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<div style="float:left; width:100%;">This page presents the code structure classes and functions of the [[Clients|BaseX clientsClients]],and the client/underlying protocol, which is utilized for communicating with the database server protocol needed to write [[Clients]].in other programming languagesA detailed example demonstrates how a concrete byte exchange can look like.

==DescriptionWorkflow==

* First of allAll clients are based on the client/server architecture. Hence, the a BaseX database server must be running in order to use the clientsstarted first.

* Each client provides a session class or script with methods to connect to and communicate with the database server. A socket connection will be established by the constructor, which expects a host, port, user name username and password as arguments.

* For the execution of commands you need to call the <code>The {{Code|execute()</code> }} method with the is called to launch a database command as argument. The method It returns the result or throws an exception with the received error message.

* The <code>{{Code|query()</code> }} method creates a query instance. Variables and the context item can be bound to that objectinstance, and the result can either be requested by <code>via {{Code|execute()</code>}}, or in an iterative manner with the <code>{{Code|more()</code> }} and <code>{{Code|next()</code> }} functions. If an error occurs, an exception will be thrown.

* The <code>{{Code|create()</code>}}, <code>{{Code|add()</code>}}, <code>replace{{Code|put()</code> }} and <code>store{{Code|putbinary()</code> method can be used to }} methods pass on input streams to the corresponding database commands. The input can be a UTF-8 encoded XML document, a binary resource, or any other data (such as JSON or CSV) that can be successfully converted to a resource by the server.

==Transfer Protocol== All [[Clients]] use the following client/server protocol to communicate with the server.The description of the protocol is helpful if you want to implement your own client. ===Conventions=== * <code>\xx</code>: single byte.* <code>{...}</code>: utf8 strings or raw data, suffixed with a <code>\00</code> byte. To avoid confusion with this end-of-string byte, all transferred <code>\00</code> and <code>\FF</code> bytes are prefixed by an additional <code>\FF</code> byte. ===Authentication=== ====Digest==== Digest authentication is used since Version 8.0: # Client connects to server socket# Server sends a '''realm''' and '''nonce''', separated by a colon: <code>{realm:nonce}</code># Client sends the '''username''' and a hash value. The hash is composed of the md5 hash of## the md5 hash of the '''username''', '''realm''', and '''password''' (all separated by a colon), and## the '''nonce''': <code>{username} {md5(md5(username:realm:password) + nonce)}</code># Server replies with <code>\00</code> (success) or <code>\01</code> (error) ====CRAM-MD5==== CRAM-MD5 was discarded because unsalted md5 hashes can easily be uncovered using rainbow tables. However, most client bindings still provide support for the outdated handshaking, as it only slightly differs from the new protocol: # Client connects to server socket# Server sends a '''nonce''' (timestamp): <code>{nonce}</code># Client sends the '''username''' and a hash value. The hash is composed of the md5 hash of## the md5 of the '''password''' and## the '''nonce''': <code>{username} {md5(md5(password) + nonce)}</code># Server replies with <code>\00</code> (success) or <code>\01</code> (error) It is possible to support both {{Code Structure|digest}} and {{Code|cram-md5}} authentication in clients: If the first server response contains no colon, {{Code|cram-md5}} should be chosen. ===Command Protocol=== The following byte sequences are sent and received from the client (please note that a specific client may not support all of the presented commands): {| class="wikitable"|-! Command! Client Request! Server Response! Description|-| COMMAND| <code>{command}</code>| <code>{result} {info} \00</code>| Executes a database command.|-| QUERY| <code>\00 {query}</code>| <code>{id} \00</code>| Creates a new query instance and returns its id.|-| CREATE| <code>\08 {name} {input}</code>| <code>{info} \00</code>| Creates a new database with the specified input (may be empty).|-| ADD| <code>\09 {path} {input}</code>| <code>{info} \00</code>| Adds a new document to the opened database.|-| PUT| <code>\0C {path} {input}</code>| <code>{info} \00</code>| Puts (adds or replaces) an XML document resource in the opened database.|-| PUTBINARY| <code>\0D {path} {input}</code>| <code>{info} \00</code>| Puts (adds or replaces) a binary resource in the opened database.|-| ↯ error| <code></code>| <code>{</code>''partial result''<code>} {error} \01</code>| Error feedback.|} ===Query Command Protocol=== Queries are referenced via an {{Code|id}}, which has been returned by the {{Code|QUERY}} command (see above). {| class="wikitable"|-! Query Command! Client Request! Server Response! Description|-| CLOSE| <code>\02 {id}</code>| <code>\00 \00</code>| Closes and unregisters the query with the specified id.|-| BIND| <code>\03 {id} {name} {value} {type}</code>| <code>\00 \00</code>| Binds a value to a variable. The type will be ignored if the string is empty.|-| RESULTS| <code>\04 {id}</code>| <code>\xx {item} ... \xx {item} \00</code>| Returns all resulting items as strings, prefixed by a single byte ({{Code|\xx}}) that represents the [[Server Protocol: Types|Type ID]]. This command is called by the {{Code|more()}} function of a client implementation.|-| EXECUTE| <code>\05 {id}</code>| <code>{result} \00</code>| Executes the query and returns the result as a single string.|-| INFO| <code>\06 {id}</code>| <code>{result} \00</code>| Returns a string with query compilation and profiling info.|-| OPTIONS| <code>\07 {id}</code>| <code>{result} \00</code>| Returns a string with all query serialization parameters, which can e.g. be assigned to the {{Option|SERIALIZER}} option.|-| CONTEXT| <code>\0E {id} {value} {type}</code>| <code>\00 \00</code>| Binds a value to the context. The type will be ignored if the string is empty.|-| UPDATING| <code>\1E {id}</code>| <code>{result} \00</code>| Returns {{Code|true}} if the query contains updating expressions; {{Code|false}} otherwise.|-| FULL| <code>\1F {id}</code>| <code>''XDM'' {item} ... ''XDM'' {item} \00</code>| Returns all resulting items as strings, prefixed by the [[Server Protocol: Types#XDM Metadata|XDM Metadata]]. This command is e. g. used by the [[Developing|XQJ API]].|} As can be seen in the table, all results end with a single {{Code|\00}} byte, which indicates that the process was successful. If an error occurs, an additional byte {{Code|\01}} is sent, which is then followed by the {{Code|error}} message string. ====Binding Sequences==== Also, sequences can be bound to variables and the context: * {{Code|empty-sequence()}} must be supplied as type if an empty sequence is to be bound.* Multiple items are supplied via the <code>{value}</code> argument and separated with {{Code|\01}} bytes.* Item types are specified by appending {{Code|\02}} and the type in its string representation to an item. If no item type is specified, the general type is used. Some examples for the <code>{value}</code> argument: * the two integers {{Code|123}} and {{Code|789}} are encoded as {{Code|123}}, {{Code|\01}}, {{Code|789}} and {{Code|\00}} ({{Code|xs:integer}} may be specified via the <code>{type}</code> argument).* the two items {{Code|xs:integer(123)}} and {{Code|xs:string('ABC')}} are encoded as {{Code|123}}, {{Code|\02}}, {{Code|xs:integer}}, {{Code|\01}}, {{Code|ABC}}, {{Code|\02}}, {{Code|xs:string}} and {{Code|\00}}. ==Example==

