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<body>
<div id="content">
<h1 class="title">Taler-Util Library</h1>
<div id="table-of-contents">
<h2>Table of Contents</h2>
<div id="text-table-of-contents">
<ul>
<li><a href="#org25ea71b">1. classes overview</a>
<ul>
<li><a href="#orgb49dd7e">1.1. amount (currency + value + fraction)</a></li>
<li><a href="#orgb7c6fb1">1.2. logging</a></li>
<li><a href="#org4307498">1.3. ‘payto’ URI particularities</a></li>
<li><a href="#org44d03ed">1.4. configuration</a></li>
</ul>
</li>
<li><a href="#orgd6a98cd">2. classes for handling currency plus value plus fraction</a>
<ul>
<li><a href="#org5d287dc">2.1. class <code>Amount</code></a></li>
<li><a href="#org56a0ae4">2.2. class <code>SignedAmount</code></a></li>
</ul>
</li>
<li><a href="#orgb9b4b04">3. classes <code>LogDefinition</code>, <code>GnunetLoglevel</code></a></li>
<li><a href="#orga6828fa">4. class <code>GnunetLogger</code></a>
<ul>
<li><a href="#org8d3839f">4.1. log definition, environment variables</a></li>
<li><a href="#org9a2a746">4.2. environment variable <code>GNUNET_FORCE_LOGFILE</code></a></li>
<li><a href="#orga5014e4">4.3. constructor</a></li>
<li><a href="#orgfb9a8c1">4.4. method <code>log</code></a></li>
</ul>
</li>
<li><a href="#orgaadd9a7">5. ‘payto’ URI parsing</a></li>
<li><a href="#orgdf9cef8">6. class <code>TalerConfig</code></a>
<ul>
<li><a href="#org03f14e5">6.1. reading</a></li>
<li><a href="#orgd929224">6.2. value types</a></li>
<li><a href="#orgc4601e4">6.3. retrieving values</a>
<ul>
<li><a href="#org76aedbb">6.3.1. specific values</a></li>
<li><a href="#org1feca74">6.3.2. entire set</a></li>
</ul>
</li>
</ul>
</li>
</ul>
</div>
</div>
<p>
The Taler-Util library provides several classes that deal with various
aspects of Taler programming in the Python language.
This is documentation for the library.
</p>
<p>
This file is in Org Mode format and can be processed (by Emacs)
to produce HTML, etc. When we figure out <b>where</b> to put this
documentation, we can convert it to Sphinx (or whatever) format.
Ongoing discussion: <a href="https://bugs.gnunet.org/view.php?id=6649">https://bugs.gnunet.org/view.php?id=6649</a>
</p>
<div id="outline-container-org25ea71b" class="outline-2">
<h2 id="org25ea71b"><span class="section-number-2">1</span> classes overview</h2>
<div class="outline-text-2" id="text-1">
<p>
These are grouped according to area of concern, which (uncoincidentally)
is also how the source code is organized.
</p>
<p>
Several of these derive from the <code>Exception</code> class.
The rest are <i>leaf classes</i>.
</p>
</div>
<div id="outline-container-orgb49dd7e" class="outline-3">
<h3 id="orgb49dd7e"><span class="section-number-3">1.1</span> amount (currency + value + fraction)</h3>
<div class="outline-text-3" id="text-1-1">
<ul class="org-ul">
<li>CurrencyMismatchError(Exception)</li>
<li>AmountOverflowError(Exception)</li>
<li>AmountFormatError(Exception)</li>
<li>Amount</li>
<li>SignedAmount</li>
</ul>
</div>
</div>
<div id="outline-container-orgb7c6fb1" class="outline-3">
<h3 id="orgb7c6fb1"><span class="section-number-3">1.2</span> logging</h3>
<div class="outline-text-3" id="text-1-2">
<ul class="org-ul">
<li>LogDefinition</li>
<li>GnunetLoglevel</li>
<li>GnunetLogger</li>
</ul>
</div>
</div>
<div id="outline-container-org4307498" class="outline-3">
<h3 id="org4307498"><span class="section-number-3">1.3</span> ‘payto’ URI particularities</h3>
<div class="outline-text-3" id="text-1-3">
<ul class="org-ul">
<li>PaytoFormatError(Exception)</li>
<li>PaytoParse</li>
</ul>
</div>
</div>
<div id="outline-container-org44d03ed" class="outline-3">
<h3 id="org44d03ed"><span class="section-number-3">1.4</span> configuration</h3>
<div class="outline-text-3" id="text-1-4">
<ul class="org-ul">
<li>TalerConfig</li>
</ul>
</div>
</div>
</div>
<div id="outline-container-orgd6a98cd" class="outline-2">
<h2 id="orgd6a98cd"><span class="section-number-2">2</span> classes for handling currency plus value plus fraction</h2>
<div class="outline-text-2" id="text-2">
<p>
The <code>Amount</code> and <code>SignedAmount</code> handle Taler <i>amounts</i>,
objects that combine a <code>CURRENCY</code> (e.g., "KUDOS")
with a <code>VALUE</code> and <code>FRACTION</code> (both integers).
