npm package: @slosarek/rets-client
Description: A RETS client (Real Estate Transaction Standard).
Author: Steve Bruno
Latest version: 5.2.4

rets-client
===========
A RETS (Real Estate Transaction Standard) client for Node.js.


## Changes

#### 5.2
Added `timeout` setting, and allow `COMPACT` format.

#### 5.1
Added TypeScript typings.

#### 5.0
A significant amount of internal cleanup, resulting in more consistent code and API.  There are some minor breaking
changes, but they're small enough that migrating to 5.0 shouldn't be much effort.  The
[Example Usage](https://github.com/sbruno81/rets-client#example-usage) has been updated to show 5.x patterns. 

- object stream queries now have events with a `type` field to make discrimination easier, with the following
possibilities:
  - `dataStream`, for a stream containing an object's raw data
  - `location`, when no stream is available but a URL is available in the `headerInfo` (as per the `Location: 1` option)
  - `headerInfo`, with the headers for the outer multipart response
  - `error`, for an error corresponding to a single object rather than the stream as a whole
- search stream queries now return an object with a `retsStream` field rather than the bare stream
- the `searchRets` method now returns an object with a `rawStream` field rather than the bare stream
- headerInfo is now available on every query made
  - login and logout set `client.loginHeaderInfo` and `client.logoutHeaderInfo`
  - every streaming query will include an event with `type: 'headerInfo'`
  - every buffered query (and most streaming queries) will return an object including a `headerInfo` field
- errors now consistently include response headers as well as the request options
- all calls made to the RETS server now obey `settings.method` for POST vs GET


#### 4.X and earlier
See [the changelog](./CHANGELOG.md) for earlier changes.


## Implementation Notes

This interface uses promises, and an optional stream-based interface for better performance with large search results.
Future development will include an optional stream-based interface for object downloads, and an improved API for the
non-streaming object methods.

This library is written primarily in CoffeeScript, but may be used just as easily in a Node app using Javascript or
CoffeeScript.  Promises in this module are provided by [Bluebird](https://github.com/petkaantonov/bluebird).

The original module was developed against a server running RETS v1.7.2, so there may be incompatibilities with other
versions.  However, we want this library to work against any RETS servers that are in current use, so issue tickets
describing problems or (even better) pull requests that fix interactions with servers running other versions of RETS
are welcomed.

For more information about what all the parameters and return values and such mean, you might want to look at the
[RETS Specifications](http://www.reso.org/specifications)


## Contributions
Issue tickets and pull requests are welcome.  Pull requests must be backward-compatible to be considered, and ideally
should match existing code style.

#### TODO
- create unit tests -- specifically ones that run off example RETS data rather than requiring access to a real RETS server
- refactor streaming API to correctly respond to backpressure


## Example Usage

##### Client Configuration
```javascript
    //create rets-client
    var clientSettings = {
        loginUrl: retsLoginUrl,
        username: retsUser,
        password: retsPassword,
        version: 'RETS/1.7.2',
        userAgent: 'RETS node-client/4.x',
        method: 'GET'  // this is the default, or for some servers you may want 'POST'
    };
...
```

##### Client Configuration with UA Authorization
```javascript
    //create rets-client
    var clientSettings = {
        version: 'RETS/1.7.2',
        userAgent: userAgent,
        userAgentPassword: userAgentPassword,
        sessionId: sessionId
    };
...
```

##### Output helper used in many examples below

```javascript
function outputFields(obj, opts) {
  if (!obj) {
    console.log("      "+JSON.stringify(obj))
  } else {
    if (!opts) opts = {};

    var excludeFields;
    var loopFields;
    if (opts.exclude) {
      excludeFields = opts.exclude;
      loopFields = Object.keys(obj);
    } else if (opts.fields) {
      loopFields = opts.fields;
      excludeFields = [];
    } else {
      loopFields = Object.keys(obj);
      excludeFields = [];
    }
    for (var i = 0; i < loopFields.length; i++) {
      if (excludeFields.indexOf(loopFields[i]) != -1) {
        continue;
      }
      if (typeof(obj[loopFields[i]]) == 'object') {
        console.log("      " + loopFields[i] + ": " + JSON.stringify(obj[loopFields[i]], null, 2).replace(/\n/g, '\n      '));
      } else {
        console.log("      " + loopFields[i] + ": " + JSON.stringify(obj[loopFields[i]]));
      }
    }
  }
  console.log("");
}
```

