If no branch is specified, use any advertised default, not just master

pom.xml

@@ -136,7 +136,7 @@
         <dependency>
             <groupId>org.eclipse.jgit</groupId>
             <artifactId>org.eclipse.jgit</artifactId>
-            <version>5.5.1.201910021850-r</version>
+            <version>5.10.0.202012080955-r</version>
         </dependency>
         <!-- end git stuff -->
 

src/main/java/com/danielflower/restabuild/build/ProjectManager.java

@@ -16,6 +16,7 @@
 import org.eclipse.jgit.lib.*;
 import org.eclipse.jgit.revwalk.RevCommit;
 import org.eclipse.jgit.revwalk.RevWalk;
+import org.eclipse.jgit.transport.FetchResult;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
@@ -96,12 +97,14 @@ static class ExtendedBuildState {
         public final String commitIDAfterBuild;
         public final List<String> tagsAdded;
         public final File workDir;
-        ExtendedBuildState(BuildState buildState, String commitIDBeforeBuild, String commitIDAfterBuild, List<String> tagsAdded, File workDir) {
+        public final String branch;
+        ExtendedBuildState(BuildState buildState, String commitIDBeforeBuild, String commitIDAfterBuild, List<String> tagsAdded, File workDir, String branch) {
             this.buildState = buildState;
             this.commitIDBeforeBuild = commitIDBeforeBuild;
             this.commitIDAfterBuild = commitIDAfterBuild;
             this.tagsAdded = tagsAdded;
             this.workDir = workDir;
+            this.branch = branch;
         }
     }
 
@@ -110,10 +113,11 @@ public ExtendedBuildState build(Writer outputHandler, String branch, String buil
         final File workDir;
         final ExtendedBuildState extendedBuildState;
         try (Git git = pullFromGitAndCopyWorkingCopyToNewDir(outputHandler, branch)) {
+            branch = git.getRepository().getBranch();
             workDir = git.getRepository().getWorkTree();
             doubleLog(outputHandler, "Created new instance in " + dirPath(workDir));
 
-            Ref headBefore = git.getRepository().exactRef("HEAD");
+            Ref headBefore = git.getRepository().exactRef(Constants.HEAD);
             Ref headAfter = headBefore;
             ObjectId beforeCommitID = headBefore.getObjectId();
             List<String> newTags = new ArrayList<>();
@@ -140,7 +144,7 @@ public ExtendedBuildState build(Writer outputHandler, String branch, String buil
                 ProcessStarter processStarter = new ProcessStarter(outputHandler);
                 result = processStarter.run(outputHandler, command, workDir, TimeUnit.MINUTES.toMillis(buildTimeout), environment);
 
-                headAfter = git.getRepository().exactRef("HEAD");
+                headAfter = git.getRepository().exactRef(Constants.HEAD);
 
                 try (RevWalk walk = new RevWalk(git.getRepository())) {
                     walk.markStart(walk.parseCommit(headAfter.getObjectId()));
@@ -154,7 +158,7 @@ public ExtendedBuildState build(Writer outputHandler, String branch, String buil
 
             newTags.removeAll(tagsBefore);
 
-            extendedBuildState = new ExtendedBuildState(result, beforeCommitID.name(), headAfter.getObjectId().name(), Collections.unmodifiableList(newTags), workDir);
+            extendedBuildState = new ExtendedBuildState(result, beforeCommitID.name(), headAfter.getObjectId().name(), Collections.unmodifiableList(newTags), workDir, branch);
         }
 
         deleteDirectoryQuietly(workDir, StandardDeleteOption.OVERRIDE_READ_ONLY);
@@ -169,10 +173,53 @@ public void close() {
     }
 
     private Git pullFromGitAndCopyWorkingCopyToNewDir(Writer writer, String branch) throws GitAPIException, IOException {
-        git.fetch().setRemote("origin").setProgressMonitor(new TextProgressMonitor(writer)).call();
+        FetchResult fetchResult = git.fetch().setRemote("origin").setProgressMonitor(new TextProgressMonitor(writer)).call();
+        if (branch == null) {
+            Ref ref = findBranchToBuild(fetchResult);
+            if (ref == null) {
+                throw new RuntimeException("Could not determine default branch to build");
+            } else {
+                branch = StringUtils.removeStart(ref.getName(), Constants.R_HEADS);
+            }
+            doubleLog(writer, "Building default branch: "+branch);
+        } else {
+            doubleLog(writer, "Building branch: "+branch);
+        }
         return copyToNewInstanceDirAndSwitchBranch(branch);
     }
 