An amount is written as follows:
</p>
<pre class="example">
CURRENCY:VALUE.FRACTION
</pre>
<p>
Note the <code>:</code> (colon) and <code>.</code> (period).
This is also known as the <code>CUR:X.Y</code> format.
</p>
<p>
The maximum <code>VALUE</code> is 2<sup>52</sup> (i.e., 4503599627370496).
The <code>FRACTION</code> can be at most 8 digits (i.e., smallest non-zero
<code>FRACTION</code> of <code>1</code> represents the number 0.00000001, and the largest
<code>FRACTION</code> of 99999999 represents the number 0.99999999).
If an amount is specified that exceeds these limits,
the constructor throws an <code>AmountOverflowError</code> exception.
</p>
</div>
<div id="outline-container-org5d287dc" class="outline-3">
<h3 id="org5d287dc"><span class="section-number-3">2.1</span> class <code>Amount</code></h3>
<div class="outline-text-3" id="text-2-1">
<p>
The constructor takes three args: <code>currency</code>, <code>value</code>, <code>fraction</code>.
</p>
<pre class="example">
>>> from taler.util.amount import Amount, SignedAmount
# KUDOS 10.50
>>> amt = Amount ("KUDOS", 10, 50000000)
>>> amt
Amount(currency='KUDOS', value=10, fraction=50000000)
</pre>
<p>
<code>Amount</code> has three getter properties: <code>currency</code>, <code>value</code>, <code>fraction</code>.
</p>
<pre class="example">
>>> amt.value, amt.fraction
(10, 50000000)
</pre>
<p>
You can use classmethod <code>parse</code> to read a string as an <code>Amount</code> object.
This function can throw <code>AmountFormatError</code> if the string is malformed,
and <code>AmountOverflowError</code> if the fraction portion is too long.
</p>
<pre class="example">
>>> Amount.parse ("KUDOS:10.12345678")
Amount(currency='KUDOS', value=10, fraction=12345678)
</pre>
<p>
An <code>Amount</code> object supports addition and subtraction.
The <code>currency</code> property must match, otherwise the operation throws
a <code>CurrencyMismatchError</code> exception.
</p>
<pre class="example">
>>> amt + amt
Amount(currency='KUDOS', value=21, fraction=0)
>>> another = Amount ("KUDOS", 5, 42)
>>> amt - another
Amount(currency='KUDOS', value=5, fraction=49999958)
</pre>
<p>
Note, however, that a subtraction that results in a numerically negative
<code>value</code> causes the operation to throw an <code>AmountOverflowError</code> exception.
</p>
<pre class="example">
>>> another - amt
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File ".../amount.py", line 124, in __sub__
raise AmountOverflowError()
taler.util.amount.AmountOverflowError
</pre>
<p>
The method <code>stringify</code> (which is also used in the <code>__str__</code> definition)
takes optional keyword <code>pretty</code> (default <code>False</code>) that changes the
output.
</p>
<pre class="example">
>>> str (amt)
'KUDOS:10.5'
>>> amt.stringify()
'KUDOS:10.5'
>>> amt.stringify(pretty=True)
'10.5 KUDOS'
>>> (amt + amt).stringify(pretty=True)
'21 KUDOS'
</pre>
<p>
The method <code>is_zero</code> returns <code>True</code> if the <code>Amount</code> object has a zero
<code>value</code> component and a zero <code>fraction</code> component.
