>               IPv6 Zone Identifiers in Address Literals and Uniform
>               Resource Identifiers", RFC 6874, DOI 10.17487/RFC6874,
>               February 2013, <http://www.rfc-editor.org/info/rfc6874>.
>
>    [UTR15]    Davis, M. and K. Whistler, "Unicode Normalization Forms",
>               August 2012,
>               <http://unicode.org/reports/tr15/tr15-18.html>.
>
> 9.2.  Informative References
>
>    [Bug107540]
>               Bugzilla@Mozilla, "Bug 107540", October 2007,
>               <https://bugzilla.mozilla.org/show_bug.cgi?id=107540>.
>
>    [I-D.hoffman-file-uri]
>               Hoffman, P., "The file URI Scheme", draft-hoffman-file-
>               uri-03 (work in progress), January 2005.
>
>
>
>
>
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>
>
>    [MS-DTYP]  Microsoft Open Specifications, "Windows Data Types, 2.2.56
>               UNC", January 2013,
>               <http://msdn.microsoft.com/en-us/library/gg465305.aspx>.
>
>    [MS-NBTE]  Microsoft Open Specifications, "NetBIOS over TCP (NBT)
>               Extensions", May 2014,
>               <http://msdn.microsoft.com/en-us/library/dd891412.aspx>.
>
>    [MS-SMB]   Microsoft Open Specifications, "Server Message Block (SMB)
>               Protocol", January 2013,
>               <http://msdn.microsoft.com/en-us/library/cc246231.aspx>.
>
>    [NOVELL]   Novell, "NetWare Core Protocols", 2013,
>               <http://www.novell.com/developer/ndk/
>               netware_core_protocols.html>.
>
>    [POSIX]    IEEE, "IEEE Std 1003.1, 2013 Edition", 2013.
>
>    [RFC1630]  Berners-Lee, T., "Universal Resource Identifiers in WWW: A
>               Unifying Syntax for the Expression of Names and Addresses
>               of Objects on the Network as used in the World-Wide Web",
>               RFC 1630, DOI 10.17487/RFC1630, June 1994,
>               <http://www.rfc-editor.org/info/rfc1630>.
>
>    [RFC1738]  Berners-Lee, T., Masinter, L., and M. McCahill, "Uniform
>               Resource Locators (URL)", RFC 1738, DOI 10.17487/RFC1738,
>               December 1994, <http://www.rfc-editor.org/info/rfc1738>.
>
>    [RFC6454]  Barth, A., "The Web Origin Concept", RFC 6454,
>               DOI 10.17487/RFC6454, December 2011,
>               <http://www.rfc-editor.org/info/rfc6454>.
>
>    [RFC7530]  Haynes, T., Ed. and D. Noveck, Ed., "Network File System
>               (NFS) Version 4 Protocol", RFC 7530, DOI 10.17487/RFC7530,
>               March 2015, <http://www.rfc-editor.org/info/rfc7530>.
>
>    [STD63]    Yergeau, F., "UTF-8, a transformation format of ISO
>               10646", STD 63, RFC 3629, DOI 10.17487/RFC3629, November
>               2003, <http://www.rfc-editor.org/info/std63>.
>
>    [WHATWG-URL]
>               WHATWG, "URL Living Standard", May 2013,
>               <http://url.spec.whatwg.org/>.
>
>    [Win32-Namespaces]
>               Microsoft Developer Network, "Naming Files, Paths, and
>               Namespaces", June 2013, <https://msdn.microsoft.com/en-
>               au/library/windows/desktop/aa365247(v=vs.85).aspx>.
>
>
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>
> Appendix A.  Example URIs
>
>    The syntax in Section 2 is intended to support file URIs that take
>    the following forms:
>
>    Local files:
>
>    o  A traditional file URI for a local file, with an empty authority.
>       This is the most common format in use today.  E.g.:
>
>       *  "file:///path/to/file"
>
>    o  The minimal representation of a local file, with no authority
>       field and an absolute path that begins with a slash "/".  E.g.:
>
>       *  "file:/path/to/file"
>
>    Non-local files:
>
>    o  A non-local file, with an explicit authority.  E.g.:
>
>       *  "file://host.example.com/path/to/file"
>
> Appendix B.  System-specific Operations
>
>    This appendix is not normative; it highlights some observed
>    behaviours and provides system-specific guidance for interacting with
>    file URIs and paths.
>
> B.1.  POSIX Systems
>
>    There is little to say about POSIX file systems; the file URI
>    structure already closely resembles POSIX file paths.