+    private Ref findBranchToBuild(FetchResult result) {
+        final Ref headRef = result.getAdvertisedRef(Constants.HEAD);
+        if (headRef == null) {
+            return null;
+        }
+
+        if (headRef.isSymbolic()) {
+            return headRef.getTarget();
+        }
+
+        final ObjectId headObjectId = headRef.getObjectId();
+        if (headObjectId == null) {
+            return null;
+        }
+
+        final Ref masterRef = result.getAdvertisedRef(Constants.R_HEADS + Constants.MASTER);
+        if (masterRef != null && headObjectId.equals(masterRef.getObjectId())) {
+            return masterRef;
+        }
+
+        for (Ref adRef : result.getAdvertisedRefs()) {
+            if (!adRef.getName().startsWith(Constants.R_HEADS)) {
+                continue;
+            }
+            if (headObjectId.equals(adRef.getObjectId())) {
+                return adRef;
+            }
+        }
+
+        return null;
+    }
+
     private Git copyToNewInstanceDirAndSwitchBranch(String branch) throws GitAPIException, IOException {
         File dest = new File(instanceDir, String.valueOf(System.currentTimeMillis()));
         if (!dest.mkdir()) {

src/main/java/com/danielflower/restabuild/web/BuildResource.java

@@ -12,6 +12,7 @@
 import io.muserver.rest.ApiResponse;
 import io.muserver.rest.Description;
 import io.muserver.rest.ResponseHeader;
+import org.apache.commons.lang3.StringUtils;
 import org.json.JSONArray;
 import org.json.JSONObject;
 
@@ -51,7 +52,7 @@ public BuildResource(FileSandbox fileSandbox, BuildQueue buildQueue, BuildDataba
     @ApiResponse(code = "400", message = "No gitUrl form parameter was specified.", contentType = "text/plain")
     public Response create(@FormParam("gitUrl") @Description(value = "The URL of a git repo that includes a `build.sh` or `build.bat` file. " +
         "It can be any type of Git URL (e.g. SSH or HTTPS) that the server has permission for.", example = "https://github.com/3redronin/mu-server-sample.git") String gitUrl,
-                           @DefaultValue("master") @FormParam("branch") @Description(value = "The value of the git branch. This parameter is optional.") String branch,
+                           @FormParam("branch") @Description(value = "The value of the git branch. This parameter is optional.") String branch,
                            @FormParam("buildParam") @Description(value = "The parameter for the `build.sh` or `build.bat` file. This parameter is optional.") String buildParam,
                            @Context UriInfo uriInfo) {
         BuildResult result = createInternal(gitUrl, branch, buildParam, uriInfo);
@@ -69,11 +70,7 @@ private BuildResult createInternal(String gitUrl, String branch, String buildPar
             throw new BadRequestException("A form parameter named gitUrl must point to a valid git repo");
         }
 
-        String gitBranch = branch;
-        if(null == branch || branch.trim().isEmpty()) {
-            gitBranch = "master";
-        }
-
+        String gitBranch = StringUtils.trimToNull(branch);
         GitRepo gitRepo = new GitRepo(gitUrl, gitBranch);
         String id = UUID.randomUUID().toString().replace("-", "");
         Map<String, String> environment = getEnrichedEnvironment(id, uriInfo);

src/main/resources/web/index.html

@@ -44,7 +44,7 @@ <h2>Submit a build</h2>
     </label>
     <label>
         Git Branch:
-        <input type="text" id="branchBox" name="branch"  placeholder="master">
+        <input type="text" id="branchBox" name="branch"  placeholder="<default>">
     </label>
     <label>
         Build Parameters:

src/main/resources/web/restabuild.js

@@ -21,8 +21,13 @@ document.addEventListener('DOMContentLoaded', function () {
         var value = urlBox.value;
         var branch = branchBox.value;
         var buildParam = buildParamBox.value;
-        cc.textContent = 'curl -LNs -F \'gitUrl=' + (value || 'git-url') + '\' '  + '-F \'branch=' + (branch || 'master') + '\' ' + '-F \'param=' + (buildParam || '') + '\' ' + form.action;
-        history.replaceState(null, null, value ? encodeURI(path) + '?url=' + encodeURIComponent(value) : encodeURI(path));
+        cc.textContent = 'curl -LNs -F \'gitUrl=' + (value || 'git-url') + '\' '  + (branch ? ('-F \'branch=' + branch + '\' ') : '') + (buildParam ? ('-F \'param=' + buildParam + '\' ') : '') + form.action;
+        var encodedQS = '';
+        if (value) encodedQS += "&url="+encodeURIComponent(value);
+        if (branch) encodedQS += "&branch="+encodeURIComponent(branch);
+        if (buildParam) encodedQS += "&param="+encodeURIComponent(buildParam);
+        if (encodedQS) encodedQS = "?"+encodedQS.slice(1);
+        history.replaceState(null, null, encodeURI(path) + encodedQS);
     };
     urlBox.addEventListener('input', update);
     branchBox.addEventListener('input', update);