</p>
<pre class="example">
>>> amt.is_zero ()
False
</pre>
<p>
An <code>Amount</code> object can be numerically compared with another <code>Amount</code>
for both equality and inequality.
Comparison can throw a <code>CurrencyMismatchError</code> exception
if both currencies are not the same.
</p>
<pre class="example">
>>> amt > another
True
>>> amt == another
False
</pre>
</div>
</div>
<div id="outline-container-org56a0ae4" class="outline-3">
<h3 id="org56a0ae4"><span class="section-number-3">2.2</span> class <code>SignedAmount</code></h3>
<div class="outline-text-3" id="text-2-2">
<p>
A <code>SignedAmount</code> object is an <i>amount with a sign</i>.
It has properties <code>is_positive</code> and <code>amount</code>.
You can derive a <code>SignedAmount</code> from a simple <code>Amount</code> with the
<code>as_signed</code> method.
</p>
<pre class="example">
>>> p = amt.as_signed ()
>>> p.is_positive
True
>>> p.amount
Amount(currency='KUDOS', value=10, fraction=50000000)
</pre>
<p>
A <code>SignedAmount</code> object supports addition, subtraction, and comparison
(equality and inequality) with another <code>SignedAmount</code> object.
</p>
<pre class="example">
>>> q = another.as_signed ()
>>> (p - q).is_positive
True
>>> (q - p).is_positive
False
</pre>
<p>
The <code>stringify</code> method, like that for <code>Amount</code>, takes optional keyword
<code>pretty</code>. It always prefixes the output with either <code>+</code> or <code>-</code>.
</p>
<pre class="example">
>>> (p - q).stringify (pretty=False)
'+KUDOS:5.49999958'
>>> (q - p).stringify (pretty=True)
'-5.49999958 KUDOS'
</pre>
<p>
The classmethod <code>parse</code> recognizes a leading <code>+</code> or <code>-</code>, and
additionally accepts a plain <code>CURRENCY:VALUE.FRACTION</code> form as a
positive <code>SignedAmount</code>.
</p>
<pre class="example">
>>> SignedAmount.parse ("-KUDOS:2.34")
SignedAmount(is_positive=False, amount=Amount(currency='KUDOS', value=2, fraction=34000000))
</pre>
<p>
Lastly, a <code>SignedAmount</code> object can flip its sign using a unary minus.
</p>
<pre class="example">
>>> n = q - p
>>> n.is_positive
False
>>> (- n).is_positive
True
</pre>
</div>
</div>
</div>
<div id="outline-container-orgb9b4b04" class="outline-2">
<h2 id="orgb9b4b04"><span class="section-number-2">3</span> classes <code>LogDefinition</code>, <code>GnunetLoglevel</code></h2>
<div class="outline-text-2" id="text-3">
<p>
These two classes are deliberately undocumented (until further notice).
They exist primarily to support the <code>GnunetLogger</code> class.
</p>
</div>
</div>
<div id="outline-container-orga6828fa" class="outline-2">
<h2 id="orga6828fa"><span class="section-number-2">4</span> class <code>GnunetLogger</code></h2>
<div class="outline-text-2" id="text-4">
<p>
The <code>GnunetLogger</code> class wraps the native <code>logging</code> module and provides
two primary entry points: the constructor and the <code>log</code> method.
It supports the usual list of <i>log levels</i>:
<code>ERROR</code>, <code>WARNING</code>, <code>INFO</code>, <code>DEBUG</code>.
</p>
</div>
<div id="outline-container-org8d3839f" class="outline-3">
<h3 id="org8d3839f"><span class="section-number-3">4.1</span> log definition, environment variables</h3>
<div class="outline-text-3" id="text-4-1">
<p>
What to log is controlled by a <i>log definition</i>, lists of
which are taken from one or both environment variables when
the <code>GnunetLogger</code> object is initialized:
</p>
<ul class="org-ul">
<li><code>GNUNET_FORCE_LOG</code></li>
<li><code>GNUNET_LOG</code></li>
</ul>
<p>
A log definition looks like:
</p>
<pre class="example">
[component];[file];[function];[from_line[-to_line]];loglevel
</pre>
<p>
The <code>component</code>, <code>file</code>, <code>function</code>, and line information portions
are optional; the <code>loglevel</code> is required.
