OctetString cannot display strings correctly about weewx-snmp HOT 10 CLOSED

That is not a general issue. For example, the syslog messages for my UPS include real strings:

Mar 22 20:39:33 xxxx weewx[260440] INFO user.SNMP: SNMP-UPS SNMPv2-SMI::mib-2.33.1.1.1.0 = OctetString : "RPS SpA"
Mar 22 20:39:33 xxxx weewx[260440] INFO user.SNMP: SNMP-UPS SNMPv2-SMI::mib-2.33.1.1.2.0 = OctetString : "SDH 2200"

To convert the value to a string is the job of the prettyPrint() function of the pySNMP module. It is not in the scope of the weewx-SNMP extension. Are you sure you are using the latest version of pySNMP? Please check that first.

What does the snmpwalk command report for your device?

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My pysnmp version is 4.4.12 and system use ubuntu 20.04LTS.
Package Version

certifi 2019.11.28
cffi 1.15.1
chardet 3.0.4
Cheetah3 3.2.6.post1
configobj 5.0.6
dbus-python 1.2.16
distro 1.4.0
ephem 3.7.7.1
idna 2.8
netifaces 0.10.4
olefile 0.46
Pillow 7.0.0
pip 20.0.2
ply 3.11
pyasn1 0.4.8
pycparser 2.21
pycryptodomex 3.17
pyephem 9.99
PyGObject 3.36.0
pymacaroons 0.13.0
PyNaCl 1.3.0
pyserial 3.4
pysmi 0.3.4
pysnmp 4.4.12
python-apt 2.0.1+ubuntu0.20.4.1
pyusb 1.0.2
PyYAML 5.3.1
requests 2.22.0
setuptools 45.2.0
six 1.14.0
snmp 0.4.2
ssh-import-id 5.10
thread6 0.2.0
ubuntu-advantage-tools 8001
urllib3 1.25.8
wheel 0.34.2

snmpwalk show:
iso.3.6.1.4.1.55062.1.13.2.0 = STRING: "LV 3K
"
it not OctetString.
and the pic is MibBrowser

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I will see what I can do.

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Could you check whether the version at https://github.com/roe-dl/weewx-snmp/archive/OctetString.zip changes something?

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Almost perfect, just need to handle the line break symbols.

Mar 25 14:07:58 weewx weewx[1053] INFO user.SNMP: SNMP-SYSTEM SNMPv2-SMI::enterprises.55062.1.13.2.0 = OctetString : "LV 3K#012"

I have been recently trying to interactively install SNMP programs using apt and pip, in order to identify the possible differences between them.

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I checked the pySNMP/pyASN1 code and found the following comment in pyasn1/type/univ.py where the type OctetString is defined:

    #
    # Normally, `.prettyPrint()` is called from `__str__()`. Historically,
    # OctetString.prettyPrint() used to return hexified payload
    # representation in cases when non-printable content is present. At the
    # same time `str()` used to produce either octet-stream (Py2) or
    # text (Py3) representations.
    #
    # Therefore `OctetString.__str__()` -> `.prettyPrint()` call chain is
    # reversed to preserve the original behaviour.
    #
    # Eventually we should deprecate `.prettyPrint()` / `.prettyOut()` harness
    # and end up with just `__str__()` producing hexified representation while
    # both text and octet-stream representation should only be requested via
    # the `.asOctets()` method.
    #
    # Note: ASN.1 OCTET STRING is never mean to contain text!
    #

    def prettyOut(self, value):
        return value

    def prettyPrint(self, scope=0):
        # first see if subclass has its own .prettyOut()
        value = self.prettyOut(self._value)

        if value is not self._value:
            return value

        numbers = self.asNumbers()

        for x in numbers:
            # hexify if needed
            if x < 32 or x > 126:
                return "0x" + "".join(("%.2x" % x for x in numbers))
        else:
            # this prevents infinite recursion
            return OctetString.__str__(self)

Imho the most important note there is "ASN.1 OCTET STRING is never mean to contain text!"

This may explain the strange behavior. And it makes it difficult to process values of OctetString in a portable way. I have to think about it.

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What did you experience with the last changes?

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I found that when SNMP strings contain line breaks "\r\n", there are problems with handling OctetString. Currently, I am trying to use str.strip() to remove non-standard characters and the display is normal.

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Yes. As you see in the code snippet of the pySNMP module, values of type OctetString are displayed as characters if consist of printable characters only. If they contain at least one control character, they are displayed as hex codes.

Did you try the last version of weewx-SNMP from the OctetString branch?

If so I would like to merge the changes into the master branch and close this issue.

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Sure, I've tried it. It works fine except for the line break characters.

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