Make diff asynchronous

app.js

@@ -62,7 +62,7 @@ console.log("properties hierarchy: " + propHierarchy)
 // Define an ugly debug function
 function debug_show_variable(variable_string_name) {
     if (opts.propDebug) {
-        console.log("DEBUG:" + variable_string_name +" has value " + JSON.stringify(eval(variable_string_name)))
+        console.log("DEBUG:" + variable_string_name + " has value " + JSON.stringify(eval(variable_string_name)))
     }
 }
 
@@ -78,8 +78,10 @@ var gccProps = props.propsFor("gcc-explorer");
 
 // Read from gccexplorer's config the wdiff configuration
 // that will be used to configure lib/diff.js
-var wdiffConfig = {wdiffExe: gccProps('wdiff_exe', "wdiff"),
-                   wdiffTmpDir: gccProps('wdiff_tmp_dir',"/tmp")};
+var wdiffConfig = {
+    wdiffExe: gccProps('wdiff', "wdiff"),
+    maxOutput: gccProps("max-diff-output", 100000)
+};
 
 // Instantiate a function to access records concerning the chosen language
 // in hidden object props.properties
@@ -330,7 +332,7 @@ function getCompilerInfo(compilerInfo) {
                 }
 
                 // debug (seems to be displayed multiple times):
-                if (opts.propDebug) console.log("compiler options: "+ JSON.stringify(options,null,4));
+                if (opts.propDebug) console.log("compiler options: " + JSON.stringify(options, null, 4));
 
                 resolve(compilerInfo);
             });

etc/config/gcc-explorer.defaults.properties

@@ -11,5 +11,5 @@ optionsBlacklistRe=^(-W[alp],)?((-wrapper|-fplugin.*|-specs|-load|-plugin|(@.*)|
 allowedShortUrlHostRe=^([a-z]+\.)?(xania|godbolt)\.org$
 googleShortLinkRewrite=^https?://goo.gl/(.*)$|https://godbolt.org/g/$1
 
-wdiff_exe=wdiff
-wdiff_tmp_dir=/tmp
+wdiff=wdiff
+max-diff-output=100000

lib/diff.js

@@ -1,5 +1,8 @@
-var fs = require('fs');
-var child_process = require('child_process');
+var fs = require('fs'),
+    child_process = require('child_process'),
+    temp = require('temp'),
+    path = require('path'),
+    Promise = require('promise');
 
 function cleanAndGetIndexes(text) {
     var addRules = {
@@ -136,48 +139,88 @@ function cleanAndGetIndexes(text) {
     return {text: finalText, zones: zones};
 }
 
+function newTempDir() {
+    return new Promise(function (resolve, reject) {
+        temp.mkdir('gcc-explorer-diff', function (err, dirPath) {
+            if (err)
+                reject("Unable to open temp file: " + err);
+            else
+                resolve(dirPath);
+        });
+    });
+}
+
+var writeFile = Promise.denodeify(fs.writeFile);
+
 function buildDiffHandler(config) {
+    var maxFileSize = config.maxOutput;
     return function diffHandler(req, res) {
         var before = req.body.before;
         var after = req.body.after;
+        var error;
         if (before === undefined) {
-            console.log("Warning : Bad request : wrong \"before\"");
-            //return next(new Error("Bad request : wrong \"before\""));
+            error = 'Warning : Bad request : wrong "before"';
+            console.log(error);
+            return next(new Error(error));
         }
         if (after === undefined) {
-            console.log("Warning : Bad request : wrong \"after\"");
-            //return next(new Error("Bad request : wrong \"after\""));
-        }
-        // TODO : make async the two creation of temp files + call to wdiff ?
-
-        var wdiffExe = config.wdiffExe;
-
-        var tempBeforePath = config.wdiffTmpDir + "/gcc-explorer-wdiff-before";
-        fs.writeFileSync(tempBeforePath, before);
-
-        var tempAfterPath = config.wdiffTmpDir + "/gcc-explorer-wdiff-after";
-        fs.writeFileSync(tempAfterPath, after);
-
-        // TODO : get rid of this buffer or calculate it...
-        var maxSize = 100000;
-        var wdiffResult = child_process.spawnSync(
-            wdiffExe,
-            [tempBeforePath, tempAfterPath],
-            {maxBuffer: 100000});
-
-        res.set('Content-Type', 'application/json');
-        var cleaned = cleanAndGetIndexes(wdiffResult.stdout.toString());
-        if (cleaned === null) {
-            res.end(JSON.stringify({
-                computedDiff: "Failed to clean the diff",
-                zones: null
-            }));
-        } else {
-            res.end(JSON.stringify({
-                computedDiff: cleaned.text,
-                zones: cleaned.zones
-            }));
+            error = 'Warning : Bad request : wrong "after"';
+            console.log(error);
+            return next(new Error(error));
         }
+
+        var tempBeforePath, tempAfterPath;
+        newTempDir()
+            .then(function (tmpDir) {
+                tempBeforePath = path.join(tmpDir, "gcc-explorer-wdiff-before");
+                tempAfterPath = path.join(tmpDir, "gcc-explorer-wdiff-after");
+                return Promise.all(
+                    writeFile(tempBeforePath, before),
+                    writeFile(tempAfterPath, after)
+                );
+            })
+            .then(function () {
+                var truncated = false;
+                var stdout = "";
+                var child = child_process.spawn(config.wdiffExe, [tempBeforePath, tempAfterPath],
+                    {maxBuffer: maxFileSize, detached: true});
+                child.stdout.on('data', function (data) {
+                    if (truncated) return;
+                    if (stdout.length > maxFileSize) {
+                        stdout += "\n[Truncated]";
+                        truncated = true;
+                        child.kill();
+                        return;
+                    }
+                    stdout += data;
+                });
+                return new Promise(function (resolve, reject) {
+                    child.on('error', function (e) {
+                        reject(e);
+                    });
+                    child.on('exit', function (code) {
+                        resolve(stdout);
+                    });
+                });
+            })
+            .then(function (output) {
+                var cleaned = cleanAndGetIndexes(output);
+                res.set('Content-Type', 'application/json');
+                if (cleaned === null) {
+                    res.end(JSON.stringify({
+                        computedDiff: "Failed to clean the diff",
+                        zones: null
+                    }));
+                } else {
+                    res.end(JSON.stringify({
+                        computedDiff: cleaned.text,
+                        zones: cleaned.zones
+                    }));
+                }
+            })
+            .catch(function (err) {
+                res.error(err);
+            });
     };
 }