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A native Java library to talk to the Canvas REST API
package edu.ksu.canvas.net;
import edu.ksu.canvas.exception.CanvasException;
import edu.ksu.canvas.exception.InvalidOauthTokenException;
import edu.ksu.canvas.exception.ObjectNotFoundException;
import edu.ksu.canvas.exception.RateLimitException;
import edu.ksu.canvas.exception.UnauthorizedException;
import edu.ksu.canvas.impl.GsonResponseParser;
import edu.ksu.canvas.model.status.CanvasErrorResponse;
import edu.ksu.canvas.model.status.CanvasErrorResponse.ErrorMessage;
import edu.ksu.canvas.oauth.OauthToken;
import org.apache.commons.lang3.StringUtils;
import org.apache.http.Header;
import org.apache.http.HttpHeaders;
import org.apache.http.HttpResponse;
import org.apache.http.NameValuePair;
import org.apache.http.client.HttpClient;
import org.apache.http.client.entity.UrlEncodedFormEntity;
import org.apache.http.client.methods.HttpEntityEnclosingRequestBase;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.client.methods.HttpPut;
import org.apache.http.client.methods.HttpRequestBase;
import org.apache.http.entity.ContentType;
import org.apache.http.entity.StringEntity;
import org.apache.http.impl.client.BasicResponseHandler;
import org.apache.http.impl.client.DefaultHttpClient;
import org.apache.http.message.BasicNameValuePair;
import org.apache.http.params.CoreConnectionPNames;
import org.apache.http.params.HttpParams;
import org.apache.http.util.EntityUtils;
import org.apache.log4j.Logger;
import com.google.gson.Gson;
import javax.validation.constraints.NotNull;
import java.io.IOException;
import java.net.URI;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.Map;
import java.util.stream.Collectors;
public class SimpleRestClient implements RestClient {
private static final Logger LOG = Logger.getLogger(SimpleRestClient.class);
@Override
public Response sendApiGet(@NotNull OauthToken token, @NotNull String url,
int connectTimeout, int readTimeout) throws IOException {
LOG.debug("Sending GET request to URL: " + url);
Long beginTime = System.currentTimeMillis();
Response response = new Response();
HttpClient httpClient = createHttpClient(connectTimeout, readTimeout);
HttpGet httpGet = new HttpGet(url);
httpGet.setHeader("Authorization", "Bearer" + " " + token.getAccessToken());
HttpResponse httpResponse = httpClient.execute(httpGet);
checkHeaders(httpResponse, httpGet);
//deal with the actual content
response.setContent(handleResponse(httpResponse, httpGet));
response.setResponseCode(httpResponse.getStatusLine().getStatusCode());
Long endTime = System.currentTimeMillis();
LOG.debug("GET call took: " + (endTime - beginTime) + "ms");
//deal with pagination
Header linkHeader = httpResponse.getFirstHeader("Link");
String linkHeaderValue = linkHeader == null ? null : httpResponse.getFirstHeader("Link").getValue();
if(linkHeaderValue == null) {
return response;
}
List links = Arrays.asList(linkHeaderValue.split(","));
for (String link : links) {
if(link.contains("rel=\"next\"")) {
LOG.debug("response has more pages");
String nextLink = link.substring(1, link.indexOf(';')-1); //format is ; rel="next"
response.setNextLink(nextLink);
}
}
return response;
}
@Override
public Response sendJsonPut(OauthToken token, String url, String json, int connectTimeout, int readTimeout) throws IOException {
return sendJsonPostOrPut(token, url, json, connectTimeout, readTimeout, "PUT");
}
@Override
public Response sendJsonPost(OauthToken token, String url, String json, int connectTimeout, int readTimeout) throws IOException {
return sendJsonPostOrPut(token, url, json, connectTimeout, readTimeout, "POST");
}
// PUT and POST are identical calls except for the header specifying the method
private Response sendJsonPostOrPut(OauthToken token, String url, String json,
int connectTimeout, int readTimeout, String method) throws IOException {
LOG.debug("Sending JSON " + method + " to URL: " + url);
Response response = new Response();
HttpClient httpClient = createHttpClient(connectTimeout, readTimeout);
HttpEntityEnclosingRequestBase action;
if("POST".equals(method)) {
action = new HttpPost(url);
} else if("PUT".equals(method)) {
action = new HttpPut(url);
} else {