#### Example rets-client code
```javascript
var rets = require('rets-client');
var fs = require('fs');
var photoSourceId = '12345'; // <--- dummy example ID!  this will usually be a MLS number / listing id
  
// establish connection to RETS server which auto-logs out when we're done
rets.getAutoLogoutClient(clientSettings, function (client) {
  console.log("===================================");
  console.log("========  System Metadata  ========");
  console.log("===================================");
  console.log('   ~~~~~~~~~ Header Info ~~~~~~~~~');
  outputFields(client.loginHeaderInfo);
  console.log('   ~~~~~~~~~ System Data ~~~~~~~~~');
  outputFields(client.systemData);

  //get resources metadata
  return client.metadata.getResources()
    .then(function (data) {
      console.log("======================================");
      console.log("========  Resources Metadata  ========");
      console.log("======================================");
      console.log('   ~~~~~~~~~ Header Info ~~~~~~~~~');
      outputFields(data.headerInfo);
      console.log('   ~~~~~~ Resources Metadata ~~~~~');
      outputFields(data.results[0].info);
      for (var dataItem = 0; dataItem < data.results[0].metadata.length; dataItem++) {
        console.log("   -------- Resource " + dataItem + " --------");
        outputFields(data.results[0].metadata[dataItem], {fields: ['ResourceID', 'StandardName', 'VisibleName', 'ObjectVersion']});
      }
    }).then(function () {

      //get class metadata
      return client.metadata.getClass("Property");
    }).then(function (data) {
      console.log("===========================================================");
      console.log("========  Class Metadata (from Property Resource)  ========");
      console.log("===========================================================");
      console.log('   ~~~~~~~~~ Header Info ~~~~~~~~~');
      outputFields(data.headerInfo);
      console.log('   ~~~~~~~~ Class Metadata ~~~~~~~');
      outputFields(data.results[0].info);
      for (var classItem = 0; classItem < data.results[0].metadata.length; classItem++) {
        console.log("   -------- Table " + classItem + " --------");
        outputFields(data.results[0].metadata[classItem], {fields: ['ClassName', 'StandardName', 'VisibleName', 'TableVersion']});
      }
    }).then(function () {

      //get field data for open houses
      return client.metadata.getTable("Property", "RESIDENTIAL");
    }).then(function (data) {
      console.log("==============================================");
      console.log("========  Residential Table Metadata  ========");
      console.log("===============================================");
      console.log('   ~~~~~~~~~ Header Info ~~~~~~~~~');
      outputFields(data.headerInfo);
      console.log('   ~~~~~~~~ Table Metadata ~~~~~~~');
      outputFields(data.results[0].info);
      for (var tableItem = 0; tableItem < data.results[0].metadata.length; tableItem++) {
        console.log("   -------- Field " + tableItem + " --------");
        outputFields(data.results[0].metadata[tableItem], {fields: ['MetadataEntryID', 'SystemName', 'ShortName', 'LongName', 'DataType']});
      }
      return data.results[0].metadata
    }).then(function (fieldsData) {
      var plucked = [];
      for (var fieldItem = 0; fieldItem < fieldsData.length; fieldItem++) {
        plucked.push(fieldsData[fieldItem].SystemName);
      }
      return plucked;
    }).then(function (fields) {

      //perform a query using DMQL2 -- pass resource, class, and query, and options
      return client.search.query("Property", "RESIDENTIAL", "(RecordModDate=2016-06-20+),(ActiveYN=1)", {limit:100, offset:10})
        .then(function (searchData) {
          console.log("=============================================");
          console.log("========  Residential Query Results  ========");
          console.log("=============================================");
          console.log('   ~~~~~~~~~ Header Info ~~~~~~~~~');
          outputFields(searchData.headerInfo);
          console.log('   ~~~~~~~~~~ Query Info ~~~~~~~~~');
          outputFields(searchData, {exclude: ['results','headerInfo']});
          //iterate through search results
          for (var dataItem = 0; dataItem < searchData.results.length; dataItem++) {
            console.log("   -------- Result " + dataItem + " --------");
            outputFields(searchData.results[dataItem], {fields: fields});
          }
          if (searchData.maxRowsExceeded) {
            console.log("   -------- More rows available!");
          }
        });
    }).then(function () {

      // get photos
      return client.objects.getAllObjects("Property", "LargePhoto", photoSourceId, {alwaysGroupObjects: true, ObjectData: '*'})
    }).then(function (photoResults) {
      console.log("=================================");
      console.log("========  Photo Results  ========");
      console.log("=================================");
      console.log('   ~~~~~~~~~ Header Info ~~~~~~~~~');
      outputFields(photoResults.headerInfo);
      for (var i = 0; i < photoResults.objects.length; i++) {
        console.log("   -------- Photo " + (i + 1) + " --------");
        if (photoResults.objects[i].error) {
          console.log("      Error: " + photoResults.objects[i].error);
        } else {
          outputFields(photoResults.objects[i].headerInfo);
          fs.writeFileSync(
            "/tmp/photo" + (i + 1) + "." + photoResults.objects[i].headerInfo.contentType.match(/\w+\/(\w+)/i)[1],
            photoResults.objects[i].data);
        }
      }
    });

}).catch(function (errorInfo) {
  var error = errorInfo.error || errorInfo;
  console.log("   ERROR: issue encountered:");
  outputFields(error);
  console.log('   '+(error.stack||error).replace(/\n/g, '\n   '));
});
```