>
> B.2.  DOS- and Windows-Like Systems
>
>    When mapping a DOS- or Windows-like file path to a file URI,
>    implementations typically map the drive letter (e.g. "c:") into the
>    first path segment.
>
>    See Appendix C.1 for explicit (but non-normative and strictly
>    optional) rules for interacting with DOS- or Windows-like file paths
>    and URIs.
>
>
>
>
>
>
>
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>
> B.3.  Mac OS X Systems
>
>    The HFS+ file system uses a non-standard normalization form, similar
>    to Normalization Form D.  Take care when transforming HFS+ file paths
>    to and from URIs using Normalization Form C Section 4.
>
> B.4.  OpenVMS Files-11 Systems
>
>    When mapping a VMS file path to a file URI, map the device name into
>    the first path segment.  Note that the dollars sign "\$" is a reserved
>    character per the definition in [RFC3986], Section 2.2, so should be
>    percent-encoded if present in the device name.
>
>    If the VMS file path includes a node reference, use that as the
>    authority.  Where the original node reference includes a username and
>    password in an access control string, they can be transcribed into
>    the userinfo field of the authority ([RFC3986], Section 3.2.1),
>    security considerations (Section 6) notwithstanding.
>
> Appendix C.  Nonstandard Syntax Variations
>
>    These variations may be encountered for historical reasons, but are
>    not supported by the normative syntax of Section 2.
>
>    This appendix is not normative.
>
> C.1.  DOS and Windows Drive Letters
>
>    On Windows- or DOS-based file systems a absolute file path can begin
>    with a drive letter.  To facilitate this, the "local-path" rule in
>    Section 2 can be replaced with the following:
>
>       local-path     = [ drive-letter ] path-absolute
>
>       drive-letter   = ALPHA ":"
>
>    This is intended to support the minimal representation of a local
>    file in a DOS- or Windows-based environment, with no authority field
>    and an absolute path that begins with a drive letter.  E.g.:
>
>    o  "file:c:/path/to/file"
>
>    URIs of the form "file:///c:/path/to/file" are already supported by
>    the "path-absolute" rule.
>
>    Note that comparison of drive letters in DOS or Windows file paths is
>    case-insensitive.  Some implementations therefore canonicalize drive
>    letters in file URIs by converting them to uppercase.
>
>
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> C.1.1.  Relative Paths
>
>    In DOS- or Windows-based file systems, relative paths beginning with
>    a slash "/" should be resolved relative to the drive letter, and
>    resolution of ".." dot segments (per Section 5.2.4 of [RFC3986])
>    should not ever overwrite the drive letter.
>
>    e.g.:
>
>       base:       file:///c:/path/to/file.txt
>       rel. URI:   /some/other/thing.bmp
>       resolved:   file:///c:/some/other/thing.bmp
>
>       base:       file:///c:/foo.txt
>       rel. URI:   ../../bar.txt
>       resolved:   file:///c:/bar.txt
>
>    Relative paths with a drive letter followed by a character other than
>    a slash (e.g. "c:bar/baz.txt" or "c:../foo.txt") should not be
>    accepted as dereferenceable URIs in DOS or Windows systems.
>
> C.1.2.  Vertical Bar Character
>
>    Historically some implementations have used a vertical line character
>    "|" instead of a colon ":" in the drive letter construct.  [RFC3986]
>    forbids the use of the vertical line, however it may be necessary to
>    interpret or update old URIs.
>
>    For interpreting such URIs, the "auth-path" and "local-path" rules in
>    Section 2 and the "drive-letter" rule above are replaced with the
>    following:
>
>       auth-path      = [ file-auth ] path-absolute
>                      / [ file-auth ] file-absolute
>
>       local-path     = [ drive-letter ] path-absolute
>                      / file-absolute
>
>       file-absolute  = "/" drive-letter path-absolute
>
>       drive-letter   = ALPHA ":"
>                      / ALPHA "|"
>
>    This is intended to support regular DOS or Windows file URIs with
>    vertical line characters in the drive letter construct.  E.g.:
>
>    o  "file:///c|/path/to/file"
>
>
>
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>
>    o  "file:/c|/path/to/file"
>
>    o  "file:c|/path/to/file"
>
>    To update such an old URI, replace the vertical line "|" with a colon
>    ":".
>
> C.2.  UNC Strings
>
>    A UNC filespace selector string can be directly translated to a URI;
>    see Section 4.  The following is an algorithmic description of the
>    process of translating a UNC string to a file URI:
>
>    1.  Initialise the URI with the "file:" scheme identifier.