In the following example, a client registers a new session and executes the {{Command|INFO}} database command. Next, it creates a new query instance for the XQuery expression {{Code|1, 2+'3'}}. The query is then evaluated, and the server returns the result of the first subexpression {{Code|1}} and an error for the second sub expression. Finally, the query instance and client session are closed. * '''Client''' connects to the database server socket* '''Server''' sends realm and timestamp "BaseX:1369578179679": {{Code|◄ 42 61 73 65 58 3A 31 33 36 39 35 37 38 31 37 39 36 37 39 00}}* '''Client''' sends username "jack": {{Code|6A 61 63 6B 00 ►}}* '''Client''' sends hash: md5(md5("jack:BaseX:topsecret") + "1369578179679") ="ca664a31f8deda9b71ea3e79347f6666": {{Code|63 61 36 ... 00 ►}}* '''Server''' replies with success code: {{Code|◄ 00}}* '''Client''' sends the "INFO" command: {{Code|49 4E 46 4F 00 ►}}* '''Server''' responds with the result "General Information...": {{Code|◄ 47 65 6e 65 ... 00}}* '''Server''' additionally sends an (empty) info string: {{Code|◄ 00}}* '''Client''' creates a new query instance for the XQuery "1, 2+'3'": {{Code|00 31 2C 20 32 2B 27 33 27 00 ►}}* '''Server''' returns query id "1" and a success code: {{Code|◄ 31 00 00}}* '''Client''' requests the query results via the RESULTS protocol command and its query id: {{Code|04 31 00 ►}}* '''Server''' returns the first result ("1", type xs:integer): {{Code|◄ 52 31 00}}* '''Server''' sends a single {{Code|\00}} byte instead of a new result, which indicates that no more results can be expected: {{Code|◄ 00}}* '''Server''' sends the error code {{Code|\01}} and the error message ("Stopped at..."): {{Code|◄ 01 53 74 6f ... 00}}* '''Client''' closes the query instance: {{Code|02 31 00 ►}}* '''Server''' sends a response (which is equal to an empty info string) and success code: {{Code|◄ 00 00}}* '''Client''' closes the socket connection ==Session=Constructors and Functions==