#### Simple streaming example
```javascript
var rets = require('rets-client');
var through2 = require('through2');
var Promise = require('bluebird');
  
// this function doesn't do much, it's just a placeholder for whatever you want to do with the results 
function doAsyncProcessing(row, index, callback) {
  console.log("-------- Result " + index + " --------");
  outputFields(row);
  // must be sure callback is called when this is done
  callback();
}

// establish connection to RETS server which auto-logs out when we're done
rets.getAutoLogoutClient(clientSettings, function (client) {
  // in order to have the auto-logout function work properly, we need to make a promise that either rejects or
  // resolves only once we're done processing the stream
  return new Promise(function (resolve, reject) {
    console.log("====================================");
    console.log("========  Streamed Results  ========");
    console.log("====================================");
    var count = 0;
    var streamResult = client.search.stream.query("Property", "RES", "(LastChangeTimestamp=2016-06-20+)", {limit:10, offset:4});
    var processorStream = through2.obj(function (event, encoding, callback) {
      switch (event.type) {
        case 'headerInfo':
          console.log('   ~~~~~~~~~ Header Info ~~~~~~~~~');
          outputFields(event.payload);
          callback();
          break;
        case 'data':
          // event.payload is an object representing a single row of results
          // make sure callback is called only when all processing is complete
          count++;
          doAsyncProcessing(event.payload, count, callback);
          break;
        case 'done':
          // event.payload is an object containing a count of rows actually received, plus some other things
          // now we can resolve the auto-logout promise
          resolve(event.payload.rowsReceived);
          callback();
          break;
        case 'error':
          // event.payload is an Error object
          console.log('Error streaming RETS results: '+event.payload);
          streamResult.retsStream.unpipe(processorStream);
          processorStream.end();
          // we need to reject the auto-logout promise
          reject(event.payload);
          callback();
          break;
        default:
          // ignore other events
          callback();
      }
    });
    streamResult.retsStream.pipe(processorStream);
  });

}).catch(function (errorInfo) {
  var error = errorInfo.error || errorInfo;
  console.log("   ERROR: issue encountered:");
  outputFields(error);
  console.log('   '+(error.stack||error).replace(/\n/g, '\n   '));
});
```