No portion may contain the <code>;</code> (semicolon) or <code>/</code> (slash) character.
When a portion is omitted, it defaults to <i>all</i> of that item.
The line information can be a single line number or a range,
written in <code>LOW-HIGH</code> format – note <code>-</code> (hyphen).
For example, a minimal log definition could be:
</p>
<pre class="example">
;;;;ERROR
</pre>
<p>
This example definition matches all components, all files, all
functions, and all lines, but only the <code>ERROR</code> log level.
</p>
<p>
Multiple log definitions are specified by separating them with a <code>/</code>
(slash) character.
</p>
<pre class="example">
network;;;ERROR/database;;;DEBUG
</pre>
<p>
The difference between <code>GNUNET_FORCE_LOG</code> and <code>GNUNET_LOG</code> is that the
former takes priority over the latter, in case of conflict.
Also, logging done via <code>GNUNET_FORCE_LOG</code> respects environment
variable <code>GNUNET_FORCE_LOGFILE</code>.
</p>
</div>
</div>
<div id="outline-container-org9a2a746" class="outline-3">
<h3 id="org9a2a746"><span class="section-number-3">4.2</span> environment variable <code>GNUNET_FORCE_LOGFILE</code></h3>
<div class="outline-text-3" id="text-4-2">
<p>
The filename specified by <code>GNUNET_FORCE_LOGFILE</code> can
have special character sequences replaced (like a template):
</p>
<dl class="org-dl">
<dt><code>{}</code></dt><dd>component</dd>
<dt><code>[]</code></dt><dd>process id</dd>
<dt><code>%Y</code></dt><dd>numeric year</dd>
<dt><code>%m</code></dt><dd>numeric month</dd>
<dt><code>%d</code></dt><dd>numeric day</dd>
</dl>
<p>
For example, if <code>GNUNET_FORCE_LOGFILE</code> has value:
</p>
<pre class="example">
/var/log/[].{}.%Y-%m-%d.error.log
</pre>
<p>
then the expansion might be:
</p>
<pre class="example">
/var/log/14916.monolith.2022-02-10.error.log
</pre>
</div>
</div>
<div id="outline-container-orga5014e4" class="outline-3">
<h3 id="orga5014e4"><span class="section-number-3">4.3</span> constructor</h3>
<div class="outline-text-3" id="text-4-3">
<p>
The <code>GnunetLogger</code> constructor takes one argument, <code>component</code>.
</p>
<pre class="example">
>>> from taler.util.gnunet_log import GnunetLogger
>>> l = GnunetLogger ("ui")
</pre>
</div>
</div>
<div id="outline-container-orgfb9a8c1" class="outline-3">
<h3 id="orgfb9a8c1"><span class="section-number-3">4.4</span> method <code>log</code></h3>
<div class="outline-text-3" id="text-4-4">
<p>
The <code>log</code> method takes two arguments, <code>message</code> (a string)
and <code>message_loglevel</code> (a property of the <code>GnunetLogger</code> class with
the same name as the string log level).
</p>
<pre class="example">
>>> l.log ("user clicked button", l.INFO)
INFO:ui:user clicked button
</pre>
</div>
</div>
</div>
<div id="outline-container-orgaadd9a7" class="outline-2">
<h2 id="orgaadd9a7"><span class="section-number-2">5</span> ‘payto’ URI parsing</h2>
<div class="outline-text-2" id="text-5">
<p>
The <code>PaytoParse</code> class has only one entry point, its constructor.
The argument is <code>payto_uri</code>, a string in the <i>payto URI scheme</i>
that has exactly two components in the <i>upath</i> portion.
See RFC 8905 (<a href="https://datatracker.ietf.org/doc/html/rfc8905">https://datatracker.ietf.org/doc/html/rfc8905</a>) for more info.
If parsing fails, the constructor throws a <code>PaytoFormatError</code> exception.
