I am reading the SCSI SPC4r22. In regards to ADDITIONAL LENGTH all revisions prior to spc3 have stated the following ("shall not be adjusted"):
From spc2r20.pdf:
"The ADDITIONAL LENGTH field shall specify the length in bytes of the parameters. If the ALLOCATION LENGTH of the CDB is too small to transfer all of the parameters, the ADDITIONAL LENGTH shall not be adjusted to reflect the truncation."
But I don't see that statement in SPC3 or SPC4. Has that been changed or am I missing the phrase? If I'm missing it, can someone please quote it?
It is just worded in a more general way:
"If the information being transferred to the Data-In Buffer includes fields containing counts of the number of bytes in some or all of the data, then the contents of these fields shall not
be altered to reflect the truncation"
Related
I am working with protocol buffers to integrate two systems. I want proto file to be contract between those systems. I see no way to put some constraints on string type:
maximum length
minimum length
allowed characters
How to enforce (or at least document) those rules in .proto files?
No idea how to force it, but you can document by putting standard C comments /* comment */ . That's what I do to describe some fields of my messages.
.proto examples all seem to start numbering their fields at one.
e.g. https://developers.google.com/protocol-buffers/docs/proto#simple
message SearchRequest {
required string query = 1;
optional int32 page_number = 2;
optional int32 result_per_page = 3;
}
If zero can be used, it will make some messages one or more bytes smaller (i.e. those with a one or more field numbers of 16).
As the key is simply a varint encoding of (fieldnum << 3 | fieldtype) I can't immediately see why zero shouldn't be used.
Is there a reason for not starting the field numbering at zero?
One very immediate reason is that zero field numbers are rejected by protoc:
test.proto:2:28: Field numbers must be positive integers.
As to why Protocol Buffers has been designed this way, I can only guess. One nice consequence of this is that a message full of zeros will be detected as invalid. It can also be used to indicate "no field" internally as a return value in protocol buffers implementation.
Assigning Tags
As you can see, each field in the message definition has a unique numbered tag. These tags are used to identify your fields in the message binary format, and should not be changed once your message type is in use. Note that tags with values in the range 1 through 15 take one byte to encode, including the identifying number and the field's type (you can find out more about this in Protocol Buffer Encoding). Tags in the range 16 through 2047 take two bytes. So you should reserve the tags 1 through 15 for very frequently occurring message elements. Remember to leave some room for frequently occurring elements that might be added in the future.
The smallest tag number you can specify is 1, and the largest is 229-1, or 536,870,911. You also cannot use the numbers 19000 through 19999 (FieldDescriptor::kFirstReservedNumber through FieldDescriptor::kLastReservedNumber), as they are reserved for the Protocol Buffers implementation - the protocol buffer compiler will complain if you use one of these reserved numbers in your .proto. Similarly, you cannot use any previously reserved tags.
https://developers.google.com/protocol-buffers/docs/proto
Just like the document says, 0 can't be detected.
I'm using SNMP4J to read info of devices with SNMP. Now I found some devices which represent the system name (OID iso.3.6.1.2.1.1.5.0) as a Hex-STRING instead of a STRING.
To show the system name I use the following code:
Variable var = response.getVariable(new OID(".1.3.6.1.2.1.1.5.0"));
System.out.println(var.toString());
Where response is a PDU object.
If the system name is represented as a STRING value, this goes as I expected. When it is represented as a Hex-STRING, it just prints the Hex value.
Example:
Take the name of the system as "SYSTEM NAME".
With STRING it prints "SYSTEM NAME".
With Hex-STRING it prints "53:59:53:54:45:4d:20:4e:41:4d:45"
Now with snmpwalk in command line I can just use the -Oa flag. This makes all Hex-STRING values show as STRING. Is it possible to use this flag in SNMP4J or is there a similar option?
I'm not sure where you're getting the term "Hex-STRING" from. SNMP does not define such a data type. I suggest you read through the relevant RFC documents, they are publicly available from IETF. The wikipedia article for SNMP (http://en.wikipedia.org/wiki/Simple_Network_Management_Protocol#References) has an excellent reference list, you can start with browsing the ones marked as "STD".
In SNMP, all strings are subtypes (or in a different word, "restrictions") of OCTET-STRING, a byte string of indeterminate length. It may contain any data, even non-printable stuff, representing a jpeg image or whatever.
Some textual-conventions have been defined, which restrict the data to some specific byte range, or length. A DisplayString is defined to only contain bytes from the NVT ASCII character set, so the user may trust it to be printable.
In fact, sysName is defined to be a DisplayString with a max length of 255 characters.
sysName OBJECT-TYPE
SYNTAX DisplayString (SIZE (0..255))
Since a good SNMP manager is aware of RFC1213-MIB, which defines both sysName and DisplayString, the manager should assume that the data received is printable ASCII characters.
When you say "When it is represented as a Hex-STRING", what do you mean? "Represented" where, on the agent or in your Java code or when using the net-snmp "snmpwalk" command?
The var.toString() call should convert the contents of the variable into something that could be safely printed in a terminal, so it's possible that SNMP4j is converting any binary string to a hex string.
The documentation of elastic search states:
The index operation can be executed without specifying the id. In such
a case, an id will be generated automatically.
But it does not provide any information about the properties of the ids.
What is the length (minimun/maximum)?
my guess is 22.
Which characters are used in the id?
My guess is [-_A-Za-z0-9]
Can the properties of the generated ids change at any time (is that part of the API)?
Auto-generated ids are random base64-encoded UUIDs. The base64 algorithm is used in URL-safe mode hence - and _ characters might be present in ids.
Auto-generated ids by elasticsearch are exactly 20 characters length (not 22 characters) and encoded by url-safe base64 algorithm [-_A-Za-z0-9].
Read more in documentation: https://www.elastic.co/guide/en/elasticsearch/guide/master/index-doc.html#_autogenerating_ids
Does anyone know the format of the MAPI property PR_SEARCH_KEY?
The online documentation has this to say about it:
The search key is formed by
concatenating the address type (in
uppercase characters), the colon
character ':', the e-mail address in
canonical form, and the terminating
null character.
And the exchange document MS-OXOABK says this:
The PidTagSearchKey property of type
PtypBinary is a binary value formed by
concatenating the ASCII string "EX: "
followed by the DN for the object
converted to all upper case, followed
by a zero byte value.
However all the MAPI messages I've seen with this property have it as some sort of binary 16 byte sequence that looks like a GUID. Does anyone else have any more information about it? Is it always 16 bytes?
Thanks!
I believe that the property PR_SEARCH_KEY will be of different formats for different objects (as alluded to by Moishe).
A MAPI message object will have a unique value assigned on creation for PR_SEARCH_KEY, however if the object is copied this property value is copied also. I presume when you reply to an e-mail, Exchange will assign the PR_SEARCH_KEY value to be the original message's value.
You will need to inspect each object type to understand how the PR_SEARCH_KEY is formed but I doubt if it's always 16 bytes for all MAPI types.
This link USENET discussion has a good discussion with Dmitry Streblechenko involved who is an expert on Extended MAPI.
The sentence before the ones you quoted from the online docs reads, "MAPI uses specific rules for constructing search keys for message recipients" which makes me think that it's talking about the PR_SEARCH_KEY property on MAPI_MAILUSER objects -- or at least not on MAPI_MESSAGE objects.