#### Photo streaming example
```javascript
var rets = require('rets-client');
var fs = require('fs');

// establish connection to RETS server which auto-logs out when we're done
rets.getAutoLogoutClient(clientSettings, function (client) {
  // getObjects will accept a single string, an array of strings, or an object as shown below
  var photoIds = {
    '11111': [1,3],  // get photos #1 and #3 for listingId 11111
    '22222': '*',    // get all photos for listingId 22222
    '33333': '0'     // get 'preferred' photo for listingId 33333
  };
  return client.objects.stream.getObjects('Property', 'LargePhoto', photoIds, {alwaysGroupObjects: true, ObjectData: '*'})
    .then(function (photoStream) {
      console.log("========================================");
      console.log("========  Photo Stream Results  ========");
      console.log("========================================");
      return new Promise(function (resolve, reject) {
        var i=0;
        photoStream.objectStream.on('data', function (event) {
          try {
            if (event.type == 'headerInfo') {
              console.log('   ~~~~~~~~~ Header Info ~~~~~~~~~');
              outputFields(event.headerInfo);
              return
            }
            console.log("   -------- Photo " + (i + 1) + " --------");
            if (event.type == 'error') {
              console.log("      Error: " + event.error);
            } else if (event.type == 'dataStream') {
              outputFields(event.headerInfo);
              fileStream = fs.createWriteStream(
                "/tmp/photo_" + event.headerInfo.contentId + "_" + event.headerInfo.objectId + "." + event.headerInfo.contentType.match(/\w+\/(\w+)/i)[1]);
              event.dataStream.pipe(fileStream);
            }
            i++;
          } catch (err) {
            reject(err);
          }
        });
        photoStream.objectStream.on('error', function (errorInfo) {
          reject(errorInfo);
        });
        photoStream.objectStream.on('end', function () {
          resolve();
        });
      });
    }).catch(function (errorInfo) {
      var error = errorInfo.error || errorInfo;
      console.log("   ERROR: issue encountered:");
      outputFields(error);
      console.log('   '+(error.stack||error).replace(/\n/g, '\n   '));
    });
});
```

##### Errors
There are 6 error classes exposed by this module:
* `RetsError`: A parent class for all the errors below, to make it more convenient to catch errors from this library.
I've made somewhat of an effort to catch any errors thrown by dependencies of this library and re-throw them as instances
of RetsError, so that any error generated by a call to this library can be detected the same way; if you find an error
coming through that didn't get this treatment, please open a ticket (or better, a PR!) to let me know.
* `RetsParamError`: Used when a required function parameter is missing or has an invalid value
* `RetsServerError`: Used when the HTTP response indicates an error, such as a "401 Unauthorized" response
* `RetsReplyError`: Used when the HTTP response is valid, but the XML RETS response indicates an error
* `RetsProcessingError`: Used when a problem is encountered processing the response from the RETS server
* `RetsPermissionError`: Used when RETS login is successful, but the account does not have the full permissions expected

##### Debugging
You can turn on all debug logging by adding `rets-client:*` to your `DEBUG` environment variable, as per the
[debug module](https://github.com/visionmedia/debug).  Sub-loggers available:
* `rets-client:main`: basic logging of RETS call options and errors
* `rets-client:request`: logging of HTTP request/response headers and other related info, with output almost identical
to that provided by the [request-debug module](https://github.com/request/request-debug).
* `rets-client:multipart`: logging of most multipart parser events
* `rets-client:multipart:verbose`: logging of additional multipart parser events (too cluttered for most purposes)

If you want access to the request debugging data directly, you can use the `requestDebugFunction` client setting.  This
function will be set up as a debug handler as per the [request-debug module](https://github.com/request/request-debug).