Add option to force GET requests if URL length is low

This enables cases such as comunica/comunica#1551

Author: noahvsb

README.md

@@ -54,6 +54,8 @@ const myFetcher = new SparqlEndpointFetcher({
   prefixVariableQuestionMark: false,
   // Timeout for setting up server connection (Once a connection has been made, and the response is being parsed, the timeout does not apply anymore).
   timeout: 5000,
+  // If the url length is below this number, HTTP GET is used regardless of the value of this.method, defaults to 0.
+  forceGetIfUrlLengthBelow: 600,
 });
 ```
 

lib/SparqlEndpointFetcher.ts

@@ -20,6 +20,7 @@ export class SparqlEndpointFetcher {
 
   protected readonly method: 'GET' | 'POST';
   protected readonly timeout?: number;
+  protected readonly forceGetIfUrlLengthBelow: number;
   public additionalUrlParams: URLSearchParams;
   protected readonly defaultHeaders: Headers;
   public readonly fetchCb?: (input: Request | string, init?: RequestInit) => Promise<Response>;
@@ -31,6 +32,7 @@ export class SparqlEndpointFetcher {
   public constructor(args?: ISparqlEndpointFetcherArgs) {
     this.method = args?.method ?? 'POST';
     this.timeout = args?.timeout;
+    this.forceGetIfUrlLengthBelow = args?.forceGetIfUrlLengthBelow ?? 0;
     this.additionalUrlParams = args?.additionalUrlParams ?? new URLSearchParams();
     this.defaultHeaders = args?.defaultHeaders ?? new Headers();
     this.fetchCb = args?.fetch;
@@ -74,7 +76,7 @@ export class SparqlEndpointFetcher {
    * This will parse the update query and thrown an exception on syntax errors.
    *
    * @param {string} query An update query.
-   * @return {'UNKNOWN' | UpdateTypes} The included update operations.
+   * @return {'UNKNOWN' | IUpdateTypes} The included update operations.
    */
   public getUpdateTypes(query: string): 'UNKNOWN' | IUpdateTypes {
     const parsedQuery = new SparqlParser({ sparqlStar: true }).parse(query);
@@ -191,14 +193,24 @@ export class SparqlEndpointFetcher {
     query: string,
     acceptHeader: string,
   ): Promise<[ string, NodeJS.ReadableStream ]> {
-    let url: string = this.method === 'POST' ? endpoint : `${endpoint}?query=${encodeURIComponent(query)}`;
+    let method: 'GET' | 'POST';
+    let url: string;
+
+    if (this.method === 'POST' && this.forceGetIfUrlLengthBelow <= endpoint.length) {
+      method = this.method;
+      url = endpoint;
+    } else {
+      const getEndpoint = `${endpoint}?query=${encodeURIComponent(query)}`;
+      method = this.method === 'GET' || getEndpoint.length < this.forceGetIfUrlLengthBelow ? 'GET' : 'POST';
+      url = method === 'POST' ? endpoint : getEndpoint;
+    }
 
     // Initiate request
     let body: URLSearchParams | undefined;
     const headers: Headers = new Headers(this.defaultHeaders);
     headers.append('Accept', acceptHeader);
 
-    if (this.method === 'POST') {
+    if (method === 'POST') {
       headers.append('Content-Type', 'application/x-www-form-urlencoded');
       body = new URLSearchParams();
       body.set('query', query);
@@ -210,7 +222,7 @@ export class SparqlEndpointFetcher {
       url += `&${this.additionalUrlParams.toString()}`;
     }
 
-    return this.handleFetchCall(url, { headers, method: this.method, body });
+    return this.handleFetchCall(url, { headers, method, body });
   }
 
   /**
@@ -270,6 +282,7 @@ export interface ISparqlEndpointFetcherArgs extends ISparqlJsonParserArgs, ISpar
   method?: 'POST' | 'GET';
   additionalUrlParams?: URLSearchParams;
   timeout?: number;
+  forceGetIfUrlLengthBelow?: number;
   defaultHeaders?: Headers;
   /**
    * A custom fetch function.

test/SparqlEndpointFetcher-test.ts

@@ -303,6 +303,40 @@ describe('SparqlEndpointFetcher', () => {
         );
       });
 
+      it('should use HTTP GET when url length is below forceGetIfUrlLengthBelow', async() => {
+        const fetchCbThis = jest.fn(() => Promise.resolve(new Response(streamifyString('dummy'))));
+        const fetcherThis = new SparqlEndpointFetcher({
+          method: 'POST',
+          fetch: fetchCbThis,
+          forceGetIfUrlLengthBelow: 600,
+        });
+        await fetcherThis.fetchRawStream(endpoint, querySelect, 'myacceptheader');
+        const headers: Headers = new Headers();
+        headers.append('Accept', 'myacceptheader');
+        expect(fetchCbThis).toHaveBeenCalledWith(
+          'https://dbpedia.org/sparql?query=SELECT%20*%20WHERE%20%7B%20%3Fs%20%3Fp%20%3Fo%20%7D',
+          expect.objectContaining({ headers, method: 'GET' }),
+        );
+      });
+
+      it('should use HTTP POST when url length is above or the same as forceGetIfUrlLengthBelow', async() => {
+        const fetchCbThis = jest.fn(() => Promise.resolve(new Response(streamifyString('dummy'))));
+        const fetcherThis = new SparqlEndpointFetcher({
+          method: 'POST',
+          fetch: fetchCbThis,
+          forceGetIfUrlLengthBelow: 30,
+        });
+        await fetcherThis.fetchRawStream(endpoint, querySelect, 'myacceptheader');
+        const headers: Headers = new Headers();
+        headers.append('Accept', 'myacceptheader');
+        const body = new URLSearchParams();
+        body.set('query', querySelect);
+        expect(fetchCbThis).toHaveBeenCalledWith(
+          'https://dbpedia.org/sparql',
+          expect.objectContaining({ headers, method: 'POST', body }),
+        );
+      });
+
       it('should reject for an invalid server response', async() => {
         const fetchCbThis = () => Promise.resolve(<Response> {
           body: streamifyString('this is an invalid response'),