* Creates Most language bindings provide the following constructors and returns session with host, port, user name and passwordfunctions:<br/><code>Session(String host, int port, String name, String password)</code>

* Executes a command and returns the result:<br/div><code>String execute(String command)</codediv style="float:left; width:48%;">===Session===

* Returns a query object for the specified queryCreate and return session with host, port, username and password:<br/><code>Query querySession(String queryhost, int port, String name, String password)</code>

* Creates Execute a database from an input streamcommand and return the result:<br/><code>void createString execute(String name, InputStream incommand)</code>

* Adds Return a document to query instance for the current database from an input streamspecified query:<br/><code>void addQuery query(String name, String target, InputStream inquery)</code>

* Replaces Create a document with the specified database from an input stream:<br/><code>void replacecreate(String pathname, InputStream ininput)</code>

* Stores raw data at Add a document to the specified pathcurrent database from an input stream:<br/><code>void storeadd(String path, InputStream ininput)</code>

* Watches Put a document with the specified eventinput stream:<br/><code>void watchput(String namepath, Event notifierInputStream input)</code>

* Unwatches Put a binary resource at the specified eventpath:<br/><code>void unwatchputBinary(String namepath, InputStream input)</code>

* Returns Return process information:<br/><code>String info()</code>

* Closes Close the session:<br/><code>void close()</code>

* Creates Create query object instance with session and query:<br/><code>constructorQuery(Session ssession, String query)</code>

* Binds Bind an external variable:<br/><code>void bind(String name, String value, String type)</code><br/>The type can be an empty string.

* Executes Bind the querycontext item:<br/><code>void context(String value, String execute(type)</code><br/>The type can be an empty string.

* Iterator: checks if a Execute the query returns more itemsand return the result:<br/><code>boolean moreString execute()</code>

* Returns next itemIterator: check if a query returns more items:<br/><code>String nextboolean more()</code>

* Returns query informationIterator: return the next item:<br/><code>String infonext()</code>

* Returns serialization optionsReturn query information:<br/><code>String optionsinfo()</code>

* Closes the iterator and queryReturn serialization parameters:<br/><code>closeString options()</code>

* Return if the query may perform updates:<br/><code>boolean updating()</code> * Close the query:<br/><code>void close()</code></div><div style==Transfer Protocol=="float:left; width:100%;">

===Syntax==Changelog=

* <code>\x</code>: single byte.* <code>{...}</code>: strings, which are transfered in the UTF8 encoding.* <code>[...]</code>: binary data. All 00 and FF bytes are prefixed with FF;Version 8.2

# Client connects to server socket# Server sends timestamp: <code>{timestamp} \;Version 8.0</code># Client sends username and hash: <code>{username} \0 {md5(md5(password) + timestamp)} \0</code># Server sends <code>\0</code> (success) or <code>\1</code> (error)

- command: -> {command} \0 - create: -> \8 {name} \0 [input] \0 - add: -> \9 {name} \0 {path} \0 [input] \0 - watch: -> \10 {name} \0 - unwatch: -> \11 {name} \0 - replace: -> \12 {path} \0 [input] \0 - store: -> \13 {path} \0 [input] \0 - query: start -> \0 {query} \0 bind -> \3 {id} \0 {variable} \0 {value} \0 {type} \0 next -> \1 {id} \0 execute -> \5 {id} \0 info -> \6 {id} \0 options -> \;Version 7 {id} \0 close -> \.2 {id} \0

- command: -</div> {result} \0 {info} \0 \0 - create: -> {info} \0 \0 - add: -> {info} \0 \0 error -> \0 {error} \0 \1 - query: start -> {id} \0 \0 bind -> \0 \0 next -> {result} \0 \0 execute -> {result} \0 \0 info -> {result} \0 \0 options -> {result} \0 \0 close -> \0 \0 error -> \0 \1 {error} \0