>
>    2.  Append the authority:
>
>        1.  Append the "//" authority sigil to the URI.
>
>        2.  Append the hostname field of the UNC string to the URI.
>
>    3.  Append the sharename:
>
>        1.  Transform the sharename to a path segment ([RFC3986],
>            Section 3.3) as per Section 2 of [RFC3986].
>
>        2.  Append a delimiting slash character "/" and the transformed
>            segment to the URI.
>
>    4.  For each objectname:
>
>        1.  Transform the objectname to a path segment ([RFC3986],
>            Section 3.3) as per Section 2 of [RFC3986].
>
>        2.  Append a delimiting slash character "/" and the transformed
>            segment to the URI.
>
>    Example:
>
>       UNC String:   \\host.example.com\Share\path\to\file.txt
>       URI:          file://host.example.com/Share/path/to/file.txt
>
> C.3.  UNC Paths
>
>    It is common to encounter file URIs that encode entire UNC strings in
>    the path, usually with all backslash "\" characters replaced with
>    slashes "/".
>
>
>
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>
>    To interpret such URIs, the "auth-path" rule in Section 2 is replaced
>    with the following:
>
>       auth-path      = [ file-auth ] path-absolute
>                      / unc-authority path-absolute
>
>       unc-authority  = 2*3"/" [ userinfo "@" ] file-host
>
>       file-host      = inline-IP / IPv4address / reg-name
>
>       inline-IP      = "%5B" ( IPv6address / IPvFuture ) "%5D"
>
>    "IPvFuture", and "reg-name rules from [RFC3986].
>
>       Note that the "file-host" rule is the same as "host" but with
>       percent-encoding applied to "[" and "]" characters.
>
>    This extended syntax is intended to support URIs that take the
>    following forms, in addition to those in Appendix A:
>
>    Non-local files:
>
>    o  The "traditional" representation of a non-local file, with an
>       empty authority and a complete (transformed) UNC string in the
>       path.  E.g.:
>
>       *  "file:////host.example.com/path/to/file"
>
>    o  As above, with an extra slash between the empty authority and the
>       transformed UNC string, conformant with the definition from
>       [RFC1738].  E.g.:
>
>       *  "file://///host.example.com/path/to/file"
>
>       This representation is notably used by the Firefox web browser.
>       See Bugzilla#107540 [Bug107540].
>
>    It also further limits the set of file URIs that can be translated to
>    a local file path to those with a path that does not encode a UNC
>    string.
>
> C.4.  Backslash as Separator
>
>    Historically some implementations have copied entire file paths into
>    the path components of file URIs.  Where DOS or Windows file paths
>    were copied thus, resulting URI strings contained unencoded backslash
>    "\" characters, which are forbidden by both [RFC1738] and [RFC3986].
>
>
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>
>    It may be possible to translate or update such an invalid file URI by
>    replacing all backslashes "\" with slashes "/", if it can be
>    determined with reasonable certainty that the backslashes are
>    intended as path separators.
>
> Appendix D.  Example of IRI vs Percent-Encoded URI
>
>    The following examples demonstrate the advantage of encoding file
>    URIs as IRIs to avoid ambiguity (see Section 4).
>
>    Example: file IRI:
>
>    | Bytes of file IRI in a UTF-8 document:
>    |    66 69 6c 65 3a 43 3a 2f 72 65 c3 a7 75 2e 74 78 74
>    |    f  i  l  e  :  c  :  /  r  e  ( c ) u  .  t  x  t
>    |
>    | Interpretation:
>    |    A file named "recu.txt" with a cedilla on the "c", in the
>    |    directory "C:\" of a DOS or Windows file system.
>    |
>    | Character value sequences of file paths, for various file system
>    | encodings:
>    |
>    |  o UTF-16 (e.g. NTFS):
>    |       0043 003a 005c 0072 0065 00e7 0075 002e 0074 0078 0074
>    |
>    |  o Codepage 437 (e.g. MS-DOS):
>    |       43   3a   5c   72   65   87   75   2e   74   78   74
>
>    Counter-example: ambiguous file URI:
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
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>
>    | Percent-encoded file URI, in any ASCII-compatible document:
>    |    "file:///%E3%81%A1"
>    |
>    | Possible interpretations of the file name, depending on the
>    | encoding of the file system:
>    |
>    |  o UTF-8:
>    |       <HIRAGANA LETTER TI (U+3061)>
>    |
>    |  o Codepage 437:
>    |       <GREEK SMALL LETTER PI (U+03C0)> +
>    |       <LATIN SMALL LETTER U WITH DIAERESIS (U+00FC)> +
>    |       <LATIN SMALL LETTER I WITH ACUTE (U+00ED)>
>    |
>    |  o EBCDIC:
>    |       "Ta~"
>    |
>    | etc.