</p>
<p>
On successful parse, the object has the following properties:
</p>
<dl class="org-dl">
<dt><code>target</code></dt><dd>destination of the payment</dd>
<dt><code>bank</code></dt><dd>bank handling the payment</dd>
<dt><code>authority</code></dt><dd>payment type (e.g., <code>iban</code>)</dd>
<dt><code>message</code></dt><dd>short human-readable description of the payment</dd>
<dt><code>amount</code></dt><dd>in <code>CUR:X.Y</code> format (<a href="#org5d287dc">2.1</a>)</dd>
</dl>
<p>
Note that <code>amount</code> may be <code>None</code> if none was specified.
</p>
<pre class="example">
>>> from taler.util.payto import PaytoParse
# from RFC 8905
>>> uri = "payto://iban/DE75512108001245126199?amount=EUR:200.0&message=hello"
>>> p = PaytoParse (uri)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "/home/ttn/build/GNU/T/taler-util/taler/util/payto.py", line 41, in __init__
raise PaytoFormatError(f"Bad Payto URI: {payto_uri}")
taler.util.payto.PaytoFormatError: Bad Payto URI: payto://iban/DE75512108001245126199?amount=EUR:200.0&message=hello
</pre>
<p>
This example shows that the <i>single-component</i> IBAN fails to parse
(even though that is a valid RFC 8905 ‘payto’ URI).
It's necessary to use the <i>two-component</i> IBAN.
</p>
<pre class="example">
>>> uri = "payto://iban/SOGEDEFFXXX/DE75512108001245126199?amount=EUR:200.0&message=hello"
>>> p = PaytoParse (uri)
>>> p.target
'DE75512108001245126199'
>>> p.bank
'SOGEDEFFXXX'
>>> p.authority
'iban'
>>> p.message
'hello'
>>> p.amount
Amount(currency='EUR', value=200, fraction=0)
</pre>
</div>
</div>
<div id="outline-container-orgdf9cef8" class="outline-2">
<h2 id="orgdf9cef8"><span class="section-number-2">6</span> class <code>TalerConfig</code></h2>
<div class="outline-text-2" id="text-6">
<p>
The <code>TalerConfig</code> class represents a <i>Taler configuration</i>, a set
of <i>sections</i> with <i>options</i> and associated <i>values</i> (basically,
a nested dictionary), and provides methods for initializing,
and accessing those values, keyed by section and option.
</p>
<p>
When a Taler configuration is written to a file (the usual case),
it follows the typical Windows INI format.
For more information, see the taler-config(5) manpage.
</p>
</div>
<div id="outline-container-org03f14e5" class="outline-3">
<h3 id="org03f14e5"><span class="section-number-3">6.1</span> reading</h3>
<div class="outline-text-3" id="text-6-1">
<p>
The standard way to construct a <code>TalerConfig</code> object is to start
with one of two initialization methods: <code>from_file</code> or <code>from_env</code>.
The former reads the configuration from a file, given its name.
If no name is provided (it is <code>None</code>), <code>from_file</code> first tries
to find <code>taler.conf</code> in two directories:
</p>
<ul class="org-ul">
<li>directory named by environment variable <code>XDG_CONFIG_HOME</code></li>
<li><code>$HOME/.config</code> (where <code>HOME</code> is the user's home directory)</li>
</ul>
<p>
The <code>from_env</code> initialization method first determines a filename
by consulting environment variable <code>TALER_CONFIG_FILE</code> and then
uses <code>from_file</code> on that.
</p>
<p>
Both initialization methods take keyword arg <code>load_defaults</code>
(default <code>True</code>) that directs the method to also call
the <code>load_defaults</code> method before reading the file.
</p>
<p>
The <code>load_defaults</code> method takes no arguments.
It looks in the canonical locations (directories) and
uses method <code>load_dir</code> on them.
Once it finds a specified dir, it stops searching.
The canonical locations are:
</p>
<ul class="org-ul">
<li>environment variable <code>TALER_BASE_CONFIG</code></li>
<li><p>
environment variable <code>TALER_PREFIX</code>, with any trailing component
<code>lib</code> discarded, and suffixed with <code>share/taler/config.d</code>
</p>
<p>
For example, if <code>TALER_PREFIX</code> is <code>/usr/local/lib</code>, then
<code>load_defaults</code> would look in <code>/usr/local/share/taler/config.d</code>.
