The SANE network protocol is a client/server-style remote procedure call (RPC) protocol. This means that all activity is initiated by the client side (the network backend)---a server is restricted to answering requests sent by the client.
The data transferred from the client to the server is comprised of the RPC code (as a SANE_WORD), followed by arguments defined in the request column below. The format of the server's answer is given in the reply column.
RPC Code: 0
This RPC establishes a connection to a particular SANE network daemon. It must be the first call in a SANE network session. The parameter and reply arguments for this call are shown in the table below:
| request: | reply: |
| SANE_Word version_code | SANE_Word status |
| SANE_String user_name | SANE_Word version_code |
In the reply, status indicates the completion status. If the
value is anything other than SANE_STATUS_GOOD, the
remainder of the reply has undefined values.
RPC Code: 1
This RPC is used to obtain the list of devices accessible by the SANE daemon.
| request: | reply: |
| void | SANE_Word status |
| SANE_Device ***device_list | |
In the reply, status indicates the completion status. If the value is anything other than SANE_STATUS_GOOD, the remainder of the reply has undefined values. The device_list argument is a pointer to a NULL-terminated array of SANE_Device pointers.
RPC Code: 2
This RPC is used to open a connection to a remote SANE device.
| request: | reply: |
| SANE_String device_name | SANE_Word status |
| SANE_Word handle | |
| SANE_String resource | |
In the reply, status indicates the completion status. If the value is anything other than SANE_STATUS_GOOD, the remainder of the reply has undefined values. The handle argument specifies the device handle that uniquely identifies the connection. The resource argument is used to request authentication. If it has a non-NULL value, the network backend should authenticate the specified resource and then retry this operation (see Section 5.2.10 for details on how to authorize a resource).
RPC Code: 3
This RPC is used to close a connection to a remote SANE device.
| request: | reply: |
| SANE_Word handle | SANE_Word dummy |
In the reply, the dummy argument is unused. Its purpose is to ensure proper synchronization (without it, a net client would not be able to determine when the RPC has completed).
RPC Code: 4
This RPC is used to obtain all the option descriptors for a remote SANE device.
| request: | reply: |
| SANE_Word handle | Option_Descriptor_Array odesc |
In the reply, the odesc argument is used to return the array of option descriptors. The option descriptor array has the following structure:
struct Option_Descriptor_Array
{
SANE_Word num_options;
SANE_Option_Descriptor **desc;
};
RPC Code: 5
This RPC is used to control (inquire, set, or set to automatic) a specific option of a remote SANE device.
| request: | reply: |
| SANE_Word handle | SANE_Status status |
| SANE_Word option | SANE_Word info |
| SANE_Word action | SANE_Word value_type |
| SANE_Word value_type | SANE_Word value_size |
| SANE_Word value_size | void *value |
| void *value | SANE_String *resource |
In the reply, argument resource is set to the name of the resource that must be authorized before this call can be retried. If this value is non-NULL, all other arguments have undefined values (see Section 5.2.10 for details on how to authorize a resource). Argument status indicates the completion status. If the value is anything other than SANE_STATUS_GOOD, the remainder of the reply has undefined values. The info argument returns the information on how well the backend was able to satisfy the request. For details, see the description of the corresponding argument in Section 4.3.7. Arguments value_type and value_size have the same values as the arguments by the same name in corresponding request. The values are repeated here to ensure that both the request and the reply are self-contained (i.e., they can be encoded and decoded independently). Argument value is holds the value of the option that has become effective as a result of this RPC.
RPC Code: 6
This RPC is used to obtain the scan parameters of a remote SANE device.
| request: | reply: |
| SANE_Word handle | SANE_Status status |
| SANE_Parameters params | |
In the reply, status indicates the completion status. If the value is anything other than SANE_STATUS_GOOD, the remainder of the reply has undefined values. The argument params is used to return the scan parameters.
RPC Code: 7
This RPC is used to start image acquisition (scanning).
| request: | reply: |
| SANE_Word handle | SANE_Status status |
| SANE_Word port | |
| SANE_Word byte_order | |
| SANE_String resource | |
In the reply, argument resource is set to the name of the resource that must be authorized before this call can be retried. If this value is non-NULL, all other arguments have undefined values (see Section 5.2.10 for details on how to authorize a resource). Argument, status indicates the completion status. If the value is anything other than SANE_STATUS_GOOD, the remainder of the reply has undefined values. The argument port returns the port number from which the image data will be available. To read the image data, a network client must connect to the remote host at the indicated port number. Through this port, the image data is transmitted as a sequence of data records. Each record starts with the data length in bytes. The data length is transmitted as a sequence of four bytes. These bytes should be interpreted as an unsigned integer in big-endian format. The four length bytes are followed by the number of data bytes indicated by the length. Except for byte-order, the data is in the same format as defined for sane_read(). Since some records may contain no data at all, a length value of zero is perfectly valid. The special length value of 0xffffffff is used to indicate the end of the data stream. That is, after receiving a record length of 0xffffffff, the network client should close the data connection and stop reading data.
Argument byte_order specifies the byte-order of the image data. A value of 0x1234 indicates little-endian format, a value of 0x4321 indicates big-endian format. All other values are presently undefined and reserved for future enhancements of this protocol. The intent is that a network server sends data in its own byte-order and the client is responsible for adjusting the byte-order, if necessary. This approach causes no unnecessary overheads in the case where the server and client byte-order match and puts the extra burden on the client side when there is a byte-order mismatch. Putting the burden on the client-side improves the scalability properties of this protocol.
RPC Code: 8
This RPC is used to cancel the current operation of a remote SANE device.
| request: | reply: |
| SANE_Word handle | SANE_Word dummy |
In the reply, the dummy argument is unused. Its purpose is to ensure proper synchronization (without it, a net client would not be able to determine when the RPC has completed).
RPC Code: 9
This RPC is used to pass authorization data from the net client to the net server.
| request: | reply: |
| SANE_String resource | SANE_Word dummy |
| SANE_String username | |
| SANE_String password | |
Since the password is not encrypted during network transmission, it is recommended to use the following extension:
If the server adds the string `$MD5$' to the resource-name followed by a random string not longer then 128 bytes, the client may answer with the MD5 digest of the concatenation of the password and the random string. To differentiate between the MD5 digest and a strange password the client prepends the MD5 digest with the string `$MD5$'.
In the reply, dummy is completely unused. Note that there is no direct failure indication. This is unnecessary since a net client will retry the RPC that resulted in the authorization request until that call succeeds (or until the request is cancelled). The RPC that resulted in the authorization request continues after the reply from the client and may fail with SANE_STATUS_ACCESS_DENIED.
RPC Code: 10
This RPC is used to disconnect a net client from a net server. There are no request or reply arguments in this call. As a result of this call, the connection between the client and the server that was established by the SANE_NET_INIT call will be closed.