If the server receives a request like:
http://host/dir/foo;lines=20-30
and foo is any document with content-type
text/* it will return a text/plain document
consisting of lines 20 through 30 of file
foo. This is very useful for structured text files like
address lists or digests of mail and news. A WN utility called
wn_mkdigest will
produce an HTML file with a list
of links to separate sections (line ranges) of the structured file. It
is described below.
The option ";lines=[first]-[last]" can be appended to the
URL of any text file served by the WN server. It has the effect
of causing the server to return line [first] through line
[last] of the document to which it is attached. Line 1 is
the first line of a file. This parameter is ignored and an error is
logged if it is used with a binary file. When used with a text file the
content type of the returned document is set to text/plain
since, for example, a range of lines from an HTML document is unlikely to be a
valid HTML document.
For any file, including binaries, but not CGI/1.1 output or parsed or filtered documents, the server will honor a byte range. A request for:
http://host/dir/foo;bytes=256-1024
will cause the server to return bytes 256 to
1024 inclusive. The first byte is numbered 0 so a range of
0-100 represents the first 101 bytes. Note that while file lines are
numbered starting with 1, bytes are numbered starting with 0. The
content type of the returned document will be text/plain if
the document foo is a text document and
application/octet-stream otherwise.
A request for:
http://host/dir/foo;bytes=256-
will cause the server to return bytes 256 through the end of
the file, while:
http://host/dir/foo;bytes=-1024
requests the last 1024 bytes of the file.
Range:" Header
Requests for a specific range can also be made with the proposed HTTP/1.1 header
"Range:". For example, if the server receives a request
with the header:
Range: bytes=100-200
it will send the 101 bytes starting with the 100th and ending with the
200th. The header "Range: bytes=300-" requests all
bytes starting with number 300 and continuing until the end of the file.
And "Range: bytes=-300" requests the last 300 bytes of
the file. This is normally done automatically by the client in
appropriate circumstances and is not under the control of the server
administrator.
wn_mkdigest Utility
The wn_mkdigest
utility is executed with two regular expressions: one to match the
section separator and the other to match the section title. For example,
for a mail digest named foo, the command:
wn_mkdigest foo "^From" "^Subject:" foo
will produce an HTML file called
foo.index.html which contains an unordered list of anchors.
Each has as a title the content of the Subject line of a mail message in
foo and href the range of lines in
foo containing that particular message. More detailed
information is available in the section "wn_mkdigest" in this
guide.