The same would result if <code>TALER_PREFIX</code> were <code>/usr/local</code>
(the suffixing is unconditional).
</p></li>
</ul>
<p>
If <code>load_defaults</code> cannot find something to load it logs a warning
"no base directory found".
</p>
<p>
The <code>load_dir</code> method takes one argument <code>dirname</code>, and
uses <code>load_file</code> on all files that directory whose name ends
with <code>.conf</code>.
</p>
<p>
At its core, all file reading uses method <code>load_file</code>,
which takes one argument, the <code>filename</code> to read.
If <code>filename</code> cannot be found, <code>load_file</code> causes
the process to exit with exit value <code>3</code>.
</p>
</div>
</div>
<div id="outline-container-orgd929224" class="outline-3">
<h3 id="orgd929224"><span class="section-number-3">6.2</span> value types</h3>
<div class="outline-text-3" id="text-6-2">
<p>
There are three types of values in a Taler configuration: <code>int</code> (integer),
<code>string</code> and <code>filename</code>.
The <code>int</code> and <code>string</code> types are self-explanatory.
The <code>filename</code> type is a string that has certain constructs expanded:
</p>
<ul class="org-ul">
<li><code>${X}</code></li>
<li><code>${X:-Y}</code></li>
<li><code>$X</code></li>
</ul>
<p>
These mimic shell-style variable expansion.
In all these constructs, the value of <code>X</code> replaces the construct.
In the second one only, if the value of <code>X</code> is empty, use the
value of <code>Y</code> instead.
Also, the second type can be nested, i.e., <code>${X:-${Y:-Z}}</code>.
That is, if <code>X</code> is empty, try <code>Y</code>, and if <code>Y</code> is empty, try <code>Z</code>.
</p>
<p>
For example, <code>${TMPDIR:-/tmp}/taler-test</code> expands to <code>/var/tmp/taler-test</code>
if environment variable <code>TMPDIR</code> has value <code>/var/tmp</code>, otherwise
simply <code>/tmp/taler-test</code>.
</p>
</div>
</div>
<div id="outline-container-orgc4601e4" class="outline-3">
<h3 id="orgc4601e4"><span class="section-number-3">6.3</span> retrieving values</h3>
<div class="outline-text-3" id="text-6-3">
<p>
Once a Taler configuration is read, you can retrieve specific
values from it, or display the entire set to stdout.
</p>
</div>
<div id="outline-container-org76aedbb" class="outline-4">
<h4 id="org76aedbb"><span class="section-number-4">6.3.1</span> specific values</h4>
<div class="outline-text-4" id="text-6-3-1">
<p>
Each type <i>foo</i> has a <code>value_foo</code> method (e.g., <code>value_int</code> for integer).
The method takes two required arguments, the <code>section</code> and <code>option</code>,
both strings.
Case does not matter.
</p>
<p>
In addition to the required arguments, <code>value_string</code> accepts
the following keyword arguments:
</p>
<dl class="org-dl">
<dt><code>default</code></dt><dd>If the requested value is not found, return this
value instead. Default is no default. :-D</dd>
<dt><code>required</code></dt><dd>If the requested value is not found, print an error
message and cause the process to exit with exit value <code>1</code>.</dd>
<dt><code>warn</code></dt><dd>If the requested value is not found, log a warning.
If <code>default</code> is also given, return that, otherwise return <code>None</code>.</dd>
</dl>
<p>
(Both <code>value_int</code> and <code>value_filename</code> also accept these keyword
arguments, but they are ignored.)
</p>
</div>
</div>
<div id="outline-container-org1feca74" class="outline-4">
<h4 id="org1feca74"><span class="section-number-4">6.3.2</span> entire set</h4>
<div class="outline-text-4" id="text-6-3-2">
<p>
The <code>dump</code> method takes no arguments.
It displays to stdout each section and its options (and values)
in the format:
</p>
<pre class="example">
[section]
option = value # filename & line number pair
</pre>
</div>
</div>
</div>
</div>
</div>
<div id="postamble" class="status">
<p class="author">Author: Taler Contributors</p>
<p class="date">Created: 2022-02-22 mar 07:37</p>
<p class="validation"><a href="http://validator.w3.org/check?uri=referer">Validate</a></p>
</div>
</body>
</html>
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