EPICS_driver_modules/StreamDevice
0
0
Fork 0
Code Issues Pull Requests 1 Actions Packages Projects Releases Wiki Activity

reading web pages

Browse Source
This commit is contained in:
zimoch
2012-05-16 15:53:06 +00:00
parent fcb44ec845
commit 0e76ba6464
2 changed files with 123 additions and 7 deletions
Download Patch File Download Diff File Expand all files Collapse all files

1
doc/nav.html
View File

@ -178,6 +178,7 @@ div div div a {list-style-type:circle;}
<a target="_parent" href="tipsandtricks.html#writemany">Write more than one value in one message</a>
<a target="_parent" href="tipsandtricks.html#readmany">Read more than one value from one message</a>
<a target="_parent" href="tipsandtricks.html#mixed">Read values of mixed data type</a>
<a target="_parent" href="tipsandtricks.html#web">Read a web page</a>
</div>
</div>

129
doc/tipsandtricks.html
View File

@ -103,7 +103,7 @@ an array: (3.14, 17.30, -12.34)
<h3>B) We have up to 12 numeric values</h3>
<p>
Use a <a href="calcout.html">calcout</a> record and
<a href="formats.html#types">field references</a> in the format.
<a href="formats.html#redirection">redirection to fields</a>.
</p>
<p>
<code>
@ -128,7 +128,7 @@ record (calcout, "$(RECORD)") {<br>
</p>
<h3>C) Values are in other records on the same IOC</h3>
<p>
Use <a href="formats.html#types">record references</a> in the format.
Use <a href="formats.html#redirection">redirection to records</a>.
</p>
<p>
<code>
@ -216,7 +216,7 @@ Any non-matching input is ignored by record B.
</p>
<h3>C) Values should be stored in other records on the same IOC</h3>
<p>
Use <a href="formats.html#types">record references</a> in the format.
Use <a href="formats.html#redirection">redirection to records</a>.
To avoid record names in protocol files, use
<a href="protocol.html#argvar">protocol arguments</a>.
</p>
@ -244,11 +244,11 @@ processes record B.
</p>
<a name="mixed"></a>
<h2>I have a device that sends mixed data types: numbers and strings</h2>
<h2>I have a device that sends mixed data types: numbers or strings</h2>
<p>
Use a <code>@mismatch</code>
<a href="protocol.html#except">exception handler</a> and
<a href="formats.html#types">record references</a> in the format.
<a href="formats.html#redirection">redirection to records</a>.
To avoid record names in protocol files, use
<a href="protocol.html#argvar">protocol arguments</a>.
</p>
@ -289,9 +289,124 @@ record (stringout, "$(DEVICE):clean_2") {<br>
&nbsp;&nbsp;field (VAL, "OK")<br>
&nbsp;&nbsp;field (OUT, "$(DEVICE):message PP")<br>
}<br>
</code>
<a name="web"></a>
<h2>I need to read a web page</h2>
<p>
First you have to send a correctly formatted HTML request.
Note that this request must contain the full URL like
"http://server/page" and must be terminated with <u>two</u> newlines.
The server should be the same as in the
<a href="setup.html#sta"><code>drvAsynIPPortConfigure</code></a>
command (if not using a http proxy).
The web page you get often contains much more information than you need.
<a href="formats.html#regex">Regular expressions</a> are great
to find what you are looking for.
</p>
<h3>Example 1</h3>
<p>
Read the title of a web page.
</p>
<p>
<code>
get_title {<br>
&nbsp;&nbsp;extrainput = ignore;<br>
&nbsp;&nbsp;replyTimeout = 1000;<br>
&nbsp;&nbsp;out "GET http://\$1\n\n";<br>
&nbsp;&nbsp;in "%+.1/(?im)&lt;title&gt(.*)&lt\/title&gt;/";<br>
}
</code>
</p>
<p>
Terminate the request with two newlines, either explicit like here
<u>or</u> using an
<a href="protocol.html#sysvar"><code>outTerminator</code></a>.
The URI (without http:// but including the web server host name)
is passed as <a href="protocol.html#argvar">argument</a> 1 to <code>\$1</code>.
Note that web servers may be slow, so allow some
<a href="protocol.html#argvar"><code>replyTimeout</code></a>.
</p>
<p>
If you don't use an <code>inTerminator</code> then the whole page is
read as one "line" to the <code>in</code> command and can be parsed easily
with a regular expression.
We want to see the string between <code>&lt;title&gt</code> and
<code>&lt;/title&gt;</code>, so we put it into a subexpression in
<code>()</code> and request the first subexpression with <code>.1</code>.
Note that the <code>/</code> in the closing tag has be be escaped
to avoid a misinterpretation as the closing <code>/</code> of the regular
expression.
</p>
<p>
The tags may be upper or lower case like <code>&lt;TITLE&gt;</code> or
<code>&lt;Title&gt;</code>, so we ask for case insensitive matching with
<code>(?i)</code>.
</p>
<p>
The string should be terminated with the first closing
<code>&lt;/title&gt;</code>, not the last one in the file.
(There should not be more than one title but you never know.)
Thus we ask not to be greedy with <code>(?m)</code>.
<code>(?i)</code> and <code>(?m)</code> can be combined to <code>(?im)</code>.
See the PCRE documentation for more regexp syntax.
</p>
<p>
The regular expression matcher ignores and discards any content before the
matching section.
Content after the match is discarded with <code>extrainput = ignore</code>
so that it does not trigger errors reporting "surplus input".
</p>
<p>
Finally, the title may be too long for the record.
The <code>+</code> tells the format matcher not to fail in this case
but to truncate the string instead.
You can read the string with a stringin record or for longer strings with
a waveform record with data type CHAR.
</p>
<p>
<code>
record (stringin, "$(DEVICE):title") {<br>
&nbsp;&nbsp;field (DTYP, "stream")<br>
&nbsp;&nbsp;field (INP, "@$(DEVICETYPE).proto get_title($(PAGE)) $(BUS)")<br>
}<br>
record (waveform, "$(DEVICE):longtitle") {<br>
&nbsp;&nbsp;field (DTYP, "stream")<br>
&nbsp;&nbsp;field (INP, "@$(DEVICETYPE).proto get_title($(PAGE)) $(BUS)")<br>
&nbsp;&nbsp;field (FTVL, "CHAR")<br>
&nbsp;&nbsp;field (NELM, "100")<br>
}<br>
</code>
</p>
<h3>Example 2</h3>
<p>
Read a number from a web page. First we have to locate the number.
For that we match against any known string right before the number
(and <a href="formats.html#syntax">discard the match</a> with <code>*</code>).
Then we read the number.
</p>
<code>
get_title {<br>
&nbsp;&nbsp;extrainput = ignore;<br>
&nbsp;&nbsp;replyTimeout = 1000;<br>
&nbsp;&nbsp;out "GET http://\$1\n\n";<br>
&nbsp;&nbsp;in "%*/Interesting value:/%f more text";<br>
}
</code>
<p>
When using <code>extrainput = ignore;</code>, it is always a good idea to
match a few bytes after the value, too.
This catches errors where loading of the page is interrupted in the middle
of the number. (You don't want to miss the exponent from something like 1.23E-14).
</p>
<p>
You can read more than one value from a file with successive regular expressions
and <a href="formats.html#redirection">redirections</a>.
But this only works if the order of the values is predictible.
<i>StreamDevice</i> is not an XML parser! It always reads sequentially.
</p>
<hr>
<p><small>Dirk Zimoch, 2007</small></p>
<p><small>Dirk Zimoch, 2012</small></p>
</body>
</html>