>
> Appendix E.  UNC Syntax
>
>    The UNC filespace selector string is a null-terminated sequence of
>    characters from the Universal Character Set [ISO10646].
>
>    The syntax of a UNC filespace selector string, as defined by
>    [MS-DTYP], is given here in Augmented Backus-Naur Form (ABNF)
>    [RFC5234] for convenience.  Note that this definition is informative
>    only; the normative description is in [MS-DTYP].
>
>       UNC = "\\" hostname "\" sharename *( "\" objectname )
>       hostname   = netbios-name / fqdn / ip-address
>       sharename  = <name of share or resource to be accessed>
>       objectname = <depends on resource being accessed>
>
>    o  "netbios-name" from [MS-NBTE], Section 2.2.1.
>
>    o  "fqdn" from [RFC1035] or [RFC1123]
>
>    o  "ip-address" from Section 2.1 of [RFC1123], or Section 2.2 of
>       [RFC4291].
>
>    The precise format of "sharename" depends on the protocol; see: SMB
>    [MS-SMB], NFS [RFC7530], NCP [NOVELL].
>
>
>
>
>
>
>
>
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> Internet-Draft                 file-scheme                 December 2015
>
>
> Appendix F.  Collected Rules
>
>    Here are the collected syntax rules for all optional appendices,
>    presented for convenience.  This collected syntax is not normative.
>
>       file-URI       = file-scheme ":" file-hier-part
>
>       file-scheme    = "file"
>
>       file-hier-part = "//" auth-path
>                      / local-path
>
>       auth-path      = [ file-auth ] path-absolute
>                      / [ file-auth ] file-absolute
>                      / unc-authority path-absolute
>
>       local-path     = [ drive-letter ] path-absolute
>                      / file-absolute
>
>       file-auth      = [ userinfo "@" ] host
>
>       unc-authority  = 2*3"/" [ userinfo "@" ] file-host
>
>       file-host      = inline-IP / IPv4address / reg-name
>
>       inline-IP      = "%5B" ( IPv6address / IPvFuture ) "%5D"
>
>       file-absolute  = "/" drive-letter path-absolute
>
>       drive-letter   = ALPHA ":"
>                      / ALPHA "|"
>
>    This collected syntax is intended to support file URIs that take the
>    following forms:
>
>    Local files:
>
>    o  A traditional file URI for a local file, with an empty authority.
>       E.g.:
>
>       *  "file:///path/to/file"
>
>    o  The minimal representation of a local file, with no authority
>       field and an absolute path that begins with a slash "/".  E.g.:
>
>       *  "file:/path/to/file"
>
>
>
>
>
> Kerwin                    Expires June 3, 2016                 [Page 19]
>
> Internet-Draft                 file-scheme                 December 2015
>
>
>    o  The minimal representation of a local file in a DOS- or Windows-
>       based environment, with no authority field and an absolute path
>       that begins with a drive letter.  E.g.:
>
>       *  "file:c:/path/to/file"
>
>    o  Regular DOS or Windows file URIs, with vertical line characters in
>       the drive letter construct.  E.g.:
>
>       *  "file:///c|/path/to/file"
>
>       *  "file:/c|/path/to/file"
>
>       *  "file:c|/path/to/file"
>
>    Non-local files:
>
>    o  The representation of a non-local file, with an explicit
>       authority.  E.g.:
>
>       *  "file://host.example.com/path/to/file"
>
>    o  The "traditional" representation of a non-local file, with an
>       empty authority and a complete (transformed) UNC string in the
>       path.  E.g.:
>
>       *  "file:////host.example.com/path/to/file"
>
>    o  As above, with an extra slash between the empty authority and the
>       transformed UNC string.  E.g.:
>
>       *  "file://///host.example.com/path/to/file"
>
>
>    Matthew Kerwin
>    Queensland University of Technology
>    Kelvin Grove, QLD  4059
>    Australia
>
>    Email: matthew.kerwin@qut.edu.au
>
>
>
>
>
>
>
>
>
> Kerwin                    Expires June 3, 2016                 [Page 20]

--
Dave Crocker
Brandenburg InternetWorking
bbiw.net

--
Dave Crocker
Brandenburg InternetWorking
bbiw.net

--

Dave Crocker
Brandenburg InternetWorking
bbiw.net

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