throw new IllegalArgumentException("Method must be either POST or PUT");
}
Long beginTime = System.currentTimeMillis();
action.setHeader("Authorization", "Bearer" + " " + token.getAccessToken());
StringEntity requestBody = new StringEntity(json, ContentType.APPLICATION_JSON);
action.setEntity(requestBody);
HttpResponse httpResponse = httpClient.execute(action);
String content = handleResponse(httpResponse, action);
response.setContent(content);
response.setResponseCode(httpResponse.getStatusLine().getStatusCode());
Long endTime = System.currentTimeMillis();
LOG.debug("POST call took: " + (endTime - beginTime) + "ms");
return response;
}
@Override
public Response sendApiPost(OauthToken token, String url, Map> postParameters,
int connectTimeout, int readTimeout) throws InvalidOauthTokenException, IOException {
LOG.debug("Sending API POST request to URL: " + url);
Response response = new Response();
HttpClient httpClient = createHttpClient(connectTimeout, readTimeout);
Long beginTime = System.currentTimeMillis();
HttpPost httpPost = new HttpPost(url);
httpPost.setHeader("Authorization", "Bearer" + " " + token.getAccessToken());
List params = convertParameters(postParameters);
httpPost.setEntity(new UrlEncodedFormEntity(params));
HttpResponse httpResponse = httpClient.execute(httpPost);
String content = handleResponse(httpResponse, httpPost);
response.setContent(content);
response.setResponseCode(httpResponse.getStatusLine().getStatusCode());
Long endTime = System.currentTimeMillis();
LOG.debug("POST call took: " + (endTime - beginTime) + "ms");
return response;
}
@Override
public Response sendApiPut(OauthToken token, String url, Map> putParameters,
int connectTimeout, int readTimeout) throws InvalidOauthTokenException, IOException {
LOG.debug("Sending API PUT request to URL: " + url);
Response response = new Response();
HttpClient httpClient = createHttpClient(connectTimeout, readTimeout);
Long beginTime = System.currentTimeMillis();
HttpPut httpPut = new HttpPut(url);
httpPut.setHeader("Authorization", "Bearer" + " " + token.getAccessToken());
List params = convertParameters(putParameters);
httpPut.setEntity(new UrlEncodedFormEntity(params));
HttpResponse httpResponse = httpClient.execute(httpPut);
String content = handleResponse(httpResponse, httpPut);
response.setContent(content);
response.setResponseCode(httpResponse.getStatusLine().getStatusCode());
Long endTime = System.currentTimeMillis();
LOG.debug("PUT call took: " + (endTime - beginTime) + "ms");
return response;
}
@Override
public Response sendApiDelete(OauthToken token, String url, Map> deleteParameters,
int connectTimeout, int readTimeout) throws InvalidOauthTokenException, IOException {
LOG.debug("Sending API DELETE request to URL: " + url);
Response response = new Response();
Long beginTime = System.currentTimeMillis();
HttpClient httpClient = createHttpClient(connectTimeout, readTimeout);
//This class is defined here because we need to be able to add form body elements to a delete request for a few api calls.
class HttpDeleteWithBody extends HttpPost {
@Override
public String getMethod() {
return "DELETE";
}
}
HttpDeleteWithBody httpDelete = new HttpDeleteWithBody();
httpDelete.setURI(URI.create(url));
httpDelete.setHeader("Authorization", "Bearer" + " " + token.getAccessToken());
List params = convertParameters(deleteParameters);
httpDelete.setEntity(new UrlEncodedFormEntity(params));
HttpResponse httpResponse = httpClient.execute(httpDelete);
String content = handleResponse(httpResponse, httpDelete);
response.setContent(content);
response.setResponseCode(httpResponse.getStatusLine().getStatusCode());
Long endTime = System.currentTimeMillis();
LOG.debug("DELETE call took: " + (endTime - beginTime) + "ms");
return response;
}
private void checkHeaders(HttpResponse httpResponse, HttpRequestBase request) {
int statusCode = httpResponse.getStatusLine().getStatusCode();
double rateLimitThreshold = 0.1;
double xRateCost = 0;
double xRateLimitRemaining = 0;
try {
xRateCost = Double.parseDouble(httpResponse.getFirstHeader("x-request-cost").getValue());
xRateLimitRemaining = Double.parseDouble(httpResponse.getFirstHeader("x-rate-limit-remaining").getValue());
//Throws a 403 with a "Rate Limit Exceeded" error message if the API throttle limit is hit.
//See https://canvas.instructure.com/doc/api/file.throttling.html.
if(xRateLimitRemaining < rateLimitThreshold) {
LOG.error("Canvas API rate limit exceeded. Bucket quota: " + xRateLimitRemaining + " Cost: " + xRateCost
+ " Threshold: " + rateLimitThreshold + " HTTP status: " + statusCode + " Requested URL: " + request.getURI());
throw new RateLimitException(extractErrorMessageFromResponse(httpResponse), String.valueOf(request.getURI()));
}
} catch (NullPointerException e) {
LOG.debug("Rate not being limited: " + e);
}
if (statusCode == 401) {
//If the WWW-Authenticate header is set, it is a token problem.
//If the header is not present, it is a user permission error.
//See https://canvas.instructure.com/doc/api/file.oauth.html#storing-access-tokens
if(httpResponse.containsHeader(HttpHeaders.WWW_AUTHENTICATE)) {
LOG.debug("User's token is invalid. It might need refreshing");
throw new InvalidOauthTokenException();
}
LOG.error("User is not authorized to perform this action");
throw new UnauthorizedException();
}
if(statusCode == 404) {
LOG.error("Object not found in Canvas. Requested URL: " + request.getURI());
throw new ObjectNotFoundException(extractErrorMessageFromResponse(httpResponse), String.valueOf(request.getURI()));
}
if(statusCode < 200 || statusCode > 299) {
LOG.error("HTTP status " + statusCode + " returned from " + request.getURI());
throw new CanvasException(extractErrorMessageFromResponse(httpResponse), String.valueOf(request.getURI()));
}
}
/**
* Attempts to extract a useful Canvas error message from a response object.
* Sometimes Canvas API errors come back with a JSON body containing something like
* {"errors":[{"message":"Human readable message here."}],"error_report_id":123456}.
* This method will attempt to extract the message. If parsing fails, it will return
* the raw JSON string without trying to parse it. Returns null if all attempts fail.
* @param response HttpResponse object representing the error response from Canvas
* @return The Canvas human-readable error string or null if unable to extract it
*/
private String extractErrorMessageFromResponse(HttpResponse response) {
String contentType = response.getEntity().getContentType().getValue();
if(contentType.contains("application/json")) {
Gson gson = GsonResponseParser.getDefaultGsonParser(false);
String responseBody = null;
try {
responseBody = EntityUtils.toString(response.getEntity());
LOG.error("Body of error response from Canvas: " + responseBody);
CanvasErrorResponse errorResponse = gson.fromJson(responseBody, CanvasErrorResponse.class);
List errors = errorResponse.getErrors();
if(errors != null) {
//I have only ever seen a single error message but it is an array so presumably there could be more.
return errors.stream().map(e -> e.getMessage()).collect(Collectors.joining(", "));
}
} catch (Exception e) {
//Returned JSON was not in expected format. Fall back to returning the whole response body, if any
if(StringUtils.isNotBlank(responseBody)) {
return responseBody;
}
}
}
return null;
}
private String handleResponse(HttpResponse httpResponse, HttpRequestBase request) throws IOException {
checkHeaders(httpResponse, request);
return new BasicResponseHandler().handleResponse(httpResponse);
}
private HttpClient createHttpClient(int connectTimeout, int readTimeout) {
HttpClient httpClient = new DefaultHttpClient();
HttpParams params = httpClient.getParams();
params.setParameter(CoreConnectionPNames.CONNECTION_TIMEOUT, connectTimeout);
params.setParameter(CoreConnectionPNames.SO_TIMEOUT, readTimeout);
return httpClient;
}
private static List convertParameters(final Map> parameterMap) {
final List params = new ArrayList<>();
if (parameterMap == null) {
return params;
}
for (final Map.Entry> param : parameterMap.entrySet()) {
final String key = param.getKey();
for (final String value : param.getValue()) {
params.add(new BasicNameValuePair(key, value));
LOG.debug("key "+ key +"\t value : " + value);
}
}
return params;
}
}